Mac clutch keyway plan B

[Bill Peck]

I have a Mac crankshaft that has chipped keyway. Does anyone know someone who can cut a new keyway for me?

[Bill Peck]

If I'm unable to find someone to cut a new keyway in my Mac crank  I'm going to try the "lap and torque" method that was discussed in the thread "820 Starter Cup" from February. That thread suggested torque values ranging from 280 in-lbs to 360 in-lbs for a West Bend. What kind of torque should I be putting on that skinny little Mac clutch nut? The last thing I want to do is break the nut. The memory of Scott working for an hour or more to remove a broken nut at Thompson is way too fresh in my mind!

[steve welte]

If the key way is chipped I lighty grind to cclean it up. I then Mig it shut. tack tack tack. don't overheat the area. Then I grind it close to what the taper looks like. Chuck it in a lathe. I made a holder for my dremel so I can hold it in the tool holder. Set the angle with the good part of the shaft and use a 60 grit roll cartridge. grid that angle. then lap in on the lathe. Use no key in your crank and torque the nut to 30 ft #s. If you don't torque it, it will come loose. All those broken keyways are because the user didin't not torque the nut. They only guess at it.

[David Luciani]

the keyways were also aced by misfirtting clutches especially hartmans.
if you just stick the clutch on with key and assume it's good you'll be busting up the keyway.

i always lap the clutch and pto so they match .
then i dry fit the clutch hub without key , mark where it stops in back side with thin sharpie.
when the key is installed the clutch should still touch that sharpie mark.
if it doesn't you need to adjust the key til it does.

i haven't tried that repair yet steve but i think i'll give it a go .
i've been told by many experienced karters you can run keyless.
haven't done it yet but maybe this year i'll take the plunge.
only downside i can see is the occasional lost clutch a smaller issue than setting keys and wrecking cranks!!
d

[Bill Peck]

Yeah, I'm one of those guys who always just guessed at the torque. So I went out and bought a bigger torque wrench (mine only goes up to 100 in-lbs). I lapped the hub and crank (no problem) and am ready to mount the clutch. (Sorry Steve, but the chip is staying. I don't have access to a mig.)

But I also tried something new: It was pointed out to me that by letting the end of the nut bear against the shoulder inside the hub, it would be impossible to remove the hub without destroying it should the nut break. Rather I should have the head of the nut bear against the top of the hub. Makes sense to me, so I put a washer under the head of the nut so it's hitting the top of the hub rather than the internal shoulder. I tried it out using an old crankshaft and hub, went to torque it, trying for 350 in-lbs, and the nut broke somewhere around 300.

So I'm considering two scenarios: (1) - that by adding the washer, the nut is now in tension under the head rather than in compression against the shoulder, and the combination of tension and torque was too much for the nut or (2) -  that the nut, which has a wall thickness of only about .035", just can't handle that kind of torque. I'm not familiar with the West Bend clutch nut. Is it beefier than the Mac nut?

I also don't know if the Margay gearbox clutch (which is what I'm using) uses the same nut as a chain clutch. Is a chain clutch nut beefier? I'd really appreciate any insight you guys can provide. I only have 3 of those nuts left. And I'd really like to get this engine going for Nicholson.

[steve welte]

Yeah the nut your using can't take that torque. Many times without the full explanation of what your using it's hard to know what you have.

[David Luciani]

sounds like a max torque two shoe. they are fragile.
if you get in a jam bill contact me i have a few max torque spares i'd send ya.
in a gear box you may be able to go with less torque if the clutch gets loose it can't go anywhere!
D

[thomas kelley]

sounds like a max torque two shoe. they are fragile.
if you get in a jam bill contact me i have a few max torque spares i'd send ya.
in a gear box you may be able to go with less torque if the clutch gets loose it can't go anywhere!
D

not a good idea 
the nut has nowhere to go and it destroys your crank....i have a 91 crank thats junk now
gear box problem solving is my life lol
the taper being lapped in is more important than the nut torque
tk

[doug tenney]

Hi Bill,
Disclaimer: I have less first-hand Mac experience than any of the previous posters, but here goes:

1. Instructions for Hartman clutch said "260 - 300 in*lbs, NO TIGHTER."  (In that case, the limitation was the crank threads. In your case, it will be your nut's paper-thin wall thickness.)
   
2. I would never attempt a DIY weld repair on one of these cranks.  The metallurgical changes would be a train wreck.
   
3. I can't imagine good things coming from adding a 2nd keyway.  Not much meat, plus notch-sensitivity.
   
4. That leaves the keyless lapping method.  Many guys have had good success with it (I'm still aspiring for that).  Some guys' recipes also include adding one drop of blue (#242) Loctite to the taper.
   

See you later!
Doug

[David Luciani]

if the keyway isn't too roached adding a second key was an approach that many used back in the day. 
i never liked the idea myself.
welding a crank can destroy it but steves method if done carefully can work.
the idea is to heat locally in a tiny section.
if you just tap and leave the area heated shouldn't effect the metalurgy of the whole crank just the immediate area.
this still would be a negative if you reground a keyway as the metal there isn't tempered anymore.
personally i wonder why you'd weld at all if you're excluding the key unless there's ALOT of material missing. 
if steve w could please elaborate i'd be grateful!!
D