[adamo]

Just wondering, does anybody still turn down 3.25” crankshafts to 3” to fit in a 400 block? Looking to build a 434-440” in a 400 block. Or does anybody have one for sale?

[Mike Davis]

You can buy a new forged one for the 3" main blocks.
They use a 6.800 rod.

[adamo]

I was looking at using a crank with Pontiac rod journals

[ponyakr]

Originally Posted by adamo

I was looking at using a crank with Pontiac rod journals

I think you can still buy a forged 4.21 stroke aftermarket crank with the Pontiac rod journal. But they ain't cheap. Don't know who currently has the best price.

https://www.summitracing.com/parts/e...5/make/pontiac

https://butlerperformance.com/i-2445...ontiac-rj.html

Don't know if these prices are current. But Ohio Crankshaft shows a #44004210P shaft for $770.

http://ohiocrank.com/crankshafts/#Pontiac

Rotating assembly price is shown as $2325, plus shipping.

http://ohiocrank.com/rotating-assemblies/#Pontiac

Same price from Butler. They list .990 pins. Pretty sure that is a mistake. The 6.625 rods will use .980 pins, unless you specify that you want .990 bushings & pins. But, I could be wrong.

https://butlerperformance.com/i-2445...tegory:1459542

[Scott Roberts]

Originally Posted by adamo

I was looking at using a crank with Pontiac rod journals

Can I ask why? Do you already have the rods?

[cgeise]

don't forget about the diff in thrust bearing width

[adamo]

Yes I already had the rods. I also want to use a set of 722 heads that’s why I’m leaning towards the 4” stroke combo. I have one in the car now with 722 heads and 4” stroke and I’m getting away with 94 octane and no ping with 24 degrees initial timing and 10 mechanical. I know there’s a 4.21 crankshaft with 3” mains and Pontiac rod journals available. I just wanted to keep the dynamic compression down and not sure if the 4.21” will push it over the edge and make it ping. Was thinking maybe the 4.21” crank and use the road paver cam instead of the old faithful. That might help with running 94 pump gas? Idk. The rods are tomahawk max a lite a beams at 706 grams so I would like to use them. I already replaced the FAKE CHINESE ARP BOLTS for real arp bolts. Cliff Ruffles mentioned to me that the rpm/tomahawk rods had fake Chinese imitation arp bolts. Recommended to buy a set from arp in California ro know that I have the real ones.

[adamo]

With a dished piston.

[hurryinhoosier62]

Adamo, any reputable crank grinder should be able to weld the thrust flanges and regrind them to the proper width. The most critical part is welding the flanges. We had a submerged arc welder that was built for this purpose. The trick is interlocking the individual beads without leaving a void or overheating the base metal. Any crank shop with the required equipment could do this, but most shy away from welding nodular iron. On a forged crank it is actually easier. This is how Smokey built his first 3” main 421 in 1961 when the factory sponsored Pontiac teams were burning the bearings out of their 421s. He took a 421 990 crank, welded the thrust flange, cut the mains and thrust flange to 389 specs and installed the modified crank into one of his 389 Super Duty blocks.

[Mean Green]

What exactly is different with the thrust between 3.25 and 3.00 cranks?

I have a 4.50 stroke 3.25 main crank with center counterweights that I'm going to have cut down to 3.00.

The IA block that it came out of has small welds to hold the thrust bearing tight to the block.

[cgeise]

Guys old trick , as the 455 saddle for the thrust is wider, take an Oldsmobile thrust, it 3 in and fits the crank great, and make some half moon shims to fit in between the bearing and the block and cap, works like a charm

[chiefbigb]

Scat has the 4in stroke 3in main Forged crank. Yes it is 2.200 crank pin but I would consider selling the rods you have and buying a new set to work with your build.

