I’m currently building up a 1954/5 prefeatherbed swinging arm ES2. I have fitted a laydown box but cannot get enough clearance behind the clutch for the chaincase. I have two clutches, one is better than the other in respect of fit. I have measured the depth of the splines in both - see the pic below . The one on the left has an RGM spider which I guess is AMC . The clutch with the RGM spider gives approx 2mm more clearance than the other ( 17.5 vs 19.25 mm deep splines) so I fitted the RGM one and checked the alignment with the engine sprocket, it appears to line up with the middle offset sprocket. However you can see in the other pic that it gives only just enough clearance to miss the swinging arm mounting, there’s no room for the chaincase. If I fit the other clutch, the primary chain fouls the mounting. Prior to fitting the laydown box it was fitted with an AMC box, that gives more clearance and it was using the largest offset engine sprocket. If the gearbox is right and it can’t have the wrong shaft (the singles shaft is the shortest) then is my issue the clutch spider? Has anyone got one they can measure the depth of the splines to the stop? Thank you.
I had the same problem a few years ago when building my '55 ES2.
The mainshaft was too short. Looked just like your photos. Considered opinion from those who know more about these things than I do suggested the shaft might have been from a rigid single ?
Anyway, the NOC shop kindly measured the s/h one they had in stock and it was 3/16" - 1/4" longer, approx. So I bought it.
Took the gearbox to bits (again), fitted the replacement shaft, and it all lined up.
that probably means the info I have is missing something! I thought the single mainshaft was the shortest, perhaps it isn’t. As you say it needs a little more clearance however that still leaves the engine sprocket alignment, Can you remember which offset you used?
Curtesy of Geoff Clatworthy -
That makes it look like I ended up using a twin mainshaft ?
Can't remember which engine sprocket offset I used, but it would not keep the oil in the chaincase anyway, too badly distorted, so in the end I cheated...fitted a Mick Hemmings belt drive. Brought on a host of other problems.... like the lack of enough movement on the clutch mechanism, but got there in the end. Well worth the effort. One finger clutch.
I have just rebuilt 3 lay down gearboxes for my 1953 Model 7, 1952 ES-2 and my rigid Dommi.
The single has the shorter GT 175 mainshaft and the twin the slightly longer GT 165 mainshaft. The 165 is only 0.070" approximately longer overall. Lay down gearboxes also use a GT 172-3 mainshaft sleeve gear not the N 8032 used in other boxes.
Have you fitted the correct gearbox sprocket?
All 3 boxes required the sprocket with a parallel boss which fits up against the mainshaft sleeve gear bearing.
This parallel boss is approximately 0.44" wide and centralises the sprocket to give you the required clearance.
I believe that the hardened spacer fitted to the outside of the AMC sleeve gear will be suitable but it's now too late to check tonight. I'll have a look tomorrow.
Thanks Ian, but I’m not sure that I understand what you are saying. My problem is where the clutch is sitting on the mainshaft which gives insufficient room for a chaincase.
I know that I need to make sure I have the right gearbox sprocket (or a spacer) but I don’t understand how that would affect the clearance between the clutch and the frame, the clutch spider sits against the end of the splines and surely doesn’t touch the sleeve gear or gearbox sprocket?
I should add that I have a spare frame and have tried it in that one and have the same problem so it’s either a gearbox or clutch issue ..... I think!
Hi Dan, I've taken some measurements off my spare G102 gearbox & clutch which were originally fitted to a '56 Model 50 with single downtube swingarm frame.
The following dimensions are with respect to the flat face of the gearbox around the mainshaft:
20mm to end of sleeve gear, 50mm to end of splines, 78mm to end of shaft.
With the clutch in place, 33mm from the annular bulge on the rear of the clutch basket.
Depth to shoulder in clutch spider - 20mm
Overall length of shaft 225mm (apologies, didn't measure L)
Hope this helps (or at least does not add to confusion!)
Cheers, Ian McD
I've just measured mine, I think the key measurement is the end of the splines to the gearbox face, yours is 50mm, mine is 47.5mm. My clutch is 27.25 mm from the gearbox, yours is 33mm. That’s a 5mm difference on a shaft that seems to be only 2.5mm shorter? That’s odd!
If I use the clutch with 19.25mm to the splines (the nearest to yours of 20mm) the gap reduces to 26mm !! on the face of it that would seem that I have both a clutch and shaft issue - although I can seemingly get alignment with the engine sprocket. If I get my clutch 33 mm out then I’m not sure engine sprocket will be aligned but it will give me the room for the chaincase! I think I’m going to have to take the gearbox apart to see what is in there. Do you know what mainshaft is in yours? And if possible it would be helpful to know the distance between the gearbox face and the top mounting lug on the gearbox,
Many thanks for your help so far! dan
While the box is marked G102, and was removed from the remains of a '56 Model 50, I have just spotted that the mainshaft is clearly marked GT165 (L=3.62"). If this is a mainshaft from a twin then yesterday's measurements are not relevant to your query.
There is no quick way to determine what shaft is fitted to my '56 19S but photos of the clutch in situ show that the mainshaft does have the plain section at the end - which is missing from the GT175 example shown on Geoff's photo of the shaft variants. As Duncan has suggested maybe the sprung frames require the longer shaft to clear the swing-arm pivot? My engine sprockets are offset to the outside, which might support that idea.
The distance between the gearbox face and the upper mount face is 24mm.
Cheers, Ian McD
Geoff has commented that he’s got the Manx and single picture reversed so the single should have the plain section of shaft, but I wonder if this a common problem resulting in the twins shaft being fitted to the singles?! So you measurements are very helpful as they should confirm what I can expect if I go down that route. I’ll measure the mounting in a mo.
Mine is also 24mm so that’s a relief!