Alright, I have a 1995 GTX with the 657x engine. Got the ski for free and am rebuilding literally everything. I just had the cylinders bored out to the first oversize (78.5mm). Ring end gaps ranged between .019in and .027in which is above the new limit tolerance but still below the wear limit tolerance. The engine is still out of the ski on my bench and to check the compression I just hooked a battery straight to the starter to turn the engine over. Both cylinders read 130# (also I live at sea level). From what I could find online, perfect compression should be around 150#. Is this compression going to be to low for the ski to run? Any thoughts as to why the compression is this low on a new rebuild?
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1995 GTX 657x Engine Compression
- Thread starter Jake907
- Start date
Venturian1
Member
The rings have yet to be seated, no? What's the piston to cylinder clearance, the final cross-hatch grit used on the bore job?
I think we used around 400 grit stones for the final hone. It's getting difficult to find a good machine shop anymore. Last bore job I got for a Honda CT90, I offered the factory specs to the machinist, piston clearance was like .006" if I remember correctly, when I came back to get it, I asked about clearance, cross-hatch final grit, the prick looked at me funny, and said the piston clearance is .010". I bore everything to that. It had low compression when back together, ring end gap was near the limit too. It cost me $100 for that sorry bore job, + piston and rings, and it was not even my bike. helping a friend out.
I think we used around 400 grit stones for the final hone. It's getting difficult to find a good machine shop anymore. Last bore job I got for a Honda CT90, I offered the factory specs to the machinist, piston clearance was like .006" if I remember correctly, when I came back to get it, I asked about clearance, cross-hatch final grit, the prick looked at me funny, and said the piston clearance is .010". I bore everything to that. It had low compression when back together, ring end gap was near the limit too. It cost me $100 for that sorry bore job, + piston and rings, and it was not even my bike. helping a friend out.
