71 Brake Drum to Cush Hub- Pin Fix

T95 · Nov 18, 2011

I noticed movement on two of the three my pins that are affixed to the brake drum and engage the cush hub. I hope this is clear enough otherwise I could provide a picture. I assume this to be a common problem because someone else pointed it out.

I am not sure how these pins are affixed into the drum and referencing Old Brits didn't help.

What I would like to know is can these be replaced or repaired? I would like to know the proper fix before I attempt to tack them with the mig welder.

Thanks, Gary

bwolfie · Nov 18, 2011

They are peened in, welding is the fix, see hobot's posts

Rohan · Nov 18, 2011

Since most brake drums are cast iron, the only possible safe repair for these is to braze them (with oxy torch and braze rod /brass and flux). Need to be good and hot to do this, so preheat extensively. Check for cracks before and after, in which case it is scrap.

Unless hobot has a way of welding in new pegs as a tight fit, without welding anything to the iron ?

Opethiselps.

P.S. The way you test what your brake drum is made of is to touch it with a grinder.
Cast iron will throw a dull red spark, steel will throw bright yellow sparks.
Steel can be welded about anyhow.
But genuine Norton drums were cast iron for many a year.
Thats why you sometimes see them with new teeth - always brazed on.

T95 · Nov 19, 2011

bwolfie said:
They are peened in, welding is the fix, see hobot's posts

Hobot, where are you? I can't locate the post.

Anyone know if these are available as replacement parts? They don't seem to be a part offered by Old Britts.

Carbonfibre · Nov 19, 2011

TIG brazing is the easy way to fix this problem............clean it up and take it along to someone with a TIG set who should be able to do the work in about 15 minutes! No pre-heat required, and ideal way of repairing most things made out of cast iron.

Torontonian · Nov 19, 2011

T95 what year is your Snorter ? Early model sprocket/drums are downright risky as the drive paddles get loose. Some were brazed, some rivetted, some welded into place as Norton searched for the best answer. Welded seems best I believe, have had a few go loose,nothing wrong with brazing but if teeth worn at all why bother just buy later 828 type new and feel good.

T95 · Nov 19, 2011

Rohan said:
Since most brake drums are cast iron, the only possible safe repair for these is to braze them (with oxy torch and braze rod /brass and flux). Need to be good and hot to do this, so preheat extensively. Check for cracks before and after, in which case it is scrap.

Unless hobot has a way of welding in new pegs as a tight fit, without welding anything to the iron ?

Thanks, I had no idea that they neede to be brazed. [/color]

Opethiselps.

P.S. The way you test what your brake drum is made of is to touch it with a grinder.
Cast iron will throw a dull red spark, steel will throw bright yellow sparks.
Steel can be welded about anyhow.
But genuine Norton drums were cast iron for many a year.
Thats why you sometimes see them with new teeth - always brazed on.[/quote}
Great info on testing metal![/color] ]

T95 · Nov 19, 2011

Torontonian said:
T95 what year is your Snorter ? Early model sprocket/drums are downright risky as the drive paddles get loose. Some were brazed, some rivetted, some welded into place as Norton searched for the best answer. Welded seems best I believe, have had a few go loose,nothing wrong with brazing but if teeth worn at all why bother just buy later 828 type new and feel good.

The bike is a 71, unknow on the hub! The teeth look to be good, but then I don't have a new one or a pattern to compare it with.
Anyone have a print out on the profile of the teeth that I might be able to compar with?

aceaceca · Nov 19, 2011

You are better to just take the wheel off and have a proper look. My 71 split right round the drive pegs and I do not abuse the thing save for the porky it carries. I had to get a new drum, so did so, but I cannot remember where I got it. I did notice the new one had some re enforcing welts cast into it in the crack prone location so yours may be breaking up as mine did. Like I say have a closer look and then probably replace it.

RennieK · Nov 19, 2011

T95 said:
The bike is a 71, unknow on the hub! The teeth look to be good, but then I don't have a new one or a pattern to compare it with.
Anyone have a print out on the profile of the teeth that I might be able to compar with?

The teeth wear from the pull of the chain so the back of the tooth when you are looking at it from the chain side of the bike. With the chain off, the slope should look the same on the front side of the tooth as it looks on the back side of the tooth. When worn, the back side has more slope to it. If it's worn you will need a new chain also.

Rohan · Nov 19, 2011

Carbonfibre said:
TIG brazing is the easy way to fix this problem............clean it up and take it along to someone with a TIG set who should be able to do the work in about 15 minutes! No pre-heat required, and ideal way of repairing most things made out of cast iron.

Don't know where you get your welding info from - and we've never seen anything you have welded - but came across this quote :-

"Welding cast iron using a tungsten inert gas (TIG) welder is possible, but will challenge even the most seasoned welder. "
Goes on to mention brittle brittle brittle....
i.e. Anything cast iron that has not been preheated will be extremely likely to go brittle, and crack.

Another quote about not preheating cast iron :-
Cast iron will obey the laws of physics, even if you don't know them
i.e. brittle brittle brittle

Cast iron is a bit prone to cracking anyway, even if it hasn't been welded.
Sounds like some owners here have met this, even with factory items.

bwolfie · Nov 19, 2011

I have TIG welded barrel fins several times. If you preheat with a torch, it all goes easily. And after the barrel falls on the floor you get to do it again

Rohan · Nov 19, 2011

You mention the operative word 'preheat'.
And fins don't have to have much strength to them to stay there.

