New cylinder break-in

[Mongo]

Last fall I finished assembling my 86 250r. I had all the engine work done by a reputable mechanic in the area know for the work he does on older two strokes. I had a .050" over Wiseco piston put in and a full FMF exhaust. When I started breaking the motor in I took it nice and easy. I had the stock jets in and everything seemed to be running great until I started tuning the carb. It was always running too lean through the whole powerband even though I had gone up to a 180 main and a 46 slow jet. This weekend when I pulled the reed cage off to change out the reeeds (which weren't all that great) I could see that the rings were wearing on the exhaust side of the cylinder.

Since I'm goin gto have to replace either the rings or the piston, how should I go about breaking it in?

[struckran]

What mix and ratio? Im not sure what steps you take to break it in...I do what this guys says on the youtube video.
Works good for me..


http://www.youtube.com/watch?v=CafSquBJ0N4

[RIDE-RED 250r]

Worn rings on the exhaust side is what happens when you are running too lean. You may also have some damage to the edge of the piston crown on the exhaust side as well. The exhaust side is the hottest part if the piston and is the first to begin sustaining damage if running too lean.

There are as many opinions on premix ratio as there are members on the board it seems. I have done my share of research and have settled on 32:1 with Maxima 927 Castor oil. But do your own research and come to your own conclusions. Keep in mind, premix ratio will not have a siginificant effect on plugs fouling or not when you are properly jetted in. And keep in mind, the leaner premix you run, the less oil is getting to your major bottom end components and piston skirt/cylinder walls.

So, having said that, decide what premix you wish to run, and jet it safely rich at that premix ratio. Remember, when you "richen" your premix (ie adding a higher amount of oil) you will actually LEAN your fuel/air mix for combustion. Premix oil displaces fuel, and as such, adding more oil will actually lean your combustion fuel/air mix.

Your issues with burning your rings had more to do with jetting than break-in method.

Also, MAKE SURE RING GAP IS CORRECT AND WITHIN SPEC. Rings do not come "pre-gapped". It would be pretty much impossible as there is no way for the manufacturer to make a set of rings that the gap will be correct in every possible cylinder they will be installed in, just based on the infinitely varying degrees of wear in any given cylinder. Ring gap is VERY important. If the ring gap is too tight, as they expand with heat, the gap can be closed completely and cause a ring to push outward toward the cylinder wall much too hard and catch a port. I don't think I have to tell you why that is bad ju-ju.

Now, as to breakin procedure. Again, there are vastly varying opinions on this. But I will say, EVERY single machine I have ever owned from sleds, to wheelers, to RC engines, to boat engines, and on and on, the manufacturers pretty much all uniformly recommend breaking in easy. By that I mean, the first "X" amount of engine hours, miles, gallons of fuel, etc vary the throttle and do not exceed 1/4 throttle. After that stage is complete and the engine cools completely repeat that process only now you go to 1/2 throttle.. Let it cool completely and do it again but to 3/4 throttle. All throughout this process make sure not to have long periods of a steady, sustained speed/RPM. It is a good idea to check torque on major engine components between runs, IE head, cylinder, etc.

Many builders of aftermarket big bores for 250r's recommend 3 heat cycles with no load on the engine before even beginning the first stage of loaded engine breakin. Basic heat cycles just means start it up, blipping the throttle a little bit till the engine comes up to full operating temp and then once up to temp, shut it down. Let it cool completely and repeat.

I know there are alot of folks who use the "break it in the way you want it to run" approach to break in and if it works for them, I have nothing negative to say about it. I tend to do what is recommended by the people who engineered and built the engine...

And, when breaking in, make sure your jetting is safely rich or you will just burn another set of rings, or worse...

Make sure you don't have any air leaks at the intake, crank seals, exhaust flange, etc too. Any of those will cause you to run lean and make jetting a nightmare, along with burning down a topend.

[Mongo]

Awesome advice. Just what I wanted to know.

[barnett468]

Last fall I finished assembling my 86 250r. I had all the engine work done by a reputable mechanic in the area know for the work he does on older two strokes. I had a .050" over Wiseco piston put in and a full FMF exhaust. When I started breaking the motor in I took it nice and easy. I had the stock jets in and everything seemed to be running great until I started tuning the carb. It was always running too lean through the whole powerband even though I had gone up to a 180 main and a 46 slow jet. This weekend when I pulled the reed cage off to change out the reeeds (which weren't all that great) I could see that the rings were wearing on the exhaust side of the cylinder.

Since I'm goin gto have to replace either the rings or the piston, how should I go about breaking it in?


