Author Topic: Radiused head bolts  (Read 756 times)

Offline lawnmowerman

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Radiused head bolts
« on: 11.11. 2010 18:11 »
I have been fitting a craven rack to my SR which involved using some 4mm bar to make brackets to fit to the shock top mounts and oiltank/toolbox mounts. Also to the rear guard brackets. This has meant that the existing fixing bolts are now too short for comfort.
The existing bolts have a radiused head - not sure if this is standard but they look quite nice so I would like to replace them with the same. Also the PO has fitted the front guard with standard bolts so I would like to change them too to the more attracive radiused head type.
I have been searching the net for a supplier in the UK and all I can find is "reduced head" bolts in stainless which come with a warning that the bolt strength may be reduced. There was also a warning that unless lubed on assembly the heat produced tightening the nuts can cause the nut to "weld" itself to the bolt due to a chemical reaction caused by the heat and the only way to remove it is to cut it off.
I would welcome any advice and infomation on a good UK bolt supplier and whether to go high tensile or stainless.
Many thanks
1959 A10 SR
1938 Wolseley 14/60
1955 Ferguson TEF20 tractor
1965 Ferguson 135 tractor
1952 Matchless G80 rigid
1960 BMW R60
1954 Matchless G80S
1955 Ariel 500 VH
1951 Sunbeam S7DL
1960 Matchless G12 with Watsonian Monza
......and loads of lawnmowers

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Online BSA_54A10

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Re: Radiused head bolts
« Reply #1 on: 11.11. 2010 21:41 »
Stainless is fine for body work.
Gauling is a problem with stainless fasteners.
It is the same process as gauling of the throttle slides in concentrics.
Most metals will do it , just some do it better than others.
I always lubricate all nuts & bolts and in particular spark plugs.
It is easier to retighten or replace a fastener than it is to drill out a broken one.
Stainless bolts will work best with the nickel ant sieze paste.
it is not cheap but you only need a tiny and I mean tiny amount.
If you are using standard spanners then breakage due to over tightening is fairly rare but if you are using rattle guns or electric drills to tighten then expect some breakages unless you wind the torque right down.
Bike Beesa

Offline Brian

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Re: Radiused head bolts
« Reply #2 on: 11.11. 2010 23:53 »
I use stainless extensively on my bikes and have done for some time now. Its excellent stuff and has a lot of advantages but as Trevor has pointed out it also has some drawbacks, the main one being "galling" or picking up, this is when the nut "welds" itself to the bolt.

There are a couple of things you can do when using stainless and the main one once again as Trevor has pointed out is to use a anti-sieze compound. When using stainless you must use one of these compounds, not should, must.

Another thing you can do if you have a situation where you may have a internal thread on something and you are going to screw a shaft into that is to use different grades of stainless, for instance make the collar out of 304 and the shaft out of 316.

I use mainly 316 as it is a lot higher tensile than other grades, nearly impossible to strip the thread on a 316 bolt. It doesnt rust and when polished looks almost like chrome, its a excellent replacement where nickel plating was used. It is also available in hex bar in witworth sizes so your 1/4''/5/16"/3/8" etc spanners fit correctly. The drawbacks are its very hard on your machine tooling. I make most of my stuff on a lathe and use tip type tools but if you use taps and dies then it will blunt them very quickly. It can also be hard to indentify what grade you have, the industry uses a colour coding to identify the grades but unfortunately different companies use different colours so you can never be 100% sure what grade you have until you start machining it.