MK3 Mainshaft > Clutch oil seal 065956

Hello all,

Looking for some advice. My MK3 always has a very small oil leak. Its because the gearbox seems about a 3/16 too far forward and the mainshaft where it goes through the primary to the clutch through oil seal 065956 (the seal in the primary behind the clutch). Its not centering properly in the seal and that is where its leaking from.

Does anyone know any tricks to get the gearbox main shaft centered in the primary seal??

The gearbox wont budge back or forward, tried that.

This is the seal I am talking about, #5

Cheers, Jerry

If you open out the gearbox mounting holes that were slotted on the pre mk3 cradle then you can move the gearbox closer to the seal centre.

Evening Jerry
How close fitting are the three engine to cradle bolts? One of the mods list in the 'Norton tuning notes' was to ream these holes and swap for 'fit bolts' Presumably the works racers had problems with the location of engine to gearbox.
My own experience of this issue was having to address the missing lug at the bottom lefthand side of the gearbox cradle. A full days job. I chopped off a bit more of the cradle so i could weld on a nice triangular plate, refitted the cradle to the engine and drilled through the new lug, I then welded up the opposite cradle bolt hole and drilled through that then reamed through the whole lot. Fit Studs made from 160mm Long 10mm Bolts making sure that the plain section of the stud sits across the engine to cradle interface. All the holes in the cradle were worn and had to receive the same treatment (welding, drilling and reaming)
I also turned up close fitting gearbox mounting studs to stop the box moving about between the plates. This cured the seemingly out of line gearbox mainshaft you are experiencing.
regards
Peter

Thanks for the response.

My gearbox holes in the cradle are not slotted and I dont want to take the gearbox out at the moment. I want to ride it. I just cleaned everything up and put the inner case back on to have another look. I think I was a bit over with 3/16. I have not measured it, bit its more like an 1/16 to 1/8 off. See pic. It did not leak before, just started since I went in there to do some other work. so I might just replace the seal.

How do I know it was leaking there?
I purchased a small inspection camera and could finally see where it was coming from.

I feel your pain! It's hard to line up the parts so that the seal is aligned. I made up a tool wherein one half slides over the mainshaft, the other sits in the primary cover where the oil seal goes. When you get it to where the two fit together all is well. I had to loosen up all the engine mounting bolts, gearbox bolts, headsteady, etc. . Using ratchet straps I was finally able to get everything in line and tight. It's a job, but the only way I found to stop the leaks. Good luck!

Any use:

Andover Norton do a tool for it...............

JOHNO23 said:

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Andover Norton do a tool for it...............

Click to expand...

But that tool is not for a MK3 as its for 'Up to 74' the 74 has been clipped but is on a photo.

kommando said:

But that tool is not for a MK3 as its for 'Up to 74' the 74 has been clipped but is on a photo.

Click to expand...

Oh yes, I only saw “fits all commandos “

I’m glad I didn’t buy one then! I’m literally fitting the inner primary case today. I will have to do it by eye................

milfordite said:

I feel your pain! It's hard to line up the parts so that the seal is aligned. I made up a tool wherein one half slides over the mainshaft, the other sits in the primary cover where the oil seal goes. When you get it to where the two fit together all is well. I had to loosen up all the engine mounting bolts, gearbox bolts, headsteady, etc. . Using ratchet straps I was finally able to get everything in line and tight. It's a job, but the only way I found to stop the leaks. Good luck!

Click to expand...

British fettling at it’s finest.....

milfordite said:

I feel your pain! It's hard to line up the parts so that the seal is aligned. I made up a tool wherein one half slides over the mainshaft, the other sits in the primary cover where the oil seal goes. When you get it to where the two fit together all is well. I had to loosen up all the engine mounting bolts, gearbox bolts, headsteady, etc. . Using ratchet straps I was finally able to get everything in line and tight. It's a job, but the only way I found to stop the leaks. Good luck!

Click to expand...

Hi milfordite,

Can you please post a picture of your alignment tool? Is it applicable when g/box is in place?

The problem with the Mk3 design is tolerances on all bolt connections adding up (cases to primary cover, cases to cradle, cradle to gearbox bolts, gearbox lugs to g/b bolts). While I guess it is possible to negate all the tolerances by using a clever alignment tool, there is no guarantee the centralising is maintained (bolts will move around unless there is some expander mechanism fitted to each of them). Reaming holes for "fit bolts" may be necessary but will require the cradle to be modified also.
One way to get around this problem permantly is by intagration of an outrigger bearing in the primary cover, thereby centralising the mainshaft to the cover. It would have been rather easy for N-V to incorporate this change in the original design. The modification has been discussed here before.

-Knut

Certainnly no idea why the seal protection tool would not work on the MKIII. The sleeve gears are sometimes chamfered and would prevent seal damage. The chamfer is however NOT consistent as I have both early #5 profile and late # 6 profile sleeve gears with either chamfer or sharp edged.
I know I made one of these tools decades ago but it is hiding real good right now...

mdt-son said:

Hi milfordite,

Can you please post a picture of your alignment tool? Is it applicable when g/box is in place?

The problem with the Mk3 design is tolerances on all bolt connections adding up (cases to primary cover, cases to cradle, cradle to gearbox bolts, gearbox lugs to g/b bolts). While I guess it is possible to negate all the tolerances by using a clever alignment tool, there is no guarantee the centralising is maintained (bolts will move around unless there is some expander mechanism fitted to each of them). Reaming holes for "fit bolts" may be necessary but will require the cradle to be modified also.
One way to get around this problem permantly is by intagration of an outrigger bearing in the primary cover, thereby centralising the mainshaft to the cover. It would have been rather easy for N-V to incorporate this change in the original design. The modification has been discussed here before.

-Knut

Click to expand...

Sorry, I am in the middle of moving house and all my stuff is packed away. I thought I might have a pic, but no luck.

If the leak is too much to live with I would consider cutting out a larger hole in the inner primary so you could make a seal holding plate, fit it over the mainshaft, letting it find its position, then drill and tap the inner primary case to secure the plate. Perhaps 4 allen button heads with locktite.
Whatever the cure it will take several hours of work. Hope you have a milling machine.

How did you try moving the gearbox, Jerry?? Sorry if it's Granny/eggs here, but did you try standing on the bottom run of the rear chain? A bit neanderthal but it puts the pressure where you want it: At the sprocket....

MichaelB said:

British fettling at it’s finest.....

Click to expand...

NB; Norton's are going to be made in India...Gulp!

“(bolts will move around unless there is some expander mechanism fitted to each of them)”

Not so.
once properly tightened, the clamping force of bolted assemblies will hold position. If bolts “move around” that is the beginning of a relatively swift catastrophic failure.