Stroker Crank Prep

[jlmccuan]

I am putting together a Studebaker engine to run in C/CPS.  The crank was built some time ago and 49 years later it landed in my pickup.  It is a factory piece believed to have been welded up as a partially machined part then ground to final dimensions.  Not much has been done to it other than being stroked 5/8" from the stock Stude dimensions.  Mains are standard, rods 0.002 under and a polish will clean them up very well.

I'd like to prep this crank myself as much as possible before delivering it to the machine shop for final checking for straightness, and journal polishing.  Can anyone recommend a good resource on knife edging, oil passage chamfering, etc ?  I would also appreciate any input or thoughts.  Pics are available if they would help.

[Bob Drury]

  I have heard a lot of praise for Marine Crankshaft Inc. in Santa Ana, Ca.
  He advertises in our rule book on Page 194.                (714) 549-2388
  You might want to talk to him about Nitriding the crank while you are at it.................   Bob

[zenndog]

Pics always help!

[Kato Engineering]

you best not do or have someone do any knife edging untill you know what the exact bob weight is..
 knife edge-ing a crank essentially removes weight where it may need to be to make it all balance properly
some types of knife edgeing will remove weight where it needs to be and cannot allways be added by installation of tungsten heavy metal.


since the crank that you speak about has been welded

it should first be totally magnaflux checked...cracks can suddenly appear after forty years sitting on the shelf

[Kato Engineering]

oh By the way


we do that type of stuff....

[jlmccuan]

What sort of expense for nitriding the crank?  Any discussion on advantages?

[Bob Drury]

  Harder surface.
  Why don't you think about going to a dry sump oil system and forget the knife edge on the crank.
  There are a ton of advantages including probably a 50 horse power or better gain , and you can run low tension rings if you have a big enough pump to pull a vacuum in the crankcase and you can pretty much dial in however much oil pressure you want.                   Bob

[jlmccuan]

Re the dry sump, I have considered it, as my understanding is that it would be allowed.  Drawbacks, I'd like to keep things as "stock" looking as possible the first year out for historical reasons, secondly, and mainly, I have zero experience with dry sumps in Studebakers.  The only folks I know running one are the Bloombergs and they have had a bit of trouble with their setup.

[panic]

The conventional knife-edge is done to the rim of the counterweights, and greatly affects balance.
It has very little effect on aero since only the last bit of rim is smaller in cross-section as it presents to the crankcase vapor.
The leading and trailing edges of the CW are very labor-intensive to re-contour, but the as-made CWs have terrible rectangular faces and tails. The first thing is to make sure which side of the CW is the leading edge (some crankshaft mfg. don't appear to figure this out, since they make them symmetrical). It should look like an airfoil.
The leading edge gets the largest practical radius blending in to the cheeks.
The trailing edge should be as tapered as your balancing permits, which may take very different forms based on the original dims and CW mass needed.
Every change in cross-sectional area or shape passing down the CW from the nose should be radiused and blended.

[jlmccuan]

Are there any good sites for pics or drawings for the foil shaped counterweights and which way the foil sould be oriented, ie slope away from the rods or the mains?  Of course, I'll be having to send out the rotating assy for balancing, nitriding, etc.

[wobblywalrus]

What about putting a deeper sump pan on the engine and a longer oil pickup tube.  Maybe this would lower the oil level so it is below the spinning crank.

[Kato Engineering]

lowering oil pan bottom will allways help in a wet setup

but nothing can be done with the counterweights of crank untill the "bob weight" is known

way too many otherwise good cranks have been totally ruined by cutting on counterweights and then not being able to "balance" afterwords..
oftentimes there is just no "place" to add enough tungsten weight.