Tri Z Engine Build

[El Camexican]

This post has been too long in the making. For anyone thinking this project was dropped (Bill?) let me assure you a day hasn’t past when I didn’t put some thought or action into it.

Speaking of action, I came to the realization that if I just keep reading and theorizing this thing will never run again, so good, bad or otherwise it’s time to start wrenching and hope for the best.

There is no way I can coherently get all that has gone on into one post, so I will just title each aspect and spew as much info as I can under the header for now. Perhaps if the thing actually runs I’ll take the time to put it into some sort of order.

The Cylinder Head

According to what I’ve read the squish band area should range from 40% (Top end power) to 60% (bottom end power) of the cylinder bore. Here is what these heads come out to according to my math (Mr. Clean is likely shaking his head at this point):

- Shaved Stock Head 40.75%
- Sprock Pump Gas Head 53.92%

If what I’ve been reading is correct the stock head had no place on a “spirited” trail engine. It also might explain why they run hot as more of the piston crown is exposed to the heat generated by ignition. Regardless, on paper it should make a good drag head… except for two other things.

I proceeded to mock up the engine and check piston to head clearance a second time using solder wire. According to what I’ve read the clearance in the squish band area should range from a min. of .015” to a max of .060”. Less clearance being better for a number of reasons regardless of application. After rotating the engine once to compress the solder wire it was removed and measured in three places, 1mm from the edge, the middle and 1mm before the squish area starts to transition into the dome. These are the measurements I got starting at the outside:

- Shaved Stock Head .060” - .065” - .078”
- Sprock Pump Gas Head .047” - .059” - .063”

Again more reasons for the stock TRI Z to run hot as gases are given more space to spread over the piston crown.

Next was to CC the two heads. Bit of a PITA, but I repeated the measurements a half dozen times with the same results. Instead of filling the chambers with a syringe I instead filled them from the tap using a CD as a top and then extracted the water with a syringe to measure it. This left water in the sparkplug, but other than that worked pretty well:

- Shaved Stock Head 19cc
- Sprock Pump Gas Head 22cc

I had a 180psi reading on the engine before I pulled it down, so losing a little static compression shouldn’t be a bad thing.

So what next for the head(s)? In theory nothing, at least not until I run it. After that I can decide if I want the power band to be raised or lowered and depending on which deck either the top or bottom of the cylinder up to .030” where the squish would be as small as I’d dare go. .020” would be the likely cut.

As far as reshaping either combustion chamber I would say the stocker would need the most work to fit what is desired, so I think the Sprock head will be left as is until all other options have been explored. It seems to have hit the theoretical bull’s-eye dead center by being close to a perfect all round shape and leaving room for decking as well as being large enough to cover a 69mm bore. Some thought went into this thing.

[El Camexican]

Port Timing

This is where most of my time has been spent. Rather drop the big bucks on a CC Specialty tools I instead risked destruction of a Dremel 90 degree adaptor by grinding the housing down to the point that some of the factory sealed lubricant is seeping out of it and then ground down the shaft and collet as well as cut some of the bit shafts.



This barely allowed me to get the thing into the cylinder. Unfortunately the Dremel has to be turned off and on by ones second hand and during one of the hundred or so times I had to perform this trick I managed to nick the cylinder wall twice. I think I can get away with as they are below the tops of the transfer ports. Good news is that a .5mm cut will remove them on the next rebuild. Bottom line; don’t try this at home unless you’re willing to trash a cylinder.

Without stating exact measurements (as I haven’t made a complete new port map yet) I essentially raised the center of the exhaust port another 1.5mm, the transfers 1mm as well as widening them about the same amount or more.

An effort was also made to flatten the roofs of the transfer ports rather than leave them pointing towards the combustion chamber. The exception being the boost port above the intake port which had a nasty hook in the casting. That was removed and it now points towards the spark plug. The final goal was to angle the transfers more towards the center of the cylinder than the rear of it.

So how does one test all this? I wish I knew. The only thing that came to mind was smoke or water. I tried using a cigar and ended up dizzy and coughing with no results, so the lawn hose fitting was cut off and stuffed into each port. This is where having NeverLift’s almost stock donor cylinder was invaluable.

