Crankshaft main journal
 

So I had a 455 crank ground and noticed one of the mains (thrust) has the fillet missing it was cut out almost square.The radius remaining was less than a ball point pen. All the others were cut normal.I think this crank is now a paper weight.Looking for opinions?thank joe

Sad but most likely a paper weight now or a boat anchor.

Tom V.

At least you did not blindly install it and hurt more parts.

It’s not a paperweight, but the journal is significantly weakened. GM has always been bad about having thin fillets on rod and main journals. I can’t tell you how many GM cranks I ground that had next to no radius on any of the journals. What you need to do is take the crank back to the machine shop where it was ground and bring it to their attention. If it was ground ten under they should be able to correct this flaw. If they won’t take responsibility for their FUBAR find another crank grinder who will.

The only way this sgli crank will regain the proper fillet is to have it cut down to a 3" and shove it in a 400.umm interesting maybe I'll do that if the shim kit is still available

Joe, I ground several BBC “Hi Perf” cranks( Chevy put them in their heavy truck engines) that were as bad as you are describing. We had to grind them thirty under but we did successfully grind them with a proper radius on every fillet. As far as the shim kit I’m working on one for my ArmaSteel 428. Tom S sent me one that they didn’t use in his 301 based 383. Trying to find a machine shop that can produce a few sets for a reasonable price.

If I had a forged crank I would have it welder and turned before using the shims.With cast your stuck with the shim.Tom

A good fillet would require it to be at least .040 to .060 tall,that would mean a cut of at least .080 .let me know though about the shim deal.Thanks Tom for your advice

I'm making a salvage run tomorrow I was going to bring it and maybe only get 10.00 for it.Ill hold on to it for now.

How many cranks have you ground personally? I have ground between 3,500 and 4,000. What Tom is telling you is accurate. With a forged crank it is possible to weld the fillet area and regrind the journal. We did it frequently on cranks we couldn’t find a replacement for. Main journals are actually easier to correct than rod journals since you aren’t having to be concerned about getting a rod journal “on stroke”. It’s your crank; if it were me I’d be having a long discussion with the individual who screwed it up to begin with.

I assume it is a SGI forged crank, and not a cast. If it was a cast crank I would throw it in with the iron being hauled off.

But if it is a forged, I think even a .010” cut might get enough fillet to look a lot better. Hoosier would certainly know. The 3.25” main is a pretty big diameter to flex and break were the fillet is missing, it should not need a huge fillet. It looked like you have some higher hp build going on, I’d look for a better crank there unless it is fixed. But on something with 500HP or less I’d take your forged SGI crank that is missing that fillet at the thrust bearing over a off shore cast crank.

If it is forged it would be easy for a shop that weld cranks to fix it also. I think you’d end up with the entire crank turned down another .010” from were it is now.

Jay, GM cranks are notorious for having incredibly thin radiuses in the the fillets. We modified the radius on our cutting stones to provide a fuller radius without having to grind excessive amounts of material off the journal. If the OP has a radius gauge he needs to measure the depth of the current radius on one of the other fillets. That should give an approximation of how much further undersize the journal will need to be ground to provide an adequate radius. There is a problem with grinding overly generous radiuses in crank journals: the main bearings have to be modified to match.

OK everyone it's a cast crank.I have not ground any crankshafts Hoosie,but gotta ask ya in post 5 you said u "had a crank like mine with no radius"u got the required fillet with just a .030 cut,that .015 each side.I just measured the height of a good main and it was .060 tall.So gotta ask how can that be possible with only just a .015 cut u arrived to around .060 tall fillet?

If it’s a cast crank the ONLY option you have is to have it ground to 3.000 crank specs. I’ll let you know when I can find a REASONABLE machine shop to produce shims. .060 fillet? Well, what that says is you were going to have one hell of a time fitting a crank on bearings NOT manufactured or modified to run that much of a radius. What does your radius gauge indicate? You have a radius gauge to check the radiuses, yes? What you need to understand about grinding the radius on a journal is the perimeter of the cutting wheel is used; the radius does not cut the journal. Unless you “bump” the stone on the cheeks of the journal toward the end of cutting the journal you will end up with a parting line between the journal and the fillet. If your machinist went overboard while cutting the radius on the grinding stone you could have a .060 fillet. I would seriously question whether you can trust ANY of their machine work.

Thanks Hoosier. I have a radius gauge but can't find that darn thing.The 060 is with feeler gauge up against the fillet of a good journal and just measuring the height from top of journal to counterweight.It may be more closer to .050.I don't know if that helps u any.

That crank was ground over 10 yrs ago

People wonder WHY I want to come out of retirement. FUBARs like this are WHY….

Hoosie,so what's your point with the fubar ****?What does 10yrs have anything to do with the present.Im on the fence of using this crank or trashing it .The op was looking for OPINIONS not pulling u out of retirement.

I think the OP is being far too concerned with a crack leading to a crank failure in that cheek to Journal area of the thrust, especially if it’s not just a sharp edged 90 degree.

In all the pictures I have ever seen of failed cast large main factory cranks it aways seems to me that the crack that lead to the failure started inside the crank.

This looked like it was due to the sharp edges left at the internal point where the two cross drilled oil passages met.

Once I had a 455 crank that was useless to me due to a spun numbed 1 main bearing , so I tossed it up against a big rock and the it cracked right in half, and that seperation / crack ran right thru the meeting of the cross drilled oil holes.
Coincidence?

Joe, this should have NEVER happened; whoever ground this crank has no business grinding cranks. As a retired automotive engine machinist, I am growing tired of watching alleged “practitioners” of my craft causing problems for their customers. BTW.. you ARE the OP. Having a bad day?

No bad day just somewhat perplexed. I also have another crank #103 and it has a suddal"u" shaped fillet going from cheek to main ,the rod journals have same shape fillet .Should I be concerned?This must be crankshaft week for me