aspeed

I use Silvo or Brasso for lapping. You can run the crank in a drill with some 600 sandpaper on a flat piece of aluminum that is wider than the crank window. Don't polish where the bearing seats.

hsukaria

The crank is fine. It fit well in the old crankase that broke. It's only the new crankcase is too tight between the front and main bearings.
I'll try Brasso with light oil.

hsukaria

Whew!! Turning the shaft in the crankase with old bearings is too stiff for my engine starter. Have been hand turning and I'm worn out without any signs of loosening. This might take me a week.
I'm using ATF with silver polishing compound. I might need something more abrasive to start with.

Hobbsy

My Feedback: (102)

I have a Fox .25 and a .50 ringed listed in the Market place, each has less than 30 minutes run rime, I got them from a retired Dentist in New England a couple of years ago.

hsukaria

Well I got most of the friction/drag eliminated, but I still think I need to reduce it more. I turned the prop by hand with a thick mix of oil and silver polish. After quite a while of turning, it felt like it loosened up a bit. So I diluted the thick mixture with some more oil and used the engine starter for a long time. I alternated between clockwise and counterclockwise. That loosened up the binding considerably. This evening I will re-thicken the oil/polish mix and run it with the engine starter to hopefully finish the process.
I am beginning to wonder if it would have been easier to fix the old crankcase instead of loosening the new one.

aspeed

Sometimes I use a shaft or drill that is smaller, and wrap some 400 sandpaper around it, and work on the bore. Concentrate on the side opposite the carb window.or where it is rubbing if you can tell by looking at it. Maybe use a marker on the bore and see where it rubs off. Push in and out with the crank and compound too. I have had to fix a few of the more crude motors like that. T Tiger, Magnum made by T Tiger and CS come to mind. That other case looks pretty hard to fix. It would be great to run with no muffler. :-) I never mixed oil with the silver polish. Maybe it is better IDK.

hsukaria

It seems to be working. The crankshaft spins freely but I think a little less friction is better. Will run a thicker mix of oil and silver polish this evening.
I thought about a hybrid bolt/strap-on muffler on the damaged case.

hsukaria

I'm done loosening the Fox 40 crankcase to shaft interference. I used ATF and some silver polish I found around the house. It took a lot of turning but it was the safest route to loosening the case. Will to wait a while before testing. It's 15 degrees F now.

gmeyers

for those who may find this usefulI use luxtrox for break in but I use it sparingly but in a running engine. If the engine is too tight I recently started using a marvelous new variety of Dupont 7 for rubbing down automobile paint.

hsukaria

Well I'm stumped. After loosening the case the last few days, I disassembled the shaft and bearings and put in New bearings after a thorough cleanup. But now the shaft is super draggy again. I must be doing something wrong.

50+AirYears

Have you checked for the possibility tha the shaft might be slightly bent or otherwise out of line!

1QwkSport2.5r

hsukaria

It binds all the time with the new case but never binds in the old crankcase. So I don't think it's a bent crankshaft.
I worked it to quite loose with the polishing compound and old bearings. Both sets of bearings, new and old, are identical size. So it might be the new bearings are not seated correctly. But visibly they look fine.

gmeyers

Pull the conrod off of the crankpin and see how freely the crankshaft turns - it may (most likely) turn freely with little parasitic drag. If the crankshaft does turn freely then you should apply your abrasive to the crankpin and conrod including the wristpin. after some lapping in of these parts with your abrasive of choice clean them up and oil all the parts as you reassemble the engine. Note: the abrasive you use should turn black after the lapping in process. I recommend the cleanup be done with fuel or denatured alcohol.

hsukaria

The draggy crank is without the conrod and piston installed. So it's definitely shaft to case.
Aside from the bearings being possibly misaligned, I had heated the case to drop in the bearings. I don't know if heating the case somehow undid my polishing?
Regardless, I will remove the shaft and reheat the case and bearings then tap on the bearings some more to make sure they are properly seated.
I have to say, I have 3 of the small case Fox 40 engines and they are the only engines I had trouble with replacing bearings. All other engines I ever replaced bearings on were a breeze compared to the Fox 40 small cases. Maybe the tolerances are very tight on these.

aspeed

The tolerances are probably not tight, they just used them up from sloppy machining. You can use a marker on the case and insert the crank and spin it to see where it is rubbing. If it is not rubbing then the bearings may be misaligned. If rubbing, then more sanding/lapping. The bores of the bearings to the hole may be non concentric.

carlgrover

I've only been following this tight engine thing with one eye but I had a real tight motor not too long ago. It turns out that the crank was rubbing up against the backplate because the gasket was missing. Maybe it will help, maybe it's not the issue I don't know.

carl

hsukaria

Hi Carl.
I checked the backplate and the rubbing happens without it installed. I will reheat the engine and tap down on the bearings this evening. There can't be any other possibilities because I had the engine loosened before swapping the bearings. Same type of bearings just newer.

Cougar429

My Feedback: (3)

If the crank is difficult to turn even without the drive washer installed and tightened then you still have an interference problem, or one where a bearing may not be straight. If when everything tightened down then suspect bearing stack height is incorrect, either from not fully seating or incorrect dimensions.

Bring that up since I remember there being something different about the R6 front bearing on my 50BB. Think it had to do with unshielded or unsealed making it thinner. Been a while since had that one apart so might be a bit creaky on recall.

vwitte

My Feedback: (1)

vwitte

My Feedback: (1)

hsukaria

Any reason why you want to replace the carbs? The Fox carbs have always been good and easy to tune. The early ones were different and required different tuning method but still good.

gmeyers

In my early Fox Eagle days I managed to loose my Fox Eagle carb and I made an adapter to use other carbs. I had some inventory from a closed hobby shop and they had a box of OS carbs so I used my adapter for one of the OS carbs and it worked out great. I have found that the Fox 46 ABC (I have 4 of these great engines) uses the same carb so that might broaden your search. The .46 ABC uses two carbs, one air bleed the other two needle and the end result seems to work out the same.

kablake

You may want to try a Perry carb. They sell a Fox adapter for their carbs.

Perry Pumps - Carbs

kablake

Some good info on Fox engines, probably known by many already, but cant hurt...

Fliteline Solutions for Fox Model Airplane Engine Fans