The secondary transfer ports were a little disappointing. While the water does exit in a wider pattern than the stock cylinder, part of that width seems to be closer to the intake side of the cylinder than the water that spews through the stock ports. I’m trying to convince myself that the modified boost window will combine with this flow and create some sort of “super vortex”, but in reality in might just create a swirling glob of tranquility. I simply can’t get in to that port with the tools I have to change that pattern and if I could I don’t think there’s enough aluminum to do it, so next comes JB Weld and another month added to the project… you get the point.

The seeing the water pattern come out of the main transfers made me very happy. Not only were they shooting almost straight across the cylinder from side to side (the secondary transfers were too), but they were significantly flowing more towards the center of the cylinder than towards the rear and more consistently between the two that the stock cylinder as well as wider.

It was difficult to take these photos as there is a split second during which you feel that the angle of the hose is not adversely affecting the way the water is coming out of the port, but I think these two photos show the changes to the main transfers’ best.



In this photo of the stock cylinder you can see the water is shooting out of the stock port almost directly at the rear of the cylinder (perfect for bottom end power). Use your imagination a little and you can see that part of the boost port window is above where the water is hitting. Forgetting gravity for a moment this would indicate the angle of the transfer port roof is slightly towards the top of the cylinder.

Now look at this photo of the ported cylinder.



The water is shooting straight out of the port and across to the secondary transfer port on the opposite side of the cylinder. Exactly how many degrees that I I don’t know, but it’s significant.

So will any of this make the engine run better? I have no idea, but it was fun to do and it will be even more fun if this thing revs like a pissed off wasp and doesn’t blow up. Stay tuned for more unfounded, half thought out, irreversible modifications to discontinued engine parts.

[barnett468]

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Hello Nico . . I’m not sure what you are talking about regarding the piston crown so I have posted some general info below . . I realize you know at least some of it and you may know all of it but I posted it just in case any of it might be interesting or helpful to you.

HEAT TRANSFER

Heat transfer is complicated as you know but in general, a lot of the heat is transferred to the water by the piston sides and mostly thru the top piston ring, therefore, if the heat to the edges of the piston crown is reduced, the amount of cooling provided by the piston are reduced . . Obviously this heat must go somewhere so it will be focused more in the center of the piston which can overheat it plus more heat will be transferred to the cylinder head.

Depending upon design, in many applications a big percentage of heat is absorbed by the cylinder head then transferred to the coolant then the radiator [or fins if the engine is air cooled].

Because of this, if the crown of a piston is caused to run cooler by any means which includes the application of thermal barrier coatings, it is important that the head is able to process and eliminate this heat, but unfortunately, most water cooled engines do not have external cooling fins to help eliminate this heat.

One simply cooling aid on a water cooled engine is to add fins to the head and/or top of the cylinder . . On an air cooled engine, the fins can simply be extended outward.

Also, a lot of the heat is transferred to the cylinder walls by the top piston ring . . These rings are not always perfectly flat on the bottom or top . . Lapping the bottom and top surfaces if possible will increase heat transfer from the rings to the cylinder by increasing the contact area between the piston ring and ring land . . They sell piston ring lapping stones for this exact purpose.


COMPRESSION

We ran all our two stroke 250's at Kawi at around 200 psi cranking compression with race gas and had no detonation so you could go up a bit if you wanted provided your ignition timing is spot on for your particular app.

[El Camexican]

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COMPRESSION

We ran all our two stroke 250's at Kawi at around 200 psi cranking compression with race gas and had no detonation so you could go up a bit if you wanted provided your ignition timing is spot on for your particular app.

I'm actually glad the Sprock head is larger than the previous one. It will allow me as you say to go up if desired and not have to worry about going down before I even get it running. How it runs and behaves will determine the next mods. I've already made way too many without any testing. Not a good thing ever.

[poolieZerUK]

The cost of the CC porting tools has put me off, have seen these buy not sure how they would compare?

http://www.ebay.co.uk/itm/DIE-GRINDE...item2a41dd2ea8

Someone here may know, but they are a lump cheaper, and you only get what you pay for

[barnett468]

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Yeah, even at 170, its still quite respectable and I would use the same approach that you are in this type of situation . . I just posted the race bike compression so you would have some reference point as to what worked for us in high perf apps and therefore where you might be able to go with yours in the end . . The compression was similar for the pro jet skis . . Of course they had the benefit of using an endless supply of cold water so they could regulate the temp to whatever they wanted.