Hello Mongo

I read all the posts including yours and after reading yours i have a question. You can not see the exhaust side of the piston rings from the exhaust side so i think you mean you see wear on the ex side of the cylinder when viewing from the intake, is this correct?.

Please answer all these one at a time if you want me to help you, your problem is probably not so simple.

What is the exact number on your spark plug.

Was it cold the day this happened?

Are you saying you saw wear on the exhaust side of the cylinder?

Did you see grooves in the cylinder?

Did you see any aluminum from the piston on the cylinder?

Did he port the cylinder?

Did he machine cylinder head to increase compression?

How do you know it was lean, what was it doing?

What size was original main jet?

Did you switch to the 180 before you broke it in?

What was the previous bore size?

What was the previous piston brand, stock, wiseco?

What oil and ratio are you using?

Can you send photos of the cyl, piston, cyl head chamber?

Was it pinging or detonating?
Here's what happened.
Here's wha

[barnett468]

Hello

I know nothing about your builder bit I will say that any decent builder would tell you about how far to jet up from your previous jetting based upon the type of mods that he did. Did he do this or just say here you go pay me?

If you answer my previous questions I and others can help you prevent this from happening again. Here’s a partial list of causes, others have mentioned and you know about jetting. You will get plenty of opinions on this from others.

You partially seized your piston/cylinder

When a cylinder bore is enlarged that much your compression increases. At a certain point this compression becomes so great it can cause detonation and/or preignition. Since these motors have high compression anyway it doesn’t take much of an increase of comp to cause deto or pre ignition. This can be reduced by the use of race gas. Another contributing factor to pre ign and deto is incorrect squish band on the cylinder head. When you bore a cyl out you change the ratio of the squish band to the bore size this will contribute to deto and pre ign. Also a replacement piaton like a wiseco often does not have the same dome angle on it as the orig. This angle difference changes the angle of the piston to squish band. This can also contribute to deto and pre ign. If your builder machined your head for increased comp but didn’t correct the squish angle like most don’t then this is one of the causes of your problem.

Since these motors were designed to run on 100 octane the lower octane gas today contributes to deto etc so they need to be set up with less comp unless you are using race fuel.

You can not always hear deto either so this causes another problem. If you have deto which is likely it is likely you can not eliminate it with jetting up. You probably need to jet up more for sure but you might need to correct your deto problem.

Your piston to cyl bore may also be too tight.

[barnett468]

Hello mongo

The following article was written by my friend Harry Klemm. Builder of many national and series championship bikes including one of mine. Hopefully this helps you.


About Proper Break-In Procedure

We have all met him …. The racer who boldly says “I break em in the same way I race em … just ride em full throttle”. Very sadly, there are a small few sets of circumstances were this bold guy is right.

Short Term Setups for short Term Break-ins - There are a number of engine builders who (for their own reasons) will set up the top end clearances of a high-performance two-stroke (piston & ring end-gap) considerably looser than factory spec. The most common reason for doing this is that the engine is prepared in a way that will cause very rapid wear to the piston and rings. Engines like this, often run very wide exhaust ports with very little radius for the rings. Such an engine would seriously wear the piston and rings before any break-in period could be completed, and so they are clearanced to go into immediate service with no real break-in at all.

In such engines, the loose piston clearances not only accelerate piston collapse and ring wear, but they also induce very heavy wear on the cylinder walls (especially around the exhaust port). While everything about this setup sounds short sighted and perishable (it’s both) there is an abundance of builders setting up engines in this way. At Klemm Vintage, we do not (and will not) build such an engine platform. Our engine sets are built for good long term wear and performance … and as such our setups “do” require break-in….. here is why.

A Bit of History - In the early years of high performance two-strokes, most piston rings were a raw cast iron material that very literally had to “wear-in” to perfectly seal on the new cylinder bore it was fit to. With such rings, it often happened that “full ring sealing” didn’t take place until the ring had been in service for a good number of hours. Getting any racer to run the engine easy for that stretch of time just wasn’t going to happen. To help ease this problem, manufacturers applied a soft Teflon “skin” on the outside of the ring sealing surfaces. This soft Teflon skin “sealed” to the new bore in a much shorter amount of time, making for faster break-in and true “sealed” performance in a shorter amount of time. The down side was that when the Teflon wore completely away, the ring end-gap became excessive for “ideal” performance, and the ring tension against the bore was also not ideal. This was a particular performance problem on high-rpm small-bore racing setups.

