Compression problems, please help

ebelizard · Feb 18, 2010

I have a 69 with a 302. I put the car in the shop because it wasnt firing/running. After replacing the distributor, they got it to fire up, but it will not run. A compression test revieled that there was NO compression on 3 cylinders.

The guy that I got the car from told me that he adjusted the valve springs, but did not tighten them to torque spec because he didnt have a torque wrench; he tightened them to the best he could and used a gapper to try and make sure they were at a ball park setting.

My question is, could this be the only problem that only 3 cylinders arent firing?

woodsnake · Feb 18, 2010

Kind of a shot in the dark, but I think you spun a timing gear set. The reason you have NO compression in three cylinders is that the valve stems are bent, and not closing.

ebelizard · Feb 18, 2010

If the valve stems are bent, is that a hard job to replace? costly?

dcstang67 · Feb 18, 2010

This could also be a blown headgasket.

ebelizard · Feb 18, 2010

well the guy I got the car from (claims) that the car was running before the he replaced the distributor (which threw off the timing and therefore didnt run). If it was a blown head gasket, wouldnt the oil look like a milkshake from the oil/coolent mixing? and if so, wouldnt a blown head gasket mean that there would be no compression on multiple (more than 3) cylinders?

dcstang67 · Feb 18, 2010

I have blown a headgasket between 2 cylinders and the only symptom I had was no compression between both cylinders and a nasty skip to the engine, but it still ran.

mystic 96 · Feb 18, 2010

comp problems...

are u sure its compression??? and not a plug..did u check for spark...is it all one one bank on does it have 2 on one bank and one bad on another,,,maybe firing order ???? always check the little stuff first b4 major surgery....

ebelizard · Feb 18, 2010

dcstang67 said:
I have blown a headgasket between 2 cylinders and the only symptom I had was no compression between both cylinders and a nasty skip to the engine, but it still ran.

that scares me.

tonygoebel@yaho said:
are u sure its compression??? and not a plug..did u check for spark...is it all one one bank on does it have 2 on one bank and one bad on another,,,maybe firing order ???? always check the little stuff first b4 major surgery....

The mechanic at the shop told me that the cylinders are getting spark. He also did not specify if it was 3 cylinders on one bank. I'm pretty sure they checked the firing order because they told me that it would fire up but would not run. I'm really hoping it's a bent valve(s). Ill find out tomorrow if they call me.

mystic 96 · Feb 18, 2010

make sure u trust this mech....

make sure he tells you compression #'s on all cylinders if in fact thats the prob...did it over het at some time or do u know the history of this car,,,if you dont fell comforable get a second opinion...its cheaper than the repair is going to b.......and make sure if this repair has to b made that the car is worth reparing,,,,,,.....

68RCodeConv · Feb 19, 2010

Is the valve lash on those cylinders too tight? If so the valves are staying open all the time resulting in no compression.

Or you could have REALLY burnt valves.

woodsnake · Feb 19, 2010

What was the motivation for changing the distributor?

That statement is what I based my timing gear set statement on.

The shop should be able to take the valve covers off and watch the rockers to check and see it they are moving their full range.

If you have bent valves, you will need to pull the heads and have them rebuilt. If that in fact is the case, then you should look at a new cam as well, if you were ever going to change it.

rbohm · Feb 19, 2010

68RCodeConv said:
Is the valve lash on those cylinders too tight? If so the valves are staying open all the time resulting in no compression.

Or you could have REALLY burnt valves.

i agree with the valves being set too tight. loosen up the rocker arms until you can move the push rods vertically, then tighten them down until you cant. that will be zero lash. at that point you add another 1/4-1/2 turn for a bit of preload on the lifters. you want to do this valve adjustment with the lifters on the base circle of the cam. then run another compression check.

headgrinder · Feb 21, 2010

So if it is a 69 302 there is no adjustment on valves just tighten them if the studs are 3/8th you adjust if it is 5/16ths no adjustment needed.If the ex valve seats have receded/sunk in the lifters can no longer adjust valves and you loose comp. it would not be a sudden thing but gradual.

ebelizard · Feb 21, 2010

headgrinder said:
So if it is a 69 302 there is no adjustment on valves just tighten them if the studs are 3/8th you adjust if it is 5/16ths no adjustment needed.If the ex valve seats have receded/sunk in the lifters can no longer adjust valves and you loose comp. it would not be a sudden thing but gradual.

yea the guy said that he adjusted the valve springs but couldnt torque them down. Im thinking he could have over torqued them and that could lead to compression problems/leakage......If Im wrong please tell me.

ajfriz · Feb 21, 2010

I had a bent valve issues once. The piston looked fine until I took it out and I saw it was broken under the oil ring... I would hope it's either a blown headgasket or valve lash is too tight. Personally I would take all of the rockers off and pull the plugs, then use a compression gauge on each cylinder. If you still don't have compression then pull the heads.

D.Hearne · Feb 22, 2010

rbohm said:
i agree with the valves being set too tight. loosen up the rocker arms until you can move the push rods vertically, then tighten them down until you cant. that will be zero lash. at that point you add another 1/4-1/2 turn for a bit of preload on the lifters. you want to do this valve adjustment with the lifters on the base circle of the cam. then run another compression check.

69's have positive stop rocker studs. Bolt em down and go.... They could be too loose, but not too tight. Unless you install some thick washers between the nut and fulcrum ball, then you can adjust em.

D.Hearne · Feb 22, 2010

ebelizard said:
yea the guy said that he adjusted the valve springs but couldnt torque them down. Im thinking he could have over torqued them and that could lead to compression problems/leakage......If Im wrong please tell me.

If your mechanic hasn't figured it out yet.................get another mechanic. This one's not a mechanic you want working on your car.

ebelizard · Feb 25, 2010

Ok so I talked to the mechanic at the shop and he said that the rocker arm nuts are bad, and that if a new set is installed it would run without a problem. Does that sound like it could solve the problem?

D.Hearne · Feb 25, 2010

No, get another mechanic. That one's completely clueless. Groping around in the dark.

ebelizard · Feb 26, 2010

apparently the positive stop rocker studs arent setting correctly due to age/rust so they need to be replaced. D Hearne the car is already in the shop and I really dont know of any other reliable service around my area. Only if I had a technical specialist like you around, maybe I would find some time to wrench on it myself.

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