4 bolt main?

[Heinz55]

So, I went to junk yard and found an engine from a 79 C-10. Block casting code is 3970010. Besides pulling oil pan, any other way to tell if this is a 2 bolt vs 4 bolt. Given that it is a truck, I was hoping it was a 4 bolt.

Thanks in advance for any and all advice, looking to rebuild and replace non-chevy power plant in my 55

[LONGHAIR]

Unless you are planning upon a high revving screamer or a big stroker.....don't worry about it. The 2 bolt block will be just fine. A 4 bolt block may be stronger, but for 400 HP or less, not necessary. I certainly wouldn't pay extra to get one.

[baclay9]

Most truck motors (if not all) are two bolt main. Passenger cars (nova's, ect) recieved the 4 bolt mains.
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[87GMCChris]

1968 3970010 327 -2bolt A
1969-79 3970010 350 -2 or 4bolt car, truck, Vette

http://www.nastyz28.com/sbchevy/sblock.php

[1BadSS]

Originally Posted by baclay9

Most truck motors (if not all) are two bolt main. Passenger cars (nova's, ect) recieved the 4 bolt mains.
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Most big truck sbc's are 4bolt main.

To the original poster of the thread. Have a look at the balancer if it's 11-12" tall, by 2" thick. Odds are about 75% that it's a 4 bolt main. Don't hold me to it though.

[Big Port Jimmy 6]

Bore scope up the drain plug. Jay

[Heinz55]

Well, engine now at my house in back of my parts truck. Too good to pass up, someone had already removed transmission and radiatir, so it was literally a 5 minute job (just had to pull engine mount bolts) to pull the engine. Gonna put it on the stand tomorrow and monday, and will let ya'll know what I have.

Harmonic balancer is 1-3/4" thick by 9-1/2 ish (hard to tell right now) in diameter

[mongoose]

Originally Posted by 1BadSS

Most big truck sbc's are 4bolt main.

To the original poster of the thread. Have a look at the balancer if it's 11-12" tall, by 2" thick. Odds are about 75% that it's a 4 bolt main. Don't hold me to it though.

i don't think i've ever seen a balancer that is pretty much the same size as a flywheel.

[KQQL IT]

Either two or four the 010 is supposed to be the better of the 350 castings, higher tin or some b/s like that

[LONGHAIR]

Originally Posted by 1BadSS

To the original poster of the thread. Have a look at the balancer if it's 11-12" tall, by 2" thick. Odds are about 75% that it's a 4 bolt main. Don't hold me to it though.

The "big" balancers are 8" diameter, but I wouldn't bet on any external clues to a 4 bolt main block.

The old "they say" (whoever "they" are) used to believe that a 4 barrel carburetor was the clue. "If it was factory equipped with a 4 barrel, it had 4 bolt mains."......I wouldn't bet on that one either, even if you could be sure that a 30 year old engine did indeed have a factory 4 barrel.


LIke I said before, it's not important anyway.....

[BigBlocksRule]

Originally Posted by LONGHAIR

The "big" balancers are 8" diameter, but I wouldn't bet on any external clues to a 4 bolt main block.

Agreed, for sure. I've seen 2-bolts in 3/4 ton trucks and 4-bolt blocks in wimpy cars. Pulling the pan is the only way to tell for sure.
With regards to the numbers, rumor has it (I've never seen it proven) that blocks with 010 and 020 under the timing cover were cast with .1% higher nickel and .2% higher tin. Nickel for hardness, tin for machinability. My decimals are in the correct places, it's not even a full percent of either. Blocks with the digits "2482" cast into the center caps are more desirable, those caps are nodular iron versus typical grey cast iron for others. They're getting hard to find, all I've seen were late 60's, early 70's blocks.

[Heinz55]

while looking at engine at the wrecking yard ( and lack of other attached accessories that was making this engine really attractive from a labor required to pull it point of view) some dude walked up and started talking to us. Turns out he said donor truck was identicle to his, originally came with a 4 barrel carb (which looks true on this engine as well) and he was sure I had a 4 bolt.

but as stated above, only way top tell is to pull the pan, I will let everybody know what we determined shortly


thanks for all the replies so far, this site is great

[motornut]

hi hadn't heard about the dampener i'll go measure mine.
but it's the same block #
and was told said this number was the better metal content and found in the trucks or 78 novas,but havn't heard another way besides dropping the pan and can't go by carb,a dealer/anybody coulda change it .
my came new with a 305

[68 TT]

Originally Posted by baclay9

Most truck motors (if not all) are two bolt main. Passenger cars (nova's, ect) recieved the 4 bolt mains.
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In my experience it is the other way around. Many trucks with 4-bolts and cars with 2-bolts. Early rare high performance models like Z/28's got 4-bolts but otherwise even the SS cars got 2-bolt blocks at least with small blocks. They weren't shy about putting the steel crank in the 2-bolt car motors though.

In the smog years I have seen nothing but 2-bolts in the cars.

Out of the dozen or so trucks I have owned where I tore the engine apart for one reason or another I would say 75% were 4-bolts.

With big blocks it is more random. The same car model and block casting number could get either.

[68 TT]

Originally Posted by LONGHAIR

Unless you are planning upon a high revving screamer or a big stroker.....don't worry about it. The 2 bolt block will be just fine. A 4 bolt block may be stronger, but for 400 HP or less, not necessary. I certainly wouldn't pay extra to get one.

I saw a test Lingenfelter did where he tested all the variations of 2 & 4-bolt.

Turns out a 2-bolt with main studs installed is stronger than a 4-bolt with bolts.

The true failure point is really the stock rod bolts first, then the cast pistons, then the cast crank, then the stock rods and after that then the 2-bolt block.

So unless you have a steel crank, aftermarket rods and forged pistons the 2-bolt block will be more than enough to outlast the bottom end of your engine.

He was making right at 500 hp on a 2-bolt block with main studs with no sign of failure from the block.

[Heinz55]

and survey says: 2 bolt main

Crank looks great, turns easy, timing belt feels worn, rod bearings look normal.

Looks like this is a factory remanufactured engine. Rod bearings are .0005 over, but no stamps on caps (well, not before I started the teardown)

Plans will now be a mild rebuild, mostly stock, nice and quiet and dependable going down the road.