76 400 block fitment and compatibility questions
 

Hi I am considering swapping a 76 400 in place of my 350 in my 71 GT-37. I have the following questions:

1) Would the 76 400 block that came with factory automatic have a boss that could be drilled and tapped for the clutch linkage on my manual transmission 71 GT-37?

2)Would my 71 bell housing bolt up to the 76 400 block?

3) I believe the register on the crank for the flywheel got smaller in 76 on the 400’s to about 2 1/2”. Is that correct? If so would it make sense to use a flywheel listed for a 76 Firebird 400?

Any help would be greatly appreciated. Thanks!

1) It should, it might even be drilled and tapped already but not certain about all of the 577 blocks. I had a friend who converted his '76 trans am to a manual - it had the original '76 engine and 2.41 rear gears.... I think we calculated a theoretical 200+ mph top end. lol.. I don't think we pulled it and so I am pretty sure that it had the boss on the block drilled and tapped for the countershaft.
2) yes.
3) there are several ways to go about that. If I remember correctly, there is a precisely machined spacer ring available which can be used with an earlier flywheel or you can use the exact, proper 1976 flywheel.

The bell housing bolts right up.

Will you be using the heads and intake that are from 76 also?

Yes, that would be the plan at this point. I'm not sure it is original intake, but heads are 6X. It has 4 bbl intake (not sure if original) and a quadrajet. Why do you ask?

Well if the heads have not been gone thru then if nothing else while the 400 is out of the car you should replace the valve stem O ring seals.

These just dry rot to pieces once a motor of this age has sat for a number of months and the is put back in service if they are not gone already.

Hmm... Okay. Engine was rebuilt about 47K ago (not sure how long ago) but it was last run & driven about 3 mo. ago. What is involved in replacing valve seals on a Pontiac motor?

Does this block have the motor mount bolt holes for the old style mounts?

Clay

I'm not sure. How can I determine this? The engine has been in a 71 Firebird up until a couple mo ago.

It should not matter. 1969 was the last year that used the old 2 bolt motor mounts. 70 and up used the newer style, and the '76 engine should be able to use mounts compatible with the '71 Lemans, especially since he has had the '76 engine in a '71 firebird.

That's good to hear. I appreciate everybody's help with these questions!

One more question... This engine has been used in an automatic transmission car...
Did they use different cranks for manual & automatic for 557 motors? Should I be able to install a pilot bearing in this crank?

[QUOTE="QUICK-SILVER";6464280]Does this block have the motor mount bolt holes for the old style mounts?

Clay[/QUOTE]

[B][SIZE="3"]Do these shed any light on the question? These are the mounts currently on the engine.[/SIZE][/B]

Coin flip on that one. My friend's '76 had both the countershaft boss machined, drilled and tapped, as well as the crank being machined for a pilot bearing. I have seen other similar engines that did not have the crank machined for the pilot bearing. ��

The factory always used what it had cast up, machined up and still had on hand.

If sales of manual trans cars did not pan out, but more orders then foreseen came in for auto trans cars then those cranks done up for the manual trans cars got used.

Well, hopefully it is machined for a pilot bearing... If not, would the crank have to come out to do that or could it be done by bringing the whole engine to the machine shop?

The cranks gotta come out unfortunately.

https://www.motortrend.com/how-to/ea...ount-adapters/ Alot of info on motor mount locations.

The 76 block has the 3-hole motor mounts on it, that won't work in a 71 A-body, (unless your GT-37 originally had a 455 in it from factory).
The old style 2-bolt motor mounts were used up thru 1972 on the A-bodies with 350 & 400. Your 76 block has all 5 motor mount holes, so just simply remove the existing mount and use the 2-bolt motor mount for the GT-37