Wise engine builders began setting up these top ends with “much closer than spec” piston clearances in an effort to get proper ring-end gaps when the Teflon skin wore completely off the rings…. And it worked great as long as you had an oil with a very high film strength. What didn’t work out great was that the break-in time required for such setups was much longer … and no pro-racer could be trusted to “go easy” on the engine for that long.

The solution was to simply let the engine run 60-90 minutes on a stand at a high idle, with a fan or breeze blowing across the fins. This initial run-in wears away the majority of the “skin” off the piston rings. In addition, it gives the cylinder bore and piston-skirts time to “get familiar” with each other in a “low load” atmosphere. This is a procedure that we still use (and strongly recommend) today. It bears noting that after this “static” break-in running, there is still some “loaded” break-in operation needed. However the risk of a piston-scoring event during that break-in ride is greatly reduced.

About Wiseco Piston Break-in - There are an abundance of two stroke enthusiasts that speak with very little enthusiasm about Wiseco pistons. The common response is “you have to give them lots of clearance … otherwise they seize”. We couldn’t disagree more … and here is why.

In the 1970s, we made many attempts to use Wiseco pistons in two-stroke race motors…with very poor results. The truth is that Wiseco (at that time) had numerous materials and design issues that needed resolving. However, Wiseco has done a great job of evolving their materials and designs since the 70’s, and today’s Wiseco Pistons are an excellent choice for most high-performance two-stroke platforms. All that said, Wiseco pistons do have one design issue that they have intentionally have not tried to resolve … longer than average piston-ring break-in times.

The forged material that Wiseco uses for their forged pistons does require “a little” more clearance and a little longer break-in that typical “cast” type pistons … but that is not the unresolved design issue…. It’s the rings. The piston ring material that Wiseco uses is a very tough material that takes much longer than average to “seal” to the bores. While the Wiseco pistons themselves are not a particularly close clearance fit to the bores, the Wiseco rings are. In truth, the Wiseco rings are made brand new with an end-gap that is much too small for full temperature high rpm operation. However if a Wiseco equipped engine gets the slightly longer than average break-in period it deserves, the outer-skin will wear off the rings to result in an ideal “running” end-gap that will give excellent long term wear and service. If however, you try to run Wiseco piston rings prematurely hard, those rings will quickly expand until the ring ends make contact and literally “bite” the full bore diameter in the ring path. Some engine builders incorrectly give Wiseco pistons excessive piston clearance in an effort to resolve this ring end-gap issue.

We respectfully submit that Wiseco pistons can be fit with very close clearances, and offer great service … as long as you let the rings have their break-in time. Our 8500rpm Kawasaki Bighorn road race bikes are equipped with 82mm Wiseco pistons fit at .0035” clearance. These pistons never showed the slightest sign of piston scoring, even after 25+ hours of racing, dyno-passes and high speed testing. You cannot abuse a piston harder than we abused these…. But we did give the rings a long gentle break-in.

About “Dry Top End Assembly” - One step that helps reduce break-in times is to assemble the top end with no oil at all on the piston skirt or cylinder walls. This step has a history worth telling.

In the middle 1960s and early 1970s American muscle-cars were a very popular item on automotive showroom floors. At that time, it was standard procedure for Detroit manufactures to assemble all automotive engines with a generous helping of oil on the cylinder bores and pistons. When these muscle-cars were first fired up, the assembly oil on the bores would burn onto the bores as a glaze that took a very long time for the rings to wear through before sealing.

Unfortunately, this assembly process caused problems for salesmen in the showroom. When prospective buyers took a muscle-car out for a test drive, it was a given that there would be at least one full throttle blast involved. During that full throttle blast, the poorly sealing rings allowed considerable oil to pass, and the brand new muscle-car would leave a big plume of unattractive blue oil smoke that could be seen in the rear view mirror…. Buyers were understandably put off by anything that appeared to be “already burning oil”.

This was a very real problem that Detroit had to address. In time, they learned that if they assembled the top ends dry, with no oil on the bores or pistons, they could avoid this initial burned on cylinder glaze. The result was much shorter ring sealing times (because the rings didn’t have to wear through that glaze), and the absence of blue smoke from those important test drive blasts.

This same rule applies to two-strokes … vintage or not. Some owners shy away from this assembly process because they fear scoring the piston … but it is an unfounded fear. On such assemblies, we do apply assembly oil to all the lower end bearings. In the first moments of initial combustion, that lower end assembly-oil disperses on the bore in even quantities that are easily enough to avert any kind of scoring. In addition, it bears noting that the lubrication needs of an unloaded engine spinning at very low rpms are very minimal. We have been assembling high performance two-strokes in this way since the early 1970’s. It works … and it results in greatly reduced ring sealing / break-in times.

