kidneyboy

What's the difference?

Jughead

It refers to the number of bolts on the caps which hold the crank. Here are pictures of a 4 bolts and obviouls a 2 bolt only has 2 bolts per cap.

kidneyboy

thanks Jughead. Is there a performance difference?

jimvette74

The # of bolts that hold the crank bearing caps to the block. 4 bolts are desireable for very high horsepower engines. Some two bolt blocks have the place for four bolt caps- thay are just not drilled and tapped.Some people drill two bolts into four bolts (at an angle)-but withought the meat in that area of the engine you can actualy weakin the block. two bolt mains will hold up to alot of hp- more than most streetable rods can turn out.

kidneyboy

thanks jimvette...I'm still new to this and the more I think I know the less I actually do. This has been on my mind since I discovered my engine is a 2 bolt. Obviously not the original motor.

jimvette74

could be original many came with two bolt check the block casting #.

Glensgages

Flip the block-over, and remove the oil pan.....

you'll see 5 (one at the front, one at the rear, and one between each set of cylinders) 'main-bearing caps', which clamp the crankshaft 'up-wards', into the block.

Older 'passenger' cars had 2-bolt-blocks and caps (one on each side of the cap/crank), while later 'performance' blocks had 4-bolt (TWO on each side of the cap/crank) blocks and caps.....

" Thanks for calling, next caller, please.....


"Grumpy", from Malvern, Pa., you're on..... "

jimvette74

Dont assume it.s not original. could verywell be- nice pics jughead;0

Carl Granquist

On my L-48, where will I find this number? I've had folks tell me both ("probably a 4-bolt main" & "likely a 2-bolt main") and I'd like to check for myself to know for sure. Thanks.

Jughead

Casting number is on the drivers side, back of the block, right where the block & tranny meet. Shine a flash light down there & if it's not too cruddy tou should be able to read a number like this--->14015445

Sometimes though, the casting number may not tell you for certain whether it's a 2 or 4 bolt.

My number listed above is posted as being a 2 or 4 bolt. Go look HERE when you get the number.

I was pleasantly surprised when what everyone told me was a 2 bolt turned out to be a 4 bolt!

72LS1Vette

If you know for sure that your motor is a L-48 it should be a 2-bolt main. The L-82 motors were 4-bolt. I'm quoting numbers from 1979 but other years are probably similar.

Rick B.

kidneyboy

My vin# shows mine to be a L 48..so it is supposed to be a 2 bolt main. It's a 78. Thanks for all the helpful answers, tomorrow if its not too cold down in the garage I'll see if I can check the numbers on the block.

redc3

i have several blocks, and for example the #'s are 3970010 on three of them. 2 are 4 bolt, 1 is 2 bolt. the 2 bolt will hold up to alot of hp and tq. more than most will agree to. good luck

Eddie Van Vette

My 1979 C3 Corvette VIN translates to An L48, but when I took the oil pan off to paint, I see my block is a 4 bolt main, it is all original, engine, transmission-Borg Warner Super T 10,is this possible?

mikep3

Post a pictue of your engine bay. That will tell us a lot about your engine.

L88Plus

Up until the Gen 5 came out in '90, there was no way to tell from a casting number on a big block whether it had 2 or 4 bolt mains with one exception - one '89 - '90 casting is all 4-bolt and it's a Mark IV block.
SBC 400's are a bit different - almost all of the "511" castings are 4-bolt, cast in the first two years of 400 production. 509 and 817 castings are 2-bolt, at least 90% are, I won't say all until I've seen 'em all.
SBC 350 is a crap shoot just like big blocks - all casting numbers after about '70 can either be 2 or 4 bolt mains.
Big blocks have the same number of bolts on all 5 caps, small block 4-bolt blocks only have 4 bolts on the middle 3 caps, front and back are 2-bolt.
Best way to tell easily is to drain the oil and use a borescope through the drain hole. Don't buy the cheapie from Harbor Freight, the camera/light on the end are too big for drain plug and spark plug holes but the more expensive one has a much smaller end and works for both.

Cavu2u

My '73 L-48 has it's original engine (190 hp), and it's a 2-Bolt Main.

Steve

BKarol

If you are not the original owner check the engine stamp pad to see if it has your partial vin # and also the suffix should be ZAA or ZAF.

If you see a 4 bolt then it is what it is.

Pop Chevy

This is also a 10 yr old thread. However I am in the process of converting a 2 bolt 454 to 4 bolt mains for racing. it's the 445 no. block

brian76

I have a 3 bolt main - 2 studs followed by 2 nuts