[D. Rustin]

the crank in my '68 400 has been turned twice so i think it's junk and I have a '68 350 crank thats in real good shape can I use it in my 400 ?

[67 Lamnas]

Originally Posted by D. Rustin

the crank in my '68 400 has been turned twice so i think it's junk and I have a '68 350 crank thats in real good shape can I use it in my 400 ?

Yep....use it.

[Paul E]

the stroke is correct, but make sure you check the balance!
Paul

[Murf'sDad]

My late '76 400 came with a 350 crank from the factory. Obviously rebalanced for the difference in bob-weight.

Stewart

[Ken K]

A 350 N crank weighs less than a 400 N crank. You can also see where they removed material from the crankshaft throws on a 350 N crank. If you weigh the pistons, the stock 350 pistons will weigh less than stock 400 pistons.

[BVR421]

what makes a twice turned crank junk? did you spin a rod bearing?

[D. Rustin]

I'm not really sure why I think its no good.
both main bearings at each end of the crank went bad.

[gtofreek]

The cranks will interchange but you will have to have it re-balanced by a good machine shop.

[chiphead]

The 350 crank in a 400 block is a good swap, especially if you use lightweight rods and pistons. The 350 crank throws are slightly lighter so will require re-balancing with heavy components like TRW forgings and the heavy pins. The 350 N crank is the same dimensions and strength as any '67-later 3.75" stroke "N" crank. The '66-earlier 389/326 crank may have slightly different snout dimensions, but not sure.

The only reason I would be worried about using the 400 crank is the failure of the end bearings. That can indicate a bent crank or other strangeness, so I would have that crank checked for straightness. Running 20 or 30 under main bearings isnt a bad thing as long as clearances are corrrect. Heck, I run .050" under rod bearings in my 400, with the 6.8 long-rod and BBC rod bearing deal.

[Half-Inch Stud]

Try the 326 crank.

[D. Rustin]

I don't have a 326 crank.
I am thinking about using stock rods with JE pistons w/ new rod bolts.

[HWYSTR455]

End bearings, yeah, I agree, need to check things thoroughly to find out why. My guess: Line bore. It's not often I've heard of Pontiac cranks bending, but it's possible it was manufactured incorrectly. Didn't over tighten the belts and run it for a long time over tightened, did you?

If the rods need to be prepped, it's cheaper in the long run to replace them. The PPR rods are $240, don't think you can prep a set for that. Shoot, good bolts are $70. Sure, you'll have to have them checked (new rods), but still going to turn out to be less, and you'll loose the worry-factor.

.

[Z Code 400]

Years ago, there was an article by Smokey Yunick where he baked NEW rods at 400°F for 8 hours and then allowed them to cool naturally before machining them to ensure they remained dimensionally stable...a low temperature stress releiving of sorts. However, I still can't seem to find the article in my collection.

Any guys involved in cryogenics care to comment????

[sportylemans]

I have a 400 crank in my 350 now. I don't have any problems at all with it. Engine runs smooth and strong. No vibration.

[Ken K]

I have a 350 crank in a 400. The 400 pistons and rods that I used weighed the same as stock Pontiac 350 rods and pistons. I weighed a few 350 pistons and rods, there was as much as 14 grams difference between the lightest and heaviest. The 400 pistons and rods I used are within 1/2 gram.

[Murf'sDad]

On my build I went with Probe SRS pistons and Ace's 4340 rods. Much lighter parts than the stock pieces. The 350 crank still needed a lot of material taken from the counter-weights to match the bob-weight.

I think my crank was a 350 casting but was machined and balanced at the factory as a 400 crank. Best I can figure out anyway.

FWIW, Stewart

[D. Rustin]

I think I'm going to buy a ten ten crank and sell the 350 crank.
I will price new rods vs. resizing old ones and using new bolts.

[Murf'sDad]

Originally Posted by D. Rustin

I think I'm going to buy a ten ten crank and sell the 350 crank.
I will price new rods vs. resizing old ones and using new bolts.

It's still going to have to be balanced if you want to do it right. You've got a good crank, use it, just do the job properly.

Stewart

[D. Rustin]

actually the crank is out of a 350 h.o.
is it diff. from a standard 350 ?

[gtofreek]

I would have your main housing bore checked. If you burned main bearings, the heat will generally shrink the housing bore. If you just put another crank in, it will most likely do the same thing. What Z-Code was talking about can be done more effectively with cryo treatment. Also the extreme cold will finish of the heat treatment of hardened steel rods and eliminate stress risers. Cryo also makes the parts dimensionally stable so they machine more accurately, especially with aluminum. The 350 HO crank will interchange just the same as it is the same. From 65 on, all 326,350, 389 and 400 cranks are dimensionally the same. Only the balance is different. 64 and older cranks have a shorter snout.
Honestly, I've been machining engines for 16 1/2 years and DO have the main housing bore checked if not align honed. The heat WILL distort the hole. Your only asking for trouble if you don't.It may have needed align honing before and that could be why it burned up those bearings. I would not even waste my time with 40 year old stock rods. They weren't that good when they were new. Your not going to save much money rebuilding them. Maybe $40-$50 is all. That $40-$50 is very good insurance. Ace's[PPR] steel replacement rods are a steal at $240 plus they come with ARP 7/16" rod bolts. Smokin' deal!