Gearbox Peripherals - 4-Speed 2nd Synchro

[Chris KC]

A couple of quickies if I may:

- Should a 4-speed synchro box have a brass (bronze?) or a steel drain plug?
 
- Speedo drive thread (cable end) - 3/4" BSB?

Thanks, Chris

[Bob Culver]

Brass on my car but some have been rethreaded to take a plumbing fitting. Covered quite recently.

[Chris KC]

Thanks Bob, just found that thread but it's mainly concerned with damage repair. I have both steel and brass plugs to choose from in my tin of gearbox bits and both have the same thread.

[Parazine]

Earlier ones were brass, later steel. I don't know when the change was made, probably sometime after 1937 as components were shared across the 10hp and Big 7 lines. The steel plugs were also used in the engine at about the same time.

[Chris KC]

Thanks Parazine.

[Colin Morgan]

Hi,

Re. Speedo drive - this is from Austin in the Shed Oct 19 2015:

"Standard cable fitting 3/4" BSB and 5/32" square drive."


Cornish A7 Club site has table of threads on this page:

http://www.austin7.org/Data%20Pages/Tech%20Data/



Colin

[Chris KC]

Brilliant - thanks Colin

[Bob Culver]

The Cornish Club table is interesting. Has anyone confirmed that the hot and cold tappet settings correspond? What is the original source of the cold settings? 360 lb in or 30 lbs ft seems to be a remarkable tension for 5/16 head studs. 20 lbs ft as the big ends seems more prudent. Excessive tensions distort cylinders and valve seats. broken studs can be very tedious to remedy. Is it the tension which causes the common crack near centre? Note how very conservative is the effective full advance timing for th the auto distributors. One inch is 11 deg on flywheel.