Head gasket on a 400 sbc


#1

I purchased a pretty hot 406 sbc to run in my street/strip 1979 C-10. The issue I’m having is I am getting coolant in the oil. The engine does not miss (although with the big solid lifter cam it is hard to tell) and there is no smoke out of the exhaust. The engine, when running, pressurized the crankcase to the point of blowing oil from around the front and rear main seals. After running the motor for five or so minutes the temperature gauge showed no increase in temperature but the engine was up to temp because there was coolant flow in the radiator (it is not a rad in my chev, rad is something a skateboarder did in the 1980’s and a chev is something a prisoner uses to stab another prisoner, sorry, the rant is over). I put a new set of head gaskets on the engine and tried again. Same issue as before. I tried to test each cylinder by charging them individually with the hose from my compression tester. There doesn’t seem to be a leak into the cooling system with 125lbs of air pressure. Somebody please help!


#2

Did you use 400 head gaskets? If you did, did the heads have the corresponding steam holes drilled in the heads? Classic 400 Chevy problem.

The 400 SBC has 2 small holes in the deck surface between the cylinders to vent the water jacket between the siamesed cylinders (on the 400 there is no water jacket between the cylinders like on a 350). There are matching holes in the head for the block to vent. Only 400 heads have this from the factory. If you are using aftermarket or 350 heads, the small holes need to be drilled. Use the gasket as a template. Before you put the heads back on, check the heads and block for warpage. If you didn’t have this before, you might now. Good Luck


#3

If you know that much about Chevy engines why are you Mustangman- oh I get it, it’s because you know so much about Chevy engines.


#4

Every motorhead knows about Chevy engines because every enthusiast magazine (Hot Rod, Car Craft ect) does at least one Chevy engine buildup each year. They have to, its state law!


#5

Those are nationally distributed magazines. Clearly, it is federal law that governs this work.


#6

The miniscule amount of metal between the siamesed center cylinders of the 400 SBC makes it vulnerable to head gasket failures and even a burnout in the deck. The engine is somewhat weak for that reason. Most that I have seen were low compression 2 bbl versions in family sedans and wagons. It seemed like an accident looking for a place to happen.


#7

And the small block Chevrolet V-8 was the most versatile engine ever built. From hydroplanes to dump trucks they could be tailored to suit most anyone’s needs with off the shelf pieces. They were relatively easy to build. I personally preferred the 305. I was able to build them to average 20 mpg in 1/2 ton vans. Businesses that put 50,000+ miles per year on them were very pleased when I replaced a worn out 350 with a tuned 305.


#8

@Rod Knox, I’ve built a few race motors out of 305’s, NO ONE wanted them. People would give me short engine for free because they wanted a 350. Silly people! The best I ever built must have had a 350 sand core for casting because it had the thickest cylinder walls I’ve ever seen on a 305, 0.240 to 0.280 inch! Great race motor! I named him Steve.


#9

My work rarely involved anything high performance beyond factory original equipment @M-M. On the advice of a friend I installed an RV cam in a 305 and installed it in my own pickup and the results were very impressive. Whenever I rebuilt a SBC after that I recommended the RV cam. If the old engine was badly worn a 305 core was available for free from the local machine shop because everyone for years had opted to install the larger engine. No one ever complained that the swap reduced their power.

A dealership mechanic felt certain that the change in camshafts would not be tolerated by the EFI system on later models but I swapped several and everyone was happy with the results. The heavy duty trucks had a factory equivalent of an RV cam and needed all 350 cubic inches and then some on occasion so I never attempted to downsize those models.

The SBC’s adjustable valves, interchangeable components and flexibility made it the engine of choice for hot rodders for many years. I doubt that there will ever be an engine as universal as that one. And I’m a ‘Ford man.’


#10

SBC makes a great chain saw too:


#11

Ok, I know next to nothing about this engine. Well, actually nothing at all. But here’s an idea to consider. There may be a problem with the crankcase ventilation system. Especially if the engine has some kind of a blower on the air intake. If so, either the existing one is faulty, or it just isn’t capable of handling the situation. I’ve seen aftermarket systems advertised in the hot rod magazines – replace the existing parts in other words – used to address this crankcase ventilation problem with extra high power engines.


#12

Oh yeah. Back to the OP’s problem. Could it be that someone recently made an effort to correct a failed head gasket and made any of several possible mistakes and did the OP possibly match the gaskets he removed when he replaced them? As @M-M mentioned there are very specific gaskets for various versions of the SBC engine and the 400 is very particular in regard to the head gasket. The crossovers and bleed ports are very critical and a miss match in the head gaskets or the intake gaskets can lead to various problems, some catastrophic.

As for oil blowing out the front main I am curious as to whether someone has installed an air tight oil fill cap when a vented type was needed.


#13

I saw a motorcycle with a small block V-8 and thought that was as outrageous as anyone could get @Csmith but I was wrong… A V-8 chain saw. Someone had WAAAAAAAY too much time on their hands.


#14

Oh Yeah, The Boss Hoss, They make a big block version. That’s even more insane!