WM3 Rim Lock on WM2 Rear Wheel.

Stephen Hill said:

I have encountered other designs which call for a locknut BETWEEN the tube and the rim, which always struck me as weird.

Click to expand...

Most of the tubes I've installed come with two nuts and those with instructions specify a nut inside and one outside. I suspect that many people ignore than and put both on the outside.

There are lots of dirt bike riders on forums who leave a gap and put both nuts on the outside "to be able to tell if the tire has slipped".

Not only dirt riders. Done it for 60 years. Thought it was common knowledge.

Mike40M said:

Not only dirt riders. Done it for 60 years. Thought it was common knowledge.

Click to expand...

To me, at least on Norton Commandos and Triumph road bikes, common knowledge would be what the workshop manuals say and the way the bikes came from the factory - one knurled nut tight against the rim.

I have always used metal valve caps and used one of the supplied nuts as a jam nut against the valve cap. That keeps both in place and one can quickly see if a tire has slipped on the rim. I have only had that sort of creep on dirt bikes with low pressure. Those also had rim locks and they still creep mainly on the rear. A 500 matchless in low gear applies significant torque. With knobbies they'll slip but likely you'll notice between the heat races and the main event and have time to correct it.

I actually hadn't thought about rim locks preventing a disaster from a flat on a road bike. I've had that happen twice that I can remember but the tire stayed on the rim and because I have the nuts jammed against the valve cap the stem pulled out of place but did not tear the tube and I was able to patch it on the road. Once was on my Atlas and one was on my BMW. Both of them had factory tire pumps. Commandos, no.

marshg246 said:

To me, at least on Norton Commandos and Triumph road bikes, common knowledge would be what the workshop manuals say and the way the bikes came from the factory - one knurled nut tight against the rim.

Click to expand...

I agree with your logic Greg. My very original '76 MK III came with one hex nut tightened to the rim with a metal washer and black rubber washer beneath that. It would serve to keep rain water out of the wheel...

Also, I found this on the web to add a little more information:

Edfury828 said:

I agree with your logic Greg. My very original '76 MK III came with one hex nut tightened to the rim with a metal washer and black rubber washer beneath that. It would serve to keep rain water out of the wheel...

Also, I found this on the web to add a little more information:

Correct way to install valve stem nuts

www.klrforum.com

Click to expand...

I forgot to add, ... but I like the double nut above the rim method. I'm now seeing that thread shows it is subjective, lol! My apologies for any disruption of our respected forum

Someone may have said this, but . . . . to be clear . . .

The rim lock is supposed to go INTO the tire, past the two inside edges of the tire. I should even present a risk of pinching the tube if part of the tube gets pinched between the lock when it is tightened down against the tire.

That way, the rim lock when you tighten it's nut, pulls the tire down and clamps it tight to the rim.

That's why it is called a "rim lock" and that is how it prevents a low pressure tire (as is preferred in dirt riding) from spinning on the rim and causing the inner tube's valve to get ripped by that slipping/spinning.

xbacksideslider said:

Someone may have said this, but . . . . to be clear . . .

The rim lock is supposed to go INTO the tire, past the two inside edges of the tire. I should even present a risk of pinching the tube if part of the tube gets pinched between the lock when it is tightened down against the tire.

That way, the rim lock when you tighten it's nut, pulls the tire down and clamps it tight to the rim.

That's why it is called a "rim lock" and that is how it prevents a low pressure tire (as is preferred in dirt riding) from spinning on the rim and causing the inner tube's valve to get ripped by that slipping/spinning.

Click to expand...

And the strange thing was when I put the WM3 rim lock back in the WM2 wheel with tube and tire, it flopped around loosely.

I had never done one before, so I was trying to understand, and I thought it would be catching the bead of the tire or doing something, but it did not. Next I inflated the tube and it was pressed firmly in place. The tire also mounted up perfectly normally.

