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View Full Version : Pointy low compression.

Georgekp123
21-04-12, 11:51 AM
Hi,
I put something up a while back about my bike basically not starting, found the problem to be bent valves.
Anyway, I've now put new valves in (that I've grinded in), used new head gaskets, new stretch bolts, and made sure the timing is what it should be (not making the same mistake twice). So, I get it all back together, go to start it... Nothing.
Compression test is literally reading next to nothing in both cylinders - I can crank it over by hand with the spark plugs in!
I have this horrid feeling the piston rings are dead, but I can't work out how, as they were working fine before I started the work, and the pistons haven't been out of the barrel.
Any ideas?
Cheers,
George.
embee
22-04-12, 11:12 AM
Valve clearances??
Georgekp123
22-04-12, 12:52 PM
All within spec
TSM
22-04-12, 03:11 PM
check you have timed up correctly, it seems that your valves are not fully shutting, you could try turning the engine over 'by hand' without the cams in as that would make sure all the valves are closed.
Georgekp123
24-04-12, 01:54 PM
I can confirm that the timing is definitely perfect, having just checked for the millionth time.
flymo
24-04-12, 02:43 PM
remove plugs, give it a squirt of oil into the cylinders and try again. If it makes no difference then it wont be rings. Also, with the law of troubleshooting, always look at what was changed first.

Do you have a compression tester?
Georgekp123
24-04-12, 03:31 PM
You've beaten me to it, I was just about to post that I've done that this afternoon and nothing changed :S
Yeah I do have a compression tester

Shims are correct sizes, clearances are within spec, timings are spot on, valves were replaced and grinded in (I had my ex's father come round and help sort these out so I highly doubt there's anything wrong with them due to his experience), new head gasket, new cylinder head (stretch) bolts, new oil seals, new springs, new retainers, new cotters, new spark plugs, new fuel, new coolant, new oil.

I just... Don't have a clue anymore :(

George.
flymo
24-04-12, 03:58 PM
whip the cams out and check for compression. Just a thought, when the valves were ground in, did you leak test them with some fuel?
Georgekp123
24-04-12, 04:05 PM
I'm probably not going to be able to get back at it until thursday now, but I'll definitely give that a go then and let you know.

Yeah, no leaks at all, unlike before