[Mongo]

165078
(The picture is upside down the piston is on the bottom)
The previous piston was a Wiseco .030" over when I bought the bike. It was a basket case when I bought it so I know nothing of its previous running condition. The spark plug is an NGK BR9ES, I used a mix 20:1 Amsoil, the original jets were both stock. I ran it through the heat cycles described earlier though probably not exactly on a warmer day. Originally it was fouling plugs for the first couple weeks then started running leaner. I tried properly jetting it using the jetting guide on this site doing plug chops until I hit 180 on the main then I knew there had to be something wrong. I pulled the reed cage out to check the reeds and took a couple pics of the inside of the cylinder while i had the intake off when I noticed the scoring on the inside of the cylinder.

I don't know exactly what the builder did for the cylinder head. He may have told me about jetting it properly when I picked it up but I was probably more focused on getting it in the bike and in the woods.

[barnett468]

Hello

Thanks for the photo.

I still don't understand what jetting you started with i need jet numbers i don't know what sizw stock is.

HOW BIG DID YOU INCREASE YOUR JET SIZES BY.

you ran it with what you know to be stock jets or you assumed the jets were stock.

Everything i asked you is very important.

shoot me a photo of the cyl head if you can.

WAS IT SEIZED WHEN YOU BOUGHT IT? CYLINDER SCORED AND PISTON DAMAGED ETC?

ask him if

[barnett468]

Cylinder is definitely scored, hopefully it can be honed and doesn't need a bore to .060.

send photo of piston i'll tell you if it's reusable if i can see good enough.

was it running rich originally or just oil fouled.

you might have generated an intake or other air leak causing it to go lean.

[Mongo]

165079

This is what I started with.

I don't have any more pics as the engine is still in the bike. The stock main jet is a 142 and I started increasing two sizes at a time doing plug chops with each one (though it may have been after the cylinder was done in that I statrted this). I gradually increased the amount I went up on jet sizes til i hit 180 then decided to look for other things. When I bought it the motor was tore apart and the original piston was cracked.

Thanks for all your help by the way.

[barnett468]

hello

no problem your welcome. it's fun as lonmg as the people with the question help out. this means answering all questions and performing all tests requested within reason. if the pwerson with the question does not do these trgings we can't help and leave them with their problem.

At the very least you need to start with a 170 jet.

i personally would break it in by turning idle screw up till motor is at around 1500 rpm with fan on motor. i don't care what anyone else says unless it is harry klemm or dave miller.

you should use race gas mixed with 93.

yes it siezed before you got to 180

you probably need to have your head squish band fixed by a race shop. klemm may do it.

you may also need to reduce compression if not ising race gas. it can be done by modifying head,

you can use a slightly thicker head gskt instead but this is not the best way as it changer the quench volume [distance from head].

things are not as simple as many make them sound.

[barnett468]

what ratio was your oil mix?

WHAT OCTANE GAS DID YOU USE?

[yaegerb]

My .02.....you got the motor back and started at a 148 main, then went to a 152, then a 158, etc? That may be your problem. When you break in a non-stock motor (yours isn't stock due to the .50 over and full FMF) you need to start fat and work your way lean. You should have started with a 180 main and 52 pilot and then worked your way down from there. For example, I am running a full FMF with a second bore on my R and my main is a 170 with a 52 pilot. My mix is 36:1 with 927 Maxima Castor. Always better to start rich (fat) and work your way down. Either way, that cylinder scoring looks pretty bad. I hope you can get away with a hone and some new rings.

[barnett468]

HELLO

Yaegerb is also familiar with jetting from what i have seen. As you can see he uses the same jetting technique i mentioned to you. coincidental that he just so happened to end up using the same 170 jet i told you to start with isn't it?

like i said jetting is probably not your only prob and it will seize again if it isn't properly fixed.

You should check your timing marks also he may have advanced the timing too much. this will also promote detonation.

[Mongo]

I have run 93 octane through it since I first started it at a 20:1 mix. I was told by a friend that the bike needed to be jetted for the pipe and bore AFTER I had run it for a few hours. I went up slowly because I thought the bike was running great at the time but the more and more I went up it seemed like the worse it got, hence the checking the reeds and cylinder.


I'll see if I can get the motor pulled this weekend and post some pics of the damage.

[barnett468]

hello

thanks for the info. your first post said it ran rich yhen went lean then you jetted it.

is your amsoil synthetic?

believe it or not few of the factory guys use 20.1 we typically all use 32.1 unless it's a high rev machine like road race etc..

more oil does NOT mean more protection and it can cause other problems.



