Sorry if a stupid question, on a well known M20 sales site there is a wheel security bolt. Are these some sort of anti theft device?

Thanks

Danny

email (option): burt.danny@yahoo.co.uk

Hi Burt,

Could you share a photo of the particular bolt? The M20 didn't have any 'security item's' to prevent theft. But it had a bolt in the lower part of the front fork which fixated the front brake plate. This bolt with nut is important, without it it's not possible to use the front brake properly.

Regards,
Bastiaan

email (option): wdmotorcycles@gmail.com

The security bolt goes through the rim to prevent the tyre slipping into the rim well when the tube deflates.
They are not needed with modern tyres that run at 20 to 30 psi but were essential with period rubber that was running at less than 20 psi
You can ride a very long way on a flat tyre just so long as it stays on the rim.
Now days only found on trials & scrambles rims

Here is a post war Dunlop one on ebay.

https://www.ebay.co.uk/itm/324758780663?hash=item4b9d21baf7:g:fk0AAOSw27hhHj1B

There were some DME circulars about fitting them which we don't have unfortunatly.

Immediate action
B.40, 28/10/40 Fitting of security bolts to prevent damage to tyres, Norton M/C.
B.71, 3/2/41 " " " " " " ", BSA, Matchless, Ariel, R.Enfield M/Cs.
B.71/1, 31/5/41 Amendment to B.71,Delete BSA and Insert Indian Machines

General instructions
B.345, 11/5/43 Security bolt (Front wheel) All M/Cs

Norton Big4s used two on each wheel so they could run very low pressures off road.

Rob

email (option): robmiller11(a)yahoo.co.uk

['The security bolt goes through the rim to prevent the tyre slipping into the rim well when the tube deflates...']

I always believed tyre clamps were fitted to prevent the tyre turning on the rim and pulling the valve from the tube when running low pressures for increased off road grip....Thus their continued use on trials machines and generally, not road bikes these days...Ian

email (option): ian@wright52.plus.com

I knew I had one somewhere, red coloured rubber is probably correct for WW2, its marked

D.R.Co Ltd - Dunlop Rubber Company?

W.D. - War Department?

W.M.2 - rim width, correct for a Norton 16H but not a BSA M20 which used W.M.3 rims, I wonder if that's why BSAs weren't urgently given them at the same time as the other makes, the same 3.25 19 tyres being used on both widths of rim?

Rob

email (option): robmiller11(a)yahoo.co.uk

Thanks all for your time and help.

Rob,

Let me know if you want to part with that one or anyone that could help.

Thanks

Danny

email (option): burt.danny@yahoo.co.uk

Hi Danny, like I said its too narrow for an M20 and not in usable condition either, so I will hang onto it as a keepsake.

But if I get to Beaulieu next Saturday I will keep my eyes open for one for you.

Rob

email (option): robmiller11(a)yahoo.co.uk

I have a couple somewhere in the garage which I think came off a SWD Big 4 and the rubber element of the security bolt had been replaced with Khaki coloured canvas. All to do I guess with saving the use of rubber.

email (option): keithchandler@clistandchandler.co.uk

Thanks guys,

Rob,

If you do come across the right one for a M20 that would be brill. Very kind of you indeed!

As mentioned, not going to use it so condition is not a issue.

Thanks

Danny

email (option): burt.danny@yahoo.co.uk

There are quite a lot of modern type on Ebay. Of course with a metric bolt I expect. But I've sometimes fitted just a bolt through the rim as a dummy. Just ground the head down into a mushroom shape. Ron

https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=motorcycle+tyre+security+clamp+bolt&_sacat=0

email (option): ronpier@talk21.com

Not sue if we are talking about the same item.
I bought some modern security bolts to replace the ones in the B40
The B 40 ones clamped onto the actual case ( sort of ) pinching it between the rim & the sides of the bolt as made evident by rust & fretting on the inside of the tyre.
The new one s were way too narrow to touch the sides of the tyre but would stop it sliding off the lip & falling into the rim well .
Like others have mentioned, I fitted some bolts & ground the head smooth .
Without them the wheel was very hard to balance.

When I first got the WM20 I had no idea about correct tyre pressure for girder forked bikes so I used the recommened tyre pressures.
It was fitted with a ribbed front & K81 rear with security bolts.
Well I can confirm that the bolts do not stop the tyre rotating on the rib and ripping the valve out.
And I have the boots with holes in the soles from pushing the bike for very long distances to prove it .
Eventually I found with that combo anything under 20 PSI would cause the tyre to rotate probably made worse by my riding technique of heavy engine braking with light brake applications.

A You Tube search resulted in an explanation... 'How the rim locks work on your dirt bike/Fix your dirtbike.com'...
However, I'd like to find some Dunlop info. or something by another manufacturer to confirm...Ian

email (option): ian@wright52.plus.com

I made a fake one from a stainless bolt.
Looks great.

email (option): michasteinmann@gmail.com

Hi Danny
Sorry no luck at Beaulieu.
Rob

email (option): robmiller11(a)yahoo.co.uk