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Motorcycle Repair/compression 83 honda vt750c

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Question
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

Answer
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,
Lazaros.

Motorcycle Repair

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Lazaros Ampatzidis

Expertise

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.

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.

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

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