Damage to upper crankcase half.

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alastairuk

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After a busy holiday season I'm finally getting back into rebuilding my xs400 engine. I noticed in cleaning that there is damage on the the upper crankcase half at the point just below one of the cylinders. I'm adding a picture in the hope someone can identify the cause. I was wondering if it was caused by blow-by or possibly debris stuck in the cylinder wall, and if this will cause issues once rebuilt.
2017-03-07 15.04.03.jpg
 
xs400.png

Not 100% sure what damage you are referring to, is it the rough looking area below the notch in the red circle? To be honest I have never seen an XS400 apart. Does the lower part of the cylinder sleeve reach down that far? Is there wear on anything else that would have been in that area?
 
I believe the cylinder sleeve rests on that notch. However none of the piston sleeves, pistons or any part of the crankshaft is noticeably worn, which made me wonder if it was something leaking out of the combustion chamber.
 
The only thing that I can see causing those marks would be the crank. Maybe movement from worn bearings. Or when it was disassembled.

DSC03208.JPG DSC03209.JPG DSC03210.JPG two of my spare motors
 
Perhaps the original casting was flawed at that point. However the steel insert in the jugs fit inside this opening, so there probably is no negative consequence. Just an opinion.
 
My crank case was similar. It seems that the castings of the time were a little rough. Probably not the best QC with the molds. When they got a rough casting, they were machined down in additional areas.

A lot of the edges inside the engine are very sharp too.

So it will still be just fine. Once the sleeve is in place thats all that matters.
 
The sleeves have nothing to do with the damage area. My concern is where the crank passes that area. If it has bumped it due to worn bearings that's the issue that needs to be addressed.
 
xschris said:
The sleeves have nothing to do with the damage area. My concern is where the crank passes that area. If it has bumped it due to worn bearings that's the issue that needs to be addressed.
Click to expand...
So I measured the main bearings I think that's what they are called, between the shaft and the case and they were within spec. Is there any way to measure the bearings between the con rods and the shaft without removing them?, does that even relate to the damage?
 
You would have to split the con rods and use plastigauget to measure clearances.Keep in mind that you CANNOT reuse conrod bolts.
 
The rod bearings shouldn't have anything to do with what you have.
 

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