Bearing Bore Wear

[N3BP]

Curious if anyone else has experienced this:

The input shaft seal on my MMM gearbox started to leak mid season. It makes quite the mess once it hits the belt and spindle pulleys. Now that I'm done mowing for the year, I removed the gearbox to inspect it. The input shaft has excessive radial play to the point where oil drips by the seal lips. I rebuilt the box two years ago and put new Koyo bearings in it. When I pulled the input shaft, I noticed the bore was worn where both bearings seat. Dammit!

Anyone have an idea as to what might have caused this? I'm thinking of of three options:

1. Bite the bullet at by a new gearbox case at $526.00
2 Try and have it repaired (is this even possible?)
3. Fill box with JD Corn Head Grease and see if it still leaks.

 

[woodman55]

I think I would try the grease. A machine shop would use up a lot of that 500, and you would still have a old box.

 

[DustyRusty]

If the machine shop were to install a sintered bronze bushing into the box it would probably last another lifetime versus the white metal of the current box material.

Sintered bronze bearings are characterized by being self-lubricating and maintenance-free. The sintered bronze bearings are made of porous bronze or iron and are usually filled with oil. Their high permissible sliding velocities make these sintered bronze bearings ideally suited to rotating applications.

sintered bronze bushing lubrication - Google Search

 

[cthomas]

How loose are the race's? I think loctite makes a sleeve retainer that is good for a few hundunderths. Or hone the inside and install the races with a tinfoil backer(you are just trying to take up the clearance). Or I have seen many a brush hog gear boxes pumped full of corn head grease.

 

[North Idaho Wolfman]

yea if the bearing races are spinning in the case get some Loctite, new seals and call it good.

 

[jaxs]

Decide how much your time is worth to remove,strip and clean then reassemble the gear box. Make a scaled sketch of box,take couple pictures and show them to machine shop for an estimate to overbore for larger od bearing. Add your time,shop estimate and new parts. If total repair exceeds $300 (I believe it will) I'd go for new box. Regardless what you do I'd inspect pto input to make sure it isn't bent,binding of bad out of balance.

 

[N3BP]

Gentlemen, thank you kindly for the suggestions. I really like the idea of a retaining compound, so I'm going to give the Loctite a shot. After doing some research, it appears Loctite sells a "638 high-strength retaining compound" good for 0.15-0.25mm gaps, is oil resistat, and good for up to 350 degrees. Thanks Again!

 

[Russell King]

I really can’t tell exactly what is wrong with the seat but you may want to use shims from a feeler gauge to get the bearing OD centered in the hole. Just space the same thickness shim at three places 120 degrees apart. And also the retaining compound

 

[DustyRusty]

I really can’t tell exactly what is wrong with the seat but you may want to use shims from a feeler gauge to get the bearing OD centered in the hole. Just space the same thickness shim at three places 120 degrees apart. And also the retaining compound

How can you determine if the hole is worn evenly on all sides?

 

[GeoHorn]

This is similar to what I suffered with a portable generator end- bearing. Vibration eventually loosened the bearing-race in the case/casting until it was ”wallowed out” . There was no economical repair …so I re-set the bearing in a bed of JB-Weld….and let it cure overnight.

That was 5 years ago. Still works great.

 

[Russell King]

How can you determine if the hole is worn evenly on all sides?

Set it up in a machine tool and check runout.

But I am only suggesting that it is probably better to center the bearing in the hole than to let it go hard against one point.

 

[GreensvilleJay]

re: How can you determine if the hole is worn evenly on all sides?

Take some good pictures, import into computer, then run an 'optical comparison' style program ( or cut your own code ). Essentially you impose a 'grid' over the 'area of interest' and have the computer computer compute center of hole(shaft center) and then the perimeter of the hole. The radii should all be the same.

The backyard bodger's way... put new bearing in hole, use feeler gauge to measure any gaps.