stumped! any ideas?

[63gmc4x4]

well my 351E is all in and running and driving, running great plenty of power , no smoke ,but I have a slight puffing noise, on drivers side so I decided to pull covers back off and verify valve lash when hot, started it for a minute with them off and found massive amount of blow by or appears to be blow by coming up from the holes where the pushrod come up on drivers side looks like a locomotive! so I turned it over by hand and the same thing you can even hear it from there, with the cover on you can still hear it slightly reset valve lash and verify pcv valve are not stuck, it also has new ventilation filter, I'm confused on this , runs so great , if I had a problem with on of the pistons or rings or head gasket I would think it would burn oil of have low power or even over heat any ideas? I think I'll just drive it and hope I dont blow out any seals I'm gonna change the oil to 20 50 and verify oil level now that it's been ran since 1998 any insight will be appreciated thank you

[63gmc4x4]

I have come the conclusion of the problem, most likely head gasket blown out by the lifters, causing exhaust to push out and come out of these holes that's the only reason I could see this happening, funny thing is though it's not misfiring and runs strong,I guess I should of pulled heads when it was out, I was in just too big of a hurry to get it in the truck, got a wait for warmer weather than ill.pull heads off

[massey478]

Have you run a compression test? A quick way to do it is to pull the coil wire out of the distributor, ground it, and crank the motor with throttle wide open. You will hear a change in cranking speed for lower compression cylinders. We do a quick test on many motors this way.

[63gmc4x4]

found my problem cyl 5 blew out and venting into lifter galley, what may cause this? everything else looks fine

[AZKen]

History of the motor would be important. Assuming and guessing, I will give my opinion.
You did not say if you have done any work on it. So assuming you did not and assuming it's got many miles on it and not knowing where you got it ,or how long you have had it, we are left with guessing. My guess is that someone let it overheat or someone let the timing be off for a long time and these actions caused BIG heat. This created BIG pressure, and heat related damage to the gasket web. Something had to give. Probably no big deal and won't happen again. I guess. Assuming no milky oil or burnt valves, problem in valve train, no avgas or racing gas was used and assuming no other visible cracks, heat scars, etc. in head or block.

Assuming proper assembly, correct gasket and proper torque was applied. All I see is that you "freshened it up"?????????

[63gmc4x4]

well it was giving to me from my friend 20 years ago because he swapped in a 350, and yes I just cleaned it up and replaced gaskets wnated to install it In myb62 and for the making 305 it had so I chanced the head gaskets
it's ok though i can fix it husted never seen one do this i think just the age of them and sitting for 20.years

[massey478]

Did you have the heads checked for flat? Ken has good thoughts about overheating at some time in its history. This is a typical blow-out area I saw several times in the GMC shop I worked at.

[BillT]

Originally Posted by massey478

Did you have the heads checked for flat? Ken has good thoughts about overheating at some time in its history. This is a typical blow-out area I saw several times in the GMC shop I worked at.

I was thinking the same thing. The Heads may need to be Shaved.

[LEWISMATKIN]

Definitely surface the cylinder heads. This gasket is an indication of overheating. The position of the damage to the head gasket can also indicate the streching of the head bolt in that location. I had that happen to mine when I had to park it. Check everything thoroughly and re-torque those bolts after the first warm-up. Also coat those gaskets with either copper coat or high-temp aluminum spray paint-there are no perma-torque head gaskets available for our engines. Good luck!!!!!