Material for threaded insert in aluminium

[Andrew Phillips 4Participant @andrewphillips4]

I am replacing the 7 in SLS front brake backplate on my '54 AJS with one from a 180mm Honda 2LS brake. The AJS brake cable is adjusted using a 5/16 BSC male threaded adjuster, finger tightened, at the brake end, whereas the Honda brake is adjusted at the lever end. The Honda diecast backplate has a plain boss to take the cable end, large enough to take a threaded female insert to take the AJS adjuster. I intend to use engineering adhesive to secure the threaded insert in place as it is loaded in compression only and rests against a solid stop; I will make the adjuster from stainless steel. My question is what metal to make the threaded insert from (it will not be seen) – I have heard that a stainless/stainless pairing is not ideal, but this application is finger tight only. I have suitable brass and bronze bar – which metal should should I use? Thanks, Andy

[Andrew Phillips 4Participant @andrewphillips4]

[Robert Atkinson 2Participant @robertatkinson2]

I think you are bonding the bush into the deicast backplate. Assuming this is a aluminium alloy, brass or bronze is not a good idea. Even with adhesive bonding you are likely to get electrolytic corrosion. Stainless steel is better but not great. Best choice as a bush between light alloy and Stainless steel is carbon steel, preferably zinc plated.
How about a Helicoil or simlar thread repair insert?

Robert G8RPI.

[David George 1Participant @davidgeorge1]

Hi Andrew just use a piece of aluminium 6082 / HE30 alloy. No problem with corrosion and good strength. Loctite in place if nessesary.

David

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Robert Atkinson 2 on 30/12/2022 20:43:35:

[…]

How about a Helicoil or simlar thread repair insert?

.

Ideal, I would have thought … provided you use the right grade of Helicoil

I presume you are aware of the range, Robert … but, for the benefit of newcomers, this is a convenient reference:

**LINK**

https://www.bikerstoolbox.co.uk/acatalog/More_Info.html

MichaelG.

[Howard LewisParticipant @howardlewis46836]

DEFINITELY NOT brass or bronze, for fear of electrolytic action, especially where brakes are concerned..

As suggested, Aluminum., or stainless.

Howard

[MadMikeParticipant @madmike]

At the risk of stating the blindingly obvious……why not simply get a cable made by Venhill that replicates the Honda one at the brake plate end and with an adjuster at the brake lever. That would avoid all the concerns about dissimilar metals, stainless steel galling etc.

[HopperParticipant @hopper]

Then again, using stainless up against aluminium is not recommended practice either, due to galvanic corrosion. That is why stainless steel spokes when used with alloy rims come supplied with nickle plated brass nipples. Some say it's an old wives' tale but the rim and spoke manufacturers insist it is not. Not that it really matters for your application where you will never want to get the insert out again. It would work ok there. But stainless thread to stainless thread can gall and jam so I avoid it where possible.

I would use alloy 6061 etc or even just mild steel for your insert, make it top-hat shaped to ensure it cant slip out should the adhesive fail. And be sure to have the usual locknut/knurled collar in place on the adjuster as back up. It is what actually takes the load when done up even finger tight. (Bit like the top nut on double lock nuts that is endlessly debated!)

I have just been going through similar shenanigans making cables to fit a Norton Commando front brake into an Atlas front end. The later Commando uses UNF, the earlier Atlas CEI (cycle) thread. But the two models use different levers, one with adjuster, one sans. So cable lengths are all different too. Try buying a CEI threaded adjuster anywhere! And $80 plus international shipping for a cable from Venhill is not going to happen when I have a box full of useable cables and a lathe and a solder pot.

Edited By Hopper on 31/12/2022 02:41:59

[Lee RogersParticipant @leerogers95060]

I think David George has it right . 6082 T6 is as cheap as chips and well up to the job, the only reason to use expensive (in the UK) 6061 T6 is its availability in very thin walled tube and thin sheet.

[Robert Atkinson 2Participant @robertatkinson2]

Problem with an aluminium alloy insert is the you still have a stainless steel to alloy junction that will suffer from electrolytic corrosion. Carbon steel is between stainless and aluminium on the electrochemical series so will reduce the corrosion. Zinc plating it makes an even better match.

Robert.

[duncan webster 1Participant @duncanwebster1]

I suspect we are over thinking this, an old bike is liky to spend most of its time in a nice dry shed. However if electrolytic is an issue, is there room for a thin wall top hat delrin bush twixt a stainless adjuster and the ally backplate? Stainless on stainless can be an issue with galling, but I've never had an issue with stainless nuts and bolts, which have much higher loading

[Nigel Graham 2Participant @nigelgraham2]

Stainless-steel is not a safe contact companion for aluminium-alloy in potentially corrosive situations.

Depending perhaps on their respective alloys, the electrolysis destroys the aluminium, leaving the guilty steel remaining all innocently bright and shiny.

Stainless-steel fastenings can gall, but this is normally obviated by using different grades, anti-seize grease and avoiding over-tightening.

(This is something I have wondered with miniature-railways using aluminium rails and stainless-steel fishplate fastenings, in locations even more likely to encourage corrosion as garden debris drifts against the rails.)

[martin haysomParticipant @martinhaysom48469]

i am with Duncan on this one way too much thinking about things that might/could happen but its very unlikely.

[SamsarandaParticipant @samsaranda]

If you need to use two different materials in contact on your brake conversion then use a jointing medium such as Duralac it will protect against reaction between stainless and aluminium, it works on aircraft there could be no better recommendation. Dave W

[george baker 1Participant @georgebaker1]

Hi

Could you have 2 cables?

Honda brake one end into an inline adjuster,

AND

AJ brake lever to the inline adjuster

George

[Andrew Phillips 4Participant @andrewphillips4]

Hi All, thank you for your suggestions. I have decided to go for an aluminium insert, and I have an offcut of 7075 which should be plenty strong enough. I appreciate the potential for corrosion with stainless, but the bike is garaged and regularly maintained. I have used stainless studs in the aluminium crankcase with no problems. Cheers, Andy

[HopperParticipant @hopper]

A bit of anti-seize on there and it should be ok.

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