Thanks to Chris Fisher for suggesting suitable quality bearings for the 1929 onwards 3-speed gearbox I’m putting together at the moment. The gearbox will be a CT close ratio type and is for a 1928 Model 6 that has been modified in the deep and distant past to house a hybrid OHV motor. The motor employs 1930/1931 crankcases with 1927 single port head breathed on by Chris Odling to take a new Amal 289. So, the whole bike is a “bitsa” but now goes very well with a 7.5:1 forged Model 90 piston from the sunbeamland shop.
I might point the “Model 69″ up a couple of hill climbs once the gearbox rebuild stops it dropping out of 2nd gear and we fit a 19” rear rim – it will then take a pair of the excellent Avon race compound Speedmaster and GP tyres.
1 off RHP LJ1-2RSJ
1 off RHP MJ7/8-2RSJ
2 off RHP KLNJ3/4J
The earlier 1928 wide case box has a smaller mainshaft diameter and consequently an RMS 6 bearing in the case rather than the RMS 7 of the later type. In this case the RHP MJ3/4-2RSJ looks like it could be a good fit.
1 off RHP LJ1-2RSJ
1 off RHP MJ3/4-2RSJ
2 off RHP KLNJ3/4J
With the outer bearings being sealed it might be a good idea to consider implementing a small breather hole in the gearbox filler cap.
It was great to get an email from Tony Petherick to say that the new forged piston we supplied was working well in his 1928 Longstroke Model 6. It’s lovely to see one of the iconic Sunbeam models retaining its valanced guards and running with leg shields too. In addition to its lighting kit, the bike also features footboards and an enclosed rear chaincase that hasn’t been lost like so many others.
Tony has fitted more sporting cams to the bike and reports that it runs very well after advancing the inlet cam by two teeth from the marked position. Does anyone have any ideas on cam timing using different cams on these bikes? It was a common “dodge” to fit the 60:30 OHV cams to the sidevalve bikes..
If anyone has a spare petrol cap for the bike please get in touch as the one fitted isn’t quite right and Tony would be keen to give a genuine Sunbeam item a new home.
A very interesting picture here of the footchange arrangement used by the works Sunbeams in the Senior TT for their 3-speed gearbox. This was perhaps not Sunbeam’s greatest technical achievement and likely one of the reasons that after their victory in 1929 the Rudge factory was so dominant in 1930. The crash box from the hand change models is retained with the exception of a shorter main shaft that moved the clutch inwards and necessitated a dished engine sprocket. As can be seen, the lack of a positive stop mechanism meant that the lever is simply moved up and down to different positions in order to select a gear. A V-shaped spring does the job of the hand-change gate by engaging in a notched plate to hold it in particular gear with a spring-loaded catch that makes it harder to shift from middle gear. This is to avoid overshooting 2nd when changing up or down.
My own M90 has the same setup and it works well enough but Sunbeam soon moved on to their own 4-speed constant mesh type gearbox and later adopting 3rd party units supplied by Burman.
A friend just let me know that his rather nice 1931 Sunbeam Model 9 is now for sale. Obviously in lovely condition and fitted with a highly desirable 1929 single port engine. A great bike for someone? Send an email if you would like contact details.
People are often asking about the correct carburettor model and settings for their pre-war Marston Sunbeam motorcycles. Well, those helpful people over at Amal have long produced free catalogues that offer just such information. The “Amal Pre War Supplement” being of particular interest.
Here is a scan of the relevant page for the Sunbeam models covered by the catalogue.