MORE FROM HARRY KLEMM


Piston Seizure Vs Piston Scoring - Piston “seizure” and piston “scoring” are two different stages of the same problem. When the oil film on a cylinder is momentarily burned or brushed away, the bare metal surfaces of the piston and the cylinder wall will actually touch. When this happens, there is a sort of scraping that takes place between them. If the oil film is quickly resumed, the marks from this scraping will often remain on the piston and (or) the cylinder wall. A momentary scraping or "scoring" seldom causes any permanent or performance robbing damage. In a momentary scoring event like this, no significant damage takes place because the oil film is resumed before the piston and cylinder have a chance to start exchanging material onto one another.

Scoring is commonly seen on the piston face directly below the piston ring end gaps. The blast of combustion can get between the large end gap of a worn out ring and burn the oil off the piston and cylinder in that area...Hence the surface scoring. In most cases, score marks can simply be sanded off of the piston and cylinder. However when ever you see scoring, it's a good idea to find the source so that it doesn't develop into a full blown seizure.

Piston seizure is a case of scoring where the oil film does not immediately return. After a few moments of constant scoring, the piston and cylinder will scratch each other hard enough to remove material from each other. This floating material grinds itself into the piston and the cylinder as it continues to grow in size. As this snowballing material grows, it will drive the opposite side of the piston against the cylinder wall with a pressure so terrific that scoring on the other side of the piston begins to take place. While all this is going on, your engine is still running wonderfully at full throttle. However if there is a momentary lifting of the throttle, the force of this scoring can cause the piston to “seize” in the bore. In a “light seizure” event like this, the rings often escape any damage, and the engine will easily re-fire as soon as the engine cools down slightly.

The death blow of a “power-on” seizure comes when the mass of material between the piston and the cylinder wall finds it's way to the piston rings. This nearly molten mixture of aluminum and iron can lock the ring in it's groove. This ring locking, not the piston surface scoring, is what actually causes your engine to quit when you experience a “throttle-on” seizure. When the piston ring becomes locked back in it's groove, it's incapable of providing compression sealing against the cylinder wall. This instant loss of compression, while the engine is at speed, causes a dramatic loss of power. That power loss, along with the added drag of the badly scoring piston, makes the engine quit or lock up in a nanosecond. In fact this entire seizure process, from the first scoring scratch to the piston locked solid, takes less than a second at full rpm. In such a failure, a single cylinder engine will seldom restart.

[barnett468]

Hello

Here's a question which amsoil did you use, hp, interceptor, dominator or saber? Dominator is what you should use in amsoil brand not the others even though interceptor says good for power valves it is high detergent and you do not want high detergent motorcycle oil in a 2 stroke.

The maxima 927 that ride-red250r and yaegerb use is the best, however you don't need it, it's expensive and does not mix with ANY other oil.

Do not reuse your ring even if it looks good i guarantee you it is not.

JETTING TEST - Your piston can also seize if this is done improperly. You can not rev it to the moon then simply close the throttle with it still running. It may seize especially on a new bore.

Are you beginning to see your problem is not so simple as just running lean but it is a significant cause.

It seized because it got hot then the piston then either swelled up and dragged on the bore or it got hot and burned your hp or interceptor oil away.

Why do you use amsoil instead of bel ray or other's etc?

SPARK PLUG - The plug you have is perfect for ideal conditions unfortunately your conditions are not ideal yet. a br10es or b10es might be better to use untill it is broken in nest time but it still probably would not have saved you here..

REEDS - If your reeds were leaking your bike would not idle prooerly if the were leaking this is bad.

HEAT CYCLE - this is just because a new motor runs hot and they want you to shut it down before its too hat and seizes. if it is bult right this is unnecessary but it doesn't hurt if you run it under light load for 15 minutes at a time for 3 cycles once you break it in as i mentioned.

[RIDE-RED 250r]

2 things I disagree with you have said barnett,

#1: A STOCK spec 250r engine does not require race fuel. Straight out of my Honda service manual, 92-100. Octane rating is octane rating. Rate of fuel degradation amongst different types of fuels/additives IE, ethanol vs non-ethanol is a different story... But the 92-100 fuel octane range gives you options, and you may have to address running on the lower side of that range with jetting... You are right about squish band. But at normal overbore sizes for a stock cylinder the effect is minimal. Compression/compression ratio is not increased on say a stock cylinder vs boring that stock cyl .050" over.

#2: Unless that engine has a CR250r ignition, or aftermarket adjustable timing CB carrier, there are no timing marks to check and no way to adjust. Stock 250r ignitions are not adjustable.

