Help with bolt size please.

[s2c-08589]

Hello.

I'm hoping someone might be able to help me.

I have a L.R 109 2A 1962

I removed the front diff pinion seal and paper gasket from the housing and wondered if someone might know the thread size of the 6 bolts that hold the housing?

Spanner size is 7/16 but trying to find out thread size and pitch.

I attach a photo.

Thanks to anyone who might know. I have searched high and low online without luck. My caliper says 7.7mm or 0.3 inch

[Craig T]

As the diffs really didn't change from the series one days, they are likely to be a BSF thread.

Looking at the thread, most likely 5/16 BSF. The head size should be a BSF spanner as well. 0.525" is the Across flats measurement for 5/16" BSF fastenings but if you used a 7/16" AF spanner, they might be a special bolts with the next size down BS spanner which is 1/4" BSF with 0.445 AF head size. 7/16" is 0.4375" so maybe a 7/16" spanner was bit of a tight fit?

If my diffs were still in pieces, I'd have measured the threads for you but unfortunately they are all locked into place now.

Craig.

[autorover1]

Agree, probably 5/16 BSF as its a carry over from S1  - 22tpi ( Pitch 0.0454"). Parts book lists it as special as it has a slot & possibly cross hole for wiring

[Craig T]

Just looked in the series one manual and they do list them as a special bolt. I think they have an unusually small head size to clear the seal housing and they have a slot cut across them.
Part number is 237544. John Craddocks say to use 571916 but they are no longer available from them.

Blanchards have them in stock apparently.
https://pablanchard.co.uk/Bolt-571916?search=571916

Craig.

[s2c-08589]

Hi Everyone.

Sorry for the delay in reply and thanks very much for your replies.

I have news:

I ordered a couple of bolts and tried them out.

I found the 5/16 is almost correct and does fit and tighten up nicely. I say almost because I had to work the bolt in and out a few times as was a fraction tight on the thread.

I'm not at all good with imperial sizes etc as way before my time but I think this may be because the bolts I ordered were UNF and I think the original bolts were BSF - maybe someone knows?

I found this online which mentions bsp thread. I don't know if this is the same? -
 
What is the difference between BSP and UNF?

BSP threads are British standard pipe threads. The profile angle of BSP threads is 55 degrees. UNF are unified fine threads of American standard. Their thread profile angle is 60 degrees.

Anyway, I add a photo and have achieved what I set out to do which was change the hard to access original bolts to allen key heads which, in my opinion, are lovely and far easier to access and torque properly.

If you're fiddling with your axle, I would recommend this small mod/upgrade. Perhaps try running a UNF thread tap before putting the bolts in.

[autorover1]

BSP is a whitworth form Pipe thread . The Pipe threads are designated by the bore of the pipe not its outside dia  . So a 1/4" BSP has an outside dia of 0.518" .
A 5/16" UNF thread has 24 threads per inch and a 5/16" BSF has 22 threads per inch . So don't mix them up as well as the thread flank angles don't match, unified be 60 degrees and  British Standard fine 55 degrees .   If you run a tap down with the wrong pitch and flank angle it just weakens it.

[GlenAnderson]

If they are BSF, then socket head cap screws (the proper name for "allen bolts") are available if you search for them.

https://arunfasteners.co.uk/product/bsf-socket-cap-screws/

[s2c-08589]

Hi GlenAnderson,

Thanks for the link. I've ordered some BSF S.H.C.S from Arun Fasteners you kindly sent me the link to.

Cheers!