12-14 degrees of slop.

[Patch]

Sighhhhh.......hand pulling the motor around to get to TDC......look up.....rotor is pointing at between cylinder 2-4. On top of that....the timing marks travels the distance of the timing tab before the rotor starts to move...ugh. Before I go putting a new timing set in this, I suppose I should do a full compression check and see where the motors at. Did GM run nylon coated gears in these like Mopar did? It's got great oil pressure.....but if the compression is too low.....no point in going any further for now.

[Bigdav160]

Cam timing that retarded is likely going to effect compression. Leakdown would be a better test for piston/ring sealing.

I don't know what year GM started using plastic on the cam gear but they did use them

[truckster]

If the timing is off the compression numbers won't be correct. In order to develop compression the valves have to open and close at the appropriate times.

[Ol Blue K20]

My 89 V3500 with a 454 had the nylon cam gear. It let go at 190,000 miles.

[100%Chevy]

My original 75,350 had the plastic (coated) cam timing gear.
So,they did it that far back.
Mike.

[Patch]

So with a leak down vs. a compression check, I'll get it to TDC and pressurize that cylinder and see how long it holds pressure? Never done it that way but I understand the method. I hadn't even thought of the compression not being true during the test if the chain had jumped and it was out of phase. Thanks a bunch......

[toolboxchev]

Get the numbers off the block, Yes GM did use those plastic coated gear sets. But not in the original motors. Even if you have an original motor it does not guarantee you do not have metal gear sets, someone could have rebuild it with that crap.

I did a top end rebuild on my original motor with a dual roller set 75k miles ago, I have 2 degrees of slop in the timing chain now. That should give you something to gauge what you have going on without tearing the motor apart.

Lots of people neglected these vehicles for years and did not realize how much of a working machine they are.

[Patch]

Originally Posted by toolboxchev

Get the numbers off the block, Yes GM did use those plastic coated gear sets. But not in the original motors. Even if you have an original motor it does not guarantee you do not have metal gear sets, someone could have rebuild it with that crap.

I did a top end rebuild on my original motor with a dual roller set 75k miles ago, I have 2 degrees of slop in the timing chain now. That should give you something to gauge what you have going on without tearing the motor apart.

Lots of people neglected these vehicles for years and did not realize how much of a working machine they are.

Honestly....I'm surprised it even runs. I'm going to change out the timing set regardless. After I get it back together, I'll do a normal compression check, it'll be a good learning session for my 15 year old. Going to swap out the points for an HEI as well. I'll do that AFTER I get it fired back up. The block numbers came back to a 1969 truck 350, so I am only assuming it is original, everything else has been, down to the original shocks and fuel pump....lol.

[firedemon]

if the timing is so far off that you cant do a compression test a leakdown test wont work for the same reason . it will tell you your valves are open or push the piston down . going to have to replace the chain and gears first unfortunatly

[Patch]

QUOTE=firedemon;8308105]if the timing is so far off that you cant do a compression test a leakdown test wont work for the same reason . it will tell you your valves are open or push the piston down . going to have to replace the chain and gears first unfortunatly[/QUOTE]

Yep.....that's what I'm going to do.

[Rufas]

Originally Posted by Patch

Sighhhhh.......hand pulling the motor around to get to TDC......look up.....rotor is pointing at between cylinder 2-4. On top of that....the timing marks travels the distance of the timing tab before the rotor starts to move...ugh. Before I go putting a new timing set in this, I suppose I should do a full compression check and see where the motors at. Did GM run nylon coated gears in these like Mopar did? It's got great oil pressure.....but if the compression is too low.....no point in going any further for now.

Don't know about Chevy but Pontiac was using plastic coated timing gears in the late 60's. Those Pontiac engines were notorious for the plastic breaking off and plugging the oil pump pickup screen, oil starving the bottom end and destroying the engine.