Hey everybody
A local guy has been asking me for help and I'm out of ideas. He rebuilt a 1971 350 engine but when he tried to fire it for the first time it wouldn't start and he's getting a gas mist coming out of the carb. He then checked for compression and said he had zero compression. He's changed the cam thinking he had the wrong one then changed the lifters/pushrods again thinking he had put in the wrong ones focused on the idea that the valves are not closing. He says there is spark but he has heard no sounds of backfires. He used a reliable machine shop for the work, but they're out of ideas what to check. He's pulling his hair out and I'm out of ideas too. Any of you guys run into something like this before? John

 

Out of Ideas? Not what I would expect from a competent machine shop.

Did they supply the parts? Did they do any excessive head or block milling? How much of the assembly (heads, shortblock, etc) did they do?

Easier to look for any change in the valve positions while bolting on the rocker assemblies. If they did not move, the cam/lifters/pushrods, would not be at fault.

Obviously, he did not degree the cam. Did he index the gears properly?

Assuming the heads were done correctly, the right pushrod length, and that a "rookie" did the assembly, I would check to see if there are any rings on the pistons.

Norm

 

If he has zero compression he should do a cylinder leak down test and find out where he is losing compression.

 

Thanks for your comments guys. What I know, the machine shop did the machine work including a valve grind but no new seats. My first thought was that the valves may sit too deep and that the shop didn't grind anything off the top of the stems. I don't believe they milled anything but I'll double check with him on that. The machine shop suggested he put shims under the rockers. He did all the assembly and has done many Chebby engines but this is his first time playing with an Oldsmobile. It's for his nephew's 1971 Cutlass S.

 

Who supplied the parts? I'm guessing that it was not the shop.

Has it been verified that the valves are not closing?

Are the lifters solid or hydraulic?

Are the pushrods the correct (8.234") length?

Are the installed spring heights at 1.670"? How many shims were used?

New seats are not part of a normal head job. Replacement valves are.

If they do, replacement valves were not used to correct it. Also not likely that all 16 valves (or at least one on each cylinder) would be more than .060", or so, higher than spec.

If the correct replacement was used, there would be no need to, as the stem height would have been adjusted at the seat.

Instead of applying band-aids one should be looking for the cause of the problem.

I guess we can assume that he put rings on the pistons.

Norm

 

Is this zero compression for all 8 cylinders?

 

With zero compression, I think I could find the problem with just blowing air into the cylinder at TDC. or as already stated a leak down. Then we can start the fixin part.

 

Did he by chance have the timing chain and gears timed wrong? Then bending valves once he started to crank it. Remove the valve covers, make sure the valves are moving, pump air into the spark plug holes, can you hear it and where? Something has to be really wrong to have 0 compression.