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Engine basics => Engine set up tips => Topic started by: Motorman on December 01, 2020, 09:11:41 PM
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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 8)
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
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It's only a problem if the clearance goes negative when the rpm's are non-zero. If that happens, then all of the zoot precipitates out and you reestablish a guts-less Fox baseline. At least, that's been my experience....
The Divot
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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 8)
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
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Does the HZ crank work better with the standard Fox 35 Meehanite C/P or an aftermarket ABC C/P? Seems the HZ is designed to have larger counter weight that seems to me would work better with the heavier cast iron C/P and the original Fox crank would work with the ABC set up. What's the story?
Best, DennisT
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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 8)
Either you have your rod on backwards or it worn down. I never had any problem.
Al
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Does the HZ crank work better with the standard Fox 35 Meehanite C/P or an aftermarket ABC C/P? Seems the HZ is designed to have larger counter weight that seems to me would work better with the heavier cast iron C/P and the original Fox crank would work with the ABC set up. What's the story?
Best, DennisT
Dennis the short answer is both, and it works a LOT better
Randy
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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
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"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. "
Yes that is correct, in addition there is also a problem with many of the FOX drive washers, the 4 slot keys, stamped into them are sometimes boogered, and are not the same size on all 4 tab collectors. I have had to trim out metal from many of the to get things to fit right
Randy