Primary drive side spacer plate

[orabanda]

Hi all,
Up until today I had always thought that all the swinging arm engines required the circular spacer plate between the primary drive crank case half, and the inner primary drive case half.

However, a friend is putting together a bike, and says his research tells him that some of the S/A models did not use the plate.

Can anyone confirm this please.

If it is true, which model(s) did not use the plate?

Thanks,
Richard

[JulianM]

Mine has one, but judging by the rest it's probably wrong 

Best answer is to line everything up and see if you need it!  Nothing is correct if it's "wrong"  if you know what I mean 

Julian,

[Beezageezauk]

Hi Richard,

Like you, I believe that all swinging arm engines have this spacer fitted (42-7518).  My parts lists do state if different models have different fitments.  On checking the part number, all my lists confirm that these are fitted to "A Group" models.  In the 56/57 models parts list, plate 7 shows the gasket but doesn't show the spacer in the schematic diagram but it does show the part number and description listed at the bottom (below number 41) of the actual parts list.  The gasket (42-7509) is shown as 1 only is required.  Personally I think there are a couple of errors in the parts list but it could be read the same way as your pal saw it if this is where he did his research.

The 1958 on parts list clearly shows the spacer plate and 2 gaskets....1 for each side.i

Going one step further, the 3 larger screws that secure the front of the primary chaincase have the same part number in all the lists.  These go right through the crankcase and if the spacer was omitted it could be possible for these screws to tighten up on the flywheels and prevent the engine from rotating.  Just a thought!!  

FYI:- I've put later engines into earlier S/A frames and vice-versa and always used the spacer with no problems.

Hope this helps.

Beezageezauk.

[duTch]

 The Plungers don't have any of that as the inner chaincase is cast integral with the crankcases, I was thinking maybe it depends on which clutch is used.....4 or 6 spring..just guessing.?

[Beezageezauk]

Sorry Dutch,

I was modifying my input and deleted my reference to Plunger models whilst you submitted yours.

Beezageezauk.

[RichardL]

Based on the couple of times I've rebuilt my engine, it seems to me that the spacer was a corrective measure to avoid having the cush nut hit the inside of the outer cover. It would have been a lot cheaper to punch the flat washers than to hand carve a new mold for the outer cover, then make new plates for the sand casting process. (I think they were sand cast.) If this is not correct my next guess would be that, along with the gaskets, it provides a softer landing for the inner case, which is fragile compared to the crankcase.

Richard L.

[duTch]

 Sorry Geeza, Didn't mean to type over the top of you

 I had another thought, that maybe as someone asked the other day, about the case/frame mounting lug at the bottom rear of cases, that these work in conjunction- the big front ones pack inner case to ensure there is tolerance not interference between the case and frame(b/r) to prevent same distortion as in other post?
 I'll see if I can find it and add it in.
Can't see how the clutch would make a difference anyway!

 Cheers, duTch

[Rocket Racer]

My '55 and 60 A10 both run the plate. I would comment that every inner primary cover I have seen is bowed at the front ands fit much better after being put on a sheet of glass with some grinding paste. Usually the two rear bolts (that are lock wired) holes are a weak point so easily distorted so the primary doesn't sit flush.
That rear bottom bolt provides a lot of support to a long and quite fragile set up.