compression test

[jerry]

after a 130 mile ride today i did a compression test on the m750

font cylinder reached 125psi
rear was only 112psi ????

both were nice and hot and gave them both 4 crank overs to max out pressure


seems a bit too much difference to my mind

but the bike pulls like a train but does burn a bit of oil .

[pegboy]

Don't know what the readings should be but I don't think those reading would be anything to worry about.

[Dennis menace]

Haynes manual suggests there should be virtually no difference between cylinders and the higher value is normal. A squirt of engine oil in the low cylinder will bring the value up slightly if the rings are worn or valves not seating - worth doing before contemplating pulling it apart.

[pompone]

10% difference is a but on the "too much" side but still within range.

[jerry]

i will do it again ,,, im not worried ,,,it probably needs new stem seals ,, and the heads have NEVER been off in 15 years ,,,,

[GDCobra]

i will do it again ,,, im not worried ,,,it probably needs new stem seals ,, and the heads have NEVER been off in 15 years ,,,,

I don't think stem seals will alter compression, they are outside of the combustion chamber, they will only stop the engine burning oil which you say it doesn't do.
IMO

[Drumnagorrach]

My M900 has 105 psi front and 110 psi rear, Haynes says thats too low , My bike runs just fine and the Very experienced Ducati mechanic at moto mechanica ,described the bike as " going like a scalded cat "and not to be concerned .So I'm not.:chuckle:
btw mine burns no oil even with the 105 on the front.

[jerry]

mine does actually burn some oil but as i said earlier , that is probably valve stem seals , they did same on my 750ss,M900 and S4

[Sirc]

rear cylinder valve opener shim clearance ok Jerry? - exhaust in particular.

[jerry]

rear cylinder valve opener shim clearance ok Jerry? - exhaust in particular.


Yeah i got to check all the clearances as well its nearly time for that chore

[Rockhopper]

All the numbers quoted in this thread seem on the low side. I'd have expected to be seeing 180psi or above on a healthy engine. If you are getting 100psi I'm actually surprised it runs at all.

Make sure you do the test with both plugs out, the engine warm and the throttle wide open.

[jerry]

Did a compression test again today after a run , this time i put a sealing washer on the adaptor and front and rear cylinders both recorded 148psi exactly identical readings , i did the test 3 times all the same so im happy ,,