Countershaft seal leak

83 Husqvarna 500cr. Just finished splitting the cases and installing new bearings and seals. First ride resulted in a big leak at the countershaft behind the sprocket. I thought it odd that the machine was designed without a countershaft seal, especially considering that the shaft is a slip fit in the inner race of the bearing. As noted by others in other threads here, the integral seal in the countershaft bearing is the only seal. Perhaps Husqvarna felt that some slight leakage here would not matter since chain lube would gunk everything up anyway. Slight leakage I could accept... mine was slinging oil onto the cylinder fins. Here is what I did to (hopefully) resolve the problem.

First I removed the chain, snap ring, sprocket, flange and spacer. I then inspected the bearing. It rotated smoothly and the seal was intact. The bearing fit tight in the case. The shaft had no noticeable radial play, but would slide easily in and out of the bearing (there is a short amount of axial play here that is normal). Bearing is new, shaft appeared good and showed no signs of wear when cases were split, although I did not put a micrometer to it. This machine is new to me, it was leaking everywhere when I bought it. I suspected the leak to be coming from between the shaft and bearing.

Broke out the o-ring kit and found the thinnest o-ring that had a big enough diameter to fit snugly over the shaft. You may notice that there is just a small area on the shaft that does not have splines cut into it, the idea being to have the o-ring seal on that part of the shaft.

Next, I took the plastic spacer that goes behind the sprocket, put it on my mini lathe and cut a recess that would allow the o ring to seat into it. If you don't have a lathe, get one, these bikes are getting old. I cut the recess to a depth that causes the o ring to be compressed about .030 inch when the sprocket and snap ring are installed.

PUt it back together and rode it for about 30 minutes this afternoon. No leak. On the plus side, I won't have to clean my cylinder fins, the minus... I'll have to oil the chain. Is it durable? August 10th I'll be riding two classes at a vintage motocross race, we'll see how it holds up and report back.

Comments and criticisms accepted.

Looks good, let us know how it goes with the fix. How about pics of the rest of the bike!

Was the oring nitrile? If not normal rubber expands an goes mushy. Other than that my wr360 runs similar set up as stock but the plastic soacers metal with an ectra seal round it. Think the oring is to stop debris being forced past the spacer personally.
Good solution to the problem A*

I would look at the shaft to bearing dimension as I have many of these that don't leak
yes it is a fit issue as the tolerance is critical, the bearing could be off is true size, or the shaft might have wear
what brand bearing is it

Yes, nitrile o-ring, thanks for the input and advice, always appreciated.

The oil level in the gearbox is the issue here. We run 1500ml of oil and expect a little to pass between the bearing and the shaft. Later 4t Huskys ran a steel spacer with an O-ring as suggested, but they also use a roller bearing instead of a ball bearing....

Personally, I don't worry about it. It is a big ask to expect the single sealed bearing to cope with all of the load from the chain - and we will be looking at an upgrade this winter to try and improve things!

Guess that is why the side stands are on the left!!!

Andy.

When I first set out to find out why it was leaking (yesterday, on a Saturday afternoon when I wanted/ needed to be riding it), I fully intended to fabricate a puller and remove the bearing for inspection. Since I didn't know if I would have sufficient time to obtain parts to repair it properly before race day, I opted to attempt to seal it this way. The original 4 speed CR gear set had been swapped for a 6 speed WR gear set, I reinstalled the 4 speed for vintage MX. Your comment about these not leaking/ critical tolenance got me to thinking, so I measured the shaft on the six speed, which mics at .984 inches. I believe the bearing I installed was a National 6205, national shows a dimension of .9843 inches, so that would be a very close fit. Judging by the ease with which the shaft went through the bearing, you are correct, there is a dimension problem for me to find. I will go back and repair it correctly either after the next race or the season, depending of the outcome of my temp fix. Sooner may be better than later since the shaft will likely tend to rotate inside the bearing race, possibly adding to the tolerance issue. Thanks much for the advice, helps me understand what I will be looking for.

Thanks Andy, I'll be looking for the upgrade, my leak was too bad to let go, per my last post probably a tolerance issue which should be fixed.

Here's some pics. Didn't do a restoration since I will be racing it, but did a thorough refurbish... rebuilt the Ohlins, rebuilt the forks, disassembled, inspected and resealed the engine (reinstalled original 4 speed CR gears, previous owner had swapped in 6 speed WR). New fenders, tires, etc. I had wanted one of these since they came out new, finally got one 30 years later .

Looks very nice. Tank looks premo from this distance. Looks like you replaced or maybe painted the side panels.

there is a ultra narrow oil seal available that ive used, similar to what you've done, but I like the o-ring idea - simple and way easier to get hold of than that seal!

The seal from behind the ignition will fit but you have to replace the nylon sleeve with steel and use a "o" ring on the shaft.

The trick is stopping the hardened steel sleeve from rotating on the shaft! If it does start to spin, it might join itself to the output shaft - and you don't want that to happen..

Andy

Just thought of something! We will get our sprocket manufacturer to spline the bore and counterbore half of the bore for a pair of O rings (to seal it to the shaft) - then the oil seal can go in the seal holder as per the ignition seal...

I will work on this...

Andy.

A bit like this then ...

This is the first prototype! I have ordered some seals to fit between the 30 diameter of the sleeve and the bore of the cover plate. The O-ring sits in the small recess and against the bearing to stop the leak....

Andy.

I like the looks of that better than what I made , nice job. Looking forward to being able to order one.

Actually, I hit the jackpot when I bought the bike. The seat, tank and side panels had been removed early in it's life and replaced with plastic 84 WR (I think) items. I was given the originals which were in excellent condition, especially the tank and seat. Even came with owner's manual and title.

Follow-up. Rode three motos Sunday (would have been four but rained out). Countershaft is still not leaking oil. Hopefully the repair will last through the end of the season. On the other hand, I hope I last the rest of the season... this machine is a learning experience. Let's just say that my protective gear worked wonderfully and was well tested by the end of the day.

why are we not surprised.....