Matching Tri-Z and YZ case halves

[El Camexican]

Messing with case halves tonight trying to get 2 good sets out of 4 lefts and 5 rights. Not as easy as I thought it would be.

After swapping them all back and forth only one set of the cylinder base surfaces are perfect (they came matched from the factory) and a second set is flush at the rear and .002” different at the front.

All the others, including some that came as a set from the factory vary from .002” to .007”, but most are off by .004”.

I plan to get at least one set skimmed, but I don’t like the idea of the crankshaft and transmission shafts being misaligned by .004”

So word of warning to anyone building one of these engines, at the very least check what you have and lap your cylinder to your cases to avoid air leaks and stress on the cylinder mount flanges.

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Maybe Mosh will be able to add something to this topic?

[lndy650]

ya cases are matched sets for a reason. personally id never use a mismatched set.

[El Camexican]

ya cases are matched sets for a reason. personally id never use a mismatched set.

That is exactly what I used to think before I came on this site and started learning about vertically split cases. Most of my motorcycle engine experience prior to coming on this site was with multi cylinder four cylinders which as you are well aware cannot share upper and lower cases.

I do have a pretty vivid recollection of the early 80s Honda CR 125 and 250 engines having air leak problems because the left and right cases had been missed matched at the factory, but since then I’ve heard of many people replacing just one half of a set.

I guess it all comes down to the tooling and machining methods. In theory if the case halves all used the same pickup points and all machining processes were performed without removing them and placing them in different machines they woul all be close to the same, but I would think that the holes are bored on one machine and the surfacing on another. Then consider some 5 years of production and its pretty impressive that two parts that came off the line in different years could be as close as they are.

What surprised me was that some of my “matched” sets were off by .004” although they may have been switched by someone else over the past 35 years.

[lndy650]

yes people do often do it and your right its amazing how close different sets can be. I just never liked the idea of my crank being out of line even the slightest bit just makes me nervous. id rather buy a set that i was certain or as certain as one can be that they were original pairs

[Billy Golightly]

Not specifically on Tri-Z cases , but I have mix-matched 250R cases. It does require a little check to make sure they aren't off a whole lot (More likely to be off from damage than than just being unmatched it seems to me) but I've done it with no adverse affects.

[fabiodriven]

Our 86 KX500 engine has mismatched cases. Lots of naysayers had things to say when we were putting it together but it didn't have any issues.

[HondaRidr]

I used to think it would be fine using two different case halves. I tried using non matching cases on a 84 tecate engine and the crank wouldn't turn as freely as it should.

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[ironchop]

They all should be close.

When machining case halves, you'd want to machine the side gasket surfaces, bearing bores, drill and tap the bolt holes, and drill/ream or interpolate the dowel holes all in one operation. Everything being located relative to the crank bearing bores. THEN you would locate the case half off the dowel holes in the next operation and then cut the deck height correct and square to crankshaft center. The usual reason deck height could get off between case halves is that the deck height has a tolerance range like anything else and one could be at the top of that range and one on the bottom so they are both in spec but will mismatch slightly. I can't imagine the deck tolerance range being any more than .003-.005 total. The dowel holes, bolt holes, and bearing bores, on the other hand, are all absolute locations relative to each other meaning one or two holes won't drift back and forth further than others. If anything moves, ALL those features move as well the same direction so it ensures they stay in the same spot between each other no matter what. That's why you would locate off those dowel pin holes to cut the cylinder deck when manufacturing.


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[ironchop]

...

I plan to get at least one set skimmed, but I don’t like the idea of the crankshaft and transmission shafts being misaligned by .004”....



Edit to add: I'm almost certain the crank bearings are cut absolute to the dowel pin holes in the case halves. This would ensure your case half bearings are true to each other. Even if they weren't, you'd never be able to get a crank in there and pull the cases together at all if they were .004 out of concentricity. The max those dowel pin holes would be on the inner diameter is .001 over the dowel OD for a slip fit. So you could never move the cases enough to get them to match at the seam. You'd have .0005 max range.

