I was fitting  my Fox35 stunt con rod on the aftermarket zoot crank and I noticed it didn't go on all the way. It was getting hung up on the radius so I changed the radius and now the rod goes on all the way to the crank web. Problem now is the counter weight is so thick that it hits/rubs the con rod through the lower haft of the stroke. Anyone else run into this problem?

Thanks,
Motorman

I installed  near 400  of them  Never  saw that problem,  I did chamfer the  FOX  rod to match the  radius on the  crank pin, That  is  pretty well known  to people I sold  cranks as , do it your self,  I would be interested  in  seeing  exactly  what is  happening  and  how  you solved the problem, If it is  just a few  thou,  I would make sure the backside of the counterweight is  perfectly flat, and sand it or polish it  flat, then I would  trim the  rod down to clear, if it needs a  lot more , I would  search  to see if anything else is  amiss

Randy

Well I did some measuring. The counter weight is .115" behind the crankweb. I measured a few rods and they were recessed .120". So, if you blend the radius so the rod goes all the way forward you have about 5 thou clearance. From what you say it doesn't seem to be a problem but gee wiz.

Anyway, I checked my blueprint and the high zoot rod I make is actually .005" thicker so it would have no clearance.

I pulled my Fox 4011 apart to see what I did so long ago.  I think I just drilled a hole off center the amount of the stroke in a piece of round stock and bolted the crank to it with the prop nut. I chucked the assembly in the lathe and centered on the crank pin. Then I cut the counter weight down to .095" to give me .020" clearance.

Still allot more counterweight than the Fox crank and my piston's aluminum so it works just fine. I'm currently using the factory crank in the ABC engine so it should work for that too.

Motorman    

The  HZ  crank was  designed and  machined to  fit a  Standard Fox 35  with FOX parts, it was  not  designed  to work with  aftermarket home made parts, that  are  not  the same  size as  FOX parts, so  yes, that was your  problem, However  easy to fix, just trim the rod slightly

Randy

I was fitting  my Fox35 stunt con rod on the aftermarket zoot crank and I noticed it didn't go on all the way. It was getting hung up on the radius so I changed the radius and now the rod goes on all the way to the crank web. Problem now is the counter weight is so thick that it hits/rubs the con rod through the lower haft of the stroke. Anyone else run into this problem?

Thanks,
Motorman

   Either you have your rod on backwards or it worn down. I never had any problem.
Al

Dennis  the  short answer  is  both, and  it works  a  LOT better

  In nothing else, it's *straight*. People who have measured a lot of factory cranks say that many of them aren't.

    One of the many oddities about the Fox that the prop driver and the 4 little tabs on the crankshaft that it sits on do not always stack up all that well in terms of tolerances, tilting the plane of the drive washer WRT the crankshaft spin axis and creating a dynamic imbalance. One the tricks was to rotate the drive washer to different position WRT the crank to find the way it shook the least.

    Unfortunately, some of the McCoys had a similar problem, even though they used a conical seat. My rear-intake 19, the cone is at about 45 degrees and about a 1/16"wide, and so is the drive washer. So it's pretty easy to get it crooked and cause the same issue. Other McCoys had a 1/16" key on a cylindrical shaft - because McCoy was primarily about tether cars, so you wanted to be able to use conventional drive gears. Someone told me, or I read somewhere that Dick McCoy never built a model airplane.

   The arrangement on STs, PA, RO-Jetts, with a precision low-tapered cone is far better, and doesn't count on the shoulder being square, with only the problem that it can sometimes be hard to get off without a puller.

      Brett