We pulled a good running 69 G block 400 out of a 442 today to install a tri carb 455. We decided to use the flywheel from the G block but it wouldn't fit the 455. The holes wouldn't line up. The G block has provisions for a piliot bearing and appears to have a steel crank according to the notch in the back of the crank.
The only thing we can come up with now is that the G block has a 65-67 400 or 425 crank. If thats the case, I'm thinking the cubes must be around 375 or so. Anyone have another explanation? We installed a flywheel off a 455 we had in stock and got it in and running.

 

It could be an early 455 crank, but the only way to know for sure what's in there would be to drop the pan and look.

 

Thanks Randy,
I read through the 442.com info and were hoping that the crank is an early 68. It is steel like the early ones were and drilled for a stick. I should have bought the motor myself he sold the block and C heads for $500 and it runs nice.

 

Those blocks came out of the factory with two bores, and the cranks came out of the factory with two strokes. No matter how you "mix and match" them, you will get 400, 425, or 455 inches.

Edit: If stock parts are used.


More accurate to remove a head and measure the stroke at TDC and BDC. The difference between 4" and 4¼" will be obvious.

Norm

 

Better check your math, Norm. The stock bore in a G-block 400 is 3.870". Stock stroke of a 65-67 BBO crank (400 and 425 are the same) is 3.980". I get 374.5 cu in from that combo.

 

Which piston/rod combination would you be using in that engine?

Norm

 

LOL, Norm, Did you have a rough weekend?

 

Did you read something that I did not write?

Norm

 

If indeed an early 400 or 425 crank and rods were used, I'd be curious to know what pistons would work. Custom made? In other words, how could you POSSIBLY mix and match a G block with the earlier crank using ALL stock parts?

And what's this about an "early" 68 crank? Why would that have a different bolt pattern?

 

Thats the million dollar question. If there is a chance that a 400 short stroke crank and rods were used in a G block. The pin size and location would have to be the same . I thought someone would know if it is even possible without me having to research this on my own. We don't really want to pull the pan or heads because the motor runs fine.

Norm, Answer Joes question first, at least read it, he made it very clear.
I don't want to argue,

 

What question did he ask?

Norm

 

Now that I think of it, I know I have read in the past about someone using an early 400/425 crank and rods in a G block with a mild overbore (maybe 0.030 over?) and custom made pistons. Was someone who wanted the appearance of a "matching numbers" car but hated the performance of the stock 400. Was an old post on ROP that may no longer exist, but assuming my memory is correct, its possible because its been done. I remember thinking that it was a lot to go through, but cool nevertheless.

 

Exactly. That's why I (as others) suggested the early crank in the G-block. Note that there are actually SIX possible bore/stroke combinations available using stock blocks and cranks:

Early crank (3.980 stroke) x A/D/F block (4.125 bore) = 425.5 cu in
Early crank (3.980 stroke) x B/E block (4.000 bore) = 400.1 cu in
Early crank (3.980 stroke) x G block (3.870 bore) = 374.5 cu in

Late crank (4.250 stroke) x A/D/F block (4.125 bore) = 454.4 cu in
Late crank (4.250 stroke) x B/E block (4.000 bore) = 427.3 cu in
Late crank (4.250 stroke) x G block (3.870 bore) = 399.9 cu in

Yes, the "455" Olds is really a 454...

 

Norm,
Your statement
"Those blocks came out of the factory with two bores, and the cranks came out of the factory with two strokes. No matter how you "mix and match" them, you will get 400, 425, or 455 inches.
Is very misleading and if your trying to imply that the parts would have to be stock as your edit might sugggest "If stock parts are used" to the generation of blocks, the statement still is very misleading and unnessary and doesn't clarify or add anything usefull to the thread.
You then ask what combination of rods and crank would be used. It was mentioned several times what the combination would be, I would hope your smart enough to allready know the answer to that, so why ask?. There could only be one combination that would achieve 374 CI.
By the way, In this situation with .250 difference in strokes, removing the head is no more accurate than pulling the pan and measuring or finding a casting number on the crank. Infact it is a much more costly alternative. An intake gasket and head gasket are several times more expensive than a pan gasket. Again, that is poor advice.

Your right about one thing, Joe didn't ask a question.