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[El Camexican]

Edit to add: I'm almost certain the crank bearings are cut absolute to the dowel pin holes in the case halves. This would ensure your case half bearings are true to each other. Even if they weren't, you'd never be able to get a crank in there and pull the cases together at all if they were .004 out of concentricity. The max those dowel pin holes would be on the inner diameter is .001 over the dowel OD for a slip fit. So you could never move the cases enough to get them to match at the seam. You'd have .0005 max range.

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That makes the most sense (and gives the most peace of mind), thanks! These cases have 4 dowel pin locations for some reason, but only 2 are used. The manual shows which ones are used, but I've open motors to find them in the other holes, or not at all :crazy:

Interestingly on the cylinder I just lapped onto those cases in the photo there was obvious evidence of a leak on the front RH corner when I removed the base gasket as it wasn't stuck to either surface and there were stains on the cylinder that indicated it was dirty for a while.

When I started lapping I could see there was no contact on the thin surface next to the transfer area on the left side and a very large patch that didn't want to make contact on the stained corner. It took at least 45 minutes of elbow greasing to get everything nice and flat. On the first set I ever did the RH side rear corner of the cases (the one that the cylinders are known to break on when you add a boost port) was quote low and also took a long time to get flat.

I have to assume all this happens from heat cycles and stress as these surfaces were all machined at one time. Pulling the case studs to lap is a PITA, but it looks like it's worth the effort to check for a good sealing surface.

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[bkm]

As long as it's a numbers matching engine, nothing else matters.

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[El Camexican]

As long as it's a numbers matching engine, nothing else matters.

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So true!:lol:

FYI case number 38W-000009 is on eBay as you read this. Don’t miss this once in a lifetime opportunity to own the 9th TriZ cases ever produced!

[bkm]

So true![emoji38]

FYI case number 38W-000009 is on eBay as you read this. Don’t miss this once in a lifetime opportunity to own the 9th TriZ cases ever produced!OMG, Barnett Jackson, here I come.

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[bkm]

FACT, no one gives a damn about numbers matching tri-z's, but they do care if the clutch cover is broke or not.

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[HairyJR]

Nice explanation by Ironchop of possible machining processes. With as many case halves needed to build all the bikes being sold, several machine shops would be required, machine tool wear, so drawing machine tolerances are needed. As Nico mentions I too had some experience with '70s Honda's SOHC 4 cylinder motors drag racing them. You break parts so need to replace them and as we had monthly motorcycle swap meets, you could get a complete crankshaft and transmission still setting in the bottom case half never a top half as they had serial numbers. Broke a lower case once and tried to one of 3 other lowers with no success as the horizontal joint split for the crankshaft insert bearings was off.

Guilty of flycutting the mismatch surface on a couple XR600 cases.

"HJ" 249121 :beer

[El Camexican]

Nice explanation by Ironchop of possible machining processes. With as many case halves needed to build all the bikes being sold, several machine shops would be required, machine tool wear, so drawing machine tolerances are needed. As Nico mentions I too had some experience with '70s Honda's SOHC 4 cylinder motors drag racing them. You break parts so need to replace them and as we had monthly motorcycle swap meets, you could get a complete crankshaft and transmission still setting in the bottom case half never a top half as they had serial numbers. Broke a lower case once and tried to one of 3 other lowers with no success as the horizontal joint split for the crankshaft insert bearings was off.

Guilty of flycutting the mismatch surface on a couple XR600 cases.
ut
"HJ" 249121 :beer

The GS engines would usually go out by putting a rod though the lower case rendering the upper case half that was usually bored for big block sleeves useless.

The other thing that could make a grown man cry was the cam caps. The Suzuki’s were pretty close, but I remember going though dozens of Kawi caps trying to get something close enough to save a head. I know they could have been ground and line bored, but that kind of work was out of my budget.