I got a postcard today from Callies with a big picture of a chewed up crank snout and the warning "Attention Engine Builders. Callies does not recommend the use of Multi-Keyway timing gears. Stress risers generated by intermittent bore contact may result in crankshaft failure."

People have been using these timing gers for years. Anyone shed any light on this?

Rich

 

I think they're smoking something. Stress risers from intermittant contact????

 

My initial take is that the 3 to 5 keyway crank gear bores might be more out-of-round (OOR) than the one-keyway ones if the manufaturers don't correct the bores after heat treating. Heat treated timing gears are harder than the crank snout, and pressing a hard OOR gear with spaces onto the snout may indeed unevenly stress the snout.

Now add to this a blower pulley hung in front of the damper and crank up the blower belt tension. This puts the snout in bending and every revolution the crank turns fatigues the snout. The uneven stress placed on it by the crank gear could then be the straw that breaks the camel's back.

Perhaps Callies has has some failures and wants to prevent more, or perhaps they are covering their butts. I think that they might have a point, but the evidence of years of use which Rich mentioned indicates to me the problem isn't widespread.

Buying high quality parts doesn't always assure you of getting a round bore in your timing gear, but it probably helps. Even checking the roundness of a multi-keyway bore is tricky, as is touching it up with a hone. Possible, but tricky.

If I were doing a blower engine I'd look closely at the crank gear and probably kiss it with a keyway hone just to be safe. Bret is putting a blower engine together now, so he'll look into this, I'm sure.
EDIT: Bret doesn't use multi-keyed lower sprockets. I haven't seen one in his shop.

My $.02

 

That makes a lot of sense. But if so, it sure would have been more useful if Callies had provided the rationale and basis for their statement. Maybe also got some sample timing gears from various manufacturers and measured them, with the idea of recommending those that were found to be in spec?

Rich

 

I think I'm going to have to disagree with you on this. The timing gear is very light compared to the harm. bal. and pullies. It's also the first thing on the crank, which means the moment arm is very very small, especially compared to the harm. bal. It certainly is possible to scratch the snout while installing the gear, but this shouldn't be enough to cause this problem.
I know I don't have the experience of many of you, but this smacks of someone trying to cover their ***. I'd be looking carefully at the radius between the snout and rest of the crank.

 

I didn't mean the timing gear was causing the bending, just that it may be unevenly loading the outside diameter of the snout and that the cyclic bending loads from the belts could be worsened by the multiple point loads on the snout under the gear.

Callies Perma-Tough cranks have over .100 deep case hardening to Rc57, which approaches brittleness. Here's Callies tech info on Perma-Tough. You can see how deep the case is:

http://www.callies.com/tech/notes/perma_tough.html

I think they induction harden the journals as you can see by the heat pattern callout in the picture. Even if they don't induction harden the snout, a lot of heat transfers there during the heating of the front main bearing journal. There is a chance that the part of the snout nearest the front main also gets hard; it's difficult to prevent that when you are hardening this deep.

An out of round hardened timing gear (sprocket actually, right?) would point load the snout in multiple spots right near the shoulder where it could be case hardened. Add the bending from the belt tension and perhaps torsional loading from the damper, and perhaps you get cracking in the case near the area where the snout meets the rest of the crank. It's not far from there to failure.

If OOR hardened sprockets dig up the snout during assembly those marks are also stress risers.

I agree that they are covering their butts, but it's something to consider seriously especially if you are using a Perma-Tough Callies crank.

My $.02

 

I see your point. Under the loads your talking about, a crack would not be a good thing. I'd like to see the pict. they sent.

 

I've seen the picture. The gear they show must have 7 keyways cut into it, if not more. Probably more air than metal touching between the gear and the crank. I just can't imagine that a more common 3-keyway chain (or even a 5 keyway) would ever cause problems like that. I've seen a lot of funky stuff (not as much as the pro builders, of course), but enough to know that I have NEVER seen a snapped crank snout that looked exactly like their picture with perfect little divots cut into the shaft everywhere metal was touching between the gear and crank snout.

I saw the warning, thought about it and then went into "yeah, whatever" mode.

 

My mistake..... I just looked at the picture again and the gear has NINE (9) keyways cut into it!! Good lord!

 

Makes sense that they may break (having a good engineer in the shop to talk to helps explain that!)

To go on to mulit keyed crank gears and timing chain sets......

I have a slight pet peve about these things, especially on LT1 motors.

First the multiple keyway setups are all but useless on a LT1 since you then have to accomidate the change in timing IF you use the advance 4 or retard 4 keyway slot. The cam should be ground with the advance/retard in.

Second, just gets even more pointless when you go to even more keyway slots.

Third, as a engine builder who degrees EVERY cam to get it dead nuts in a motor (some guys don't which scares me) going with anything other than a adjustable like a Hex-A-Just or any equivalent just wastes my time and customers money. Multiple Keyway sets take time to pull on and off and in the end are never dead nuts in timing.

Fourth, just looking at any motor other than a LT1. When you have to adjust the timing on a motor to see what it does, you are at the dyno or someplace where time = money and not cheap at that. Pulling everything off to make a slight change in timing is dumb, when you can use 3 piece timing covers and adjustable timing sets like the Comp 8100 you can get things done much quicker and try more things to get the motor dialed in correctly.

Bret

 

Crank builder's have been for years offering a BB snout for SB CRANKS.When it comes to belt driven blower motors thats the way to go.With a cog belt and double keys 180* apart.If you damage it then it's time to go with a TURBO.