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Motorcycle Repair/compression 83 honda vt750c


I have a 80 psi difference in compression after a rebuild (rings and gaskets) on the engine. front 130 rear 210. will this be a problem riding. not wanting to put to much money into this bike

Hello Keith,

Such a difference is huge anyway, shows extensive engine wear and for sure a problem, but, after a rebuild is even more abnormal.

It is a sign that something went wrong during the assembly and assuming that the cylinders and pistons aren't extremely unequal, it's potentially dangerous to run the engine.

I would suggest that a leak-down test be performed, to evaluate engine's condition, before riding the bike.

If that's not possible, recheck camshafts timing and valve clearance and then apply a small amount (10-15ml) of engine oil in the front cylinder through the spark-plug hole and retest compression.

If the pressure rise beyond 130, your problem is that the rings haven't yet bed-in to seal combustion chamber properly.
If it doesn't change, it means the valves do not seal.

Get back to me if you need further assistance or explanation.

Best Regards,

Motorcycle Repair

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Lazaros Ampatzidis


I can help you on EVERY issue involving POST-1980 Japanese Motorcycles plus KTM and Husaberg. My field of expertise includes Engine, Transmission, Fuel system (carburation & EFI),Electrics and Electronics. Maintenance, repair and tuning. Road and off-road suspension tuning. Please don't ask me about non-Japanese Motorcycle, especially American built on which I have low to zero experience.


I'm a rider and hobbyist since childhood. 25 years motorcycle workshop mechanic.15 years motorcycle racing mechanic. In order of experience high to low:Kawasaki,Suzuki,Honda,Yamaha,KTM,Husaberg.

Hellenic (Greek) Technical School.Internal Combustion Engines Engineer. Automotive Electronics.

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