2680 crankshaft

[Timothy B.]

I found a 2680 forged crankshaft from a 63 impala SS but there is some surface rust on the journals. It does not look like pitting so my question is can I polish this with 400 wet sandpaper or best taken to the shop to be checked. I don't think 400 would leave a surface to rough.

The man told me he bought the car new and it had about 200,000 miles on the motor but no bearing problems 327/250 HP. Also got the rods, pistons and original camshaft/lifters and while I would never reuse these, the bearings in the rods look pretty good.

The crank has 2680 cast into the front and GM T further back.

I will post a pic later to show the rust, I don't want to turn the crank if not necessary.

[Duke W.]

Re: 2680 crankshaft

Without seeing, touching, it's tough to tell. If you know of a reputable engine machine shop you should get their opinion, and if it can be polished out, let them do it. It won't be expensive. They should do it on a lathe, and they should check that it is straight along with checking the journals to see if they are within OE spec. If you plan on revving over 5500, get a Magnaflux inspection.

Since the 250/300 HP cranks were not Tufftrided, grinding will only remove a little material, not this surface hardening that was added to the SHP/FI version of the 2680 forging.

If a known reputable shop recommends grinding -.010" is the minimum for the next bearing size - follow their recommendation.

Duke

[Clem Z.]

Re: 2680 crankshaft

we stroked 350 cranks to 3.562 by grinding them off set to 2.000 pin diameter which is .100 removed and we never had one gives us trouble in race engines. as long as the crank grinder puts in a nice radius in the corners there seems to be no problems

[Timothy B.]

Re: 2680 crankshaft

What's the purpose of the radius in the corners, I know the rods have a small radius also.

[Clem Z.]

Re: 2680 crankshaft

less chance of a crack occurring in that area cause by a stress riser. there is less chance of a part failure cause by a crack if all sharp edges are radiused. this is also true with connecting rods machined areas where the bolt head seats.

[Joe C.]

Re: 2680 crankshaft

What's the purpose of the radius in the corners, I know the rods have a small radius also.

If you need the journals to be turned, make SURE that the machinist leaves the largest radii fillets possible. The crank, with large fillets will actually be stronger than a std crank with small or no fillets. If the fillets are much larger than usual, the bearing edges must be chamfered, or special bearings must be used, like Clevite's H Series instead of standard P Series.

[Timothy B.]

Re: 2680 crankshaft

Thanks for that info Joe and Clem. I am going to use some navel jelley first to remove the rust before taking it to the shop.

I did a google search on crankshaft polishing and some suggest 400 wet sandpaper with clothes line rope around the journal 1 3/4 times then saw back and forth to polish. Is there a issue with a forged crank and the way the grain in the metal lays or can it be polished like I mentioned.

[Clem Z.]

Re: 2680 crankshaft

Thanks for that info Joe and Clem. I am going to use some navel jelley first to remove the rust before taking it to the shop.

I did a google search on crankshaft polishing and some suggest 400 wet sandpaper with clothes line rope around the journal 1 3/4 times then saw back and forth to polish. Is there a issue with a forged crank and the way the grain in the metal lays or can it be polished like I mentioned.

only cast cranks have a problem when polishing to make sure the "fish" scales lay in the proper direction so you don't eat up the bearings.

[Timothy B.]

Re: 2680 crankshaft

If this crank cleans up with only minor discoloration on the journals but no pits I would like to polish it myself. Is this a waste of my time given the cost to polish at the shop? What's the best way to store a crankshaft??

This crankshaft also has GMT cast into it and I was wondering if this means cast at Tonowanda. Were all cranks cast there in that time frame?

[John H.]

Re: 2680 crankshaft

This crankshaft also has GMT cast into it and I was wondering if this means cast at Tonowanda. Were all cranks cast there in that time frame?

That crank is a forging, not a casting. Tonawanda had their own foundry for cast cranks, and had their own forge plant for forged cranks. Flint's cast cranks came from the Saginaw Foundry, and their forged cranks came from Detroit Forge.

[Joe C.]

Re: 2680 crankshaft

If this crank cleans up with only minor discoloration on the journals but no pits I would like to polish it myself. Is this a waste of my time given the cost to polish at the shop? What's the best way to store a crankshaft??

This crankshaft also has GMT cast into it and I was wondering if this means cast at Tonowanda. Were all cranks cast there in that time frame?

If it were mine, I would not. As you know, I like to do stuff myself, but critical surfaces like crank journals, cylinder bores, etc, must have special surface characteristics.

If you DO decide to polish it yourself, make SURE, SURE, SURE, that every trace of iron oxide (rust) and ALL traces of abrasive grit are removed from the surfaces. Wash thoroughly using a brush with soap and water, then wash again with Gunk, finally rub repeatedly using a white rag soaked with acetone or lacquer thinner until ALL traces of contaminants no longer show on the rag.

If not thoroughly cleaned, you will quickly score your main and throw bearings.

Store a crankshaft by coating with WD-40, kerosene, diesel fuel, or similar. Enclose in a plastic bag, and seal until air-tight. Store it standing vertically, on-end.

Joe

[Timothy B.]

Re: 2680 crankshaft

Thanks for the information everyone, this crank was given to me and I wanted to keep it for a spare. Am I correct that GM T means Tonowanda forging and would this crank work OK in a Flint cast block?

[John H.]

Re: 2680 crankshaft

Thanks for the information everyone, this crank was given to me and I wanted to keep it for a spare. Am I correct that GM T means Tonowanda forging and would this crank work OK in a Flint cast block?

Tim -

The crank will work fine - they're completely interchangeable regardless of crank source or block source.

I'd let a machine shop polish the journals.

[Timothy B.]

Re: 2680 crankshaft

Thanks again everyone, one more question.

If I have this crank drilled and tapped for the retaining bolt how deep should the threads go inside the crank. I know the bolt is 2 1/4" with that thick washer and I believe a star washer.