My timing chain jumped a couple of teeth on the left cylinder head because of a bad tensioner. I replaced the tensioner, rails, and gears inside and outide the timing cover(huge job). The chain has 40,000 miles and shows no stretch. Timing marks on both cams line up when the harmonic balancer points to 0 degrees. I tried to start the car and allit would do is pop and backfire. So I checked the distributor rotor was pointing to the #1 plug wire at 0 degrees on the harmonic balancer and both cam lobes pointed upward. Still no start. Now the heart wrenching part. I checked compression on the cylinders. All show 145-150 psi in 20 degree outside temperature with new10W-40 oil except #8 which is not showing any compression at all. How bad is the damage likely? Is this compression normal. It was around 125-130 psi on all cylinders last fall when I checked but the engine was warm and the air temp was around 60 degrees?

Thanks again,
jmdunn

engines need at least 100 psi to run. it looks like you might have alot of bent valves or the valve are not seating correctly.

sorry wrm,
I should have looked more closely before I posted. The post is edited now. my current readings should have read 145-150 psi on all but # 8 cylinder which reads 0 psi.

thanks

The crank revolves twice for every camshaft revolution. You could be 180 degrees out of phase with the ignition. Check that your spark isn't occuring while valves are actually open.

Steve

When the cam lobe are pointing up which=valves closed on # 1 cylinder. The timing marks are in alignment and the rotor points to # 1 spark plug wire.

Still should start and run poorly to terribly.

Try advancing the timing - 0 is kind of retarded.

Dumb questions:

What are you calling #1? Should be right (passenger side) front.

Did you get the plug wires on correctly according to the firing order?

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

No compreesion on #8? - You have a bent valve stuck open. Take off the valve cover and look at the cam lobes as they contact when you crank engine over by hand. I will bet one valve or both on #8 are not moving. Time to pull the head. DO NOT TRY TO START THE ENGINE UNTIL THIS IS RESOLVED. As it is an interference engine - the stuck valve can puncture the top of the piston.

I had a 78 450SEL that ran reasonably well with no plug in #4 so no compression in one cylinder will not make it impossible to start.

Backfiring means you're getting fuel. It's a continuous system so there's no fuel timing to check. Recheck cam and ignition timing.

Sixto
91 300SE
87 300SDL
83 300SD

when you jump timing on a v8 99 % of the time the exhaust valves are bent on the left head. if you want to be sure it's simple to find out. remove the rockers on the cyl with no compression. run a test again to confirm the obvious. paul

__________________
Paul Roberts
Mercedes Centrum Inc.
Bellevue,WA.

If you run a compression test without the intake valve opening, there won't be anything to compress.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

sorry for not being clear.as to preforming another test it would be injecting air into that cylinder(leak down) you'll hear air going out the tailpipe, big time, or you'll hear it if you push down on the airflow meter if it happens to be a bent intake valve.
paul

__________________
Paul Roberts
Mercedes Centrum Inc.
Bellevue,WA.