[79 Phoenix]

Trying to find out what year crankshaft I have. Below are pictures of the casting marks I could find. Can anyone tell me what year crank this is?

[steve25]

Yes, it’s out of a 1971 motor.

[steve25]

If I recall right I had a 400 that also used that same part number crank, or I rebuilt I fellows 400 that used that same crank.

[79 Phoenix]

Originally Posted by steve25

Yes, it’s out of a 1971 motor.

Okay, what identifies it as a 71? Also, did 400's use the same crank with just a bigger bore?

[steve25]

Both the 350 and the 400 have the same 3.750” stroke.

Why are you so concerned with what year the crank was installed in?

That N on the crank cheek identifies it as a good Nodular crank.

This sheet is what I am going by, but maybe another member has better and more accurate then I have presented.

[Joe-Touring]

Here’s the site I use for crank ID:

http://www.pontiacpower.org/PontiacCranks.htm

[Sirrotica]

326, 350, 389, and 400 use basically the same crank, same stroke, 3.75, same main size. The difference is the blocks, and the bore that they will accept. I.E you can't bore a 350 block to accept a 400 piston, but a 389 may be able to be bored .060 over to accept a 400 piston. The block castings are different in how much wall thickness there is cast in initially, depending on the bore needed.

The balance would be close, but probably not perfect if someone swapped cranks between 2 different displacements. The smaller piston mass is going to be a different weight than a larger one. You might get away with it on a stock rebuild, but you'd want the balance corrected on a high performance build.

I have swapped a 400 crank into a 389, and not rebalanced it, but it was a low RPM daily driver engine. I didn't have any money, and used what I had lying around to patch up an engine to save it, no ill effects due to balance.

[79 Phoenix]

Originally Posted by Joe-Touring

Here’s the site I use for crank ID:

http://www.pontiacpower.org/PontiacCranks.htm

Okay thanks... First, I'm just trying to learn about Pontiac engines. I'm not very knowledgeable on these.

But secondly, I have a 350 engine which I thought was a 71 that I was considering putting in my car. But the machine shop guy did a quick check and concluded that my crank was a 74-76 version (because of the 4813 casting mark) which may be different from the 68-73 version with regard to the register area where the flywheel bolts on. I wanted to make sure my 71 flywheel bolts on. He said I should do some research before I spend money cutting the crank.

Curious--Can a 350 block be bored to make it a 400?

[79 Phoenix]

Originally Posted by Sirrotica

326, 350, 389, and 400 use basically the same crank, same stroke, 3.75, same main size. The difference is the blocks, and the bore that they will accept. I.E you can't bore a 350 block to accept a 400 piston, but a 389 may be able to be bored .060 over to accept a 400 piston. The block castings are different in how much wall thickness there is cast in initially, depending on the bore needed.

The balance would be close, but probably not perfect if someone swapped cranks between 2 different displacements. The smaller piston mass is going to be a different weight than a larger one. You might get away with it on a stock rebuild, but you'd want the balance corrected on a high performance build.

I have swapped a 400 crank into a 389, and not rebalanced it, but it was a low RPM daily driver engine. I didn't have any money, and used what I had lying around to patch up an engine to save it, no ill effects due to balance.

Okay, thanks much. That's very helpful info. answers the boring question...

[79 Phoenix]

Originally Posted by Joe-Touring

Here’s the site I use for crank ID:

http://www.pontiacpower.org/PontiacCranks.htm

Thanks--very helpful!

[steve25]

I can see how placing a 400 crank into a 389 can not be much of a issue in terms of balance , but that being said how the heck do you know for sure what motor a crank really came out of unless you did so?

If you had two 4813 cranks in front of you and one was out of a 350 and one out of a 400, how would you know which was which for use in a 350.

I would not just drop in a crank from a 400
Into a 350!

[79 Phoenix]

Originally Posted by steve25

Both the 350 and the 400 have the same 3.750” stroke.

Why are you so concerned with what year the crank was installed in?

That N on the crank cheek identifies it as a good Nodular crank.

