Back before his passing, I was working with George Aldrich on the exact problem addressed by Dennis T.
There is a material, manganese bronze, that has the exact outstanding properties that we need for our front bushings.
I also used it in quite a few aerospace actuator applications and it performed flawlessly.
Here is an excerpt from an article I wrote in the January 2011 Control Line World magazine.
I have used this procedure on many engines and never had a wear issue.
There are 12 photos that go with the article - I will pot them if anyone is interested.
Bob Z.
"OK, now for a bit of a challenge. You've got a neat old engine that you would like to use to power an OTS model.
Trouble is, the front bushing is shot - so bad that you can move the prop tips 1/8 inch or more.
Fear not - the engine can be saved. It's a relatively simple job but requires a lathe, drill press, angle vise and a good solid engine-mounting stand. And, of course, some measuring equipment. Added to this, it will give you an opportunity to hone (!!!) your machining skills.
I've done this on a number of engines. Here is the procedure for a sand-cast Fox 35. The bushing was really bad. The wear was .009 at
the rear and .016 at the front. Also, it had been crashed and the case was slightly bent, resulting in a non-perpendicular condition.
Disassemble the engine and set it up on the lathe as shown.
Different engines may require different mounting techniques but here is the most important thing to keep in mind:
You must insure that the cylinder axis is perfectly perpendicular to that which you are boring. Use a dial indicator as shown.
Insuring that the engine is rigidly mounted to the chuck (and centered, of course), very carefully start the boring procedure.
Take small cuts - .005 max with plenty of cutting fluid. At one point, you will cut through the old bushing and in all probability,
you can extract it with needle nose pliers. Now, continue the boring procedure until you have cleaned up the entire bore in the case.
Now you need to make a bushing. I use ALFA Romeo valve guides. They are made from manganese bronze with a .350 inch bore
and .553 inch OD. Length is as shown in the photograph.
The guides are available from International Auto Parts (800-726-0555), part number 37253.
Now, very carefully measure the bore that you made in the case, as well as the required length of the bushing.
Chuck the guide in the lathe and begin turning the OD.
Make the OD such that the fit is line-to-line up to .0001 interference - NO MORE or the case will crack when you press the bushing in.
The bushing length should be around 1/32 more than the required length. Now, chuck the turned down diameter in the lathe and cut off the
remaining material. Leave around 1/32 inch width of flange. Then, carefully face off the flange until it is .020 inch thick.
Next, make up an aluminum mandrel as shown. Make the nipple OD .005 less than the bore of the bushing.
This tool will allow you to press the bushing into the case.
Slide the bushing onto the mandrel with the flange against the shoulder. Apply some grease to the smaller OD of the bushing.
Put the assembly in the freezer. Put the case in the oven at around 300 degrees F. After around 30 minutes, quickly take the
parts to your press and carefully press the bushing into the case. Insure that the flange is flush against the inside of the case.
You now have a new case/bushing assembly. Take the crankshaft and while spinning it in your drill press and using crocus cloth,
polish the bearing surface to a mirror-like finish.
Now it's time for the critical boring procedure. Mount the assembly in the lathe. Again insure that the cylinder bore is perpendicular
to the lathe axis.
Triple check the alignment. Carefully face off the front of the new bushing, making it flush with case.
Take a small clean up cut on the front of the case.
Taking small cuts - .005 max, bore the new bushing to within .005 of the crankshaft OD. Now, go to very small cuts - .0002 max.
After each cut, try the crankshaft for fit. At one point, it will just slip in and turn smoothly. Admire your work.
OK, we're almost done. Attach the engine to the mounting stand and into the angle vise as shown.
Adjust the vise such that the venturi is vertical.
Find a drill bit that is the exact ID of the venturi. Insure that it is SHARP. Now very carefully and slowly, drill down through the
venturi and new bushing.
Remove the engine from the stand and deburr the intake hole. Finally, using a piece of 400 sandpaper wrapped around a dowel,
clean up and smooth out the venturi inlet, down to and through the bushing.
If you've done everything as described, your engine bushing/crankshaft assembly will be as good as or better than new.
So, that's about it for now. Hope you enjoy the article and find it helpful.
Until next time, Bob Zambelli"