Gearbox clutch-shaft oil seal replacement – 13 Jul 2016.

Having got access to the gearbox, it was now time to tackle the leak from its front end. Just to backtrack a little, before removing the gearbox I like to tie the clutch arm on the ‘box so it can’t swing about and get damaged. It also means the return spring can’t get lost either.

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Once the nuts have been removed the gearbox can be pulled back off the engine. It needs to be pulled back squarely.

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I transferred the gearbox to the workbench to take a look at what I’d got. It was clear where the leak was coming from. As I’d expected, the oil seal around the input (or clutch) shaft had failed. You can see where the oil has run down the front of the ‘box.

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Luckily there is no sign of any oil getting to the clutch. If this seal fails or the rear crank seal fails on the engine you are usually (but not always) OK as the clutch itself is housed inside the flywheel away from the oil.

To reach the oil seal I had to remove the clutch hub which is held in place by a peg nut and a star lock washer. These can be problematic. The first thing to do is to find which slot in the nut has got a tag from the washer folded into it.

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I abused a small screwdriver to start levering the tag clear. Then used a punch with a flat end to knock it back out of the way.

To undo the peg nut holding the splined hub you ideally need three Guzzi special tools. The first is a bracket you bolt the gearbox to so that it can’t move about. The second is a tool to fit the splines of the hub and hold it still (I keep meaning to pick up a worn out clutch plate to make one from). Finally you need a four-pronged socket to fit the hub nut.

Years ago I made a special socket by grinding a 30mm socket. It’s ugly but it works. To hold the hub nut still I used some rubber on the splines and a set of stilsons which are equally nasty.

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The hub then just slides off the splined shaft. The back of the peg nut which goes against the hub is curved as is the lock washer. This is so you can reach a tag to bend it forward. Both nut and lock washer were in good condition so I could reuse them.

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It seems that when I fitted the gearbox I broke one of my own rules. I would say that it’s worth replacing this seal whenever you have the box off because it takes so much work to reach it. However, I can see that this is still an old seal and, what is worse, I replaced the clutch hub and still left the old seal in place. This was just asking for trouble!

I also recognised some old damage I’d forgotten about. It’s very old (1970s), from before I owned the bike and is to the part of the gearbox where the seal fits. I don’t know what could have caused the wear but something appears to have let go in the clutch housing at some time. The oil seal itself has been rubbed as well.

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I tried to get the old oil seal out by putting a self-tapping screw in it and levering on it but the screw just pulled out.

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However it weakened the seal enough to be able to put a small screwdriver in the hole and lever it out that way. I noticed there is some damage to the face where the seal sits. It looks like a little triangle. I think it should be fine and won’t cause any problems. In the photo it looks neat enough to be supposed to be there.

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That wear to the “boss” on the front of the gearbox caused me a bit of a problem. Normally you would knock the new oil seal in until it is level with the surface. However the surface is now crooked. I measured the depth of the housing to the outer race of the bearing with my calipers.

9.87mm at 12 o’clock.
9.74mm at 3 o’clock.
10.17mm at 6 o’clock.
9.64mm at 9 o’clock.

I made a mistake with my first attempt. I set the seal in square but too deep so that it was partially recessed. Of course it was ruined taking it back out again. I had bought two seals which was lucky. The second time I carefully tapped the seal in until it was flush at the 6 o’clock position. This meant the seal was standing a little proud elsewhere but it was secure. To check that it was actually in square, I held a small steel rule across its face and slid the clutch hub onto the splined shaft to check the back of that was also flat on the rule. I tested it at different angles and I had got it right.

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When I oiled and slid the clutch hub partially into the seal I could see that the witness mark from the old seal also lined up well. The hub was pushed on properly and the locking washer inserted. It locates in a slot in the shaft.

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That peg nut was tightened by hand then some means was needed to lock the hub again. I didn’t resort to the stilsons this time. Instead I used a piece of wood and a small scrap of metal to jam the splines.

