TR7 AC Delco Rotor/Distributor cap Piranha

[bonnietiler]

Hi guys..slowly working my way through this genuine low miler (50k) TR7 and I'm replacing all the rubber parts..hoses/breathers etc.
Decided to change the oil rotor etc standard servicing stuff...Got the dizzy cap off and removed the 2 screws that retain the delco rotor.
well...I say removed one came away nicely the other ...somebody had forced a metric in there so it snapped...excellent..I have drilled it out.
So...2 questions please?

1. what on earth are the threads on those delco screws? My service kit ( it was in the boot) didn't come with replacement screws.
2. There is a Piranha electronic ignition unit beneath the rotor and as the screws came away a plastic part which appears to be fastened just under the weights with a screw/bolt on each side holding it has come loose..any ideas what it is?
Cheers
Bonnietiler

[sonscar]

2BA?that is what is fitted to mine but that could have been altered along its chequered past.The plastic bit could be the pickup but just guessing.Steve.

[Howard722]

2BA?-does that question mark mean `unsure`? -because a BA thread (British Association) would be a tad unusual in a GM derived product of the 1970`s era.
If the size is about right it could be 10-32 UNF as the diameters are very very close 0.185" c/w 0.190" and the threads per inch (tpi) also very very close at 31.35 c/w 32 !!
I`m just asking the question here--does somebody have a fact based answer?

[kippy]

Howard,
I have a spare AC Delco distributor from which I got the thread pitch dimensions. I used a tap to fit to the thread that has 8UC32 stamped onto its shaft.
Does that make any sense to you or help?
Michael

[Howard722]

Well I`m not sure that it moves things forward-what size thread tap did you use?
As 2BA and UNF 10-32 are so close dimensionally they are virtually interchangable and I don`t think a thread tap would give a definitive answer whereas an accurate measure of an original screw probably would-as would a detail manufacuting drawing!
It`s all slightly acedemic but it would be good to know the correct size for the record.

[Cobber]

2BA threads have a thread angle of 47.5 deg, a thread pitch of 0.810mm, a thread density of 31.5 per inch, and a diameter of 4.7mm (0.1850")

Whereas a 10-32 UNF thread has a thread angle of 60 deg, a thread pitch of 0.7938mm, a tread density of 32 per inch and a diameter of 4.8260mm (0.1900")