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

Just In Case
 

Old thread somewhere here on PY about a non GM bushing that can be made to work with automatic only cranks.

Clay

Don't get rid of the old 350 you may very well need it again ... any good running 350 is better than a broken 400

[QUOTE="QUICK-SILVER";6464804]Old thread somewhere here on PY about a non GM bushing that can be made to work with automatic only cranks.

Clay[/QUOTE


THANKS, I will try to find!

Is this the thread you were thinking of?

https://forums.maxperformanceinc.com...+pilot+bearing

The engine I'm considering buying is a 76 400 with automatic attached to it. It may have originally been in an automatic or manual car.--no way of telling. My transmission is manual.

I wonder if it's a good idea to buy this engine without knowing what the crank looks like on the back?? According to post #40 in the thread below, mid 70's Pontiac cranks weren't drilled at all??

https://forums.maxperformanceinc.com...+pilot+bearing

Is the crank register the smaller one?
(looks like it could be)


:confused:

Originally, the 500557 400 blocks used the 2.75" register cranks. That practice lasted at least a year/ well into mid '76 engine production. Later '76 model 400 blocks received the smaller register cranks, do remember checking a few.

For many years i had a Pontiac V8 engine core program going. On occasion I would pick up '76-78 500557 shortblocks, then simply shell them out for the good condition smaller register 400 cranks, as well as oilpans, timing covers, valley pans, & hardware. Two of the '77 500557's I stripped down, the stock cranks had the correct recess for a pilot bearing. Both of those cranks were needed in 4speed W72 TransAm engines where the owner had spun a rod bearing & was still wanting to run the stock small register 11" cast flywheel.

Is this 400 a used stock engine? My plan would be to cc both sets of heads and try to get the compression up to 9 or 9.5 and change the camshaft.
Those 94 heads should have a smaller combustion chamber.

I see the big "75" cast by the Distributor hole, so I'm betting that date is A155, or Jan 15, 1975. Hard to tell for sure in the pic, maybe hard to tell in person as well. Try a wire brush over the casting date and see if it doesn't become more of a '5' at the end.

It seems unlikely to me to be cast with the big number 75 by the distributor and be a 76 engine, which A156 would be.

:confused:

The best way to ID the year is by the partial VIN on the block.
The pic of the date code is hard to tell for sure if the last digit is a '5' or '6', but I think it is a '6' (1976)

I have seen some blocks with the 2 digit cast year for the next year of production. (would have to check notes if any in 1976 though)

:confused:

examples;
1976 year before,
1973 no year,
1972 year after.
No sure what the big numbers are supposed to mean.

The large numbers are intended model year fitment the 4 digit codes are the actual day the molten metal was poured into the mold

The OP's block has a 1976 casting date with a large 75 being previous year. The block in post 38 also has a 1976 casting date with a large 75 being previous year. Attached is another one. I thought the general rule is casting dates are not after model year is finished.
Also the crank in the B046 dated block had a 2 1/2" register.

I dont have an explaination for every part number casting date anomoly..

no industry that is run by humans will be perfect SOP is 4 digit code is cast date and the large number near it is intended model year it went into or cast for

service replacement parts WILL / CAN have a cast date later than model year IE. i have a set of 1970 RAIV 614's that were cast in 1973
RAIV's dropped alot of valves in the warranty period

The cast Year doesn't mean it's for the model year. In 1969 when they cast the '70' it was put in quite a few 1969 Firebirds because of the extended run of Firebirds.

Not sure what they mean, but I figured it might be for a change in the block.
1970 went to 5 bolt mounts for example, and 1975 late went to the 500557 blocks.

But I do know that the partial VIN would be for the model year. 79 Phoenix block was a 1976 model.

:)

Quad, is the block you posted have a 1976 partial VIN?


:confused:

The B046 block has the same partial VIN as the 1976 Firebird it is in. In hindsight I should have mentioned this in previous post.
Reading through this site there appears to be exceptions to so many general rules.