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]

(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]

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.