[dmac]

can the 3.25 main journals in a standard 455 crank be turned down to fit the smaller 350/400 3" block? Or can the 400 block be opened up? Which is better? I have the chance to buy a new 455 crank for about 1/2 price

[Frank R]

It's more complicated than turning down the mains on a 455 crank to 3". The thrust journals are different on a 455 versus a 400. They did sell a conversion kit at one time that consisted of a Oldsmobile bearing. Between the machine work and conversion kit you would most likely be spending more than a new stroker crank.

[ponyakr]

Yeah, Ken Keefer(P-dude) use to sell those.

https://www.facebook.com/profile.php?id=100009186127041

https://www.facebook.com/kensautomachineshop/

Smokey use to do it, putting a 421 crank into a 389 block, for NASCAR racing. It worked. His cars were fast & won lots of races.

"...Smokey Yunick discovered that the bearings in the 3-inch mains survived race conditions, and the 3.250inch diameter did not...All of Smokey’s 421 engines were fitted with 3-inch main journal diameter crankshafts..."

The only 3" main 4.21" stroke cranks I am aware of today are forged, and cost over $700 shipped.

Cast 3" main 4.25 stroker cranks are cheaper. Summit has 'em for $283 shipped.

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

But with these, you'll need 6.8" BBC rods, and stroker pistons. The cheapest stroker pistons I know about are Auto-Tec brand sold by an Ebay seller.

https://shanonsengineering.com/produ...at-top-pistons

Icon stroker pistons are a little higher, bought from CNC Motorsports or RPM Machine.

http://www.cnc-motorsports.com/icon-...ore-48671.html

I have no idea what prices Pontiac vendors on this site offer, for 400 block stroker pistons. Those are just some online prices that are easy to find.

Butler sells complete balanced stroker assemblies for the 400 blocks.

http://butlerperformance.com/c-12348...495-cu-in.html

[hurryinhoosier62]

Originally Posted by ponyakr

Yeah, Ken Keefer(P-dude) use to sell those.

https://www.facebook.com/profile.php?id=100009186127041

https://www.facebook.com/kensautomachineshop/

Smokey use to do it, putting a 421 crank into a 389 block, for NASCAR racing. It worked. His cars were fast & won lots of races.

"...Smokey Yunick discovered that the bearings in the 3-inch mains survived race conditions, and the 3.250inch diameter did not...All of Smokey’s 421 engines were fitted with 3-inch main journal diameter crankshafts..."

The 3.25" mains bearing speeds were too great for the bearing materials available in the early 1960s. Welding a nodular crank is always an "ify" proposition, not to mention finding a competent crank grinder to properly machine it after welding. You'd be better off purchasing one of the readily available 4.21" stroke 3" main forged cranks.

[dmac]

Originally Posted by hurryinhoosier62

The 3.25" mains bearing speeds were too great for the bearing materials available in the early 1960s. Welding a nodular crank is always an "ify" proposition, not to mention finding a competent crank grinder to properly machine it after welding. You'd be better off purchasing one of the readily available 4.21" stroke 3" main forged cranks.

I guess if I had a 455 block, buying this crank would make sense. Thought I might be able to drop it in the 350 or 400 block I have.

[Formulajones]

I've done the nodular 428 crank in a 400 block. You need to have a good crank grinder. Had to weld the thrust area and re-machine. This engine still runs after 20 years and runs fantastic.

I did this when aftermarket cranks ready to go weren't readily available. Today I wouldn't bother with the procedure with all the 3" main cranks available, I'd just buy the crank.

[gtofreek]

Not to mention the overlap area between the rod journal, and main journal get thinner, thus weaker. This is the reason Pontiac went to 3.25" mains in the longer stroke engines. With a forged crank, the steel is strong enough for this, but a cast crank is an iffy proposition.

[Formulajones]

I've noticed they make the 3" main stroker cranks in cast and forged. They get pretty darn inexpensive too. Hard to say no.

Do you use any of the cast versions of these Paul or do you prefer to avoid them?

[gtofreek]

I never use the cast versions. Had one break in 3 pieces years ago before the forged ones were out, so they scare me now. It broke #3 journal off it, when all the bearings were good.

[Formulajones]

Oooo, that's good to know.

[Navy Horn 16]

http://butlerperformance.com/c-12348...et-blocks.html

Here ya go.