Engine smoking

[68 50th]

What do you guys think the problem is with my engine.
I bought this 73 454 that was supposed to be OK a while back. Put my newly rebuilt (new guides and new teflon seals) 72 402 heads on it and yesterday I started it for the first time. It ran good but smoked from the left exhaust pipe. Then suddenly it stárted to run on 7 cylinders and a mecanical noise came on. I took the engine out of the truck and found a very oily exhaust port on #5 cylinder. Is it a bad oil ring/piston ring or what do you guys think?
Thanks in advance.
Mats.

[71tahoe]

The last time I had a problem like that, #1 or #3 cylinder dropped a valve. Thankfully it didn't trash the piston.

See if either of the retainer cups move side to side on #5.

With those symptoms you will have to pull the head regardless of what it is.

[68 50th]

Thanks 71 tahoe,

I will check the retainer cups.

Mats

[Billla]

Did you run the engine prior to installing the new heads? Agree with checking the heads as noted...but I'd also consider a worn cam lobe (easy to check) or...the engine wasn't as OK as communicated and you've got a bad cylinder - a compression/leak down test will tell you if that's the case.

[71tahoe]

Also, how did the plug look? How long did it run and what RPMs did it turn. There may be some distortion in the picture but if you hold a straight edge on #3 exhaust it looks straight. If you do the same to #5 it looks like it's bent. If the new guide was installed at an incorrect angle it could have had enough resistance to let the valve come in contact with the piston without the retainer letting go.

[68 50th]

I didn't run the before I installed the new heads, and when I started it I ran it for about 5-10 minutes. All cam lobes look OK and so do the valves and the rest of the heads.
I took the whole engine apart and found a stuck oil ring expander/spacer on #5 piston.
It was overlapping at the ends and had slipped in to the slotted hole in the piston side.
The cylinder wall looks and feels OK but I will take the block to a machine shop to have it measured.
Thanks for your comments and advices.

[68gmsee]

Hey, 68 50th, thanks for the update. Too many times we have a problem and get opinions/advise and no one knows finds out what fixed it...

My 69 has been fouling the plug on cylinder #1 and I've always assumed it to be the valve guides. I may have to take a deeper look inside the tired, old 350...

[Billla]

Rats The oil rings are fairly low tension, so hopefully all is well. Have to admit that I would have never suspected that...

[68 50th]

I went to the machine shop yesterday to have the engine checked.
The oil ring issue on #5 cylinder didn't damage the damage the cylinder wall. We measured all pistons and cylinders. Cylinders was glazed and just honing and new rings would give to much piston play so the engine will have a 060 over bore (was 040 already) and new pistons.

[Billla]

Ouch. So are you doing a complete bottom-end overhaul then?

[68 50th]

Originally Posted by Billla

Ouch. So are you doing a complete bottom-end overhaul then?

Yes, I will do a complete overhaul. Bore, pistons, crank grind, all new bearings, new cam, lifters and cam drive, new oil pump and the heads was done already.
Hopefully everything turns out fine next time I start it up

[71tahoe]

Originally Posted by 68 50th

I didn't run the before I installed the new heads, and when I started it I ran it for about 5-10 minutes. All cam lobes look OK and so do the valves and the rest of the heads.
I took the whole engine apart and found a stuck oil ring expander/spacer on #5 piston.
It was overlapping at the ends and had slipped in to the slotted hole in the piston side.
The cylinder wall looks and feels OK but I will take the block to a machine shop to have it measured.
Thanks for your comments and advices.

That's good to know it wasn't the heads. Is the ring gap orientation the same as when it was in the block? If so, that would be something that could have contributed to the oil ring spacer rolling in the slot of the piston. It would be something to watch on reassembly. I think they should be turned about 90 deg. from each other but I don't have my Haynes manual.

[68 50th]

Originally Posted by 71tahoe

That's good to know it wasn't the heads. Is the ring gap orientation the same as when it was in the block? If so, that would be something that could have contributed to the oil ring spacer rolling in the slot of the piston. It would be something to watch on reassembly. I think they should be turned about 90 deg. from each other but I don't have my Haynes manual.

71tahoe, thanks for notifying me on that.
Yes the ring gap orientation was like that, I also noticed that when I took it apart.
I have the "How to rebuild Big Block Chevy Engines" book by Tom Wilson, there is a good explanation for where all the rings gaps should be.

[71tahoe]

Looks like a PO gotcha. You know it will be right when it's finally done now.