Which screwtreat in brass casting front susp. Grantura Mk1

[cantus]

Which screwtreat is fitted in the two holes in the brass casting of the front suspension of the Grantura Mk1 ?
Is it 3/8 UNC or is it 3/8 BS (British standard)?
I tried a 3/8 UNC bolt and it didn't go in easy. I am afraid I will damage the treat when I put the UNC in. UNC and BS are slightly different in pitch. Who can tell me what it is ?

[GAjon]

Not familiar with Grantura's, but would guess UNF thread.

[heightswitch]

GAjon said:

Not familiar with Grantura's, but would guess UNF thread.

I would go with a whitworth thread. the bit on display looks too course a thread for a unf, you said UNC was tight. a BSW is courser and would be suited to brass.

failing that, looks plenty meat on the casting can you re-tap to a fatter UNC

N.

Edited by heightswitch on Tuesday 18th December 01:06

[cantus]

It is definitivly no UNF ! Whitworth (BSW) could be the tread but I personally think it is BSF .
I will check tonight.
Re-tap to a fatter UNC 7/16" or 1/2" is alway a good option.

Edited by cantus on Tuesday 18th December 15:34

Edited by cantus on Tuesday 18th December 15:36

[dcr]

If it helps, 3/8 unc has a 60 degree thread angle and a root diameter of 0.307" , 3/8 whit has a 55 degree thread angle and a root diameter of 0.295", both have 16 tpi so the chances are that a tight fitting unc bolt should be replaced by a correct fitting whitworth one ,(3/8 bsf is 20tpi and 3/8 unf is 24tpi) Dave

Edited by dcr on Tuesday 18th December 20:09

Edited by dcr on Tuesday 18th December 20:12

[TaimarSE]

3/8 UNC and 3/8 BSW have identical pitches, BSW has 55 degree thread angle.UNC has 60 degree thread angle, this is why the UNC is a tight fit in a BSW thread

[cantus]

TaimarSE said:

3/8 UNC and 3/8 BSW have identical pitches, BSW has 55 degree thread angle.UNC has 60 degree thread angle, this is why the UNC is a tight fit in a BSW thread

Dave and Gerry,
You both are absolutely right !! the slight difference in diameter is the problem why the UNC bolt is a tight fit. I will tap to UNC and use UNC bolts !
Thank you all for thinking and replying.

William

[luckycarter]

Hi William,
Just been dealing with the same parts as you, yes 3/8 UNC , i had to make some new studs as the other ends (3/8 UNF) were all mangled, all the parts in that area seem to have had a rough time over the years on my car, are those counter bores on the faces of your holes for the bushes or wear marks ? , mine dont have them just wear marks,
Rich.

[cantus]

Hi Richard,
They are wearmarks ! But that is no problem. I will fill them with a washer before I install the Superflex bushes.
This coming weekend I will cut the screwtread to 3/8 UNC.
I ordered the Superflex bushes 5/6 weeks ago, but there seems to be a problem that these bushes are not in stock anymore. They told me that they were going to manufact a new small serie for Grantura's.
Also this weekend I will collect the original Ford engine incl. supercharger !!

I will keep you informed

kind regards
William