Mixing and matching engine case halves?

[SkyFive]

I hate to start a new topic for this but I need some advice. I have two engine cases, one with a good top half and one with a good bottom half. Can the cases be mixed matched? Has anyone ever done this?

[racerrad8]

No mixing & matching...

The case halves are machined as a pair. You will not be able to get the main bearings to set/adjust correctly or most likely get the crank to turn. Also, they do not make "oversize" bearings so you would not be able to have it machined and install an oversize bearing. On top of that you have the two bores that are also machined for the transmission...

I presume the bad top half has a bad thrust, what is wrong with the bad bottom half?

Honestly, you have two good cases for scrap aluminum.

Randy - RPM

[SkyFive]

Thanks Randy,
I have a 50H and a 1WJ, the 50H has a huge crack near in the top half at the rear mount, the 1WJ has a weld repair just above the oil pump cavity in the lower half. The 1WJ is usable as a whole case but the notion of putting a $750. to $1000. into a repaired case makes me feel uneasy. The weld on the 1WJ appears to be solid but with thermal expansion, contraction and vibration I'm not sure what will happen if anything.
The thought occurred to me that since the main bearings are sold by piece rather than pairs that I could mate the two cases using different color code bearings, ie. green top bearing yellow bottom bearing. I'm a former machinist and I deal in dimensions and tolerances, not color codes.

[racerrad8]

I am the same way; it was hard to figure the number system out. I have determined what rod size to re-size all of my rods and then I use the number system provided by Yamaha.

You might bolt the cases together and see if the bores are even close. From there the number system would have to be used for each respective case for bearing size; but the trans has no options.

Can you shoot me some pictures of the damage area of the 1WJ case to my email; randy@rpmracingca.com. I am wondering why a case would be welding in that area.

You might be better off having the upper crack fixed since it is farther away from the machined portion(s) of the case. I do remember seeing that crack, but do not remember the specifics about the location.

Send me pictures of what you have and lets see if we can figure out which one will be the best.

Randy - RPM

[SkyFive]

Randy,
I didn't get any pictures but last night I cleaned up the original 50H case and the "weld" turned out to be a combination of JB Weld and silicon. I cleaned all of that off and today I'm taking that case to a machine shop to be welded. It's the best solution and like you said the repair will be farthest from the machined area's.

[racerrad8]

Bolt the two halves together to prevent distortion of the welded half when welding.

Randy - RPM

[Travis398]

let us know how it turns out