But I do agree, it sounds as though he just started too lean on jetting for the bolt-ons he is running... :(

How are the crank seals?? Replaced? If so, it's possible they were not installed or the crank not installed correctly??? May have folded a seal lip over and now is leaking??

This is why I do my own engine work other than machine work... And I only dont do that because I don't have the access to the machinery needed. When I put an engine together, I know that everything is right... at least to the best of my ability.

[fastatc70]

Looking at the cylinder it looks like you may have a air leak between your carb and air filter.( unfiltered air). What ever you run for oil you must go very rich on your main, pilot and needle.

Run through three heat cycles and start to go lean.
I have been running a 250r 4 wheeler for 4 years before rebuilding. Sand, road, ice racing and trail riding. Just started to loose compression. Just jet a little rich. It keeps the combustion chamber a little cooler and just a little more oil and some people say it adds a little more compression due to more oil around the rings.

Also check your ports for knife edging. If your ports are sharp it will shave oil off of the piston and you will seize and have accelerated ware


I my opinion run what oil you like ( brand name). Everyone likes something different and discussion about what oil is best is like discussing religion or politics.

I have run almost everything out there due to sponcers and friends that race and it all starts at jetting.

[barnett468]

Hello Mongo

Fast atc70 has added something else to look for. I don't think you're damage is from sucking sand into your cylinder however simply because sand would cause damage random damage throughout your cylinder and if this was the case I wrongly assumed that you would have mentioned some damage to the intake side of your piston skirt also however even if there was damage to the intake side of your piston skirt it in no way eliminates the possibility that your piston started seizing it merely increases the likely hood that sand may be at least a contributing factor to the damage. If the damage is confined to the exhaust side only however than it virtually 100% eliminates the possibility of sand being the sole cause if any, of the damage. This thinking process is called deductive reasoning. That being said by ALL means check that too I certainly would.


My sole purpose is to determine exactly what your problem is if possible and prevent it from happening again and NOT to simply suggest putting a band aid on it because it is easier, including less typing for me, or simply because I don’t realize that I don’t have the depth of experience and knowledge that some others do. Although these people mean well it can be like taking medical advice from your friends.

All the information I have provided are proven facts, I occasionally have educated guesses “opinions” but never misconstrue the two or attempt to offer known opinions as facts as some others do. If I did this I wouldn’t have been employed long.

I suggest that you carefully read ALL the information supplied from EVERYONE so far and do what you think is best. I will 100% guarantee you though that simply taking the EASIEST approach to your problem may not be the best.

To Red [and Mongo]

I am giving you the benefit of the doubt by your comments that you CLEARLY did not understand the entirety of my post or the statements I posted from Harry Klemm which were NOT mine.

Quote from big-red-250r - "You are right about squish band. But at normal overbore sizes for a stock cylinder the effect is minimal. Compression/compression ratio is not increased on say a stock cylinder vs boring that stock cyl .050" over.

#2: Unless that engine has a CR250r ignition, or aftermarket adjustable timing CB carrier, there are no timing marks to check and no way to adjust. Stock 250r ignitions are not adjustable."


Do you know if his cylinder head has ever been modified by anyone in any way including that which would increase his STATIC compression or alter his “squish” band? I do not and the owner does not so since I am not there and am not psychic as others appear to be I assumed it was reasonable to err on the side of caution and until it is determined otherwise speculate that it might be. My personal experience with squish bands including testing them for Harry Klemm on pre production t3's and my company sponsored pro level t3 [which did not detonate and holeshot many pro races two of whuch included Jimmie White, of which one also included Marty Hart which I won] that changing the squish band and subsequently the quench area including that of simply boring out a cylinder does have a significant affect on some models. I do NOT know about the magnitude of this effect on the atc250r models however but it obviously makes basic as well as scientific sense that it would have some and none of these effects would be beneficial!

1. Nowhere in my posts did I EVER say Mongo NEEDED to run race gas in his STOCK bike however now that I read my comment that I posted again below, I realize that I merely could and should have added the word “MAY” in front of the word “NEED”. So in the interest of trying to keep the peace I will agree with Red that in all the individual words that I have voluntarily spent typing in an attempt to help Mongo understand some of the potential causes of his problem that I did in fact CLEARLY make a comment that I agree is less than exactly what I meant to say and for that I apologize to anyone that takes exception to it. I have rewritten my statement below in a way that I hope more clearly explains what I was trying to say in my previous abreviated statement.

“Since these motors were designed to run on 100 octane the lower octane gas today contributes to deto etc so they need to be set up with less comp unless you are using race fuel.”