 

Joe,
Is there a crank with a 4.25 stroke with the 65-67 400 425 bolt pattern?

 

Not that I am aware of - at least not with "stock" parts. It is possible to offset grind the early crank, of course, and get a 4.250" (or some other number) stroke, forged crank. Why you'd waste this in a G-block is a mystery to me, but Olds specialty houses sell cranks configured like this.

 

Thanks Joe,
What ever happened to this engine, it happened decades ago.

 

I understood that from the original post....I was asking specifically what was meant by "early 68" crank, as mentioned by others in this thread including the O.P. Just wanted to make sure I wasn't missing something, as I thought that while there were some forged steel '68 cranks, they still would have the later flywheel bolt pattern. That is all I was asking there.

I'm curious what the displacement would be for an "early" 400/425 crank in a G-block bored say .060 over? Somewhere around 387 C.I, or about 97% of an E-block's? I bet a 68-69 owner would be very happy with the performance of such a combo, even if all else was kept stock.

 

Thats what we were hoping for, the earlier bolt pattern on a later crank. But it may not be true.

 

No "early '68" cranks with the pre-'68 pattern. The pattern was changed because they type of balancing changed. I'll defer to Joe P for further explanation.

 

Thanks Kurt,
It looks like we got us a 375 Rocket motor.

 

Do you think it is logical, that someone might go to the time and expense of using custom parts, in order to achieve a significant loss in power?

And this statement is not a mature contribution to a productive discussion.

Why would you think it not a legitimate question?

Where was it mentioned?

Nothing to do with "smart". Everything to do with the reason boards like this exist. When questions are asked, and answered, learning happens.

That displacement is not achievable, using stock parts, hence my question to joe_p.

On the other hand, if custom parts were used, there would be hundreds of displacement possibilities.

Wouldn't the piston/rod assembly make it hard, if not impossible, to get an accurate measurement of the cylinder dimensions? Would the casting number show if the stroke had been altered?

Considering the amount of information that can be found under a head vs an oil pan, why would anyone want to "cheap out"?

Depends whether one wishes to sacrifice quality, in order to save a couple of dollars.



That would be the third bore diameter I failed to include.

Its 6.735" rod and 1.74" compression height, when combined with a 3.98" stroke, would place its piston top about .160" below the deck. An easy 374 inches, if one can live with an extreme lack of power.

Now, if the bore was increased to 4" in order to use "early" 400 pistons (1.615" compression height) with 7" rods, and a 3.98" stroke, it would have the same spec's as an "early" 400, including the flange pattern.



Better check your math, Joe. This time use 4.126" for the bore.

Norm

 

Or, more likely, a custom-ground early forged crank. It will be interesting to measure the actual rods and crank throws on this motor.

 

You're really suggesting a greater than 1/8 inch overbore on a G block is possible, huh? Guess that's one way to get the displacement into the range of possibilties you originally offered.

 

Not only possible but, in this case, highly likely.

Norm

 

Sure.

 

Norm most of your last post was not worth reading., however this information is very useful.
That is a possibility but would require a .130 over bore on a G block. It would then be a simple installation of a roating assembly from a 4 in. stroke rotating assembly. It may be the most logical scenero next to a custom crank as Joe mentioned. My friend is unable to pull the pan this week, I told him to get a piston diameter also. I'll be sure to post the findings.

Aliensatemybuick, We had a 324 bored .125 over years ago. It will be interesting to find out. It does seem extreme.
Thanks

 

"Maybe" they used the shorter stroke 400/425 crank,with the 7" rods,& a 350 piston.I've seen some things like that done before.

 

Good call.

Norm

 

But that would bring it to 4.057" bore, even a greater overbore (of 0.187")? HOW about a 330 piston (if this is an absurd suggestion, I apologize in advance).

I guess an investigation of the motor itself will tell...assuming it is from the underside, I presume a precise measure of the bore can be made with the rods in the way?

 

Rolling it around, I'm really liking my theory, as it involves using stock parts and a mild overbore. An application of Occam's razor? This would be ths same basic build as I suggested in my post (#18) above, with the advantage that custom pistons would not be needed.

 

Another good call.

Norm

 

I had some old Jahns flat tops for a 330,& that is what they got used for.Heck,maybe it's that motor.