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Old 08-14-2019, 01:48 PM
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Default 70 400 Block in 79-81 w Clamshell Mounts

A friend is dropping in a '70 400 stroker in an '81 body, and has the clamshell type mounts on the frame. He's saying it won't set in there to get both bolts in, and has tried multiple brackets.

Any suggestions?


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Old 08-14-2019, 04:18 PM
Grand73Am Grand73Am is offline
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I suggest checking the part numbers on the brackets he's trying to use. The correct ones have the numbers 496892 and 496893 stamped on them. They are off of a Pontiac engine(455, 400, 350, or even 301) that was in a 75-81 Firebird or TA. No other brackets from any other Pontiac car will work.

They aren't reproduced so if he needs some he'll have to find some good used ones. They can sometimes be found on eBay for around $100, more or less. Here's an example: https://www.ebay.com/itm/75-81-Ponti...gAAOSwk3NdUJ36

If he's already using the correct brackets, he might need to loosen the bracket and motor mount bolts so he has some play to be able to get the long bolts through and then tighten everything.

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Old 08-14-2019, 11:09 PM
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What engine was in car previously? If it wasn't a 265 or 301, AND the clamshell mounts are still bolted to their original locations, they need to be relocated....I tried using the full size 78 Catalina brackets when I temporarily install a 350 in my TA, way back in 1992 (it's still in my car...)
I had everything going smoothly. Dropped the engine in, got the trans bolted up, BUT, and a BIG BUT, I was unable to put enough grunt on a pry bar to close that approximate 1 inch gap in the mount location!!'

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Old 08-15-2019, 01:00 AM
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Check and see if the mounts will slide on the clamshells by themselves OFF the motor. Sometimes they are too tight and have to be spread out a little. I jacked with the IA in the Camaro for a a hour or so before I figured that out on my mounts. Used the next smaller sized bolts with a nut on the inside to spread it out.

Also not sure what year blocks had all 5 holes that use the 3 hole later mounts. I know some early blocks had to use an adapter.

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Old 08-15-2019, 07:38 AM
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I believe the one set he is attempting to use now was listed on eGay as correct, but it doesn't appear there are any numbers on them, so they are suspect.

There was a P350 when the car was purchased, trying to find out now if he has those brackets.

I think it's a 5 hole block, but the brackets only bolt on one set of holes, so sounds like they work, and again, there was a P350 in it before.

.

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1970 GTO Judge Tribute Pro-Tour Project 535 IA2
http://forums.maxperformanceinc.com/...d.php?t=760624
1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car
https://forums.maxperformanceinc.com...ght=procharger
Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be
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Old 08-15-2019, 08:01 AM
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He can't get the old brackets back from the P350 that was in it before, but he did order used GM brackets with part number from eGay.

Guess I will have to wait until he takes another shot at it before I can provide any updates. But will throw the suggestions out there as posted here.

Thank you all for you suggestions!

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1970 GTO Judge Tribute Pro-Tour Project 535 IA2
http://forums.maxperformanceinc.com/...d.php?t=760624
1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car
https://forums.maxperformanceinc.com...ght=procharger
Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be
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Old 08-15-2019, 08:12 AM
Grand73Am Grand73Am is offline
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Quote:
Originally Posted by HWYSTR455 View Post
I believe the one set he is attempting to use now was listed on eGay as correct, but it doesn't appear there are any numbers on them, so they are suspect.
The numbers can be faint, especially if the brackets were rusted or heavily painted. But usually can be seen if you look close enough. Might have to sand or scrape them. Here's an example of where on the bracket to look:

002 by grand73am, on Flickr

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Old 08-15-2019, 01:09 PM
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I think he got some that were repops that the seller said would work, but, obviously, they didn't. No worries, he has a set of used OE ones on the way.

I will ping him in a day or two, see how he's doing.

So doesn't have to have an 'F' stamped on it?

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1970 GTO Judge Tribute Pro-Tour Project 535 IA2
http://forums.maxperformanceinc.com/...d.php?t=760624
1971 Trans Am 463, 315cfm E-head Sniper XFlow EFI, TKO600 extreme, 9", GW suspension, Baer brakes, pro tour car
https://forums.maxperformanceinc.com...ght=procharger
Theme Song: http://www.youtube.com/watch?v=7zKAS...ature=youtu.be
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Old 08-15-2019, 02:15 PM
Grand73Am Grand73Am is offline
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Quote:
Originally Posted by HWYSTR455 View Post
I think he got some that were repops that the seller said would work, but, obviously, they didn't. No worries, he has a set of used OE ones on the way.

I will ping him in a day or two, see how he's doing.

So doesn't have to have an 'F' stamped on it?

.
I have found an F on the 893 bracket before. So, you might find that situation. But I haven't seen an F on the 892 bracket, like the one I pictured above. I go by the numbers to be sure.

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