If they had serious stress applied to them , thats when you find out how strong welded cast iron really is = 'snap'. ?

Cheers.

Cheesy · Nov 19, 2011

Rohan said:
You mention the operative word 'preheat'.
And fins don't have to have much strength to them to stay there.

If they had serious stress applied to them , thats when you find out how strong welded cast iron really is = 'snap'. ?

Cheers.

In our friend carbons favor here he did say bronze welded.... even so Im not sure I would be totally happy with the localised heat input from a tig, Oxy Acetylene would be a safer way of doing it. The preheat isnt actually so much preheat but significantly reducing the cooling rate so the FCC to BCC phase transformation happens at a similar time through the work piece.

Now for another method when I fixed a couple of fins on my cylinder I used mild steel for the replacement bits and used 316 filler wire (Tig and pre-post heat, well I let it cool down in a hot oven), as the 316 is austenitic (FCC) it doesnt go through the volume change that a BCC filler would so the stresses are less and the FCC structure is significantly more ductile. That said for the brake drum I would still braze it.

madass140 · Nov 19, 2011

I removed the 3 pins just to investigate, its virtually impossible to remove them with out destroying the drum, they appear to be screwed in and then riveted, they are made of hardened steel, the drum is cast iron, TIG welding wont work, really any welding or brazing wont be successful as you are only welding the end of the pin, it will soon crack, there is no successful fix,

Rohan · Nov 19, 2011

Cheesy said:
In our friend carbons favor here he did say bronze welded.....

No he didn't.
He said TIG brazed. With no preheat.

Brazing is NOT bronze, its brass.

And as that quote above says, cast iron goes brittle if its not preheated. And cooled out carefully.

Rohan · Nov 19, 2011

madass140 said:
I removed the 3 pins just to investigate, its virtually impossible to remove them with out destroying the drum, they appear to be screwed in and then riveted, they are made of hardened steel, the drum is cast iron, TIG welding wont work, really any welding or brazing wont be successful as you are only welding the end of the pin, it will soon crack, there is no successful fix,

Brazing, which is really only a hi-temp version of soldering could well work - the braze wicks into the gaps, and when solidifies should hold everything tight. Just make sure the pins are straight when this is done though.

Despite the misinformations here, cast iron needs to be about BRIGHT RED HOT when doing any brazing, you don't want local hot and cold pockets, the whole bloody thing needs to be good and hot. And cooled out slowly, no need to rush.

Hopethishelps.

T95 · Nov 19, 2011

Cheesy said:
Rohan said:

You mention the operative word 'preheat'.
And fins don't have to have much strength to them to stay there.

If they had serious stress applied to them , thats when you find out how strong welded cast iron really is = 'snap'. ?

Cheers.

Click to expand...

In our friend carbons favor here he did say bronze welded.... even so Im not sure I would be totally happy with the localised heat input from a tig, Oxy Acetylene would be a safer way of doing it. The preheat isnt actually so much preheat but significantly reducing the cooling rate so the FCC to BCC phase transformation happens at a similar time through the work piece.

Now for another method when I fixed a couple of fins on my cylinder I used mild steel for the replacement bits and used 316 filler wire (Tig and pre-post heat, well I let it cool down in a hot oven), as the 316 is austenitic (FCC) it doesnt go through the volume change that a BCC filler would so the stresses are less and the FCC structure is significantly more ductile.

That said for the brake drum I would still braze it.

Cheesy,
Your throwing aroud some terms that are new to me; FCC to BCC, austenitic. I'll do the research on the definitions. What questions should I be asking a welder to ensure he approaches it properly?

T95 · Nov 19, 2011

Rohan said:
madass140 said:

I removed the 3 pins just to investigate, its virtually impossible to remove them with out destroying the drum, they appear to be screwed in and then riveted, they are made of hardened steel, the drum is cast iron, TIG welding wont work, really any welding or brazing wont be successful as you are only welding the end of the pin, it will soon crack, there is no successful fix,

Click to expand...

Brazing, which is really only a hi-temp version of soldering could well work - the braze wicks into the gaps, and when solidifies should hold everything tight. Just make sure the pins are straight when this is done though.

Despite the misinformations here, cast iron needs to be about BRIGHT RED HOT when doing any brazing, you don't want local hot and cold pockets, the whole bloody thing needs to be good and hot. And cooled out slowly, no need to rush.

Hopethishelps.

Yes and it's certainly encouraging providing I can find someone confident to do the work !

Rohan · Nov 19, 2011

Thats called blinding you with science. And referring to the carbon phases in cast iron that give it its properties. Not important you know anything of them - as long as you get cast iron GOOD AND HOT before brazing, and allow it to cool down slowly.

I'd be a bit wary of this statement though

The preheat isnt actually so much preheat but significantly reducing the cooling rate

which suggests the science is not that understood !. Cast iron needs to be GOOD AND HOT - BEFORE its brazed, or it will locally crack around the area of the welds.

71 Brake Drum to Cush Hub- Pin Fix

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