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Oil Pump Bolt

16K views 18 replies 9 participants last post by  jimfulco 
#1 ·
What's the size of the bolt used to bolt the oil pump on the block for a chevy 350 engine?
 
#8 ·
bolt sizes

divide the head size by 3 and multply by 2. If its and indust. bolt subtract 1/8 before diven. 3/4 head*3=1/4x2=1/2
7/8-1/8=3/4*3=1/4x2=1/2 on indus.
read the tool and rember where the cali. is .
 
#10 ·
bolt sizes

Well I still don't understand how a 3/8 bolt in a 7/16 hole could hold an oil pump on?
 
#16 ·
RPM said:
If you use too long of a bolt it could hit the back of the main bearing. That would cause a major engine failure for sure. If you can't find the right bolt ARP has them and the local speed shop should have it.
Maybe my brain is a little fried and I don't have one in front of me to look at but I believe the hole is a blind hole and not a through hole on the small blocks.
 
#17 ·
back to bolts 101

I guess we're talking lenght instead of dia.
A nut or threaded hole is as deep or thick as the dia. of the bolt used in it. So onced we found the dia. of the bolt we see how thick the object we're going through is and add the dia. of the bolt= lenght of the bolt.If you might want some extra threads add1/8. When you tighten it if it torks and is loose, you shorten the bolt or add a lock washer. If you use the lock washer, be sure to install the washer upright and not upsde down.
 
#18 ·
engineczar said:
Maybe my brain is a little fried and I don't have one in front of me to look at but I believe the hole is a blind hole and not a through hole on the small blocks.
I don't know exactly when (sometime in the 80s), the hole was drilled all the way throught to the back of the bearing. Guys were having trouble when they used a bolt that was too long. You can guess what happened.

Using too short a bolt can caust the top few threads to pull out. If that has happened, the hole can be repaired with a heli-coil or similar repair. Another alternative is to use an oil pump stud, Moroso and others have them (that's probably the est way to go in any case).

When in doubt, thread the bolt to the bottom of the hole (in the cap with the blind hole) and compare the OP mounting boss to the length of the bolt. That will tell you if the bolt is too long. If your main cap has the hole that goes all the way through, use a bolt that doesn't.

I find the short bolts from the 4 bolt main caps works well in either case.

tom
 
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