SU damper thread

[PeterCrespin]

Anyone know what the thread is for the screw-in damper? The damper only has a couple of external threads and I can't decide between 27 tpi and 28 (or 26 for which I have no gauge blade). The dashpot has more threads but gauge fit is hard to judge at an angle.

The major diameter on the plastic damper top is about 0.633" but may be distorted from overtightening. I'm guessing Cycle thread 5/8 26 tpi but I called just after 5pm BST and SU were shut until after the hols.

Pete

[christopher storey]

As arcane questions go, this must be an outstanding leader of the pack. I have to say, that without going and looking at my collection of SUs, I thought both the size and the pitch varied with the size of the carb and therefore of the dashpot. Are we talking HD8 here?

Incidentally, I hope all is well with you and yours

[mgcjag]

Hi Pete...have a look here viewtopic.php?t=10443 Steve

[christopher storey]

Peter : I've now been and measured 2 samples . Brass HD8 was major diameter of 0.679" and as best as I could measure had a pitch of 38 thou which equates to 26 tpi ish

Plastic HS6 was 0.670 major diameter with the same pitch, so again possibly 26 tpi.

11/16 as per Burlen's in Steve's thread ( pun intended) suggest a major diameter of .6875 nominal so my diameters are much closer to that than your 0.633 which sounds way out . I am a bit surprised that my pitch estimate is as far out as 26 when it is really 24 but Burlen's should know !!

The thread tables I have looked at suggest that if these threads are indeed 24tpi then they are SAE Fine threads (That seems to be the only standard which uses the 24 tpi except for some very small - #10 and #12 - UNF threads) . If they are 26 tpi which both our estimates suggest, then they are either British Standard Brass or Cycle thread

I didn't measure any plastic HD8 in case there is a difference but if you wish me to I will do so tomorrow morning

[abowie]

I asked Burlen a while ago. It's 11/16 24tpi. I got a tap off Ebay.

I just checked it in a carb and it fits.

[abowie]

I asked Burlen a while ago. It's 11/16 24tpi. I got a tap off Ebay.

I just checked it in a carb and it fits.

Dear Sir
The thread size for the damper cap is 11/16 x24TPI .

Kind Regards

Stan Rawlins
Customer Services Advisor
Burlen Limited - The SU and AMAL Carburetter Companies
Spitfire House, Castle Road, Salisbury, Wiltshire. SP1 3SA
Tel: +44 (0)1722 412500 Fax: +44 (0)1722 334221 Email: customer.services@burlen.co.uk Website: http://www.burlen.co.uk

[PeterCrespin]

Thanks Gents. My measurements don't fit the 11/16 major and minor diameters but if Andrew tried the tap in his carb, then that's good enough for me.

Am coming over next week for a family funeral. It's a brief visit as I'm up against deadlines for the Nov-Dec issue, so I probably won't have time to nip over.


Pete (who did search before starting the thread, but got lots of hits where 'thread' referred to sequences of posts, not screwed fasteners.)

[abowie]

Stan Rawlins is never going to let you down.

[christopher storey]

Unfortunately, what is not stated is what the threadform is i.e. 30 degree, 27.5 degree or whatever and whether the threads are attenuated or not. This does matter, particularly with plastic , which will not last any time at all if the thread angles are wrong