Fox 35 crank bushing

[Rick_Huff]

My brother gave me his old 4-(head)bolt Fox 35 to see if I could get it running.  I took it apart and the crankshaft is very loose (rattles back and forth) in its bushing.  Can this bushing be replaced, or does it take a whole new body?  If it can be replaced, where would I find one?
Thanks,
Rick 

[kenneth cook]

            Rick, that's not a bad thing unless fuel economy is really suffering due to fuel bleeding out the front. They run their best when they're loose like you describe. In addition, if it's loose like that, so is the rod on the crank pin and possibly the wrist pin hole. Replacing the bushing isn't a simple task. The bushing is molded into the case when it's made and it's not meant to be service removable. Dan Banjock has replaced a few of them but for the time spent, it would've been easier to replace the case. For as many of these engines out there, it would just be easier to get another. A worn out version like your mentioning makes a great Bi-Slob engine. Ken

[Chris Wilson]

My brother gave me his old 4-(head)bolt Fox 35 to see if I could get it running.  I took it apart and the crankshaft is very loose (rattles back and forth) in its bushing.
Thanks,
Rick  

Back and forth as in axial (not radial) to the crankshaft?
Could simply need a shim behind the prop driver and not necessarily be unrepairable wear as such.

[Rick_Huff]

It's worn both axially and radially.  The axial wear is due to wear on the backplate.  The connecting rod is also worn where it connects to the crank, though isn't bad where it attaches to the piston wrist pin.  Compression isn't bad.   I think I'll go with Kenneth's suggestion and try flying it and see what happens. 
I do need head and backplate gaskets, any idea where I could get these?

Thanks,
Rick

[Rick_Huff]

I ordered gaskets and a backplate from Fox mfg.  I guess they still have parts.
Rick

[Dennis Toth]

Rick,
If you want to use the engine for say OTS you could send the case and shaft to Fox and have them replace the bushing. Don't know what it costs but they can do it.

Best, DennisT

[Jim Kraft]

With a prop on a Fox 35 the shaft should never hit the back plate. The rod can but not the shaft. If it is not extremely loose it should run fine. You can tighten it up by running a reverse 7/16" tap through it which will tighten it up and keep the oil from going down the shaft.

[Rick_Huff]

I ran the old Fox 35 today and it ran, but vibrated badly.  Looking at the prop from the side I could see the tips moving in and out 3/16".  It's a balanced BYO prop that spins true on the lathe so I guess its the worn bushing.  I sent an inquiry to Fox, and ordered a left handed 7/16-20 tap.  Thanks for your help, I'll let you know how it turns out,
Rick

[Chris Wilson]

I am not getting this - what does a left hand tap do?

[Air Ministry .]

Bent Crank ?

[Andrew Hathaway]

I am not getting this - what does a left hand tap do?

It puts a counter clockwise spiral groove in the bearing, so that normal rotation of the crank pushes oil/fuel back into the case instead of letting it out the front bearing.  Also it has a slight knurling effect that raises the surface around the thread, tightening the bushing.  I haven't tried it and can't comment on how it actually works, but that's the theory anyway, as I understand it.

[Rick_Huff]

I didn't think about the crank being bent (should have) but I checked it and it's fine.  Fox mfg got back to me and they no longer will re-bush the case.  I'll think I'll try to "dull" the 7/16" tap.  That should cause more deformation of the bushing around the threads.  By the way, the crank is 0.435" in diameter, the inside diameter of the bushing is 0.439-0.440". 
Rick   

[Chris Wilson]

It puts a counter clockwise spiral groove in the bearing, so that normal rotation of the crank pushes oil/fuel back into the case instead of letting it out the front bearing.  Also it has a slight knurling effect that raises the surface around the thread, tightening the bushing.  I haven't tried it and can't comment on how it actually works, but that's the theory anyway, as I understand it.

Thanks for getting back to me Andrew, but a lot of the technique I still don't understand to be of any benefit.

Firstly the bushing will have barrelled and running a parallel tap down it will the greatest effects
where it is least desired.
Secondly, let's assume that you can  improve the fits where needed - how long will a notoriously short plain bearing last running on raised point contacts?
Thirdly, if the engine has heirloom value ( and I do get that) then far better to get a machinist to replace it properly.

Cheers.

[Jim Kraft]

It probably won't help forever Chris but it should help to tighten it up and also it will keep the oil from leaking out the front so bad. Some of the later Fox 35's have a groove in the right bottom to do the same thing with the excess oil. Frankly I have some that are way loose that still run good although they do blow out quite a bit of fuel through the bearing. It sure could be bored out and replaced with a new bearing pressed in and then drill out the intake hole. I have no experience with the tap either, but others that I trust have used it. It stands to reason that it should work and may work much longer than we think it should. 

[Rick_Huff]

I received the left-handed 7/16-20 tap today.  I dulled the cutting edge a little with a stone and mounted it in my lathe to make sure of the alignment of the tap.  It cut a very small thread into the bushing.  The crank went it with a "snug" fit, but began to turn freely after a few rotations.  I bolted it on the bench and ran a tank of fuel through it.  After the run, the crank was just about as loose as before tapping.  Oh well, it didn't work for this engine, but it may have been too far gone.
Rick

[Chris Wilson]

Hmm, as I suspected sorry to say.

There are engine builders here in Oz who could push a new bush in for you if you are willing to spend the money on it though.

(Or you could look around for a new case.)

[Russell Shaffer]

Rick, if you have a lathe and the engine is toast anyhow, why not try boring the bushing out and making a replacement?  Nothing to lose and it might be a good winter project. 

[Chris Wilson]

http://controlline.org.uk/phpBB2/viewtopic.php?t=11225&highlight=max++bushing

Here is one way to do it.

[Rick_Huff]

I'm game.  The loctite method looks better (well easier) to me.  What is the preferred material for the bushing?
Rick

[Robert Zambelli]

I have replaced many bushings - Fox, McCoy, etc.

Here is an article I wrote in January, 2011.

Text first, then photos (10 total)
Bob Z.

[Robert Zambelli]

Last photos.

Bob Z.

[Jim Kraft]

Those AlfaRameo valve guides make excellent bushing material. I machine spacers out of them to replace the thrust ball bearings in old sparkers that blow up and destroy the rest of the engine. Thanks Bob.

[Rick_Huff]

Robert,
Thanks so much for the article.  I already ordered some 932 bearing bronze, so I'll use that.  I'll let you know how it turns (hah hah) out.
Rick