Since that in my extensive personal first hand experience I as well as others including obviously Honda has determined that these motors were IDEALLY designed to run on 100 octane gas that due to the current “blend” of todays pump gas and it’s occasionally inaccurate octane ratings that If you determine that you are having levels of detonation that can cause engine problems one easy, but not always guaranteed, way to reduce your levels of detonation to those that are minimal and acceptable then one can simply use gas with a higher octane rating.

The problem with this technique is that not all detonation is easily heard and not all people are experienced enough to know what deto sounds like and therefore might not know when this is occurring. Also you may be having unacceptable levels of detonation that are either difficult or impossible to hear. Both audible and audible levels of detonation that can either contribute to, or be the EXACT cause of the type of engine damage you currently have.

2. By your own comments you say the Factory Honda Owner’s Manual says to run octane levels of between 92 and 100. I personally have no idea what the Honda manual says regarding proper octane levels for their bikes. I would assume if that’s what they say then that is absolutely correct. The problem I personally have with running 100 octane pump gas in ANY bike is that where I live they quit selling it at the local gas stations around 25 years ago! This leaves me with the following dilemma, if my bike dertonates on 93 octane pump gas and I want to run a higher octane gas to try and reduce the detonation instead of properly modifying it so it will run on 93 octane, or if I want to run a higher octane gas because I simply like the smell and/or exhorbinate expense of it or whatever then I have the option of using additives, which have never been very successful for me or buying race gas and mixing it with regular gas or just running it straight if I want.

3. I never said his STOCK timing was adjustable so again, it’s impossible to disagree with me regarding a statement that doesn’t exist. I merely felt that because I honestly did not know whether it was adjustable or not and his bike is around 25 years old and has had previous owners that could have changed ignitions etc over those years that it might be beneficial to suggest this just in case it was adjustable since no one else mentioned this possibility. I again apologize for not being psychic and therefore not knowing what his current ignition system is.

Quote from ride red - "You are right about squish band. But at normal overbore sizes for a stock cylinder the effect is minimal.

Excerpt from my previous post - "When you bore a cyl out you change the ratio of the squish band to the bore size this will contribute to deto and pre ign. Also a replacement piaton like a wiseco often does not have the same dome angle on it as the orig. This angle difference changes the angle of the piston to squish band. This can also contribute to deto and pre ign. If your builder machined your head for increased comp but didn’t correct the squish angle like most don’t then this is one of the causes of your problem.

I can only suggest to you that if you want to debate the FACTS I posted that you contact either Harry Klemm, builder/tuner of bikes, trikes, quads and jet ski’s that easily claimed over 30 National AMA Professional motocross titles, National Pro Watercraft titles, National Pro 250 ATV titles [enter “Jimmie White” in your search engine] series championships like mickey Thompson off road champion ships and annual annual pro race championships of which I have two, beating Team Honda at both of them or Dave Miller currently Previously of FMF or DG the owner of Miller Mano [whom I was sponsored by] and currently of DMC products. Sorry I forgot to mention that you could also call Honda, Kawasaki, Yamaha etc. also to discuss the issue with them if you are so inclined, I’m sure they’d love to do that.

Do you know if his cylinder head has ever been modified b anyone in any way including that which would increase his STATIC compression or alter his “squish” band? I do not and the owner does not so since I am not there and am not psychic as others appear to be I assumed it was reasonable to err on the side of caution and until it is determined otherwise speculate that it might be.

EFFECTS ON BORE SIZE VS COMPRESSION – In the case of the 86 250 r as well as the tecate t3 and other 2 stroke engines of the era with similar compression ratios, increasing the bore size from a stock purported bore size of 70.0 mm [that of the 86 250r per online info], to your current purported bore size of = .050” which converts to 71.25mm. Using the free online compression calculator [url posted below] your compression increases by an approximate factor of .4%. This may not sound like much but as I mentioned these motors were high compression and the tecate t3 definitely had NOTICEABLE detonation under hard riding conditions as delivered stock from the factory [causes of which are not necessary for me to go into here]and the smallest increase of compression can EASILY push it to the level of engine damaging detonation. I can absolutely guarantee you that if one bored out [which you can’t]a box stock t3 to .040 over or more I guarantee you it would not last long. Race gas did eliminate the audible detonation on the stock t3’s 100% in research testing ergo another one of the reasons for my suggestion you might try using higher octane gas etc.

[barnett468]

Quote from ride red 250r - "Remember, when you "richen" your premix (ie adding a higher amount of oil) you will actually LEAN your fuel/air mix for combustion. Premix oil displaces fuel, and as such, adding more oil will actually lean your combustion fuel/air mix."