This sheet is what I am going by, but maybe another member has better and more accurate than I have presented.

Both your sheet and chart link above confirm it is a 71 crank and probably a 71 block... I will do more research to confirm that. Thanks for your help!

[79 Phoenix]

Originally Posted by 79 Phoenix

Thanks--very helpful!

Well according to the chart it's definitely a 1971-74 crank with the 4813 #. There is no 79 or 80 casting mark on the front weight though to show whether it's a 350 or 400 crank. But it's definitely not a 400 block with bore size a little over 3 3/4"...

And judging by lots of normal wear on the bearings and the condition of the crank, it's been with this engine a long time... So, I would say it's a 1971 350 crank probably original to this block.

Next I will check the block #s to see what they tell me. Really appreciate everyone's help!

[steve25]

350s of this era had a 50 cast into the lifter valley.

[Sirrotica]

Also most Pontiac blocks have a year that they were cast next to the distributor hole. It is a 2 digit number such as, 71 for 1971, 73 for 1973 etc. etc. There are lots of identifying marks cast into the blocks to tell you when the block was cast, and what cubic inch engine it was cast for.

Most have the 3 digit cubic inch numbers cast in right near the motor mount holes in both sides of the block, 350,400,428, 455. As has been already mentiuoned the last 2 digits are cast into the center of the lifter valley such as 50, for 350, 00, for 400, and on.

Pontiac revised their castings in 1967, and those previous engines did not have the cubic inch number cast into them, I can't remember if they had the year near the distributor, or not, on the 66 and earlier blocks. I seem to remember that the 66 and earlier didn't have the year cast into them, but I'm not absolutely certain.

There's also the pyramid cast near the bell housing area, I'll save that for later though.....

66, and earlier only have 2 soft plugs in either bank, 67 and later have 3 in either bank, one way to determine if a block is early or late style.

In 1970 pntiac engineers redesigned the motor mounts, 69, and earlier had 2 holes in either bank just above the oil pan rail. 1970 through 1976, had 5 holes in either bank to fit late, and early chassis with both styles of mounts. In 1977 they quit drilling and tapping the early position, and just used 3 holes for the late style mounts.

This information will hopefully at least give you enough info to determine what you're looking at.

[79 Phoenix]

Thanks! You guys have been very helpful to me in figuring out what I have. I have a GT-37 with engine still in it. I have identified it as a 250 HP 350 w/manual transmission with numbers matching block with last 6 digits of vin on serial # on block.

You have helped me determine the other engine I have has a 71 crankshaft and I have now identified the block as a 71 250 HP 350 w/automatic trans.

Now I need to determine which one I will use... If the numbers matching engine is not too badly worn out or damaged, I will probably rebuild that. Thanks again!

[Bermuda Blue]

Originally Posted by steve25

I can see how placing a 400 crank into a 389 can not be much of a issue in terms of balance , but that being said how the heck do you know for sure what motor a crank really came out of unless you did so?

If you had two 4813 cranks in front of you and one was out of a 350 and one out of a 400, how would you know which was which for use in a 350.

I would not just drop in a crank from a 400
Into a 350!

There is a stamp (79 or 80) which will designate the crank as a 400 or 350. I don't recall its a exact location but I think its on the damper end.

[79 Phoenix]

Originally Posted by Bermuda Blue

There is a stamp (79 or 80) which will designate the crank as a 400 or 350. I don't recall its a exact location but I think its on the damper end.

Yes I have looked for one of those numbers on the front weight of the crank but could not find a number but it makes sense that this crank is a 350 crank.

[Bermuda Blue]

79 stamped on face of front counterweight. Note that this 350 crank weighs 67 lbs.

[P@blo]

Originally Posted by steve25

Both the 350 and the 400 have the same 3.750” stroke.

Why are you so concerned with what year the crank was installed in?

That N on the crank cheek identifies it as a good Nodular crank.

This sheet is what I am going by, but maybe another member has better and more accurate then I have presented.

Good info Steve. And some later 350 nodular iron crankshafts do not have the 'N' marking.