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I can’t find any torque figure for this nut so just did it up as tight as I could manage and then bent a tab of the lock washer forward.

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I had intended to change the oil seal at the output end of the gearbox as well while I had it on the bench. They are both the same and is why I had bought two seals but, now I haven’t got one spare. There was no sign of any leak from the back of the ‘box so I decided to refit it as it was. At least if this seal fails it can be reached just by taking the wheel and swing arm off rather than having to dismantle the whole bike or crab the frame.

Before refitting the gearbox I remove the rubber blanking plug that you use when timing the engine, from the side of the gearbox. You also need to have a long-handled screwdriver handy. I get the ‘box on the mounting studs and, if the clutch hub doesn’t slide into the driven plates I can turn the hub a touch with the screwdriver through the hole until it goes together. I find that easier than having the ‘box in gear and turning the output shaft.

Un-crabbing the frame!

This is basically the reverse of the dismantling process (but you might swear in different places). There are a few things to remember;

  • Leave the final tightening of the frame/footrest bracket bolts, front and rear engine bolts, the lower crashbar mountings, and the screws holding the plate under the battery to the gearbox until they are all in place and screwed home.
  • Adjust the swing arm bearings so there is no slack but they do not bind. The pins should project from the frame by the same amount on each side (7.1mm both sides in my case) before fitting the lock nuts.
  • Take the opportunity to grease the splines on the back of the gearbox, the driveshaft, its sleeve and the bevel box as you refit them.
  • Leave the final tightening of the four nuts holding the bevel box to the swing arm until after you’ve got the rear wheel in and the axle tightened. this is to make sure the axle is properly aligned and can be removed and inserted easily.
  • Grease the splines between the rear wheel and drive box.
  • Also grease the bushes that hold the gearchange crossover shaft in the lower frame rails.
  • Adjust the rear brake cable.
  • Adjust the front brake cables at the lever to keep the two front brake drums synchronised.

The reassembly took a little longer than the dismantling because I spent some time cleaning the exhaust system and putting it together with silicone sealant. My experiment with this was a success so I’ve done it again. The only problem is that you have to leave the exhaust and sealant for 24 hours before running the engine.

Result!

As it happened it was two days before I could get back to working on the bike. Today I removed it from the bench and re-did the carb synchronising just in case! There was no gear oil leak and this afternoon I went for a quick 50 mile ride. All seems fine.

Before going out I had removed some of the blueing from the exhaust header. I don’t use commercial chrome cleaners usually as they can damage/remove the chrome surface. However I tried a little this time. I didn’t try to get rid of all the discolouration but just reduced it. The blueing didn’t reappear during the ride but I’ll just have to see how it goes.

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2 thoughts on “Gearbox clutch-shaft oil seal replacement – 13 Jul 2016.

  1. Brilliant! Just what I need as have to do this job shortly. Are you going to change the gearbox driveshaft oilseal??? That is the one that is leaking for me….big time! Oil is coming out of gearbox and ending up in bevel box! Although there is quite a bit online written about it. I am still a little unsure how you actually get the old one out. I presume much the same way you have for drive shaft seal. Would love to see you do it!

    Really love the Red Guzzi.

    But then I would:

    http://bitly.com/2adpzN1

    Best wishes

    Ed

    1. I was going to change the output/driveshaft seal but mangled one of the 2 seals I bought so have left it for now. Mine seems to be holding the oil in anyway.

      You wouldn’t think it possible for the oil to migrate from gearbox to bevel box or the other way, which seems more common, but I’ve heard of it before. That rear seal can be reached without removing the gearbox. I’ve done one before (probably on my old S3) and seem to remember extracting the seal was fiddly because it’s inside the back of the ‘box, but nothing had to be dismantled in the gearbox itself.

      Red is the best colour for a Guzzi and a T3 is a proper Guzzi!

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