[El Camexican]

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Yeah, even at 170, its still quite respectable and I would use the same approach that you are in this type of situation . . I just posted the race bike compression so you would have some reference point as to what worked for us in high perf apps and therefore where you might be able to go with yours in the end . . The compression was similar for the pro jet skis . . Of course they had the benefit of using an endless supply of cold water so they could regulate the temp to whatever they wanted.

Yep, I have a peak PSI of 200 in my notes. Keep in mind I'm at 1,770' and Haspin Acres is well under 1,000'. Any one know what it is where the drags are held?

[El Camexican]

Made a little progress over the weekend. Started by taking the cylinder to PG Racing to have .020” removed from the top. Anyone remember Pedro “Speedy” Gonzalez? He’s the only Mexican to ever get a factory ride on the AMA Supercross circuit. His dad runs the business and is a heck of a nice guy who’s always happy to show off his latest projects.


With the cylinder almost done I started on the intake. The first order was to match the rubber boot to the aluminum and then the aluminum intake to the stock cage.
The rubber was easy, but transitioning the aluminum Sprock Racing to the stock reed cage required some epoxy filler on the top and bottom as well as opening up both sides of the block.


I’ve decided to start off with the stock steel reeds with the stops opened up 1.75mm on each side and if need be I may try fiber reeds to see what the difference is. Until I can see and touch a V Force reed cage I’m not going to drop the coin on one.

Next task was to change the clutch springs. Got lucky and was able to save the gaskets. A little oil on the paper pre-assembly is a wonderful thing. Check out the mesh pattern on the clutch/crank gears. The clearest image in the Yamaha manual shows the same.



Once the cylinder is back I plan to match the Tri-Z piston skirt to the cylinder base, take some measurements and button it up. I have a YZ piston on order, but it’s 3 weeks out, so it will have to wait its turn.


Once it’s running and jetted with the DG pipe I will have to decide if another pipe configuration is needed.

[onformula1]

Yes, I race with him a few times, really nice guy.

He is best known for racing for- Mitch Payton’s Pro Circuit Kawasaki team and came away with a win in the 125 AMA Supercross at San Jose. He did well at the Mammoth Mountain Motocross against the best races from around the world too.

[El Camexican]

Yes, I race with him a few times, really nice guy.

He is best known for racing for- Mitch Payton’s Pro Circuit Kawasaki team and came away with a win in the 125 AMA Supercross at San Jose. He did well at the Mammoth Mountain Motocross against the best races from around the world too.

Small world. The oldest of the two shops here in MTY is 5 minutes from my house. Pedro Jr. raced MX in 11 different countries, not bad for a local boy. If you were a little older you might know this guy too He's a little heavier these days and owns a VERY nice 1992 WR250

[onformula1]

Did you use JB Weld, the color looks close.

Just use the stock cage to try and get some high tension carbon fiber reeds for $54.95
Check with them but the 1988-92 YZ125 reeds should be correct

http://www.carbontech.com/motor/yamaha.html

Also, check how close the reed cage is to the Boyesen boost ports, if it's blocked off a lot run a reed spacer.

[onformula1]

Small world. The oldest of the two shops here in MTY is 5 minutes from my house. Pedro Jr. raced MX in 11 different countries, not bad for a local boy. If you were a little older you might know this guy too He's a little heavier these days and owns a VERY nice 1992 WR250

It that you?

Ammex was cool, stands for- American-Mexican, Gary Jones company, 4 time AMA national champ and a very nice guy! He got hurt and Can-Am bought out his contract so he formed his own company to continue to race...Bad

Those engines were half CZ and half YZ like.

[El Camexican]

It that you?

Ammex was cool, stands for- American-Mexican, Gary Jones company, 4 time AMA national champ and a very nice guy! He got hurt and Can-Am bought out his contract so he formed his own company to continue to race...Bad

Those engines were half CZ and half YZ like.

Me? Hell no, I still had playing cards and clothespins on my bicycle spokes when that photo was taken! #73 was sponsored by Islo and raced MX for them for many years. He also helped them develop (copy) the Husky laydown shocks by moving the mounts on his factory frame here in town and them letting them copy it.

[onformula1]

Who else owns a VERY nice 1992 WR250?

I thought only you did.

[El Camexican]

Who else owns a VERY nice 1992 WR250?

I thought only you did.

Nope, not mine. That bike was rebuild for him as a X-mas gift (his son-in-law is friend of mine). I did get to ride it a few weeks ago though. It needs jetting badly, so it will be back at my place soon enough