Installed roller chain, compression low...
Thread Starter
Racer
Joined: Apr 2000
Posts: 499
Likes: 0
From: Kristiansand
Installed roller chain, compression low...
I recently had got a major engine problem. Vacuum gauge reading was low with needle vibrating wildly and the engine lost power. I barely made it home. (No abnormal noise from the engine)
Since I new my timing chain was worn I suspected a problem here. But it looked ok.
Then I measured the compression and found zero at cylinder 7. Removing the valve cover revealed a broken exhaust spring.....
Installed new springs and a roller chain.
Then I tested the compression again. To my horror I found that it was only 6 pounds. (before all cylinders was around 11). My conclusion was a bent valve.
But when I tested a known good cylinder this was 6 pounds also!
Then I was sure my chain was offset, but as far as I can tell it's not.
Any suggestions what to do next?
Since I new my timing chain was worn I suspected a problem here. But it looked ok.
Then I measured the compression and found zero at cylinder 7. Removing the valve cover revealed a broken exhaust spring.....
Installed new springs and a roller chain.
Then I tested the compression again. To my horror I found that it was only 6 pounds. (before all cylinders was around 11). My conclusion was a bent valve.
But when I tested a known good cylinder this was 6 pounds also!
Then I was sure my chain was offset, but as far as I can tell it's not.
Any suggestions what to do next?
Burning Brakes
Joined: Feb 2001
Posts: 929
Likes: 5
From: Marietta GA
Re: Installed roller chain, compression low... (Ingar, Norway)
I am not an expert in this area but it seems to me that even 11 pounds is very, very low. If you had a stretched timing chain then the cam was not properly in phase with the crankshaft. This out of phase condition might have altered the valve timing enough to give you a little more compression than when it was properly in phase after installation of the new timing chain. I will leave it to others for a positive verdict but I think you should pull the cylinder heads. Either you have bent valves or your piston rings are worn out.
[Modified by BB68Vett, 6:23 AM 9/1/2001]
[Modified by BB68Vett, 6:23 AM 9/1/2001]
Le Mans Master
Joined: Sep 2000
Posts: 9,078
Likes: 7
From: DFW TX
Cruise-In VII Veteran
St. Jude Donor '07
Re: Installed roller chain, compression low... (Ingar, Norway)
Ingar,
Is it running the same as before? Did the timing chain have single pre-set notches or was it one with the three different advance notches? If you are off a notch or two, I would believe there would see a change in compression. There a few cam gurus on the web, so an solution is near.
Budman
Is it running the same as before? Did the timing chain have single pre-set notches or was it one with the three different advance notches? If you are off a notch or two, I would believe there would see a change in compression. There a few cam gurus on the web, so an solution is near.
Budman
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
Re: Installed roller chain, compression low... (Ingar, Norway)
6 bar does sound low. However, you do know the engine rotates without valves hitting pistons, so you can try and start it. The low reading would worry me also, but what shape was your battery in? If it was low from a lot of cranking, you can get a lower reading.
Thread Starter
Racer
Joined: Apr 2000
Posts: 499
Likes: 0
From: Kristiansand
Re: Installed roller chain, compression low... (Ingar, Norway)
Thanks all!
yes Budman, I have a sprocket with -4o/0o/+4 slots, was using the 0 position.
Anyone who can explain in which applications you would use the other positions?
Have done some more investigating. Measured all the other cylinders and to my surprise found that some were at normal (11bar) and others were zero! Since I experienced no leakage while installing the springs I loosened the rockers on a zero reading cylinder until the pushrod rotated freely. The compression was then back to normal 11 bar!
So something is wrong with my valve adjustment.
Here is how I did it: Tightened the nut until no lash, then tightened one turn.
However, after adjusting all valves I found that the pushrods again moved freely (0 lash) so I did the procedure once more, tightening them all approx. 1 turn. This obviously caused the problem.
Why the lash increased during the adjustment (turning the cam one turn) I don't know...
Also I'm confused about this preload thing. Since the valves lash is compensated for by the hydraulic lifters I would have though there should be some lash when oil pressure is absent...?
yes Budman, I have a sprocket with -4o/0o/+4 slots, was using the 0 position.
