Stripped engine sprocket nut

[RichDesmond]

I picked up a thread gauge at Lowes. The thread pitch is 1.5. I measured the inside diameter of the new nut and got 18.5 mm. I assume that means 18 mm nominal bolt size.

Also was wondering if the thread file or a die would be the better choice? Currently I have neither in my tools.

Thread file, unless the threads are in really bad shape.

[bwringer]

McMaster-Carr sells some nice metric thread files for not much dough. They include several thread pitches.

https://www.mcmaster.com/#8309a11

However, it's going to be tough to reach the countershaft with this style of thread file since the swingarm is in the way.

This style thread file might make it easier or possible -- it's basically sort of a "knife" shape that works to clean up any thread.

https://www.mcmaster.com/#2617a12

Metric threads are 60 degrees, so you could also clean them up with a small triangle file if you're careful and patient.



You could reach the threads easily with an internal thread file, but I don't know how effective you could be. And it's a good bit more expensive.

https://www.mcmaster.com/#2542a42

[goggles]

Thanks for the reply. Been trying to get back to it. Too many interruptions .

I hope to post a picture of the threads tomorrow. I am losing the light and the flash tends to affect the clarity.

[goggles]

Here is a picture of the threads.

PICT0291.jpg

[hillsy]

Hard to tell from the pic.

If it was me I'd grab one of these for your drill and clean it up to assess how bad it is:

[bwringer]

Yoicks, that's definitely some boogerage. (sorry to throw these fancy technical terms at you...)

Those flattened tops are problematic. Still, it might be salvageable with some patience. You may be able to clean it up to the point a new nut will thread on, but strength is unknown.

Start by cleaning off the rust and old thread lock with a wire brush and see what you've got. You don't need a lot of torque on the nut, but you do need to be VERY sure it can't come off. So perhaps somewhat lower torque and some good high strength red thread locker would be enough. It's very hard to say from here.


I really, REALLY hate to even mention this, but... one way to "salvage" such situations is a few spot welds between the shaft and the sprocket or nut. (Use very short bursts and let the welds cool between so you don't build up a lot of heat in the shaft and nuke the seal.) You can get away grinding off the welds and re-welding a few times, and since a major brand modern x-ring chain and quality sprockets (not the no-name Chinese "Volar" or "El Chaino" crap from fleaBay) will easily last 30,000 - 40,000 miles on a 550 with a little care, you can defer the "real" solution far into the future. If you end up with this plan, replace the countershaft and clutch shaft seals beforehand so you don't have to start over if and when they wear out start leaking later on.

Or some combination of the above... if you can get a little torque on the nut, but not full torque, then a couple of easily-removed spot welds could be a reasonable bit of insurance.

[goggles]

Too summarize the situation:

Shortly after I bought the bike, about 7 or 8 years ago, the nut and sprocket fell off as I was turning into a parking lot. At that time I replaced the sprockets and chain. I used an oem nut and am fairly sure that I purchased and bent the locking washer to lock the new nut in place.

Recently, I was very surprised to find the nut laying inside the cover, the locking washer missing but the sprocket still in place when I pulled the cover while removing the non o ring chain to clean and check it.

So I have purchased a new o ring chain and both sprockets. Peace of mind is worth the price. I appreciate the reminder that you can be too particular and forget the age of the bike. (I have been guilty of that).

I like this forum because you get a good range of information and opinion to sort through.

The obstacle is to figure out if the threads on the shaft, which have "suffered boogerage" (I love technical terms ), can be repaired well enough to be strong enough to safely hold the sprocket in place.

So far the options seem to be try to repair by
1. filing and see whether the nut will then torque enough to hold. (using the locking washer and loctite)
2. getting the nut to fit and spot weld
3. replace the spline that nut fits on which means a whole lot of work.

Appreciate all the replies.

[Cipher]

I once had a sprocket nut back off. It was held onto the shaft by the foam on the inside of the sprocket cover.
This allowed the output shaft to spin inside the nut damaging the threads but happily not allowing the sprocket to fall off with a resulting catastrophe.

I cleaned up the threads which were in somewhat better shape then yours and put on a new nut. Been changed twice at least now no looseness or backing off. I used loctite to be on the safe side.

[goggles]

I finally got the time to use a thread file on the shaft. I have the threads repaired enough to get the nut all the way on by hand.

I saw online that some recommend following the thread file up with a rethreading die. Anyone have any experience with doing that/

[RichDesmond]

If a nut spins on by hand the die isn't going to much more than you've already done. I'll declare victory and call it good.

[goggles]

Ok, thanks for the input. Hope to get it back together this weekend. The sprocket issue lead to swing arm check and the need to replace the bearings. Also decided to replace front hoses while it is torn apart.