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Old 10-13-2004, 07:59 AM   #1
MudFlap
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How to tell if it is a 4 bolt main

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
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Old 10-13-2004, 08:06 AM   #2
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Re: How to tell if it is a 4 bolt main

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.
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Old 10-13-2004, 08:07 AM   #3
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Re: How to tell if it is a 4 bolt main

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.
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Old 10-13-2004, 09:16 AM   #4
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Re: How to tell if it is a 4 bolt main

Thanks fellas, I'll try and get the numbers.

Trey
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Old 10-13-2004, 09:35 AM   #5
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Re: How to tell if it is a 4 bolt main

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!. [img]/forums/images/graemlins/crazy.gif[/img] [img]/forums/images/graemlins/screwy.gif[/img]
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Old 10-13-2004, 05:13 PM   #6
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Re: How to tell if it is a 4 bolt main

Diesel4me is correct, no sure way to tell without pulling the oil pan.
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Old 10-13-2004, 10:01 PM   #7
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Re: How to tell if it is a 4 bolt main

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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Old 10-13-2004, 10:46 PM   #8
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Re: How to tell if it is a 4 bolt main

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?
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Old 10-14-2004, 05:13 AM   #9
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Re: How to tell if it is a 4 bolt main

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. [img]/forums/images/graemlins/dunno.gif[/img]
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Old 10-14-2004, 07:28 AM   #10
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Re: How to tell if it is a 4 bolt main

[ QUOTE ]
unless you are building a serious HP maker who gives a flying XXXX if it has 4 bolts or 2 on the mains

[/ QUOTE ]

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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