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How to tell if it is a 4 bolt main

M

MudFlap

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If there an easy way to tell if a 350 is a 4-bolt main without pulling the oil pan? Do casting numbers tell this? It is in a 75 blazer with a 465/205 behind it and I know the motor was rebuilt but I don't know if it was the stock block or not.

Thanks
 
1. Measure the harmonic dampner. Should be larger of two diameters available on 350. Can't remember what they are.

2. Should be an oil port on the top right portion of the timing chain cover. It kinda points up and to the right.

Those are the only two things I know of. Not sure if the casting numbers will tell you or not.
 
There is a machined pad on the front right bank of the block.
Right by the alternator.
Get all the numbers and post em up.
 
The short answer is NO--the only sure way to know is to pull the pan and look.You can look up the casting numbers,look for oil plugs near the timing chain,guess by measuring the balancer,the number 010 on the side of the block,etc--I've had 350's that had all the "sure signs"of being a 4 bolt main going by the casting numbers,and all the other "it might be" things they tell you to look for,but still had only two bolt mains when the oil pan came off--others I've had showed none of the things that point to it being a four bolt main--and they WERE four bolt mains!.I've concluded that pulling the pan(or at least the timing cover)is the ONLY sure way to tell if its a four bolt block or not.Too bad Chevy had to be so secretive--it would be nice to just look up the numbers and be SURE it was a four bolt main--guess they like to keep us guessing!. /forums/images/graemlins/crazy.gif /forums/images/graemlins/screwy.gif
 
unless you are building a serious HP maker who gives a flying XXXX if it has 4 bolts or 2 on the mains
 
besides, isnt there a 2 to 4 bolt main conversion kit out there (i think milodon makes it) thats sposed to be as good or better than a factory four bolt?
 
Summit sells the Milodon 2 to 4 bolt kit $215.88. I bought a used block for $50. I always pulled the pan to find out what I got. /forums/images/graemlins/dunno.gif
 
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unless you are building a serious HP maker who gives a flying XXXX if it has 4 bolts or 2 on the mains

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Exactly my thoughts here. My engine builder says he'd rather have a two bolt block any day of the week for himself. His customers seem to believe the 4 bolt block is better. He says "2 bolt mains will allow the crank to flex which in turn adds longevity to the life of the motor." Now if your gona put together serious horsepower and ear peircing RPM's he'd still prefer a 2 bolt main and then put the splayed pattern main caps on. Apparently he has some engines out there that turn 7000 rpm's all night on two bolt mains and don't have any trouble.
 
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Diesel4me is correct, no sure way to tell without pulling the oil pan.

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Yep.

And as you guys say, who cares? /forums/images/graemlins/whistling.gif
 
I would still get the #'s and cross check them.
They may not identify a 4 bolt main but will have relevent info such as year,hp,what it was installed in, ect. ect.
Then you would know if that is the block that came in the rig.
 
For the record--I've seen more 4 bolt mains throw a rod through the block than 2 bolts--might be because the owners of the four bolt main motors were braiwashed into thinking they are indestructable,and they thrashed them without mercy-- /forums/images/graemlins/deal.gif--NEWS FLASH! ALL chevy motors can and will blow up!--sure the 4 bolts are supposed to be stronger,but you must also consider the fact many of the 4 bolt motors had steel cranks along with the additional main bearing cap bolts,that helps longevity too.I dont think you can hold your foot into it long enough to hurt a 2 bolt main on the street(too much other traffic in the way!)--and I've seen several cars that drag race at new england dragway that are 2 bolt mains--two of them have 6-71 blowers on them,with no add on bolt kits,just stock gm parts,and they run well--I dont see why people get so excited over a 4 bolt main block--for the average Joe street and strip muscle car,or off road rigs a 2 bolt is plenty strong. /forums/images/graemlins/crazy.gif
 
The crank, nor the main caps, have nothing to do with throwing a rod. /forums/images/graemlins/rotfl.gif
 
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The crank, nor the main caps, have nothing to do with throwing a rod. /forums/images/graemlins/rotfl.gif

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tim i think your kinda off there man, if the crank getts out of round just a little bit, it is very possible that the vibration that would coause would cause a dor to stress and break, also the lack of a stong man cap can a will cause the crank to go out of round(or blance) and destroy the engine too.. There is a reason the built motors use splayed main caps
 
I disagree. Cap walk and all that stuff is likely to break crankshafts in two, but the most likely culprits for throwing a rod are stretched rod bolts, poor quality rods, balance issues, and of course the ever popular too much RPM. /forums/images/graemlins/thumb.gif
 
yup there is
the chev block isnt that tough
these days rather then spend $ on a production block it is a better deal to buy from Dart or World
 
I disagree, but I have for a long time. /forums/images/graemlins/smile.gif

It hasn't been fully explored as to whether the suffix code (one on the pad behind the alternator) indicates 2 vs 4 bolt by application.

Obviously there are going to be exceptions in production, there always are, but GM tried to keep things consistent when they could.

The oil galley plug front, PS above timing cover seems to be fairly reliable as an indicator, but so does any truck application. (also checked with Suffix code)

A racing friend states there is a cast in marking on the back of 4 bolt main blocks that is 100% reliable indicator, but I'd never bet on that. I can't recall the lcoation he said it was, I don't see enough blocks to test that theory though.

I don't really care 2 vs. 4 bolt, but I'm just curious to find if there is a common denominator for 2 or 4 bolt blocks.

So far my suffix code "theory" has proven itself out, but I've only had two matching suffix codes come back...not nearly enough to prove my "theory".
 
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