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Message started by Tim_C on 06/06/06 at 10:21:49

Title: Low compression
Post by Tim_C on 06/06/06 at 10:21:49

Hello,anotherFNG here.I have an '02 with 19000 miles that became hard to start,then needed more and more choke to run decently.After sitting for 2 weeks,cheked fuel and spark,both good,then found only35psi in cylinder,wet or dry.Ran the valves,double checked de-comp cable...all seems good....this is where it gets wierd.Figued I'd test for blown head gasket by pressurizing the cylinder my compressor then listen for leak or use soapy water...no leak...and the engine held 90psi steady for 3 hours.So.......the rings,valves and gasket are all good.Found this site the other day and learned more in three hours than in the previous 4 yearsso if there is a logical answer,you guys will know where I go next.Suggestions?

Title: Re: Low compression
Post by lancer on 06/06/06 at 13:11:16

Something changed between the first 35 psi and the 90psi pressure check. I would suggest going through the same procedure again and see what results you get this time.
As for it needing more choke to run each time you try it again...that is a carb issue and not associated with the cylinder pressure issue...my thoughts anyway.

Title: Re: Low compression
Post by Tim_C on 06/06/06 at 14:19:55

Thanks,Lancer.When I crank for compression test it will only come up to 35psi,yet at TDC, all valves cloed,I can pump in 90psi w/an air compressor and have absolutely no leakdown,meaing no cooked or bent valves,perfect ring seal and a solid head gasket.Do these timing chains jump?Thanks so much for the input,this forum is very educational as well as entertaining...nice group of people

Title: Re: Low compression
Post by Guido on 06/06/06 at 15:33:15

Doesn't the decompression solenoid reduce compression for easier starting and less wear and tear on the battery? That being the case, you wouldn't get a high reading while cranking.

Title: Re: Low compression
Post by Tim_C on 06/06/06 at 18:13:54

Seems to me I did A compression test about 2 years ago and had around 140 psi...well,back to my top secret laboratory to disconnect the de-comp cable and test that theory..will be back shortly...thanks,Tim

Title: Re: Low compression
Post by Gramps on 06/06/06 at 19:05:40

Did you hold your throttle wide open when you took the compression test ?
I've done a leak down test on mine & there is no way I could hold the piston on top dead center at more than 50 lbs air pressure. How did you hold TDC with 90 PSI ?

Title: Re: Low compression
Post by Tim_C on 06/06/06 at 20:44:16

Relized when I got out there that I'd have to put the cyl head cover back on to test...then my grand daughter came over...not looking forward to that if indeed the head has to come off.Anyhow,I had the bike in neutral and at TDC because I had just pulled the cover and you have to relieve the sring pressure on the cam.My neighbor made me a compression adapter from a hogged out spark plug,so I just plugged it into my air compressor,which had 90 psi in it.Ten I waited and listened.NothingI guess the motor is tight, but it cranks over easily.I need to read up on the witness marks for the cam timing but dont know if I can disturb the engine whie rocker cover is off.And they wonder why I drink!

Title: Re: Low compression
Post by Dorri732 on 06/07/06 at 05:58:49

Two things I can think of one, and Gramps beat me to one of them.

1. The throttle must be held open while cranking for a compression test. You didn't answer whether or not you did this.

2. Timing chain might have skipped a tooth or two. As long as valves aren't hitting the piston, and the valves are closed at TDC, this could give you the results you got. (Intake valve might be open partway through the compression stroke.)

Good luck.

Title: Re: Low compression
Post by slavy on 06/07/06 at 09:26:05

99% sure You don't have any compression issues.If You are cranking the engine the normal way, the decompressor keeps the EX valve open. The leak-down test is 10 times more acurate.
Two possibilities:
1. Fuel- carb issue
2. Spark-battery. Make sure the battery is FULLY charged before You start chasing Your tail. And make sure the spark plug is good, because it might have gotten contaminated while cranking the engine.
Luck !

Title: Re: Low compression
Post by Tim_C on 06/07/06 at 10:51:46

Thanks for all the input..yes,yhe throttle was opened while cranking so later I will check the timing chain and see if it skipped.Will make a donation next week as the info gleaned thru this site is and will continue to be invaluable.

Title: Re: Low compression
Post by SeattleSavage on 06/07/06 at 18:31:34

I can say 20k is the norm on the timing chain life expectancy and your tensioner is probably maxed and the bore on the tensioner is probably hogged out and ready to drop the tensioner cylinder. Mine was @ 21k and from a search of the good folks here that does seem to be the standard.

Kev

Title: Re: Low compression
Post by Kropatchek on 07/11/06 at 04:14:54

@Tim_C sent you a PM

Kropatchek ;D

Title: Re: Low compression
Post by azjay on 07/11/06 at 07:01:36

20k? really? ??? wow, that is hardly two years of riding. :( bummer, is there a better part?

Title: Re: Low compression
Post by Keith_B on 07/11/06 at 14:46:58

Before cranking the engine over, disconnect the wires to the decompresion solenoid, then hold the slide open on the carb., you will need to block it open someway, and hold the throttle open, just turning the throttle open on a constant velocity carb. does not hold the slide up so you can get full flow of air in the intake. That or remove the carb. to get full flow. Then run the compression check!