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Discussion Starter #1 (Edited)
At 11,500 miles, I decided to change the fluid in the rear end. I also noticed some leaks. Well, the leaks are due to the drain threads being stripped and an aftermarket bolt being shoved in place! It looks like some sort of self-tapping bolt.

Do I try to re-tap the threads and go up another size? Or do I swap rear ends with my other bike?


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Is it leaking because of that rubber washer? Is that another flat washer under the rubber? If it is, I would change that arrangement.

Will the self tapper still thread into the case?

Swapping is always an option.
 

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Discussion Starter #3
I think the self-tapping bolt is still too small, and isn't able to tighten. It was definitely not tight when I removed it.

I thought about swapping the rubber washer. It wasn't coming off easier. I might try again tomorrow.
 

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That doesnt look like a self tapper, but more like someone was trying to make the threads fit tighter during a kludge situation. Some vibration resistant nuts use similar deformation techniques. I'd check the internal threads for damage and use a new bolt if possible, otherwise swap rears.
 

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You might be able to use the next size self tapping drain plug, depends on the size.

Could also probably tap it for pipe threads and use a pipe plug, again depending on the size of the hole now.
 

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Although a pipe thread will seal very well, care must be taken when tightening because a pipe plug is tapered (wedge shaped) and over tightening can crack the casting.
 

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Discussion Starter #7
The threads won't hold the new bolt either.

I have a tap set, and I am going to try to tap it as an M10 x 1.25. The hole is a touch small for that, but too big for a M8, so I am going to drill it out to the recommended hole size (8.9mm or 0.350". 11/32 is 0.343 if I can't find the exact bit).

I'll flush it with oil to remove the shavings and try it out with an M10 x1.25 bolt. Can I use a copper washer instead of aluminum? Not sure if the local shop has aluminum washers. Otherwise, I will dril out the aluminum washer and reuse it.

Worst case, I'll swap rear ends, but would be a shame to dispose of this one over stripped threads!
 

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Coating the drill bit and tap with grease will help grab some of the metal chips.
 

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The copper washer will probably work, but the aluminum one is easy to drill.
 

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Discussion Starter #10
One trip to the hardware store and one beer. I bought a M10x20 1.25 bolt, a 8.7mm-11/32 drill bit, a M10 copper crush washer and 2 qts of 80W90 gear oil. Bolt length is important. Shorter would work, but I bet a 25mm bolt would bottom out.

I drilled the hole out and tapped it to 10 1.25. I flushed the case with 1qt of oil. I didn't see any chips after 1/2 qt. Put the bolt and washer in, and filled it up. I'm going to change it again after about 200 miles or so, just to make sure.

At least any chips remaining are aluminum, so it's less likely to damage the steel gears.

There's just enough clearance to drill and tap to M10. I think M12 would cut into the case wall somewhat.

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Good save, and you still have the spare gearcase.

Gas, diesel, or kerosene would flush it pretty well. Could even hit with the garden hose without hurting it.
 
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