I hadn't yet verified that my wheel was a WM3 as the lock said it was for. Being suspicious of something not right, I measured the outside of wheel and determined it to be a WM2. Still, I wonder about the fit even with the rim lock being wrong. My new WM2 rim lock should arrive today. I'll see how that one fits on my WM2 rim. I would think it should fit as you say?

I believe my rim to be original from '76. The tires had manufacturing dates of 2002. The inside of rear rim and bottom of rim lock were painted with a dark red paint, probably rust inhibitor maybe done when the 2002 tires were installed?

The tubes should've been changed then too. They did have one hex head nut with metal washer and rubber grommet tightened to the wheel. My speculation is that the original tube had the knurled valve stem nut as Greg mentioned, indicating replacement tubes with new 12 mm hex nut, combined with original metal washer and grommet on valve stem. That being said, where did the WM3 rim lock come from, why was it in there, and why did it not grab the tire bead?

I will post when I can compare the the old with the new rim locks and possibly conclude this gripping endeavor!

Edfury828 said:

I believe my rim to be original from '76.

Click to expand...

What's the MC number (assuming it has one)?

L.A.B. said:

What's the MC number (assuming it has one)?

Click to expand...

Do you mean this?

Edfury828 said:

Do you mean this?

Click to expand...

No, the number on the rim.

I'll watch for that when I switch locks, maybe tonight. Is it always in a certain location? With the inside painted dark red it may be hard to see.

It should be on the outside near one of the valve/rim lock holes.
A Mk3 rear rim I would expect to be stamped MC 287 or MC 289. Probably on the disc side.

L.A.B. said:

It should be on the outside near one of the valve/rim lock holes.
A Mk3 rear rim I would expect to be stamped MC 287 or MC 289. Probably on the disc side.

Click to expand...

Looks like a poorly stamped MC289! I didn't see anything on the front wheel.

Edfury828 said:

I didn't see anything on the front wheel.

Click to expand...

I would expect the Mk3 front to be stamped either MC 275 or MC 288 if original Dunlop.

It looks like this rim has been re-chromed, in which case stampings are often obscured or very faint.

lazyeye6 said:

It looks like this rim has been re-chromed, in which case stampings are often obscured or very faint.

Click to expand...

Yes, after finding no markings on the front wheel, I contacted the PO, not that it's a big deal, but just curious to know. He said he'd had both rims re-chromed. He asked the shop to "reverse chrome" the wheels in order to keep the original markings. When he got them back, they had not done them that way. Still, I think the chrome did come out nice...

He also said the rim lock was the same one in there since he got the bike about 30 years ago, from the original owner.

Upon breaking loose the bead on the wheel today, I found that the old WM3 rim lock was indeed holding down the bead of the tire to the WM2 rim just fine. I also concluded that the difference in a WM3 rim and a WM2 is 0.30" or 0.15" per side, and the new rim lock had about 1/4" or 0.25" of soft rubber on each side so the difference in size should just squish in. I could see no deformation of the sidewall, and I think the rim lock only contacts the tire at the bead anyway... at least that's my speculation.

Conclusion; that rim lock has been working fine in that wheel for at least a few decades, maybe longer, it should continue to be fine.

I put the wheel back together and spent the rest of my day finishing my new Girling disc installation, including relieving the calipers for bobbin clearance!

EdFury828 - it's not clear to me that you have the tire sandwiched BETWEEN the rim lock and the rim. The rim lock CLAMPS the tire to the rim.

Apologies If this is my misunderstanding.

xbacksideslider said:

EdFury828 - it's not clear to me that you have the tire sandwiched BETWEEN the rim lock and the rim. The rim lock CLAMPS the tire to the rim.

Apologies If this is my misunderstanding.

Click to expand...

I do believe all is well with the rim lock. Once I had the wheel back on the bench and had separated the bead of the tire from the rim everywhere except at the rim lock, I found that the rim lock is locking the tire bead to the rim very well. At that point I decided to leave that rim lock in place for now.

Next time I have the tire off, I will may switch to correct the WM2 1.85" lock. For now, the WM3 lock which has been in my WM2 wheel for decades should suffice.