Mk1 - oil pump stud threads

[camstevens]

Hi All
Does anyone out there know the thread used on the two oil pump studs in crankcase (MK1)? I want to use the bolts supplied by Morgo, but they are very tight in the casing thread...to the point where it felt like they would pick up. Will chase the new and existing threads with tap an die.

Regards
Cam

[simon.holyfield]

From the pics in my blog, they look like 5/16". They'll be BSW.

[paul.jameson]

Somewhat unusually, for an Ariel thread in alloy, the stud holes for the oil pump on the 4G (and therefore almost certainly on the Mk I, as they used the same oil pump) are 5/16 x 26 tpi cycle thread. 5/16 is 7.9375mm. I have a nasty suspicion that the tight bolts you mention could well be 8mm x 1mm which equates to 8mm x 25.4 tpi. No wonder they are a bit tight.

[camstevens]

Got them fitted. The bolts were 26 tpi cycle, but I think were made on a CNC machine.......ran a die over the bolt threads, which did the trick

C