Engine Trouble Bad machining/assembly

CT Rider

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I just received a Mzmiami bottom end ($70). I bought it as a back up, and since it has the curved clutch arm I know it's one of the better motors. However I don't believe the cylinder will sit flat enough to not leak. Is there a way to fix this correctly without it being completely disassembled ? I don't want to disassemble if I can avoid it, but I feel that doing so is the only was to fix it the right way.
The case halfs do not crate a flat plane for cylinder to mate to. They sit more that a 32nd different from each other.

Dry fit with no gasket confirms this needs to be addressed.
 

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I would loosen the halves and see if you can even the mating surface. As long as it hasn't been run the gasket should seal back up.

Or you can contact mz to let them know about the problem and ask them to correct it.
 
I tried loosening the bolts to correct it, can't be done.i half to disassemble the whole thing, then bolt case halfs together and lathe it. If I do that, then I'm worried about removing too much material and changing the port heights and compression. Mz will exchange it, but that is a pain in the butt. It's kind of a crappy situation either way
 
Sand it down flush on something flat, that might do it, or if your confident enough file it.
 
yeah seen many like that and some some up by at least 1/16in - posted about it here before

usually, machining is good as mill marks are on the surface, but without steel inserts in a couple case bolt holes to pin them where they were when milled, the worker putting in crank gets it off centered

this is why I soak base gaskets in oil before putting on cylinder, and if real bad I'll add a small piece of gasket material half as thick as gap about a 1/2in long on low side to make two lesser steps each half as bad as before

I suspect it is due to the crank that is being put in being out of true a bit.
 
yeah seen many like that and some some up by at least 1/16in - posted about it here before

usually, machining is good as mill marks are on the surface, but without steel inserts in a couple case bolt holes to pin them where they were when milled, the worker putting in crank gets it off centered

this is why I soak base gaskets in oil before putting on cylinder, and if real bad I'll add a small piece of gasket material half as thick as gap about a 1/2in long on low side to make two lesser steps each half as bad as before

I suspect it is due to the crank that is being put in being out of true a bit.


I thought that may be the case. I'm going to dissassemble it to see what's going on, and file if I need to
 
I've usually thought that the gap matched the amount the crank was out if true - but since they're disposable, I've not taken it apart to check. Truing the crank a bit may fix it.
 
Well if you loosen the case and rotate the crank you will know. I doubt the crank would be that far out. The wobble would beat the s**t out of the bearings.
 
with the newer balanced cranks it is no where near as bad as it was when mains might go bad in just a thousand or so miles

look at old threads in which prying up on crank ends was a common test for loose mains whenever a seal failed to hold pressure
 
Will do, this is a brand new, never run engine, and the case halves line up correctly everywhere else. That being said I don't think it's a crank problem. It turns and feels true when rotated
 
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