Help !! Motor and Frame Mounts ?'s for BB - Chevelle Tech
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post #1 of 10 (permalink) Old Sep 12th, 99, 3:54 PM Thread Starter
Join Date: Mar 1999
Location: Canton, OH, USA
Posts: 17
Can anyone tell me what the major differences are between the small block frame motor mounts and the Big Block mounts. Also, what is the major differnences for the engine mounts for the two blocks?

I'm trying to install my 396 in my 69 Chevelle and the motor mounts do not line up. I purchased brand new motor and frame mounts from Ground Up that were suspose to be for a 69 BB. When I get one side lined up and a bolt thru it the other side is way off alignment. The motor mount hole on the other side is approximately 3/4" off in a diagonal direction towards the inside of the motor.

When I compared the old frame mounts from a small block to my new mounts I noticed that the BB frame mount hole was about a 1/4" lower than the small block mount hole. I also noticed that the two new frame motor mounts were not identical to each other. Both were the same height, but some of the holes were missing on one of them. One had the same mounting holes as the old one and the other did not. One of them has a regular hole and the other has a slot type hole where the bolt goes thru to connect the motor to the frame mounts.

Another thing I notice with the new motor and frame mounts is that the motor mounts are 1/4" wider on both sides than the frame mounts. Is this normal? Seems to me that I'd have to torque down the bolts too much to close these gaps.

Any help anyone could provide me would be greatly appreciated. I have take the hoist back tomorrow and it's currently holding the block up. Thanks...

[This message has been edited by DS76462 (edited 09-12-99).]
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post #2 of 10 (permalink) Old Sep 12th, 99, 6:55 PM
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Location: Mustang, OK USA
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ALL of my experiences with, or friends experiences with replacing a SB with a BB have been to remove the SB, bolt the engine mounts to the BB and install the BB. Period. I have never seen or experienced thiis to be a problem, although for other people it seems to create a problem.


Therefore, if you want to replace your 307/350 with a 396/502, there should not be a problem. There never has been for me.

There is a possible exception to this. There may be some Chinese made engine mounts that are less$$$$$$$ than US made engine mounts that are just a little too narrow to slip down over the frame brackets. whenever you buy new engine mounts, test fit them on the frame brackets first. If they fit, then everything should be fine. Otherwise, take them back and buy a better quality US made mounts. Other than that, there should be no difference in the dimensional location of the motor mount holes where the long bolt goes through the mounts/brackets.

Tom Parsons
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post #3 of 10 (permalink) Old Sep 12th, 99, 7:52 PM Thread Starter
Join Date: Mar 1999
Location: Canton, OH, USA
Posts: 17

If I remember correctly, some people on this site recommended that I get the big block frame mounts so i wouldn't have clearence problems with my headers.

The BB frame mounts that I got from Ground Up sit 1/4" lower than the ones I took off from my small block. It appears that if I put the old frame mounts on then everything may will be lifted up 1/4" and line up. I'm just worried about clearence problems with my headers. Seems to me that the BB should sit up higher than the SB too elimate header clearance problems.

Another question, if Chevy recommends the same frame and motor mounts for both SB and BB, then why do so many Chevelle catalogs specify separate ones for each type?

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post #4 of 10 (permalink) Old Sep 13th, 99, 3:48 AM
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Join Date: Dec 1998
Location: just south of Tulsa, OK, USA
Posts: 85
I agree with DZAUTO, the Chevrolet parts book I have lists the frame mounts to be the SAME for small block AND big block Chevelles '68-72.

I've also done as he said... pulled out a 307 and bolted in a 454 (bought NEW rubber TRW mounts however). No problem at all.

Are you putting the engine and transmission in as one UNIT or are you trying to stick the engine in with the trans already in??
Getting the engine aligned with the mounts AND the trans can be a BIG chore.

I usually put them in a one unit.

Good luck.

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post #5 of 10 (permalink) Old Sep 13th, 99, 5:45 AM
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I went to all the trouble to get a set of frame mounts for a rat for my 67. I have the small block and big block mounts on the bench, can't tell the difference!

Gold #67
67 malibu
post #6 of 10 (permalink) Old Sep 13th, 99, 11:32 AM
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Location: Pittsburgh,Pa.
Posts: 7
Thats all I did when I replaced the 350 in my '71. took the mounts off the 350,bolted them to the 454, and in it went.. no problems whatsoever.

I also experienced the problem Tom is talking about with import mounts. I was cursing the parts counter person that sold me those for hours!!
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post #7 of 10 (permalink) Old Sep 13th, 99, 11:55 AM
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DS, just for the fun of it, try swapping them from side to side. They look the same but this might be all you need. Good luck ,Rick....
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post #8 of 10 (permalink) Old Sep 13th, 99, 3:41 PM Thread Starter
Join Date: Mar 1999
Location: Canton, OH, USA
Posts: 17
I think I know what the problem is. I talked to Ground Up today and it appears they gave me the wrong motor mounts. He told me that the ones he gave me were for a Camaro and not for a Chevelle. Since I didn't have the old ones to compare it too and the boxes that the new ones came in had no description on it, I just assumed I had the right ones.

The guy I talked to said the BB and SB mounts were a little differnt. Are they? What I'm hearing from you guys is that they are the same and are interchangable. If you look at the Tech Reference Page #10 (Big Block Conversion) written by Bob Tiley, it says you need new engine mounts for a BB. I'm confused....

I do have the old ones from my 307 and they are totally differnt from the new ones I got. I might try to see if they will fit for now until I get the right ones from Ground Up.

Thanks everyone for your input..

[This message has been edited by DS76462 (edited 09-13-99).]
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post #9 of 10 (permalink) Old Sep 13th, 99, 8:40 PM
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This is my experience with 67's.

I have a Malibu that was originally a 283 car. The assembly manual listed two part numbers for the frame mounts. The mounts are shaped differently. The big block ones have extra metal that sort of wraps around the perimeter of the pad that the block sits on. As far as the location of the pad/motor mount relative to the car, they are the same. Bottom line is two options.
1. Re-use the SB frame mounts. Buy SMALL BLOCK motor mounts and bolt them to your BB. BB motor mounts will not fit on SB frame mounts.
2. Buy junk yard or aftermarket BB frame mounts and then you can use the standard BB motor mount. The aftermarket frame mounts I have are fabricated and do not look factory at all, but appear beefier than the SB mounts.

I spent $99 on aftermarket frame mounts, the yards want upwards of $150 for Chevy mounts.
Hope this saves someone a little hassle.

John Walker
67 SSClone
Metro Atlanta, GA
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post #10 of 10 (permalink) Old Sep 14th, 99, 3:58 AM
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jmw, I noticed the lip that is turned up on the BB frame mounts for the 67. That looks like the only difference. If I put the 27 in, I will use them just because I have them.

Gold #67
67 malibu
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