[Jay S]

I clamp 2 trust main caps together, insert some stock 400 thrust bearings and make shims. Makes nice looking shims, and easy to machine. I have one with a cut down N crank to do coming up, waiting on pistons. I think I spent an extra $50 over a normal crank grind to take the Mains to 3”. I cut the seal surface down in our lathe, that is what adds up if you have a shop cut the seal surface down. They have to change to a narrower stone. I have some defunct Olds Deisel stuff in storage, haven’t even had to buy bearings. The Olds Diesels used full grooved H series clevites and had a really nice looking thrust surfaces with better oiling than a standard 400bearing. The one coming up I found a N crank from a 455 for $75 on Craigslist, and spent another $50 to put in the 400. Have the shop do large fillets and clean up and debur the casting flashes. Pretty tough set up, I know of one running 600 HP and has a 200 shot of NOS on top of that. Mine I have done are about 600 hp. I run one that I had offset ground to 4.25” stroke and BBC RJ’s., no big deal with a good shop.

[cgeise]

Originally Posted by Jay S

I clamp 2 trust main caps together, insert some stock 400 thrust bearings and make shims. Makes nice looking shims, and easy to machine. I have one with a cut down N crank to do coming up, waiting on pistons. I think I spent an extra $50 over a normal crank grind to take the Mains to 3”. I cut the seal surface down in our lathe, that is what adds up if you have a shop cut the seal surface down. They have to change to a narrower stone. I have some defunct Olds Deisel stuff in storage, haven’t even had to buy bearings. The Olds Diesels used full grooved H series clevites and had a really nice looking thrust surfaces with better oiling than a standard 400bearing. The one coming up I found a N crank from a 455 for $75 on Craigslist, and spent another $50 to put in the 400. Have the shop do large fillets and clean up and debur the casting flashes. Pretty tough set up, I know of one running 600 HP and has a 200 shot of NOS on top of that. Mine I have done are about 600 hp. I run one that I had offset ground to 4.25” stroke and BBC RJ’s., no big deal with a good shop.

cant see it is there a shim on each side ????

[Jay S]

The shim only goes on the front side of the thrust bearing. On first one I did I was expecting there to be equal shims on the front and the back. I tried that , then also checked the alignment to see where the crank is suppose to be positioned. It usually comes out that all the shimming is on the front side. Pontiac apparently indexed the throw positions of crank from the back thrust face of the block on all their engines. I think it is possible on some cranks you could need a very very thin shim (a few thousandths) on the back side on some cranks with shim stock. I have not had to do that yet, wouldn’t be surprised if some others have though.

[cgeise]

I did equal size front and rear when I did it

[Jay S]

Interesting. That is good to know. I noticed that equal shims centered the crank better on the 2 and 3 bulkheads, but seemed worse on the ends and the time chain was out of alignment quite a bit, the crank gear would go to far back. The gear on the crank could be shimmed forward though to align it better.

That leads my to wonder how much that alignment matters within .030” if the thrust clearance is correct, the pistons have that much play up on the small end pretty easily. I think that single shim is something like .068” thick. Best I can recall anyway. Yours was likely .034” ish on both sides by the sound of it. I know I am not the only one that has done a single shim, but I have heard of guys talk about 2 shims too. Be interesting to see what this next crank and block combo likes. Maybe I will have to do 2 shims

[Mean Green]

What holds the shim in place?

[Jay S]

Originally Posted by Mean Green

What holds the shim in place?

On a factory block there are machined groove’s for the thrust surface that will hold it in place, if it is tight it can’t come out or go anywhere once the cap is installed. But to make sure it can’t move at all either a small amount of JB welded or green Loctite are used to bond the shim to the back side of the thrust face.

[RUDOLFSSON]

Equal thickness here as well and big block Olds thrust bearing.

I did mine on the cnc mill in one operation for tight parallelism. Aircraft grade aluminum raw stock and tight OD and ID... same results can easily be achieved on a good manual lathe.

I don't think I ever glued them or anything like that.. it's all just snug and tight

My findings showed variable block groove OD between blocks.... so I see this always as a custom job



KRIS.




PS. click pics to enlarge