Clutch pushrod hardening.

[Beezageezauk]

Hi Guys,

I'm in the process of building up a swing arm A10 using a standard 6 spring clutch but unfortunately I can't get any adjustment because the pushrod appears to be too short by about 6mm.  The easiest way for me to overcome the problem is to cut the pushrod into two pieces and insert a 6mm ball bearing between them.

I realise that the ends of the pushrod that I cut will need hardening but I'm not sure how to do it.  Can anybody advise?

I have a contact where gas welding equipment is available so the heating is no problem.  All I need to know is what sort of temperature to heat it up to and do I quench it in oil or water, or do I let it cool naturally.

Cheers.

Beezageezauk.     

[trevinoz]

I make new ones out of 1/4 bright shafting and harden ends with Hardite which is a powder that you dip the ends in after heating to red hot. Alternatively you could get the ends tipped with Stellite.
Trev.

[groily]

In principle, to harden steels with normal range of carbon content (should include this rod), heat to 'clear red' / 'bright cherry' and cool fast. Very cold clean water is fine. The steel will now be hard and brittle. Don't leave it to cool gradually - you'll just have annealed it and it could be softer than when you started. Clear red means between 'dull red' and bright red/orange. Dull red, or less, won't do it properly, and anything from bright red/orange to white heat will destroy the grain, which becomes very coarse. To see the whole range of colours, it's worth using a bit of scrap to note the differences before attacking the thing that matters. Stuff like Trev's 'Hardite' is probably an easier row to hoe though.

Test for hardness when you've done it, with a file - if it's hard, the file won't bite.

A decent blowlamp - one of those 'turbo'  plumber's ones for example - will do a little job fine. So should a propane torch.

For this sort of thing it may not be necessary owing to the nature of the modest compression load it will take (others here will know), but I would also temper it - to remove the brittleness. To do that, clean the thing up till it's bright and shiny again, and then gently reheat until the colour of the metal goes to 'pale yellow' or, a tad hotter, 'light straw' (pale yellow is c. 430F or 220C) - then cool the piece the same as before. The hotter you reheat it, the more of the hardness is lost. If you reheat it to 'black', then all the hardness will have gone.

All sounds like alchemy, I know, but in fact the process is only the work of a few minute from start to finish.

The vintage reference source I use for a lot of this sort of basic stuff is 'Elements of Machine Work' a Classic Trade School Textbook by Robert H Smith, published by Massachusetts Institute of Technology as recently as 1910! It and a few other similar books are darn useful as well as interesting, and the info still holds good except in relation to some modern materials . For example, doesn't say much about hardening agents and the name 'Stellite' isn't even in the index! Groily

[Brian]

Groily your book may have reference to "case" hardening. I havent seen it for many years but it was a dark coloured powder that you dunked the red hot piece of metal in. I think it was basically carbon.
The way you describe to harden and temper steel is how I was taught and have always done it.
Interestingly a lot of articles you read say to cool in oil, one theory for this is that it draws the carbon from the oil to increase surface hardness. If this is correct would it make sense to use dirty [used] oil as this should have more carbon in it. Interesting stuff.                          Brian.

[fido]

Oil quenching is just used as a slower form of quenching, mainly for items which may otherwise distort through thermal shock. There would not be significant carburising in the few seconds it takes to quench. In the case of high speed steel tools you quench them in a bath of molten salt at about 500 degrees centigrade for similar reasons.

[groily]

Oh yes, Brian, plenty on case hardening, the temperatures, time to leave it, in bone meal or whatever 'try to get it from a gunsmith and don't use the stuff you can buy in garden supply shops because it's got something else in it' sort of thing! Never tried to do it, although would quite like a little electric muffler to try to make small parts, like shafts etc. But haven't got finish grinding facilities in my shed, so probably not worth it. And I'm not going to put a toolpost grinder on my little lathe and fill the ways up with grinding paste! Plenty also on oil quenching, but I've never tried that so didn't want to go there. All great stuff, and once you get the mystery out of it, pretty easy for anyone to do, at least to a sufficient level for our sort of things. Groily

[Beezageezauk]

Thanks very much Guys for your prompt and informative replies.  I know now what is required and the basics seem so easy.

FYI, this bike is being built on a budget from genuine BSA spare parts and has been an ongoing project for 15 years now.  There is still a little way to go but the challenge is to get it on the road in the next few months and do about 1000 miles on it before I load it up with camping gear, attend the BSAOC International Rally on the Isle of Man in August and ride it round the TT Course.

Why is it taking so long I hear you ask!!  Well, every time I get a complete bike to renovate, this one goes on the back burner. This gives me the time to obtain more genuine parts at the right price.  As I am sure you all know....a project like this can easily run away with the cash if a certain amount of care isn't taken.

Beezageezauk.