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RD400 countershaft leak

Started by SoCal250, February 26, 2026, 07:28:20 PM

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SoCal250

A few months ago I replaced the countershaft seal with a new OEM one (93102-35109-00). Noticed the bike was still dripping on the floor and had oil running down the kickstand. :whatever:

Pulled the left engine cover and sprocket and discovered I still have a leak there. The OD of the seal is dry. Looks like it's coming out around the collar, but not sure if it's seeping out of the OD or from the ID and spline area. The collar doesn't appear worn and the inner lip of the seal is in good condition. Anyone have any tips for resolving a leak like this? Hate to throw another $20 seal in there and get the same result.

The other seals on that side that were replaced are all dry (clutch pushrod, shift shaft, neutral switch). :thumbs:

rd400_trans_parts_CSseal.png
75 Yamaha RD125B   75 Yamaha RD125B (project)
75 Yamaha RD250B   75 Yamaha RD200B (project)
73 Yamaha RD350     77 Yamaha RD400D   79 Yamaha RD400F  
91 Yamaha TZR250R  89 Yamaha FZR400   05 Yamaha FZ6   
05 Yamaha XT225TC  82 Honda MB5  02 Aprilia RS250 Cup (sold)

DesmoDrew

  The seal, #34 only seals the OD of the spacer, #35.  Oil can creep along the splines of the countershaft and through the ID of the spacer, #35.  The only 'seal' formed then is the metal-metal interface between the outer face of the spacer, #35, and the back face of the C/S sprocket.  Make sure that interface is smooth and flat.  Maybe try some yamabond???  :twocents: 

rodneya

One of the manuals I have, either Rd, Banshee, RZ or Suzuki GS mentions case sealer on the collar #35 so I always put some in there.

m in sc


RDnuTZ

is it possible to fit a small O-ring on shaft directly behind counter sprocket?
1987 TZR250R Restricted Japan Domestic market bike (Project)
1977 RD400 (Project)
1974 RD350 (2) (Projects)
1973 RD250 (Project)
2022 Beta 300 X-Trainer, Yamaha Vintage MX, YZ (18)

SoCal250

Thanks for the suggestions. When I have a chance this weekend I'll check the outer face of spacer for flatness and put a little Yamabond on there. :thumbs:
75 Yamaha RD125B   75 Yamaha RD125B (project)
75 Yamaha RD250B   75 Yamaha RD200B (project)
73 Yamaha RD350     77 Yamaha RD400D   79 Yamaha RD400F  
91 Yamaha TZR250R  89 Yamaha FZR400   05 Yamaha FZ6   
05 Yamaha XT225TC  82 Honda MB5  02 Aprilia RS250 Cup (sold)

1976RD400C

A little sealer on the lock tab washer and threads too.
'76 RD400 green  '76 RD400 red   '84 RZ350

m in sc

put it in the inside face of the spacer. take spacer out and put it there, then reinstall.  it'll never make it down.

if you know somebody w a lathe  have them bevel the id at the bearing side and use an oring there.

rodneya

Quote from: RDnuTZ on February 27, 2026, 11:58:23 AMis it possible to fit a small O-ring on shaft directly behind counter sprocket?
Would need a groove machined in for the oring like a yz

automan

Kaw's have an o-ring that gets smash smooched for spline sealing.

RDnuTZ

#10
Some Yamahas like mid-1970s singles do too on primary side of crank between collared end of primary gear and main bearing. The O-Ring is #17 in below parts blow up diagram. It is for 1975 MX400B.


https://yamaha-motor.com/parts/diagram/13301662/305836756
1987 TZR250R Restricted Japan Domestic market bike (Project)
1977 RD400 (Project)
1974 RD350 (2) (Projects)
1973 RD250 (Project)
2022 Beta 300 X-Trainer, Yamaha Vintage MX, YZ (18)