Afternoon all,
I’ve just refitted the heads on my rebuilt jubilee engine and I’m only getting about 35psi compression on each cylinder. Stripped & cleaned all parts, honed bores & fitted new std pistons & rings as bores showed very little wear.
I haven’t yet refitted the idler timing gear and there are clearances under all the tappets.
Any ideas where I should start looking first?
Many thanks
Kieren
Check out the
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Ignore me - brain fart moment!
Thanks George,
Your closed throttle comments have enabled me to realise what an idiot I’m being -
no timing idler = inlet valves closed = low compression!!
Dunce hat please!
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what should the psi be.
What should the psi compression be on these engines.
John
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Norton data says 128psi
According to the engine data sheet I have, attached it’s a compression ratio of 8.75:1 which works out to be about 128psi.
once I get a chance to assemble the timing gears properly and then check my compression I’ll update the thread with the results!
Kieren
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Managed to get 125psi on…
Managed to get 125psi on both cylinders finally, but needed to put some eng oil into the bore, dry pressures stayed very low, approx 50-80psi.
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With that
Hi Kieran, I would expect the hot engine figure will be close to your oiled figure. Important bit is that they are similar on each cylinder. Personally I would worry about other things on the bike now rather than compression until it has bedded in/run a bit.
Regards, George.
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Yep agreed!
Yep, considering it’s only an engine on the bench at the moment - definitely!
now to prep the frame & forks for painting & rebuild....plus the fact that my priority is to replace the headlight on my main ride - melted it with the heat gun trying to split it to upgrade the projectors (2011 Triumph Tiger)
whoops!
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Waaayyy toooo clean
Kieren:
Your engine is way too clean!!! No staining at all.
What did you use to get it that way?
Mike
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Vapour Cleaning
Hi Mike,
It’s a restoration job, engine hasn’t run in 40yrs so I stripped it and had a local guy vapour clean it.
it’s not run yet that’s why there’s no staining!!
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Similar thread on the singles section M50 compression.
Most answers will be similar - WOT, crank speed, temperature etc,etc.
Fwiw, 35psi is very low and sounds like a closed throttle figure.
George.