4 bolt or 2 bolt mains

[Rufus1050]

The L98 motors used in the 85 plus vettes...are they 4 or 2 bolt mains? How about windage trays in the oil pan? I am curious. Thanks in advance!

 

[Ken]

When I pulled the factory L-98 from mine, with 102,000 miles on it, it had two-bolt mains.

 

[WhalePirot]

Mine too, and I am advised that 'two bolt' engines are just fine for most street engines, to a rather high level.

 

[Vettefan87]

Yea when I had all this work done on my motor I found out that they are two bolt mains, up until then I always thought they were four.

 

[Ken]

If one was so inclined to want four-bolt mains, a two-bolt block has a bit more meat to it and is a better candidate for using the aftermarket (Milodon for example) four-bolt mains. The aftermarket "splayed" caps are stronger as well.

However, as Mike said, you shouldn't need four-bolts until you're into the 500 horsepower range.

 

[vetteboy86]

Wasn't the older chevelles and camaro's 4 bolt main engines? If so why did they go away from this?

 

[Ken]

 

[PLRX]

LT1 are also 2 bolts

 

[G Winter]

My understanding is that 2 bolt are good for anything under 7000 rpm. I am sure they went away from the 4 bolt because of cost. 4 bolt mains were used in preformenc engines in the late 60s . Many pickups had the 4 bolt in the early 70s.

 

[Nitronick]

It's all about the money!
I remember between '73 and '74, all GM cars with 2 barrel carbs went from 4 mounting bolts to 2. Saved them something like $10 million in nuts, bolts and less machine work, labor time saved tightening less hardware, etc in that one year.
BTW, I know this because my family has been in the carburetor remanufacturing business for over 40 years.:crazy:bash;squint:

 

[brimis]

Two bolt mains.

 

[vetteboy86]

Any thing to save a buck
Craig

 

[redc4corvette]

All 260 hp corvette engines are just truck motors chevy could not figure out what to put into the vets from 84 to 90 the truck motor was cheap and vet owners went for it because of the tork and they thought they had a fast car.
Thats why they never made any good aftermarket parts for the L98.Insurance !also.

 

[Ken]

Thats why they never made any good aftermarket parts for the L98.Insurance !also.

Surely you jest! :L

 

[nmacdonald]

Could some one help me understand what you are talking about when you refer to 2 bolt or 4 bolt mains? Also, I've read several places about 9 (?) bolt or 12 bolt rear ends. Does this all have to do with power and torque capabilities?

Thanks

 

[tomtom72]

Hi All, I would like to put in a plug for GM SB truck motors from the late 80's. Mercury Marine used them for the small V8 power package, MCM 260 Alpha I was a 350 cu. in. @ 260 hp. Those went in most run-abouts up to 27'. They were good & durable motors and you could get almost anything for them that you wanted in the way of hop-up parts. I had one in a 1980 23' Formula, it was a 1988 MCM 260 ( one pc rear main seal block ) and I had no trouble getting a cam & intake set-up for it. MM would offer a 5 yr optional warranty on it ( 2 bolt main block ) and they thought it was $ in the bank as far as paying out on motor failures was concerned. I know that MM figured the load on the motor vs life expectancy was about 2000 hrs @ 80% load in a 4,000 lb boat. They explained that by telling you if you drove a 4,000 lb car up a 45* incline at 60 mph it would fail after 2000 hrs. That isn't so bad for a stock motor.

I am not sure what the # of bolts on a chevy rear tells you. I think I've been told it has something to do with the gear ratio???? I am fairly sure my 72 vette had an 8 bolt cover and the ratio was 3.55:1. If I remember correctly the vetts with the 4.11:1 rears had a 10 bolt cover???? I think! Tom.

 

[mike weyman]

the "bolts" we are talking of are the bolts that hold the crank shaft in place the center caps that hold the crankshaft in have 4 bolts. mike

 

[Hib Halverson]

Could some one help me understand what you are talking about when you refer to 2 bolt or 4 bolt mains? Also, I've read several places about 9 (?) bolt or 12 bolt rear ends. Does this all have to do with power and torque capabilities?

Thanks

"Two-bolt mains" means the engine's main bearing caps have two bolts each. "Four-bolt mains" mean the engine's main bearing caps have four bolts each, however....small-block Chevys with four-bolt main bearing caps only have them on the center three caps.

Generally, a four-bolt main bearing block is used in high-performance applications. For example, After 1967, typically, when power got above 340hp gross or 290hp net, GM used four-bolt mains in small blocks.

"12-bolt" refers to the number of bolts used to hold the back cover on the rear axle diff. housing. When GM enthusiasts talk about 12-bolt and 10-bolt axles, they are talking about the live axles used in passenger cars and trucks. The "12-bolt rear axle" was never used in a Corvette.

The 63-79 Corvette axle uses 12-bolts to hold the diff. housing together but it shares nothing with the GM 8.875-in ring gear "C-axle" which virtually all GM enthusiasts call a "12-bolt".

The 12-bolt axle is reliable and higher torque loadings than is the 10-bolt but that has nothing to do with the number of bolts holding the cover. It has to do with pinion shaft diameter and ring gear diameter.

 

[Achilles]

Hib...I used to think that the 12 bolt rear end was a posi, or limited slip posi rear end and the 10 bolt was just a single drive unit. My reason for thinking this is when I blew out the stock rear in my 69 GTO, I replaced it with a 12 bolt out of a Chevelle that had a lower gear and a posi. Am I correct or misinformed?



John

 

[G Winter]

Number of bolts in a rearend has little to do with ratio and nothing to do with posi. Positraction was an option. The ratio is controled by the ring gear diameter. A matter of what was physically possible.