Early OSSA shift shaft Orings

[pmk]

I have a 73 MAR, but it appears many OSSA models are similar regarding the shifter shaft and the O rings that seal the shaft.

My MAR has a splined stub on both sides of the engine, and could be run as left or right side shift.

The O ring in the clutch cover is easily replaced by removing the clutch cover.

With the clutch cover removed, can the shifter shaft be removed to replace the right side O ring or must the cases be split to replace the O ring.  When I had the clutch cover removed previously, I noticed there was quite a bit of movement where possibly the shaft could be removed, but I did not attempt it.

[scot taco]

The cases will have to be split to remove the shift shaft.Here are a few pics to give an idea what it looks like.

 

[woody]

On 03/01/2017 at 11:06 AM, pmk said:

With the clutch cover removed, can the shifter shaft be removed to replace the right side O ring or must the cases be split to replace the O ring.  When I had the clutch cover removed previously, I noticed there was quite a bit of movement where possibly the shaft could be removed, but I did not attempt it.

Although you can push the shaft through from the sprocket side, it won't go through far enough to clear the O ring. As above post, you have to split the cases to replace that one.

I wouldn't split them unless absolutely necessary

[pmk]

Good info guys.  Thanks.

The countershaft side seems to not be weeping, but clutch side is weeping slightly.

For future planning, if the right side shift spline was cut off and deburred, would the shorter shaft then allow Oring replacement without splitting the cases?

[woody]

I was going to offer that as a possible solution to avoid splitting the cases but I'm not absolutely certain there would be enough clearance, so didn't...  When I'm back in the shed at the weekend I can try and measure up against a part dismantled engine, see if I can get a definite answer

[woody]

Had a quick look at my stripped engine this morning. The O ring on the sprocket side is seated 7mm inside the casing, that's measured to the inside edge of the O ring housing / groove.

As you can only move the shaft by 5mm, even if you could cut it off flush with the casing, you still couldn't slide it far enough to clear the O ring.

With the engine apart and the shaft out,  you may be able to remove enough to enable it to slide far enough to get at the O ring with the engine assembled, but there would only be 2 to 3mm left of the shaft extending past the O ring and I wouldn't know if this would compromise the sealing effect.

[pmk]

Woody, thanks so much for checking that.

No doubt OSSA has a simple low cost method with the O ring, but it does become more complex if leaking.  Back in the day, I guess the idea of pulling the engine, and splitting cases for a small leak or replacing a bent shift shaft was no big deal.

Possibly I became spoiled by Japanese engines allowing an entire shift shaft to be removed by pulling the side cover and clutch.

Regardless,, and with no leak on the right side shift shaft, this MAR is moving forward.

Thanks again very much for checking that.

[pmk]

I started this topic asking if the right side shift shaft O ring could be replaced without splitting the cases.  This week I trimmed the shift shaft.  The engine was on the bench, still assembled.  The MAR will never be a right side shift, so trimming the shift shaft was not harmful.  I knew I needed to remove the clutch cover.  So today was the test. At least on my motor, with a close trim of the right side shift shaft, the shaft can be withdrawn exactly enough to allow the O ring to be easily replaced.  I think the photos will explain it better than words.

I did use a hardened thin washer to act as a guide when trimming.  Also, the clutch side cover was installed, holding the shift shaft extended out of the case as far as possible.

Edited May 27, 2017 by pmk