Mac 1-50 MC5 conversion

[Bill Hermsted]

I like David's idea to counterbore the inside of the crankcase for a 1203 / 012 ball bearing. But in this case it would be for an mc 91 whose crank became gnarly on the pto bearing journal from probably 40 some years of storage. I'd like to give an otherwise mint 91 crank a new lease on life as i'm told its kind are now extinct. It's too bad there's not enough meat for a bore that would accept a 1204 bearing to allow my favorite crank, the 60313a, to be fitted, or any of the other ones with a .787 journal, which i'm told are still out there. I thought of making a pto side plate to be mounted over the four side holes with shoulder bolts for alignment, but didn't think a good sealing face could be had what with all those curves in the casting below. for the 1203/012, though, many small machine shops should be glad to do this work reasonably in this economy for those who might not have a mill and boring head.
bill
P.S. If you go this route, be careful of the bearing's country of origin. There's a lot of junk out there nowadays, as you know, that will never stand 12000 RPM's.

[david a luciani]

Bill,

if it's just a bad crank bearing suface i have been thinking that the yamaha cranksaver job should work on mcculloch cranks too.
talked with Duane Eberhart about it and he gave me some pointers.
said we'd need to find a inner bearing sleeve that either had the right o.d. or id to fit and centergrind the crank or sleeve to fit with a press fit.
should fix your problem crank.
also Duane did say he would be willing to work out a price for me to rekey damaged cranks.
both as a opposite keyway recut (less money) and a reweld and recut the taper and keyway with retemperimng job the second costing more.
as we just talked about this and he's way busy it'll be a while before this is available.
but i know he can do the work i have two cranks he repaired in the past both excellent work.

dave

[Bill Hermsted]

David-
Great idea using a sleeve to save the roughed up pto journal on a mac 91 crank. It looks like an inner race from an old 1203 ball bearing will fit if the journal is ground down to .6690, the diameter of a small bearing 101. Then the race od can be ground to .750 to fit the 91 needle bearing once again( a new one, of course) ! This will leave a .040 wall, hopefully enough for the sleeve to survive a light press fit.
Do you guys think this mod will fly?
I'm still mulling over the counterbore approach, never being tickled with any shaft serving as an inner race directly, be it a mac 91 or a mopar 8 1/4 axle. The shaft pto journal would still have to come down to, in this case, .6680 for a ball bearing slip fit, a trick that was handed down to me from the late, great Raymond Jett by way of Hank.
Either way Ill need Duane's expertise when he gets caught up! Not many have a cylindrical grinder, me included.
bill
P.S.- I think the 91 crank might be worth all this fuss, as its rod journal is a shiny . 630 all the way around, and it is straight as a dog show judge. The race is on the shaft before its od grinding, of course!