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Old 09-15-2020, 10:48 AM   #1
rechinca
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Bellhousing to block bolts

Trying to figure out what this bolt looks like. Mine was a mix of bolts, some with washers and some missing, none of them stock bolts. What should I have for a 350 with a cast iron bell housing for the 3 speed Saginaw? I have the bolts for the bellhousing to trans, just not for the block.

I have seen they are 3/8" - 16 x 1 5/16", but I have seen flange style and various others and some sources that say if using a certain bolt you must use a washer. Not that I am doing a restoration, but would like to use what the factory would have used on a SBC to bellhousing. Appreciate any help and pics you might have.
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Old 09-15-2020, 10:58 AM   #2
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Re: Bellhousing to block bolts

Factory bolts usually have a flange
I have installed and pulled many engines

Parts store bolts with out flange hold well enough with out washer as long as there tighten to specs

Too loose they may back out to tight they may break
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Old 09-15-2020, 11:39 AM   #3
rechinca
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Quote:
Originally Posted by gmc684x4 View Post
Factory bolts usually have a flange
I have installed and pulled many engines

Parts store bolts with out flange hold well enough with out washer as long as there tighten to specs

Too loose they may back out to tight they may break
Thanks gmc, that is what I was believing to be correct, but then I looked at the 4 Speed Conversions website and they showed a set with 4 shorter and 2 longer standard bolts without the flange. Those at least somewhat matched up to what I removed, but mine is more an example of what not to do than the correct way.
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Old 09-15-2020, 08:58 PM   #4
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Re: Bellhousing to block bolts

Put bolt in check the all the bell housing holes and they all stick out equally

To short a bolt may not grab enough threads to long bolts may not keep the bell housing secure to engine
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Old 09-15-2020, 09:00 PM   #5
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Re: Bellhousing to block bolts

The main thing i do is clean all threads on block and bolts as clean threads are easier to tighten and real dirty may feel tight but be very loose or strip threads
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Old 09-15-2020, 09:48 PM   #6
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Re: Bellhousing to block bolts

Use bolts that have at least the same penetration into the block as the size of the thread. For a 3/8" bolt, that is (obviously) 3/8". That's an engineering standard. If you want to use a flanged bolt, that is fine. But I've removed and replaced literally hundred of bolts that mate a trans to an engine, and seldom have seen bolts with flanges. In the mechanical design world, we call it "spec creep", where someone sees something that might make the product better, but ignores the engineering aspect of a design...which drives up the cost with no benefit.
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Old 09-16-2020, 07:25 AM   #7
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Re: Bellhousing to block bolts

Just go to Tractor supply / rural king / loews / home depot and you can buy a bag full of grade 8 bolts /washers/lock washers to replace old mis matched /worn hardware . a grade 8- 3/8 bolt with a lock washer is all you need to mate the bell housing to the block . Use ARP bolts on fly wheel and pressure plate install .
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Old 09-16-2020, 10:30 AM   #8
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Re: Bellhousing to block bolts

Factory was 3/8''-16 x 1-1/4 no flange or washer. Never seen anything different in 40 years of working on these trucks. Personally I upgrade to a flange bolt. They are a little pricey at about a 1.50 or so each, especially when you buy a box of them at a time
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Old 09-16-2020, 11:16 AM   #9
rechinca
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Re: Bellhousing to block bolts

First off thanks to everyone for the responses. As usual this truck is always an example of how to cut corners and how not to do things. I’ve bought and sold a lot of vehicles, but this one has been the worst example of never trust the previous guys work.

Doing some digging last night I found my parts catalog. Interestingly it lists two part numbers for the bolts. One of which specifies that you must use a washer when using it. Seeings that I have had good luck with 4 Speed Conversions I went back to their site and found the following bolt set that says it is used for the bellhousing in our, or at least my, truck. It has (4) 3/8”-16 x 1 1/4” and (2) 3/8”-16 x 2 1/4”. I already had some shorter flange bolts and when I compared it to the bellhousing, the 1 1/4” long ones were never going to work. The cast boss on the lower edges is almost an inch thicker. At least it confirms the bolt sizes listed. Style is up to the beholder.
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