I rebuilt the stock 350 for my 71 last spring. Block was bored 0.030" by reputable machine shop. Heads were gone through with valve job and new comp seals that came with the cam kit. I used Hasting plasma moly rings and all were withing spec. Assembled using light film of motor oil. I have a flat tappet that required the 25 minute 2-3k rpm break in. First round on breaking cam in it appeared engine was overheating, slightingly, shut it down at 220. I have a 180 thermostat in it. Ended up running garden hose on radiator to get the cam broke in and keep temp below 210. Everything went well, no valve train noise, no obvious debris in oil when I changed it. So I began chasing this overheating issue. Changed thermostat, ensured no air in block, did cooling system pressure test. I eventually had Lars rebuild the orgininal carb, as I had bought one of the over the shelf rebuilt Quads and it was running lean. Each time I did something I would let the car get to op temp to see if that cured it. Last time was when I put the new carb done by Lars on and it seemed to still get warm, checked total timing, right on at 36 degrees. Ended up being that the stock sending unit was not compatible with the autometer gauge that previous owner install, so overheating was never happening. But all of the sudden now the car is smoking. I took it out for little maybe 5 mile drive and accelerated ect to load rings. I did a dry compression test and got the following results. 1=144, 2=152, 3=155, 4=155, 5=155, 6=155, 7=157, 8=155. I am hoping that the cylinders did not glaze when I was trying to figure out the overheating issue. All eight plugs look the same as the picture below. I read online from many that with plasma moly rings they seat before cam break in is finished. It did not smoke at all during cam break in. It didn't smoke after new carb, the smoking began after reving it up to check total timing ~3,200 rpm. I plan on removing PCV first and running it, the aftermarket valve covers have baffles but they are not as deep as stock, but it did not smoke at first, so makes me thing this isn't the issue. I am thinking of doing a leakdown test next, or am I worrying too early and need to get it out on the road and put more miles on it?

 

intake

 

Hmm. "Intake"...

Just spitballing here: Have you retorqued the heads and intake?
Is that plug representative of all the other plugs?

 

Yes, I agree it could be the intake. Get one of those borescopes you can plug into your phone and send it down the intake passage of each cylinder looking for evidence of oil intrusion. It will be shiny where the oil is the others will be dry and dull looking.

 

I have not retorqued anything. This plug is representative of all. There may be very slight differences, but none that stand out either way.

 

Could one or two runners pulling oil from lifter valley lead to all 8 plugs burning oil?

 

Is the smoke blue or black?
what manufacturer and number plug are you using?

 

ACDelco 41-803 plugs. Smoke is Very light blue almost grey. It burns your eyes.

 

As others have said could be intake manifold leak at engine valley.

 

What exact valve seals were used?
Does it smoke all of the time....? At idle?
How bad is it when you are at WOT?

Jebby

 

The seals were the umbrella style, below is the kit I purchased. It smokes all the time. It is not so bad that driving I see a cloud of smoke behind me. I can try to get a video this week. I am worried that the cylinders glazed over, but not sure the likely hood of that and to happen on all 8 cylinders at the same time.

 

I would also check your carb and make sure the choke flap is returning ,, did you use sealant on the manifold ends or the gaskets

 

No. Only the cylinders where the Intakes gasket failed. Its more common to be on the same bank of cylinders, due to a gasket installed improperly.

 

What were the rings gapped at and did any require an up/down position? It is usually marked with a dot…and dot goes up….no dot and it can go either way.

Jebby

 

They all gapped within spec, check before installation. I believe #2 compression ring has a dot for up, they were installed correctly, like I mentioned before, no smoke during cam break in.

 

Throw a wrench on the intake bolts and pull them down hard to see if it makes any difference. Will need to change gaskets anyway..but might show a general direction.

JIM

 

Reason I ask is that a ring installed upside down won't smoke right away....
And what was the spec used? You should be at about .022 for the top....024-.025 if it is a hyper.....
Are you seeing excessive blow-by?


Jebby

 

I followed the Haynes specs for compression ring end gaps, don't remember what they were exactly, but they were within spec.
Top = 0.010 to 0.020
2nd = 0.010 to 0.025

How would I check for blow by? I am thinking of trying a leak down test next. I also did order one of those borescopes OMF mentioned. Should be here in couple days and I can look into each of the runners.

 

Well...I can tell you that if these are Hypereutectic pistons and the gap is .010....then you found the problem.....if they are that tight, and you leaned into it.....the ends of the rings will butt together and distort the ring land, possible crack the ring.....this is not a measurement that can be fudged from a Haynes manual......it has to be set per piston manufacturers spec.
If you leak it down and it is getting past the rings...this is probably what happened. What happens is the rings expand as they get hotter......the gap closes up.....too hot and too tight and the rings have no where to go but up after the ends butt together......Hyper pistons hold a lot more heat than forged or even standard cast pistons....this extra heat requires a wider ring gap and is very common to overlook this and install pre-gapped rings out of the box....which will always be too tight....always.
Get a leak down on it and you will know.....
Blow by is pretty easy to see with 8 cylinders burning oil.....smoke comes from the breather even at idle......high crankcase pressure.

Jebby

 

Drive it.
Got a long way to go for breakin.

Rings will seat. Comp test will end up at 200 psi with throttle open. That 140 psi is low for broke in rings.
Your gonna like it. Drive it.
Stop looking in the mirror.....................