no compression non comprenez

Taffy · Jul 15, 2007

just recently i had a call about the complete loss of compression feedback when kicking over.

aaaah! i said, i know that feeling as well but i've never actually KNOWN what it was?

it seems to happen when people have kicked for ages and all of a sudden when feeling for the engine lock - the thing kicks like a 2-stroke!

anyone have any thoughts on it let alone have you ever had it happen to you too?

regards

Taffy

LeFrog · Jul 15, 2007

RE: no compression non comprene

Hmm and the bike starts?

nsman · Jul 15, 2007

RE: no compression non comprene

Hi Taffy,
I have come accross this many times.I have a yam SR500 and is not used very often,it is not uncommon that it appears to have very little compression during startup.As soon as it starts and runs for a few minutes you can stand on the kickstart.Billtech had the same thing on a older Honda Xl350r just this past week,bike had been sitting for at least a year as the owner had stripped the spark plug thread.Seemed to have little or no compression then it started and all was fine.
If i had to come up with a theory i would suggest that the rings are not seating for a moment.this could be because they are dry of an oil film or because the oil film has been washed away as in an extended kicking bout.
...anyone else
NSMAN

Smorgasbord · Jul 17, 2007

Not uncommon on the Yamaha SR and XT 500. 8mm valve stems and weak springs. The exhaust valve hangs on the coke formed on the stem. It's hung just the last half a mm or so before it is completely shut. It could also be old lead deposits?, these bikes have been around for a while. The valve will blow shut if you can get the motor to ignite and once running and warmed up it is no problem. No worries and no reason to do anything about it. Just be happy and ride.
If it happened on the Hussey I wouldn't dare to guess what was causing it.

farfast · Jul 19, 2007

ihave a theory and it is only a theory ,but makes sense to my mechanical mind ,if the rings groove has some gunge and carbon in it kicking for a while may squash the rings into theyre grooves a little where they could get stuck thus lowering compresion this could also cause some slight tilt in the piston thus lowering compression further,upon startup the oil gunge and carbon build up heat up very quickly allowing the rings to spring back out , no harm done. a conventional combustion engine requires very little compression to actually run and husa's have a fairly high compression any way so this would not be detremental enough to stop bike running ,but as i said this is only a theory ,give me your thoughts :twisted:

Hambergler · Jul 19, 2007

I have seen it happen many times with automotive engines, sometimes when the engine doesnt start right away as you are cranking it over the gas just keeps on pumping into the cylindersand washes the cylinders of oil. I have done a compression test on cars that have been towed in with no starts. It seems as tho the engine is junk, because you get very little compression readings. So you dump a little oil into the plug holes, reinstall the plugs crank it over and kapow engine starts and runs like a champ. Just remember that there has to be an oil film on the cylinders for the rings to seal. Flooded engine washes the oil away, and then no compression.

Curtis

Taffy · Jul 20, 2007

thanks troops!

i will put that in the poor starting guide!

regards

Taffy

no compression non comprenez

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