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Pontiac Forum: pontiac 1967 400CID manual engine rebuilding
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  #1  
Old June 22nd, 2018, 03:17 PM
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pontiac 1967 400CID manual engine rebuilding

I have a Pontiac GTO 1967 4 speed manual.
I bought this car last year in NJ from a guy who serviced the car for 27 years. (I am european, living in Europe so it was a bit difficult for me 😊 )
I have been looking for that car for many years to get it in very original shape. The only not original thing is the engine.
O have been told that this is 1968 GTO 400 engine and it seems to be truth.

Production date seems to be D158
Block casting number 9790071
Engine code 623216 WT

Camshaft 540 / 253 (i have no idea what those numbers are), another numbers 521? / 31 / A /? /D
Crankshaft 9773524 / 107 / N
The diameter of connecting rod journals is 2,241 which means that the crankshaft was at least 2 times repaird (Am I correct?)

There are correct heads 670 (L216)

What is weird is the bore of the cylinders we measured: best value 4,106, worst value 4,118
Also used pistons 9787610 they used to be a part of 421 CID engine

I have no idea how this can happen. A 400 CID block with bore smaller than 4,120. Do you have some explanation for it?

Piston rods: there is no single same number. It seems that there were used piston rods from different engines with the same stroke. The connection rod lenght seems to be 6,625

All the data above seems to allow me to rebuilt the engine to the very original shape.

What I would like to have at the end is an engine better than a factory one with more than 360 HP and 450 Lbs torque. Max safe RPM at about 6500 (BTW: I am using 95 octane fuel)

What I would like to do is:

Change the crankshaft to the right one with a standard (factory new) diameters of journals
Increase the bore to a standard 4,120
Change the pistons and connecting rods to some of better quality than original
If the camshaft is correct, then to keep it. It is mosly untouched. If not then change for the right one
Change the rocker arms (used up) for roller rocker arms
Change valve springs for another with at most 300 lbs (but also not much less)
Of course oil pump and all sealings and gaskets

Might you please help me with yours experience I am lacking to find the right way how to do that and to find the right parts for that purpose?

Many thanks in forward

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Old June 22nd, 2018, 04:02 PM
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If the engine was really a 389, 4.062 bore stock, 4.092 with .30 over pistons and worn out bores.
The 421 pistons are 4.093 so they would roughly fit a .030 bored 389.
With your aim of 6,500 rpm and the collection of parts you have you would best served to contact this company
https://butlerperformance.com/rt-503...ac-engine.html
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Old June 22nd, 2018, 04:15 PM
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Quote:
Originally Posted by melsg5 View Post
If the engine was really a 389, 4.062 bore stock, 4.092 with .30 over pistons and worn out bores.
The 421 pistons are 4.093 so they would roughly fit a .030 bored 389.
With your aim of 6,500 rpm and the collection of parts you have you would best served to contact this company
https://butlerperformance.com/rt-503...ac-engine.html
Hi,
You are right... if it was 389 CID engine, the answer would be exactly like this... but the numbers say, it can not be 389 engine...
The only thing what we could imagine was that ... someone could buy an unfinished new 400 CID block and bore it less than 4,120, because he had some 429 pistons...
I have no other explanation...

Last edited by Dedek963; June 22nd, 2018 at 07:06 PM.
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Old June 22nd, 2018, 08:14 PM
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melsg5 thank you for the link. I already contacted them.
:-)
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Old June 22nd, 2018, 11:14 PM
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an unfinished block wouldnt have WT on it.
Is the number 623216 the last 6 digits of the VIN?
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Old June 23rd, 2018, 09:07 AM
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Quote:
Originally Posted by melsg5 View Post
an unfinished block wouldnt have WT on it.
Is the number 623216 the last 6 digits of the VIN?
Nope, the last 6 digits does not match with the VIN.
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Old June 23rd, 2018, 11:50 AM
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everything points to a 68 400 even the crankshaft number is late 67/early 68 400.
Any chance the measurements you have are not correct?
another shop you can contact is www.wallaceracing.com
good luck and let us know what you end up doing with the car, if you can post pictures that would be great
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Old June 23rd, 2018, 08:25 PM
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Quote:
Originally Posted by melsg5 View Post
everything points to a 68 400 even the crankshaft number is late 67/early 68 400.
Any chance the measurements you have are not correct?
another shop you can contact is www.wallaceracing.com
good luck and let us know what you end up doing with the car, if you can post pictures that would be great
My first feeling was, the measuring is wrong (despite all other measurings were correct). So I used also another device to be really sure.

Here are the photos of the measurings. please note > one is inches, the other in mm (inch> cm = 1 x 2,54)












Last edited by Dedek963; June 23rd, 2018 at 08:58 PM.
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Old June 24th, 2018, 10:49 AM
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very puzzling, Butler had no ideas?
have you tried contacting Wallace?
could you post a picture of the back of the car?
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Old June 24th, 2018, 04:19 PM
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Yes very puzzling > dismounted to the very last bolt. I want to do it really bottom up and get it into the shape of a new engine.
Some photos above are before cleaning, some after.

Butler has no ideas so far. Maybe because of the weekend.
Wallace will I contact today.

The back of the car corresponds to the date of production > June 1967. Or did you have another reason for seeing it?
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