Rear sprocket/drum (2013)

madass140 · May 4, 2013

Does anyone know exactly what they are made of ? I guess the Indian ones are cast iron but I machined a genuine one, one of the later ones with the 4 gussets and it machines like steel not like cast iron at all
?????

Hobot · May 4, 2013

I know it welds drills and machines and sparks like decent high carbon steel so definitely not cast iron. I did a grinder spark test a while back and compared it with the online charts but forgot which class of alloy that revealed but you could check your self if not definitive Id here.

http://www.google.com/#hl=en&gs_rn=12&g ... 39&bih=576

madass140 · May 4, 2013

Thanks Steve, thats interesting, I'll wait to see if any of our knowledgeable chaps here have any clues before I break out the grinder.

kommando · May 4, 2013

Could be cast steel which is lower carbon than cast iron, the grind test will only tell you the carbon content not the production type. I have a B40 crank with cast wheels but it grind tests as steel. I took a sample to work and they analysed it as low carbon too.

madass140 · May 4, 2013

yep, I'm fairly certain they are cast steel, if so the brake drums wear very well, maybe not so efficient though compared to cast iron.

kommando · May 4, 2013

I only have cush ones, maybe they went to cast steel when they introduced the cush as cast iron is not strong in shear.

madass140 · May 4, 2013

good thinking, if the later cush type were cast iron, the 3 pegs would probably just break out. obviously the reason they went to steel, now what grade of steel ???????

Hobot · May 4, 2013

I've a couple trashed rear Combat era drums to offer to test, but what's its matter as long as you know its pretty good steel to take the peg loads and resist teeth wear and what to use to weld or mill it.

kommando · May 4, 2013

ZDF will know but probably want to keep it secret

Doubt it will be exotic as if my guess on the cush drive being the reason for the change they just needed to add some tensile strength, so a standard cast steel grade but one selected to reduce teeth wear as well perhaps but more likely to have easy machinability.

http://en.wikipedia.org/wiki/Steel_casting

Quote Steel castings are used when cast irons cannot deliver enough strength or shock resistance

lcrken · May 4, 2013

madass140 said:
good thinking, if the later cush type were cast iron, the 3 pegs would probably just break out. obviously the reason they went to steel, now what grade of steel ???????

I think you're likely right. You'll notice that the 3 cush drive pegs are welded into the drum, not part of the casting. That would lead me to believe the drum is cast steel.

Ken

Hobot · May 4, 2013

Being Norton there may of been a number of ways to fasten the pegs but 5 of the Combat era ones I've dealt with were all staked or crimped in place, which with heat and time and loads eventually allowed all of these 5 drum pegs to twist so needed welding in place, but need to grind out or melt down below surface as brake shoe sweet past close enough to leave witness marks, ie: cant have any bead above surface to matter. Put question to other lists so may get it ID'd.

Rohan · May 4, 2013

I'm fairly sure I spark tested the drum on an early 850 as cast iron - the paddle type.

What comes out of the furnace in an iron foundry depends on what they put into it - maybe they had a lot of scrap steel the day they cast yours ?

Cast iron brakes better than steel...

madass140 · May 4, 2013

I've machined a few paddle types and they certainly dont machine like cast iron, or weld like cast iron, I'm convinced, especially the later ones if not all paddle types are cast steel.
a bit of Googling suggests this also.

Rohan · May 4, 2013

I'll spark test my spare drum, again.
Although maybe that doesn't tell the whole story.

They certainly had an assortment of a few problems with iron drums over the years, specially with the attachment pegs, so maybe going steel was seen as the answer to reliability.

madass140 · May 4, 2013

me thinks so

pete.v · May 4, 2013

I cannot say i have machined cast steel but have machined enough cast iron to fill a 1000 barrels of chip. I spit up black crap for a year after that nasty ass job. The smell is distictive and the feel obvious.

When cutting the teeth to accomodate an oring chain, it sure seemed and smelled like cast iron. I may be wrong for i only know half the story.

When googling the difference, it would seem the either would work for this application.

The spark test will surely tell. Dim orange for iron, brighter yellow for steel.

Madass, I hope you are doing what i think your.

pete.v · May 4, 2013

Madass140. I am excited to hear you enquire in regards to the rear brake hub. I can only hope that your intention are to improve the rear brake system. If this is so, I am sure you will be creating the ability to change rear gearing as well?

I don't think that it is all the far fetched to design and creat a rear disk brake mod for the early Commandos either.

Sorry for trying to pick your brain.......no, maybe i'm not.

Hobot · May 4, 2013

Jim Comstock just reported on mc-engine list that its cast steel, but not the alloy or how tempered.

madass140 · May 4, 2013

at least the later ones are definitely cast steel, no doubt as we discussed to be stronger in the cush drive pin area,
now about a new setup??? well its not really successfully possible for production to have a 42t bolt on sprocket on the 7" drum. its been done but only as a oneoff.
I believe a more satisfactory cush drive setup is more important than different sprocket sizes.
stay tuned.

DogT · May 4, 2013

I remember my BSA B33 had the 'cush drive' in the primary. It was like a single gear only rounded with a spring on it, so when you let off the clutch too fast, it would sort of let loose a bit. I guess it worked. Mine doesn't have any cush drive. And I guess I've got a cast iron hub?

Dave
69S

Rear sprocket/drum (2013)

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