Morris Minor Owners Club

Does anyone know the size of the thread in the chassis leg for the bolts holding the cover plate retaining the poly bush part of the clutch relay shaft? I have the bolts for the gearbox side, but don't have any for the chassis side and can't find them listed on suppliers sites. Any help much appreciated.

Since they are chassis bolts - I'm guessing at whitworth thread - probably around 5/16" or 3/8".

Try a 1/4 Whit and a 1/2 A/F spanner on the top radiator mounting bolt (because it is easy to get to). Whichever spanner is the best fit remove the bolt and try it in the chassis hole. If it fits using the whit. spanner then the thread is 1/4 BSF. If If it fits using the A/F spanner then it is 5/16 unf.
If that confuses you look through Spanner Sizes

1/4" UNF, 7/16" AF spanner.

Oh well - wrong again!! Most of the chassis stuff is BSF or Whit - this must b the exception.

Unless they were changed later, the bolts in the chassis are 1/4 Whitworth, 1/4-26 as I recall. The bolts into the gearbox are 1/4 UNF, 1/4-28. The heads are roughly the same size, however, a 3/16 Whitworth spanner is slightly bigger.
The general rule I found at least through Series III production is anything designed prior to BMC is Whitworth and anything from Austin is UNF. Was the relay shaft located in the same spot for MMs? With these bolts so similar, it would make sense to change them.

Well = that's what I thought too!

jaekl wrote:Unless they were changed later, the bolts in the chassis are 1/4 Whitworth, 1/4-26 as I recall. .

Come on chaps, let's have a bit more rigour over this Whitworth/BSF lark.

1/4" Whitworth is 20tpi, 1/4"BSF is 26tpi. The spanner size is 0.445" A/F, and may be marked 3/16 Whit.

5/16" Whitworth is 18tpi, 5/16"BSF is 22tpi. Spanner size 0.525" A/F, may be marked 1/4 Whit.

The other easy way to distinguish UNC/UNF from BSW/BSF is head thickness of bolts and setscrews: UN are noticeably thinner. Other ways include some UN bolt heads having circular markings, and some UN nuts having several circles on one of the flats.

If you can't see a perfection of proportion in a 5/16 BSF bolt, you really shouldn't be allowed to work on old cars,

Kevin

well kevin we are not all engineers

but we all like to work on our cars so why do you say we should not be if we do not know threads

[quote="aupickup" we all like to work on our cars so why do you say we should not be if we do not know threads[/quote]

Oh, don't be so sensitive. Of course, not everyone is up to speed on old thread types, which is why I tried to help people to distinguish between them.

I suppose I should have put some sort of smiley after my throwaway line about the perfection of BSF, but the serious point is that we can all cultivate an appreciation of good engineering design, whether we're chartered engineers (I'm not), mechanics, (nor one of those), or just interested (I am). You don't have to be able to recite tpi tables to see proportion and "rightness".

Kevin

we are all indeed grateful for any advice given to give us a more understanding of threads etc

it was your throw away line that could indeed belittle the newbie to morris minors

Hey, I was pretty close for a Yank. I was tempted to call it BSF but I thought they were only for the smaller threads. Don't forget to flip the 3/16 Whitworth spanner over and it will be 1/4 BA (is BA the right term), some of mine are marked that way.
What's with the 55° profile? Do both Whitworth and BSF have it. Over here the common thread are 1/4-20 and 1/4-28 but with a 60° profile. Are there any Whitworth threads on a Minor? I sure wouldn't want to mix the 55 and 60° profile nuts and bolts in the same bin.

Yes - Whitworth and UNC are to all intents and purposes the same tpi in most sizes - just the 55/60 thread form difference - and they are pretty well interchangeable, it's not that important - unless you are a Perfectionist of course!

Can't decide if this question has been answered or not. The bolts in question are 1/4 BSF!

it's not that important - unless you are a Perfectionist of course!

Or just like things right!

Oh my goodness I don't call them anything - I just keep picking them up till I find one that fits ....... if that fails I get the adjustable out