93ZM6Tally

The crankshaft I purchased is a Cola, actually made for a 400 block engine, on a contract to GMPP. At any rate the crank had been pre-balanced for the counter weighted balancer at the front, so the front counterweight has several decent size holes in it. (Please no comments on the level of intelligence for purchasing this crank.)

At any rate my machinist finally had time to put it on the balancing machine and after doing the calculations determined that balancing the crank, with a counter-weighted LT1 flywheel would take approximately four or five pieces of tungsten.

What he is suggesting, to save money, and I've already agreed to this, is to turn down a couple of steel plugs and then TIG weld them into the holes where material was previously removed. He estimates that he would then be able to properly balance the crankshaft with one or two slugs of mallory. He tells me that he has done this before and has never had a "plug" come out.

The practice seems sound to me but I wanted to know if this is something that some of you "Big Dogs" might have experience with. What do you think?

SStrokerAce

Yeap, I've had cranks like that (but not to that extent) no big deal. Welding 4340 isin't horrible it's better than trying to weld a casting.

Bret

WS Sick

Now the next question is, can Journals be welded and reground?

93ZM6Tally

I have no first hand knowledge of this but during my research did find a number of machine shops on the internet offering this type of service.

WS Sick

The reason I'm asking is I have a nice cast steel crank that is worked over good, but has a messed up thrust surface (too much clearance by far).

LameRandomName

If the NASCAR boys can do that to cam lobes, then I don't see why not.


BTW, on the slug idea, might it not be better to machine the slugs to an almost zero tolerance, put them in a freezer overnight and then press fit them in the next morning?

I'm asking because I really don't know, never having done it. It would just seem to be a more controlled process than welding/brazing/whatever.

93ZM6Tally

He didn't give me exact details on the process, other than to say that he will turn a couple of pieces on the lathe to insert them into the holes and then weld them. He's a machinist, pretty exacting guy, I've got a feeling that the slugs will have little tolerance difference than the hole. I do think they need to be welded in any case, cause it would kind of suck if they came flying out while turning 6K.

EviLZ28

Yes they can, I have had forged cranks rebuilt after spinning a bearing or 2. I have one now I am running that was rewelded, recut and rebalanced. Runs great and after he was done, You couldnt even tell.

SStrokerAce

Moldex is the place if you need to fix journals like that.... or a good crank grinder.

All the guy is going to weld on the plugs is the top of them to make them stay in the crank.

bret

LT1 Bunny

as with everyone, yes it can be done. just thought i'd throw in my two cents. also out of curiosity (sp) what the diameter of the ltx main journals?

OldSStroker

Welding to repair a cast crank is probably a bad idea. You'll change the structue of the material around the area that is heated which may lead to failure there. If the crank were steel (forged) it might be an alternative for a moderate power engine. If the 4340 forged crank had been heat treated by the manufacturer, welding will mess that up. Re-heat treating the entire crank would then require straightening and regrinding all the journals, which isn't cheap...and you still end up with a welded crank.

Are there thrust bearings with wider thrust flanges? It seems like an easy way to solve this problem; you can't be the only one who experiences this.

Hardfacing a steel billet cam specifically designed for this is a lot different from welding to repair a cast crank.

IMO, if you are going to be making much hp and rpm, replace the cast crank if you can't find wider thrust bearings.

93ZM6Tally

LT1 Main Journal Specs:

#1 2.4484 - 2.4493
#2,#3,#4 2.4481 - 2.4490
#5 2.4479 - 2.4488

Main Journal Taper .0002 Max
Out of Round .0010 Max

Specs are out of the Rebuilding LT1/LT4 Smallblock Book by Mavrigian.

LameRandomName

OK, stupid question time...

If they can specifically design a steel billet cam for welding; why don't they specifically design a cam that doesn't NEED to be welded?


I'm not being a wiseass, I'd really like to know.

OldSStroker

Great question! I'm sure the Cup cam builders have been pondering that for years (decades?). I've though about it from time to time.

The problem with flat lifter Cup cams is the extreme compressive and wear loads the lifter puts on the lobe. These are much higher than almost any other flat tappet engine. Remember they spin over 9500 and run over a million revs in anger during a race. OK, half a million cam revs. 10 seconds at 9500 in a flat tappet drag car is about 1600 engine revs. you'd need 600 plus runs to duplicate a Cup race. Endurance is the bugaboo for a Cup engine. Geeze, if they make them go to 2-race engines like F1 it will REALLY get expensive.

Finding a metal that will take the wear abuse the Cup lobe sees isn't too tough (pun intended). Something like Stellite (which is about 1/3 each chrome, nickel and cobalt) should work. The problem it that while it's hard and VERY wear resistant, it is brittle and makes a lousy shaft which is constantly loaded in torsion bending and reversing loads like a cam. There really is no free lunch. A solid stellite cam wouldn't work, so it is welded into grooves in the Cup cam lobes where it's needed. My guess is that there aren't too many shops that do this well. Not only is it costly, but if the welding isn't perfect the cam could have a tragic flaw which leads to failure. Big no-no. I suspect the demand for Cup cores is relatively large, and probably often exceeds the supply.

Another method of producing cams is to make individual lobes and journals from materials which work best, then assemble them onto a steel tube which is the "shaft" part of a cam. This is done in OEMs by expanding or swaging the tubular shaft into the serrated or non-round bore of the lobes and journals. Just think, you could have different materials and different hardness for the lobes, journals and distibutor gear. Neat, huh? AFAIK, NASCAR didn't like the idea and outlawed it. Back to the drawing board...or back to welded-lobe cams.

So the search goes on. I suspect that just about every alternate one could imagine has been tried. If one works as well or better than the standard welded lobe, and passes NASCAR muster, we won't even know about it for a long while. That's the nature of the business that is NASCAR Cup racing.

My $.02 worth of conjecture. If I really knew what was going on, they would have shot me by now.

LameRandomName

No, I get it...

The lobes have to withstand intense pressure loads and the cores; torsional loads. Plus NASCAR says the other logical option is a no-no.

Thanks.