yet another gearbox rebuild... with a few questions.

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First, thanks to the people who post good information here in the forum. Thanks to old britts for their article on gearbox rebuilding too.

I've torn down my box. everything looks amazingly clean and unworn. My bike has just under 20,000 original miles on it. I really don't abuse my bike, but I do open it up occasionally. I keep the rev's sensible most of the time. Anyway, I have a couple of questions:

I pulled both shafts and bearings. The original mainshaft bearing is "sealed one side only" bearing and the seal was on the outter side of the bearing facing the sprocket . I assume the new bearing goes the same way, but I thought that the person I talked to where I ordered it said the sealed side goes on the inner side of the bearing... This sounds wrong, so I think I misunderstood him.

Also, I don't want any leaks. should I use permatex on both gaskets??

I also bought X ring gaskets for the kick shaft and the gear selector shaft, I read that they should be set in silicone because the gear oil tends to sneak behind them. should I silicone them in ?

Also should I locktight the cover screws? they always seem to loosen, so I feel like maybe that makes sense...

** I had a scarey moment and couldn't loosen the mainshaft nut for a few hours. I Had to build a jig to hold the sprocket and the box, then added some heat to the nut and use a breaker bar to bust that nut loose,.. thankfully. I've checked numerous threads to see if my layshaft bearing was the original that blows up, and it is, so I am glad I am changing it, but the bearing that I removed is rock solid. Did bad layshaft bearings have certain years where they were bad or were all years for that bearing bad???

thanks in advance for all the help...
 
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Mk IIIs had the crappy layshaft bearing.

When you say "permatex" what, exactly are you referring to? Permatex is the brand name for many different products. The better gasket sealer you use, he more difficult it will be to get it apart the next time. I've been using Permatex Copper-Coat gasket spray lately. Another experiment to hit the happy medium between permanently stuck and permanently leaky.
 
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Not sure about the sealed bearing, mine was not sealed. I believe there is a gearbox seal there already.
I use a SKF 9815 seal available from Napa on the kickstarter, its a metal outer ring with rubber inner seal. Very effective and needs no additional sealant. I've found the gearshift doesn't leak very much with the original type seal as its mainly above the oil level.
Hondabond or Yamabond or similar on both sides of the gaskets. Comes apart fairly easily and cleans up with acetone. The gasket will be toast though.
Blue loctite on all of the bolts.
Superblend or quality roller layshaft bearing.
Here's a good resource on gearbox rebuilds. Check his index for some other gearbox articles. Be sure and check the end float as shown.
http://www.oldbritts.com/gearbox_a.html
 
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I also bought X ring gaskets for the kick shaft and the gear selector shaft, I read that they should be set in silicone because the gear oil tends to sneak behind them. should I silicone them in ?

Also should I locktight the cover screws? they always seem to loosen, so I feel like maybe that makes sense...


If you have any movement in the kick starter bush to shaft, to g/box, the x ring is useless. That seal inside the cover as recommended sounds good. My shaft has play so I use an exterior o ring compressed against the housing behind a shim washer. Doesn't matter how much play there is, it now doesn't leak. Helps remove the end float from the shaft as well.
My g/box covers screws don't com loose. Use the correct sized screw driver.
Dereck
 
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FWIW..I used the SKF seal on my kickstart shaft and had nothing but leaks. Tried it twice just to make sure it wasn't installer error. Went back to the O/X ring and no problems. The leakage was not between shaft and seal, but between the seal and case. The second time around I used gasket sealer on the outer edge of the seal and it still leaked. Perhaps my case is a few thou oversized where the seal sits, or in their quest to lower costs the Chinese factory that made the SKF seal got it wrong...whatever. Sometimes new and improved is not always so.
 
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I rebuilt my gearbox over 35 years ago now to replace a blown layshaft bearing and have only gone back in to replace the kickstart pawl (4 times now), my gearbox has never leaked oil, I don't have problems with gear oil getting into my clutch and have never had kick start or gear lever seals leak, I replaced my outer screws with allen head screws and have never had them come loose at all, the biggest problems some have is they over fill their gearboxes, I don't use the fill pipe to messure my oil level, I use a messuring cup and fill with the recommed amount that the book say to use, if you look in the filler hole the oil should only be half way on the kickstart spring, if its over that you have to much oil in your gearbox, another thing I also do is to put grease on my clutch rod, I have been doing this for over 40 years now and have never had any problems with my gearbox.

Ashley
 
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I have a leak at the kick start shaft that a new oring failed to stop. I would like to get through balance of riding season before sending cover to be modified for a proper seal. I am not sure if I am reading kerinorton correctly that he put oring and washer between kick starter and outside of case? Does this seem to be worth trying?
 
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Try the SKF 9815 seal. You can get them at NAPA. Mines been in there for 5 years and doesn't leak a drop. I never could get an oring to seal.
 
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o0norton0o said:
Did bad layshaft bearings have certain years where they were bad or were all years for that bearing bad???
It wasn't so much that the bearings were 'bad', it was more a case that Nortons didn't fit a heavy enough duty bearing in there as the motors got bigger.
And then let the customers do the reliability testing....
 
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michael levato said:
I have a leak at the kick start shaft that a new oring failed to stop. I would like to get through balance of riding season before sending cover to be modified for a proper seal. I am not sure if I am reading kerinorton correctly that he put oring and washer between kick starter and outside of case? Does this seem to be worth trying?


Have a go with the skf seal.

If it then doesn't work, PM me and I will go through what I did.

Dereck
 

comnoz

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The Mk3 is the bike which had the EARLY layshaft bearing failure. Usually about 10,000 miles.

If your gearbox has a sleeve gear [output] bearing with a seal on one side then someone has been in there before -as the factory bearing was open.[no seals]

The lay shaft bearing was marginal in all the bikes. I would replace any of them with the roller bearing upgrade. They will last pretty much forever. Jim
 

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