Author Topic: Primary drive side spacer plate  (Read 991 times)

Online orabanda

  • Wise & Enlightened
  • *
  • Join Date: Nov 2008
  • Posts: 1010
  • Karma: 21
Primary drive side spacer plate
« on: 11.10. 2012 06:39 »
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

Offline JulianM

  • A's Best Friend
  • ***
  • Join Date: Jun 2012
  • Posts: 233
  • Karma: 14
  • www.historiccompetitionservices.be
    • Historic Competition Services
Re: Primary drive side spacer plate
« Reply #1 on: 11.10. 2012 06:56 »
Mine has one, but judging by the rest it's probably wrong  *smile* *smile* *smile*

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,
55 Ariel HS mk1,
58 BSA Super Rocket Scrambler special,
60 BSA Gold Star, Jim hunter desert racer,
64 Norton N15CS,
65 Triumph TR6 SS,
66 Triumph Bonneville,
71 AJS Stormer,
71 BSA Rocket 3,
71 Laverda 750SF,
71 Laverda/Egli 750SF, Race bike,
73 Norton Commando 850,
74 Moto Morini 3-1/2 Sport,
74 Bultaco Sherpa 350,
76 Beta Cross 50,
77 Moto Guzzi Le Mans Mk1,
80 Ducati 900 MHR,

Offline Beezageezauk

  • N.E. England
  • Resident Legend
  • *****
  • Join Date: Mar 2006
  • Posts: 669
  • Karma: 20
Re: Primary drive side spacer plate
« Reply #2 on: 11.10. 2012 10:25 »
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.

Offline duTch

  • Ricketty Rocketty Golden Flashback
  • Wise & Enlightened
  • *
  • Join Date: Oct 2011
  • Posts: 4540
  • Karma: 41
Re: Primary drive side spacer plate
« Reply #3 on: 11.10. 2012 10:33 »

 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.?
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline Beezageezauk

  • N.E. England
  • Resident Legend
  • *****
  • Join Date: Mar 2006
  • Posts: 669
  • Karma: 20
Re: Primary drive side spacer plate
« Reply #4 on: 11.10. 2012 10:53 »
Sorry Dutch,

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

Beezageezauk.

Online RichardL

  • Outside Chicago, IL
  • Wise & Enlightened
  • *
  • Join Date: Nov 2007
  • Posts: 5062
  • Karma: 48
Re: Primary drive side spacer plate
« Reply #5 on: 11.10. 2012 13:02 »
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.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.

Offline duTch

  • Ricketty Rocketty Golden Flashback
  • Wise & Enlightened
  • *
  • Join Date: Oct 2011
  • Posts: 4540
  • Karma: 41
Re: Primary drive side spacer plate
« Reply #6 on: 11.10. 2012 22:21 »

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

 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
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline Rocket Racer

  • Wise & Enlightened
  • *
  • Join Date: Jun 2009
  • Posts: 1430
  • Karma: 16
  • A kiwi with a racing A10 rig and too many projects
    • NZ Classic Sidecar Racing
Re: Primary drive side spacer plate
« Reply #7 on: 13.10. 2012 22:17 »
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.
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
New Zealand