Thread size

[phil bsa b31]

Hi all can anyone tell me thread size of head bolts bsa b 31 1948 the thread in head please  thanks Phil

[iansoady]

No, but I find my thread gauge invaluable and suggest you get one.......

They may of course not be what it started out with. I have a horrible feeling the ES2 I  bought recently has metric allen screws securing the rocker cover to the head.........

[phil bsa b31]

If I had wanted a flippant reply I would have called you of course I have gauges just ordering bits thought it might be quicker but obviously to much effort for some people to be sivile still I can be proud of my curtesy and manners regarding the rest of the human race ,but hey YOU HAVE A NICE Day.   Phil

[Rex]

Hi all can anyone tell me thread size of head bolts bsa b 31 1948 the thread in head please  thanks Phil

Pretty sure they're 3/8 BSCY but as I'm not 100% you're still going to have to check..

[cardan]

Hi Phil,

It's worth pointing out that Ian has a long record of being extremely helpful, and always civil, both here and elsewhere.

In this case, he makes an excellent point. The question is not so much the thread size on a brand new B31, but the thread size on a particular 70-year-old B31. They could easily be two different things. Measure the threads on your bolts with a micrometer/vernier and a thread pitch gauge, and look up the corresponding thread (Radco's The Vintage Motorcyclist's Workshop has comprehensive tables). If it's bizarre or unexpected then it's worth asking on a forum, but otherwise...

Leon

[chaterlea25]

Hi All
Originally they were 3/8 x26 as suggested

(Goldie and the other alloy headed pre unit singles engines are 7/16 x 20)

John

[33d6]

I thought Ian's reply utterly sane and sensible. All this forum can do is state what thread the factory used when the engine was new. Who knows what has been done to it in the 60 odd years since? Only the person holding the part in their hand can do the necessary.   A range of measuring instruments are an essential part of any tool kit and they last a lifetime and more. I'm still using my grandfathers Imperial thread gauge.
Cheers,   

[iansoady]

Thanks for the support chaps!

[mini-me]

This is the problem with internet bike forums, it's too easy for the lazy to ask a simple question instead of looking in the manual.

Plus its a very good point that no-one else knows what bodgery your bike has put up with inthe past.

Getting the huff about a sharp answer also pisses me off, I, and expect many others are giving away free the knowledge of a lifetime. If I could diagnose a fault over the phone or internet I am damned if I'd ever log into a web forum again, because the money would roll in.

'ere mister my bike won't start wot is it?

[TGR90B]

Glad to see you're still snapping at a few heels. I thought you'd retired.

[mini-me]