timing chain broke

[marko]

Hi all, this is my first post but I need some info.

I broke the timing chain on my 94 sunbird 3.1 back at the beginning of april. I was about to go off for knee surgery so I didn't try to fix it until this past week. Anyway, I have done the replacement and when I tried to start it, it wont run on its own. I can keep it running by keeping my foot on the accelerator, but it will die soon after I lift.

I was led to believe that these are not an interference engine, but after a search on here I read that they are. I did a compression test on the #2,4,6 cylinders. (easiest to get to) and got 50psi on them all. I also took the valve cover off on that side and the rocker arms feel good, not sloppy as you would expect from bent valves.

In doing the timing chain, I found that the book is not clear as to the alignment of the timing marks. The crank is obvious and the dot on the crank sprocket points straight up. The one on the cam sprocket is where I am confused. I believe it is supposed to point straight down towards the crank, and that's how I installed it. when the cam sprocket is on the dowel pin, the pin is close to the 3 o'clock position. Is that right?

I am getting low compression, but if I had bent the valves then I would get none. This is what is leading me to think that the timing is out some how. After reading some of the articles on this board, I am thinking that the crank is 360* out, or the cam is 180* out.

What do you guys think?
thanks in advance.

[bszopi]

First off, welcome!

Secondly, it sounds like you installed it correctly. The dots should line up, and it doesn't matter if the cam sprocket dot is at 12-o'clock, or 6-o'clock, as they are the same location (since the cam spins at half the speed of the crank).

[Azrael]

Sounds like the car was sitting for quite awhile. How long did you try to keep the engine running? Maybe the lifters are just starved of oil and started sticking.

[marko]

The car has been sitting for 4-5 months. That is a good point, but does it explain the low compression?

[Azrael]

It can hold a valve slightly open. You can check by taking the front valve cover off and getting one of the front cylinders to TDC/firing position. Both valves for that cyl should be closed so back off the rocker nuts and see if a valve closes any further.

[marko]

Update.

I did as Azreal suggested and brought #4 up to TDC. both rocker arms for the cylinder were slightly loose, meaning I was able to wiggle them very slightly. If there was a lifter problem then they would have been too tight to move like when a valve is slightly open. I ran the car for a good 5-10 minutes on and off as I was trying to keep it running and not stall. eventually I got a piece of lumber to hold the gas pedal down while I worked from the front. In the end I think I know what is wrong but don't know why. I hooked up my timing light to see if there was a mark on the crank pulley that lined up with the mark on the front timing chain cover. At first I didn't see one then I found it when the car had stalled. There is a line cast into the crank pulley that I ASSume is the TDC timing mark. I know that the timing is not adjustable but I found that the crank pulley mark was WAYYYY retarded from the timing chain cover mark. By advancing the timing light I found that it was out by 60*!!!

Now, I am guessing that the timing is off by at least one or two teeth. So the question now is how is that possible? I set both the crank and the cam dots pointing towards each other and am very certain it is right. should I have set the crank so that the key way for the sprocket is pointing at the cam? then the dot would be facing the timing mark on the timing chain cover... Or is it the cam that is out somehow?

[95SleeperAcheiva]

first rule of installing a timing chain or belt. ALWAYS roll the motor by hand with a breaker bar or ratchet, 2 FULL revolutions of the crank and recheck you marks, before you re-assemble and/or hit the starter. It may have been 1 RCH off and that did it to you. Also, if you look in the parts store you can find compression gage with a quick disconnect hose, like on air tools. Get one. an air compressor would also be needed, even a small one. then....
1. Remove oil cap!
2. remove all spark plugs
3. screw in compression gage hose at spark plug hole
4. bring the cylinder your hooked up to to TDC
5. hook up air compressor to hose.
6 listen for air leaks at throttle body and then tail pipe.

If you hear something whistling, you have a bent valve. BUT, make sure your timing is correct first only since you just did the repair.

[marko]

If you are talking about a leak down tester than I don't have the equipment to do that. What is RCH?

[95SleeperAcheiva]

leak down tester is an expensive way to go about it. a simple compression tool, air compressor, and your ear is all you need. RCH=a mechanics crude form of measurement, referring to a smaller fine size. opposite of the scale would be a BCH, which is much courser. 1 RCH= 1 Red *unt hair. 1 BCH= Brunette *unt Hair. See instructions above. ie, you hear air at throttle body=bent/leaking intake valve. ie, hear air leaking in tail pipe=bent/leaking exhaust valve.

[marko]

I took it apart again today and verified that the timing marks are indeed lined up perfect. Can anyone tell me if #4 is on the compression stroke or the exhaust stroke when the marks are lined up.

[Azrael]

With the crank mark pointing up and the cam's down, #4 should be at TDC compression and #1 will be at TDC exhaust.

[mfewtrail]

Valve damage *can* occur on these when the chain breaks. Since you have the timing chain installed correctly, you're likely looking at some valve train damage.

[Joseph Upson]

Valve damage *can* occur on these when the chain breaks. Since you have the timing chain installed correctly, you're likely looking at some valve train damage.

I agree, as with direct ignition systems it shouldn't matter whether cyl 1 or 4 is on the compression stroke because they both get a spark regardless. This is important on an engine with a distributor.