head bolt thread size

RoverP6B · Post by **RoverP6B** » Mon Aug 25, 2008 11:54 am

The inlet manifold bolts are 3/8" UNC. That is the thread size.

As for the head bolts,...

Someone will let us both know.

Ron.

ChrisJC · Post by **ChrisJC** » Mon Aug 25, 2008 7:44 pm

7/16ths Whitworth.

Chris.

blknight05 · Post by **blknight05** » Mon Aug 25, 2008 10:58 pm

ChrisJC · Post by **ChrisJC** » Tue Aug 26, 2008 7:08 am

BSW

Chris.

russell_ram · Post by **russell_ram** » Tue Aug 26, 2008 6:27 pm

They are actually 7/16 UNC.

TVRleigh · Post by **TVRleigh** » Wed Aug 27, 2008 4:03 pm

russell_ram wrote:They are actually 7/16 UNC.

Have to agree with russell_ram here, I had to helicoil my block and they are 7/16UNC

Bigest problem if your heli-coiling is re-tapping the larger thread straight.

blknight05 · Post by **blknight05** » Wed Aug 27, 2008 8:03 pm

ChrisJC · Post by **ChrisJC** » Thu Aug 28, 2008 7:21 am

Interesting. I tapped a block of aluminium with 7/16 BSW and my head bolts fitted.

I guess if 7/16 UNC and 7/16 BSW share a thread pitch, then that's possible. I was expecting them to be UNC before I started that particular project, and was a bit surprised to find that I needed my BSW taps. I can't recall if I had UNC in the correct size, but I think I did and it wasn't right.

Mysterious.

Chris.

blknight05 · Post by **blknight05** » Thu Aug 28, 2008 10:54 pm

TVRleigh · Post by **TVRleigh** » Fri Aug 29, 2008 1:01 pm

As said in the previous thread, use masking tape to tape up the bores and any other holes.

Then put the heads back-on put some tape on the drill bit above the distace you want to drill.

Put the drill bit on a tap holder and then use the head hole to make sure the drill bit goes in straight.

worked fine for me.

ian.stewart · Post by **ian.stewart** » Fri Aug 29, 2008 1:38 pm

The British Motor industry has not used BSW or BSF since the second world war, Nearly ALL thread forms on the Rover are either UNC or UNF, as is on most cars up to the 90s, where they switched over to Metric form,of which there are 3 basic types , Metric course Med Fine and Fine, and of course Pipe threads which is a different subject alltogether,
Imperial threads, Whitworth and UNC share the same thread pitch from 3/16ths thru to 7/16ths, the thread angle is different, ie from the tip of the thread to its root is the part where the included angle is measured,
UNC and Witworth will interchange but its not ideal and will cause stripping problems if loaded heavily,
Drilling Square is almost impossible without a guide using hand tools, as TVR leigh says use the head as a guide for the drill if the helicoil drill will fit, When I was an apprenticeI made a drilling guide from a piece of 1" thick steel, drilled a set of various sized holes that were common threads, and next to each one I drilled the tapping size for each , case hardened it and I still use it today, drill the tapping size thru the plate, than use the plate as a guide for the tap to ensure it runs square, even today I still get other engineers copying this as it can save all sorts of aggro,

blknight05 · Post by **blknight05** » Fri Aug 29, 2008 4:28 pm

ChrisJC · Post by **ChrisJC** » Fri Aug 29, 2008 7:51 pm

I can confirm what Ian says - I checked my Zeus tables to see if 7/16ths BSW & UNC are similar. They are both 14TPI, so yes they will interchange. I haven't got a 7/16UNC tap so I found that a Whit one would do. But yes, apologies, they are 7/16ths UNC.

Chris.