Ride Red 250r

The above statement from you which is posted on the internet in dozens of places is in fact correct for most intents and purposes however I have yet to see any of these individual statements fully and accurately explain the complete effects that different gas/oil ratios have on a 2 stroke engine. If you know anything additional regarding this topic including that which you can locate on the internet if you feel a need to please post it for others to read as I'm sure it would be interesting and possibly beneficial to some peoples understanding of the subject and how it can affect their engines performance etc.

I personally avoid making statements I do not understand within reason unless I supply links to and/or excerpts from qualified articles that accurately and adequately support my statements. Occasionally I will still supply supporting documentation when I feel others might want to contest my statements.

FYI - You could also use the word 'enrich" in place of "richen" if you wanted to be more technically correct in your statement above however I certainly don't always use the most technical lingo either but in my case it is usually by choice and not due to a lack of a technical vocabulary.


I will be happy to answer ANY questions that ANYONE has for me including any from ride red 250r to the best of my ability if in fact I have an answer for them in the first place as long as they are intelligent and meaningful and NOT intentionally designed to be argumentative or create problems. I will rarely if ever answer the same question twice within the same post. If one doesn't read my answer or ANYONE else's for that matter I don't think they are either intelligent enough to understand the question or courteous enough to read ones reply in the first place.

I am the last person to think I know it all and there have been many on this site that have come up with things I didn't think of and/or explained their answers in reasonably to very concise articulate ways. This is a very difficult thing for anyone to do.

I never argue as there is no point in it. I try to do it right the first time or I realize I may possibly have to do it again later at probably a much higher cost. I never assume anything where that assumption could have a negative impact of any consequence.

[atc300r]

Did the mechanic relieve the exhaust bridge and drill holes in the piston where it rides against the exhaust bridge.I always break in a new engine or two stroke on non sinthetic oil.

[RIDE-RED 250r]

Ya know Barnett, you seem a smart fellow with alot of knowledge..

But, your attempt to bismirch and discredit me for factual information I posted is neither warranted nor appreciated. I like your sarcastic invitation to be educated by you and your indirect accusation that I post about subjects that I don't understand.

I'm not going to go to the trouble of qouting examples of this from your posts.

If you want to discuss it further, PM me.

[barnett468]

Hello Mongo

Ride Red 250r

Unfortunately for you anyone that reads our posts can easily see that you were the first to question [disagree] with my FACTUAL statements not the other way around like you are now trying to make it sound. So using your own terminology, you were the one who tried to “besmirch” and discredit me first not the other way around. My subsequent reply to your original attempted “besmirching” of me was merely a corrective one to counter your inaccurate, incomplete and or “out of context” information. It was not designed as an attack or a first strike which all can see.

Another problem you have is I supported my statements with documented FACTS and also with articles from other professional sources, you supplied no such documentation to support your counter claims did you? Is this because it doesn’t exist?

Another problem that everyone can also see is that for some reason it “reads” like you are absolutely 1,000% positive that Mongo’s head and cylinder etc are 100% stock and unmodified after going through previous owners and over 25 years of existence. After reading this statement for the third time now are you still going to tell everyone here that you believe this is true. I guess we’ll just have to wait and see.

Mongo has a problem, I assume nothing and try to find out via photos and hopefully from his builders info EXACTLY what he might have. I as well as everyone here including you are trying to help him “blindly” from a computer. Now you want to try and berate me for simply trying to help the guy using my accumulated knowledge [what ever that may be] and for trying to cover ALL the bases not just a few? Why would you do this to anyone? It looks to everyone that you are missing the point which is trying to HELP Mongo and you instead want to try to turn it into a “who’s right” contest.

I have no desire to make enemies but I will not sit back and allow someone to tell me I’m wrong when clearly I am not. I will also be the first one to admit I’m wrong if I find out I am. I am all about FACTS, I am not about being RIGHT.

FACTS or NOT the facts, friends or not friends the choice is up to you!

[Howdy]

barnett468, Do you have ANY friends? I ask because I don't see you gaining any here. Custom user title is under review.

FYI, We do have a rule that allows us to ban stupidity.
Howdy

[Mosh]

There is more text in this thread than the whole damn service manual for a 250r. Mongo. Your jetting on a stock carb with over bore cylinder and FMF system should be in they 48 pilot and 165-170 main range in my experience. Without seeing better pics of the jug I will make the assumption that your machinist did not chamfer your ports and your rings were clipping causing premature: wear. But run anything other than Amsoil. I have no confidence in that stuff. Regardless we need more pics of the jug and piston and how you ride and in what conditions.