Author Topic: Plunger box mainshaft seal  (Read 177 times)

Online Minto

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Plunger box mainshaft seal
« on: 08.06. 2020 00:32 »
Good evening all.
So, on to my next dilemma...
I've read about it being possible to pretty much completely dismantle and reassemble the gearbox without removing it from the frame, though I'm assuming that this applies to the SA models rather than the plunger type. If it is possible with the plunger box, how is it done? I can't see how as the rear of the primary chain case is cast in with the crank case, so removal of the final drive sprocket would be impossible without separating the engine and box, which is an engine out operation.
I've got quite a leak on the main shaft oil seal, it used to be an occasional drip, but since rebuilding the engine it's much worse. Am I going to have to remove the lump again to sort this?
Thanks all
Jase
52 A10 plunger
Aprilia RSVR

Offline Swarfcut

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Re: Plunger box mainshaft seal
« Reply #1 on: 08.06. 2020 09:10 »
 In a word ......YES.  Check gearbox is not overfilled, for starters.

  Make sure it is the seal that has failed, not a drip from primary case, case seal or breather. After all your effort, if you did not disturb the gearbox, it is strange that the seal has started to leak.

 As a test, make a nice thick cardboard gasket for the clutch adjuster cover. Then cut a  narrow slot in the top edge, to act as a breather vent. This will relieve any pressure in the box, and is not a permanent modification, like drilling holes in castings. This may stop the leak until you have time and inclination to rip it apart.  Seal is the same across the range.

 The Plunger gearbox can be dismantled in the bike, with the exception of that seal, drive sleeve, bearing and sprocket. Sod's Law in action.

 Swarfy.

 

Online Minto

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Re: Plunger box mainshaft seal
« Reply #2 on: 08.06. 2020 10:56 »
Thanks Swarfy
I couldn't see how that could have been possible. At least now I have some experience of removing it all, and the box to crank case bolts should come out without having to bully them with a big drill next time.
I'll check all the other likely sources but
It's always had a bit of a drip from the box, was never sure where from though.
That's a great suggestion re the vented gasket, I'll try that this weekend but I reckon I'll have to live with the leak til winter now though.
Cheers
Jase
52 A10 plunger
Aprilia RSVR

Online Minto

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Re: Plunger box mainshaft seal
« Reply #3 on: 08.06. 2020 14:34 »
Well having cleaned everything up and dried all the oil off everything, I gave it a few minutes running and the majority of it seemed to be coming from the joint between the box and crank cases. However, when I left it on the side stand for a few minutes after running it, I had a few drops from behind the final drive sprocket, possibly the frost plug, but maybe the sleeve gear or oil seal, difficult to see down there.
Whatever, it looks like the lump's coming out again. Oh joy!
Cheers
Jase
52 A10 plunger
Aprilia RSVR

Offline Swarfcut

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Re: Plunger box mainshaft seal
« Reply #4 on: 08.06. 2020 15:59 »
What a shame. Engine Oil from between the box and motor means its coming from the crankcase halves' joint.  Gear oil is from the camplate pivot mount or the two inspection screws rarely touched.  So yes, another excavation.

    The "frost plug" is the back of the layshaft blind bush. Best left alone, a replacement bush usually requires reaming to fit the layshaft, and is a bit awkward to get right. So make certain there is a definite problem here, it's unlikely but possible.

 Alternatively, cheat, with custom drip tray to cover the underside........and just keep checking the levels.


 Swarfy.


Online Minto

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Re: Plunger box mainshaft seal
« Reply #5 on: 08.06. 2020 18:07 »
Hi Swarfy
The drip tray is tempting but the oil was everywhere rearward of the gearbox when I started to look and clean it up,  exhausts, frame, wheel, floor etc.
I'm not so daunted by it this time, I reckon a weekends work if I can get rid of all my distractions (Mrs Minto)!!
Incidentally, when I was rebuilding the motor, I'd left the gear box in a plastic crate, when I took it out it was totally covered in oil. I just thought that I'd left it in a position that allowed it to leak past the sleeve gear or something, I'll investigate that properly this time.
Ho hum!
Just a thought... When I was separating the engine and box, a couple of the bolts were a total mare to remove and I ended up using quite a bit of heat on them (and a big drill on one). Is it possible that this heat could've wrecked a gasket or seal on the gearbox?
Cheers
Jase
52 A10 plunger
Aprilia RSVR

Online berger

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Re: Plunger box mainshaft seal
« Reply #6 on: 08.06. 2020 19:05 »
minto I solved the leak on mine, it was creeping out of the bearing and out at the sprocket seal and circlip. it got the silica treatment and never caused a problem since, I also changed the worn sleeve gear bushes but the majority was coming out around the seal and circlip

Offline Swarfcut

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Re: Plunger box mainshaft seal
« Reply #7 on: 08.06. 2020 19:11 »
Minto
    There are gaskets between the outer cover and inner cove, inner cover and main casing. A small gasket under the camplate pivot mounting. One big oilseal behind the sprocket, that's it.  There are no seals on the kickstart or gear selector shafts.  Any of these, plus the sleeve gear is a potential source, along with the drain and level plugs and the unsealed camplate plunger housing underneath. So it would have to be a bit warm to damage these.

 When its out, look for cracks, pulled studs, missing gaskets. Assembled correctly with a bit of care the boxes are oiltight, all depends on what rough treatment and use it has had over time.

    No point agonising, all will be revealed when you make a start.  Make a peg spanner for the sprocket nut, which has a normal right hand thread. The sprocket pulls off, revealing the offending seal, held in place with a circlip.  Grease the lips of the new seal to prevent damage before the oil gets round.

   You may consider some sealer around the outer edge of the new oil seal to avoid berg's problem. Some seals have a nice soft underside, and seal well against the bearing and case, others are rock hard and need some additional sealer.  Plenty on the forum concerning the foibles of gearboxes, their problems and fixes.

 Swarfy.