Sorting out mothballed 277 project


XS650 Member
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Melbourne, Australia
Hey All,

I've got an engine that was rebuilt a few years back with 750 kit and a 277 rephase and then ended up having to store it for a couple years due to other priorities.

After changing the oil I did a compression test on it and one cylinder read low (90 psi) for maybe five or six tests then started to read normal (146psi on one cylinder then 150psi on the other) - if it does that again after sitting a few days is there anything I should look into?

Have checked valve clearance and will check cam chain tensioner, existing ignition is faulty and was a weird prototype the mechanic used instead of the pamco I supplied so just waiting on a tri-spark 277 ignition to turn up as they were nearby and looked good. I need to mark TDC as mechanic didn't when installing the PMA, using a piston stop do you just have to make sure it's on the power stroke to not risk hitting a valve with the piston stop? I presume left cylinder when sitting on the bike is considered the first cylinder on a rephase.

Thanks for the help, hope I'm not asking to repeat stuff from the tech section but wasn't anything obvious that answered those questions.

...having to store it for a couple years... cylinder read low (90 psi) for maybe five or six tests...
... is there anything I should look into?

Welcome to the forum, Allan.

A momentarily stuck valve comes to mind.

A protruding valve, over time, its stem can develop a bit of corrosion, inhibiting valve seating. Several cycles of movement can rub off the offending surfaces, freeing it. You could ignore it, now that it appears to be freed. Or, get in there and shoost some lube on *all* protruding valve stems.

Myself, if expecting extended park time, like to rotate the engine to a point where the valves have minimal protrusion, and valve springs uncompressed. On a stock 360° twin, that would be at TDC.

Don't know where that would be on a 270/277 rephased...
Thanks for the reply - valves all seemed okay, turned the engine over occasionally while stored. Good idea storing with valves uncompressed though.

Checking it again it actually reads 120psi on either cylinder when testing with the spark plug out on the opposite side but about 150psi with plug in on the opposite side which might just be because it's kick start only and with the plug in it creates more force once the first cylinder gets through its compression stroke. Seems healthy as can repeatedly produce 150psi when the spark plug is left in on opposite side so won't worry about it.

Have found a guy a few hours drive away with a dyno and many decades of experience tuning older Japanese bikes so once new ignition is installed going to take it to him to check my work setting the timing and jet the carbs on the dyno so I know the engine is really sorted before spending the time tidying up the rest of the bike and having it inspected as road legal as I moved country back home with it from Australia where it was previously registered.