Torque pattern for four bolt mains
Thread Starter
Race Director
Joined: Mar 2008
Posts: 15,161
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From: coffee
Torque pattern for four bolt mains
I did a bit of searching, and could not find definitively what the sequence needs to be for torquing four bolt main bearing caps.
I know that, in general, you need to go inside out, but does anyone have a link to a diagram or something?
I have a 290 HP GMPP engine that will be going in my '81 shortly, and I have read about several people having bad experiences with the mains not being properly torqued down from the factory.
Many thanks...
I know that, in general, you need to go inside out, but does anyone have a link to a diagram or something?
I have a 290 HP GMPP engine that will be going in my '81 shortly, and I have read about several people having bad experiences with the mains not being properly torqued down from the factory.
Many thanks...
Thread Starter
Race Director
Joined: Mar 2008
Posts: 15,161
Likes: 17
From: coffee
Thanks. I am presuming that everything should be seated properly from assembly at the factory, but the issue seems to have been too little torque applied.
Drifting
Joined: Feb 2005
Posts: 1,738
Likes: 2
From: San diego ca
yeah better go buy a book ar head to your nearest bookstore with a pen and paper...big block specs are different than small block.. 75# inner 65# outer on a small block IIRC - but again get some reference material...
As far as pattern goes... #3 (center main first) #2 - #4 - #1 - rear main last is the pattern I use.
As far as pattern goes... #3 (center main first) #2 - #4 - #1 - rear main last is the pattern I use.
Thread Starter
Race Director
Joined: Mar 2008
Posts: 15,161
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From: coffee
I have a haynes manual that I need to look through, but I'm not sure that it would have four bolt main specific recommendation since (to my knowledge) C3's did not come from the factory with anything but 2 bolt mains.
I need to get a better book anyway, maybe the "how to rebuild the small block chevy" will have it...
I need to get a better book anyway, maybe the "how to rebuild the small block chevy" will have it...
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Melting Slicks
Joined: Oct 2001
Posts: 2,062
Likes: 1,360
From: Halifax, Nova Scotia, Canada
I have a haynes manual that I need to look through, but I'm not sure that it would have four bolt main specific recommendation since (to my knowledge) C3's did not come from the factory with anything but 2 bolt mains.
I need to get a better book anyway, maybe the "how to rebuild the small block chevy" will have it...
I need to get a better book anyway, maybe the "how to rebuild the small block chevy" will have it...
Here is the page from "How to Hotrod Small Block Chevys". It gives most of the torque specs you should need. I verified the torque specs for the mains with a Chevrolet service manual, which states the same.
Also, just to clarify, there were several C3 small blocks that came with 4 bolt mains.
All the L46 and LT-1, I'm not sure about the later L82s.
Regards, Barry
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
Various C3s came with 350 4 bolt blocks. My late '69 with the base motor has them. Not sure of all the years, but they did appear over the years.
Here's the straight scoop from the 1969 Chassis Overhaul Manual (Official GM book), Engine Torque Chart - page Specifications 11:
7/16-14 Main Bearing Cap - 75 ft. lb. with a note, Outer bolts on engines with 4 bolt caps 65 ft. lb. There is no chart giving the order.
No guesses, that's the official word.
Cheers,
Pete
Here's the straight scoop from the 1969 Chassis Overhaul Manual (Official GM book), Engine Torque Chart - page Specifications 11:
7/16-14 Main Bearing Cap - 75 ft. lb. with a note, Outer bolts on engines with 4 bolt caps 65 ft. lb. There is no chart giving the order.
No guesses, that's the official word.
Cheers,
Pete
Thread Starter
Race Director
Joined: Mar 2008
Posts: 15,161
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From: coffee
Many thanks...
I will use those specs and just basically work from the inside out on the inner bolts, then do the same on the outers.
I did not realize that there were ever any 4 bolt main SBC cars from the factory, but I suppose that I should have known better, thanks for the info...
I will use those specs and just basically work from the inside out on the inner bolts, then do the same on the outers.
I did not realize that there were ever any 4 bolt main SBC cars from the factory, but I suppose that I should have known better, thanks for the info...
Last edited by nate99; Oct 15, 2008 at 09:27 AM.
Instructor
Joined: May 2006
Posts: 184
Likes: 1
From: Oak Grove MO.
i am glad you started this thread because i will need this info soon also. but i thought all c-3 vette engines were 4 bolt. Does anyone know anybody who had a 2 bolt factory? I have never heard of any.
Burning Brakes
Joined: Dec 2007
Posts: 952
Likes: 0
yeah better go buy a book ar head to your nearest bookstore with a pen and paper...big block specs are different than small block.. 75# inner 65# outer on a small block IIRC - but again get some reference material...
As far as pattern goes... #3 (center main first) #2 - #4 - #1 - rear main last is the pattern I use.
As far as pattern goes... #3 (center main first) #2 - #4 - #1 - rear main last is the pattern I use.
Le Mans Master
Joined: Mar 2004
Posts: 7,449
Likes: 1,477
From: Little Rock AR
75# on the longer ones 65# on the shorter ones for 4 bolt mains. It does not need to be in a pattern. You might want to sneak up on the final torque reading by going around in several steps like 35#-55#-Final# but honestly that is probably overboard.
Get Vizard's book - It's the Bible.
-Mark.
Get Vizard's book - It's the Bible.
-Mark.
