• Welcome to the website of the Vincent H.R.D. Owners Club.

    Should you have any questions relating to the Vincent H.R.D. Owners Club, or Vincent H.R.D. motorcycles in general, please contact Graham Smith, Hon. Editor and Webmaster by calling 07977 001 025 or please CLICK HERE.

    You are unrecognised, and therefore, only have VERY restricted access to the many features of this website.

    If you have previously registered to use this forum, you should log in now. CLICK HERE.

    If you have never registered to use this website before, please CLICK HERE.

H: Hubs, Wheels and Tyres Brake drum skimming

overdale

Website User
VOC Member
Having got the wheels rebuilt for my 1951 Black Shadow, I'm now preparing to fit the drums. However closer inspection of the drums shows some areas of corrosion an the braking faces (previously hidden by masking tape) as I think the bike stood outside for some time before I bought it in 1971.
Set up in my lathe jig, the run out on the undamaged faces of the drums are all less than 0.1mm but the rough areas of corrosion need to be removed. They are the standard ribbed cast iron drums and I'm all set up to skim them, but would like to know what is the maximum diameter I can safely take them out to.
 

Magnetoman

Well Known and Active Website User
VOC Member
When set up in the lathe we simulate how things are with the brake applied. This is not necessarily exactly the same as when the whole assembly is installed and working on the bike, particularly with the brake plate.
The problem with your line of reasoning is illustrated by the following diagram where for clarity I've exaggerated the combined effects of new linings that aren't quite the same thickness as each other, shoes manufactured with pivot points that are slightly different, and pivot pins in the brake plate that weren't made by the factory perfectly concentric with the axis of rotation.

Brake_issues.jpg

Although the result of any or all of the above would result in the brake plate not being concentric with the brake drum, shown by the offset 'x's, it can be seen that the shoes still would make 100% contact if bedded using the emery paper approach. Unfortunately, this would make for a terrible brake when installed on the bike because at that point the two axes shown in the diagram would be forced to be the same. In contrast, none of these production tolerance effects would matter if the shoes were arced to size on a lathe.
 

Magnetoman

Well Known and Active Website User
VOC Member
it seems to me that the emery cloth/paper solution is at least one way for us to try improving our brakes, all be it that it will be a slow process.
A slow process indeed. If half the circumference of an 8"-dia. × 2" brake drum needed to have just 0.001" removed from it to make the drum round, that's 0.025 cu.in. of material. That may not sound like much, but it's the same amount of material as in a ⅛" length of ½"-diameter rod. Imagine how long it would take to remove that much material from a ½" steel rod by rubbing it back and forth on a piece of emery paper. That's how long it would take to make the drum round by manually removing "only" 0.001" from half of it with emery paper. Compare that with how long it would take to remove the same amount of metal in a lathe.

This is why motorcyclists who work on their own bikes, but who don't have a lathe, should do their best to become best of friends with someone who does.

I've been lucky (or prescient, or foolish, or ...) in obsessively accumulating tools, machinery and machining skills specifically for my motorcycle interests throughout my totally-unrelated career. As a result, this has reduced the number of times I have to rely on "Argentine engineering" to keep my bikes running. JB Weld, sheet metal screws, duct tape, etc. can work sufficiently well in some situations but, although emery paper might improve brakes in some cases, it only will accelerate the onset of arthritis and elbow-replacement surgery in others.
 

Monkeypants

Well Known and Active Website User
VOC Member
I spent about an hour to go from a severely pulsating brake to a smooth very strong brake.
An hour isn't much on an old motorcycle.
It takes quite awhile to set things up in the lathe by the time both procedures are done.
I doubt that I could have completed the work with the lathe in one hour.
Then when you consider removing and replacing the tire as required for the lathe...the emery method was much faster on that drum.
The analogy of rubbing emery back and forth on a rod doesn't fit.
With the brake linings you have mechanical advantage and a large abrasive area.

Glen
 

Martyn Goodwin

Well Known and Active Website User
VOC Member

davidd

Well Known and Active Website User
VOC Member
It was 2017 where we covered this:


Many old drums can be skimmed to remove the inner and outer ridges. Sanding to finish.

DSCN4152.jpg

David
 

Martyn Goodwin

Well Known and Active Website User
VOC Member
It was 2017 where we covered this:


Many old drums can be skimmed to remove the inner and outer ridges. Sanding to finish.

View attachment 42005

David
what's old is new again!
 

fogrider

Active Website User
VOC Member
The photo shown at 47 above reminded me of the way I checked then trued my touring twin drums : Before I fitted the rim and spokes, I put the assembled hub, drums and spoke flanges in the lathe and skimmed the whole assembly true, running on its' own bearings which were set to nil play. A slight slackening of the drum bolts let me fit the spokes, nip back up and Bob's your uncle as the bolts are a zero fit.
Regards all, Terry.
 

Can't Find What You Need?

Buyer Beware: Fake or Real?

The Mighty Garage Videos

List of Forum Categories

Top