Anyone who can explain in which applications you would use the other positions?
Have done some more investigating. Measured all the other cylinders and to my surprise found that some were at normal (11bar) and others were zero! Since I experienced no leakage while installing the springs I loosened the rockers on a zero reading cylinder until the pushrod rotated freely. The compression was then back to normal 11 bar!
So something is wrong with my valve adjustment.
Here is how I did it: Tightened the nut until no lash, then tightened one turn.
However, after adjusting all valves I found that the pushrods again moved freely (0 lash) so I did the procedure once more, tightening them all approx. 1 turn. This obviously caused the problem.
Why the lash increased during the adjustment (turning the cam one turn) I don't know...
Also I'm confused about this preload thing. Since the valves lash is compensated for by the hydraulic lifters I would have though there should be some lash when oil pressure is absent...?
Race Director
Joined: Oct 2000
Posts: 15,009
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From: central FL, near the beach.
Re: Installed roller chain, compression low... (Ingar, Norway)
Ingar
move the pushrods up and down until the play drops to zero. then 3/4 turn
DO NOT turn the pushrod
OR do it with the engine runing (messy) when tap stops add 3/4 turn
move the pushrods up and down until the play drops to zero. then 3/4 turn
DO NOT turn the pushrod
OR do it with the engine runing (messy) when tap stops add 3/4 turn
Thread Starter
Racer
Joined: Apr 2000
Posts: 499
Likes: 0
From: Kristiansand
Re: Installed roller chain, compression low... (drives61)
drives61:
Yes, the problem was that I used the turning method. I found that, for one like me without experience, it's difficult to find zero lash.
I followed your advice and everything seems fine so far!
My compression has no gone up one bar up to 12 for all cylinders. Guess that's because my old timing chain had so much slack.
No I have to finish bits and pieces and try to fire it up....
Yes, the problem was that I used the turning method. I found that, for one like me without experience, it's difficult to find zero lash.
I followed your advice and everything seems fine so far!
My compression has no gone up one bar up to 12 for all cylinders. Guess that's because my old timing chain had so much slack.
No I have to finish bits and pieces and try to fire it up....
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Race Director
Joined: Oct 2000
Posts: 15,009
Likes: 79
From: central FL, near the beach.
Re: Installed roller chain, compression low... (Ingar, Norway)
Ingar
glad that it's looking better
Many books say to turn the pushrod, but if it is properly oiled, it turns so easy it goes way too far. i never turn it.
glad that it's looking better
Many books say to turn the pushrod, but if it is properly oiled, it turns so easy it goes way too far. i never turn it.
Burning Brakes
Joined: Dec 2000
Posts: 1,183
Likes: 2
From: Des Moines Iowa
Re: Installed roller chain, compression low... (drives61)
I agree completely with Drives61 on this one. I too originally had my valves adjusted too tightly when I did my rebuild last fall, and it was because I could still spin the pushrods after hitting zero lash. I've since that time gone to the pushrod 'jiggle' method to determine zero lash, and go 3/4 turn past that and call it good.
Thread Starter
Racer
Joined: Apr 2000
Posts: 499
Likes: 0
From: Kristiansand
Re: Installed roller chain, compression low... (Ingar, Norway)
Thanks for all help!
My car is on the road again, better than ever before!
The increased compression also made it sound a bit more aggressive....
My car is on the road again, better than ever before!
The increased compression also made it sound a bit more aggressive....
Drifting
Joined: Mar 2001
Posts: 1,411
Likes: 2
From: St. Louis, Missouri
Re: Installed roller chain, compression low... (Ingar, Norway)
"....have a sprocket with -4o/0o/+4 slots, was using the 0 position.
Anyone who can explain in which applications you would use the other positions?"
The +4 position advances valve timing 4 degrees which improves low speed torque with some sacrifice at top speed power.
The -4 postion retards timing 4 degrees and produces opposite results.
Anyone who can explain in which applications you would use the other positions?"
The +4 position advances valve timing 4 degrees which improves low speed torque with some sacrifice at top speed power.
The -4 postion retards timing 4 degrees and produces opposite results.
