Compression test on a '1200km old' engine. How much?

bonester · Post by **bonester** » Thu Apr 19, 2007 8:15 pm

Gave the mighty GT a compression test today- 140Psi across the board. Is low for a GT if you read the manual, but above service limits. I re-ringed it and lapped the valves. Whaddya reckon? Is it too low, or OK. Wonder if it could be my 'Supercheap' compression tester which I broke doing the test. Brand new gauge....

Gosling1 · Post by **Gosling1** » Thu Apr 19, 2007 8:20 pm

140 is fine mate.....I think stock for those babies is only 155 or something like that ?

As long as they are all within 10%, all is well. Not sure about the comp tester though.....broken on its first outing ??

I would be looking for a refund...

bonester · Post by **bonester** » Thu Apr 19, 2007 10:05 pm

Thanks Gos. 169 is supposed to be the minimum. 128 is the service limit. I think I'm getting some blowby coz the airbox is getting a fair amount of oil in it. Rubber tip of tester cracked.

bonester · Post by **bonester** » Fri Apr 20, 2007 11:38 am

Checked with a local mechanic today who reckons that 140 is really good. He said it depends on altitude, and as we are up so high 140 is good. He has built some engines with hi-comp pistons that only gave him 110psi. Just gotta fix or bypass the blowby problem.

Strika · Post by **Strika** » Fri Apr 20, 2007 1:18 pm

bonester wrote:Checked with a local mechanic today who reckons that 140 is really good. He said it depends on altitude, and as we are up so high 140 is good. He has built some engines with hi-comp pistons that only gave him 110psi. Just gotta fix or bypass the blowby problem.

If it's only been 1200 klms from a re-ring and hone then it may need a bloody good thrashing to seat the rings! Get up the fucker for a good days riding in the hills and see if it fixes it!

If not then the rings aren't seating properly. (Considering they are new...did you check for oval bores??)

bonester · Post by **bonester** » Fri Apr 20, 2007 9:31 pm

I didn't check for oval bores, per se- checked piston to bore clearance front-to-back which was less than 3 thou. Good enough supposedly. Runs quite well though.