Margay Gearbox Bearings

[Dick Teal]

I'm in the process of restoring three Margay gearboxes. All three boxes had failed input shaft bearings; it seems that this must be a common problem. All boxes turned freely whan I purchased them but I decided to split the boxes to check them.

The caged ball bearing closest to the input shaft drive fingers all had failed cages and the parts were loose inside the boxes.

The needle bearing on the other end of the input shaft had failed on one box and the other two were OK but the needles were loose when the shaft was pulled out.

The input shaft caged ball bearing is the same size as a caged front wheel bearing and it looks like two of them were replaced with front wheel bearings because the retaining ring groove was on the outer surface. I replaced all three of the input shaft bearings with front wheel bearings but would like to know if there is a better bearing that someone has a part number for.

I was able to insert the loose needles into the needle bearing cages on two of the boxes and the boxes are assembled. I had to press out one of the needle bearings and it was pretty tough but I finally got it out. I'm in need of a source for the closed end needle bearing assembly; it is similar to an upper wristpin bearing on the exhaust side. The shaft diameter is .437, the cage outside diameter is .625 and it is .500 long.

Any ideas and/or part numbers would be appreciated.

Dick Teal

[Mark Havery]

Hi Dick
If any of the needles came out of the bearings you can count on the fact that that bearing has died and will need to be replaced. The gearboxes are easy to rebuild, but all the bearings should be replaced along with the seals. Once minute particles of metal start circulating around the box that alone will damage all the bearings in the gearbox. You might not be able to easily see the damage, but it will be there none the less. If possible find the copy of the VKA's magazine that had the rebuild article, it isn't necessary but it will help. All of the bearing and seal numbers are on the parts themselves, and a bearing house can help you order all of the bearings and seals. You pretty much need access to an arbor press to assemble all the bearings and seals in the case halves. A hammer and socket won't cut it if you want your bearings to last any appreciable time. Originally Ford ATF was used as a lubricant, these days
there are vastly superior gearbox oils made for high performance two stroke dirt bike transmissions that work better and keep your gearbox cooler that the ATF. You might have to fabricate a few simple pressing fixtures for the seals and bearings.
Mark

[Mark Havery]

Dick,
I forgot to mention the bearing and seal numbers.
They are:
Input shaft bearing 6202, this comes in metric sizes to so make sure you get the right one!
Output shaft bearing R24
Closed end beaing M781
Cheek block bearings B78
Output shaft seal 14855
Input shaft seal 11123
small o-ring 246
large o-ring 242
Mark

[Dick Teal]

Mark,

Thanks for the information; I plan on rebuilding all three gearboxes with all new bearings and seals.

I have two boxes together and they will be used for fit-up and fixtures while the third is being put together. I've found that it pays to have a spare or two when I'm learning how to do things.

I have access to an arbor press and will make press tools as necessary. I know that I need something to press the input shaft needle bearing into the box. Do I need to heat the box before pressing the bearings in place???

Does anyone know of a good online bearing house that I can call?? We live out in the boondocks and it may shorten the time if I can talk to someone.

Thanks again,

Dick Teal

[Tom Smith]

Don at Margay told me that the output shaft seals they used were special, the drag characteristics on the design they used was much lower than a standard seal. You can do a number of things to a Margay to cut down on the drag and rotating gear mass just by using your Chraftsman home workshop laser cutter, CNC precision grinding machines, and REM machinery.

[Mark Havery]

Dick,
The needle races have too much compression to be helped by heating up the case. Generally I just use a slight smear of anti seize in the bores and on the bearing ODs. Just wipe off any excess.
Mark

[Dick Teal]

Mark,

Thanks again for the help.

Tom,

I know you're having fun but gearbox repair is about the same as working on engines and most people like me don't have the equipment; fortunately I have access to someone who does.

Dick Teal

[Tom Smith]

Dick, yes I was joking about the home workshop, but Don Freiber did tell me that his father Elmer insisted on the special seals and excellent gear tolerances. Before Elmer got into karts he had USAC cars. I think Johnny Parsons was their driver.
The REM Isotropic finishing would be something I'd have done. Cuts parasitic gear drag by a good percentage. It costs about $50.00 to do an Mc-101 crank.
http://WWW.remchem.com
Tom