Tacho drive oil leak solutions (2013)

PM999S said:

Sorry to jump in on a really old thread but after fitting the RGM modified tacho housing I'm seeing oil forced up the tacho cable as far, as you said, to the clock itself. Any know fixes?

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There is a slot machined in the tach gear's shaft which is really sharp. So there is a chance that when assembling the tach housing the oil seal can get cut, thereby making the oil seal junk.

When I assembled my RGM tach housing a few years ago I made a filler 'tool' that fills the space of the sharp slot in the shaft and protects the seal from being cut. Once assembled, I just pulled the filler out.

Additionally, if the tach gear shaft has a groove for an O-ring, it also has a sharp edge that could damage the seal. What I did with mine is filled the groove with an O-ring that had been buffed down so that the oil seal in the tach housing could slip over that as well.

I have had no oil leaks at all with my RGM Tach drive housing. Here is my 'filler' tool for protecting the tach housing seal (simple but effective):



Peter Joe

Clean and inspect the tach drive housing, gear and oring.

I had a cable break not too long ago which left a groove in the housing from the circlip and left a small piece of metal debris in the tunnel, which nicked the oring. I didn't catch that and after it leaked like a sieve.

Installing a new oring sourced from a local bearing shop to fit the drive gear returned it to its previous leak free state.

PeterJoe said:

There is a slot machined in the tach gear's shaft which is really sharp. So there is a chance that when assembling the tach housing the oil seal can get cut, thereby making the oil seal junk.

When I assembled my RGM tach housing a few years ago I made a filler 'tool' that fills the space of the sharp slot in the shaft and protects the seal from being cut. Once assembled, I just pulled the filler out.

Additionally, if the tach gear shaft has a groove for an O-ring, it also has a sharp edge that could damage the seal. What I did with mine is filled the groove with an O-ring that had been buffed down so that the oil seal in the tach housing could slip over that as well.

I have had no oil leaks at all with my RGM Tach drive housing. Here is my 'filler' tool for protecting the tach housing seal (simple but effective):

Peter Joe

Click to expand...

Thanks but the housing doesn't leak at all what is happening is that oil is now forced up the tacho cable at high revs and even mists under the tacho clock itself. Apart from a previous response that suggested greasing the taco cable, would there be another fix for this?

PM999S said:

Thanks but the housing doesn't leak at all what is happening is that oil is now forced up the tacho cable at high revs and even mists under the tacho clock itself. Apart from a previous response that suggested greasing the taco cable, would there be another fix for this?

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That is the symptom I had with my issue noted above, oil coming out from the tacho end of the cable.

Your problem is the seal (oring and/or RGM seal) on the drive gear not sealing in its housing which allows oil up the cable. You need to inspect those parts and ascertain why this is happening.

This is also what PeterJoe is talking about, why the seal may fail on installation due to sharp edges on the drive gear.

PeterJoe said:

There is a slot machined in the tach gear's shaft which is really sharp. So there is a chance that when assembling the tach housing the oil seal can get cut, thereby making the oil seal junk.

When I assembled my RGM tach housing a few years ago I made a filler 'tool' that fills the space of the sharp slot in the shaft and protects the seal from being cut. Once assembled, I just pulled the filler out.

Additionally, if the tach gear shaft has a groove for an O-ring, it also has a sharp edge that could damage the seal. What I did with mine is filled the groove with an O-ring that had been buffed down so that the oil seal in the tach housing could slip over that as well.

I have had no oil leaks at all with my RGM Tach drive housing. Here is my 'filler' tool for protecting the tach housing seal (simple but effective):

Peter Joe

Click to expand...

I have not seen a modified drive housing that has a seal. Does the oring sit above the seal or does the groove sit in it? I would have assumed the former.

I went through a number of seals with no luck. Fitting the one way breather fixed it. I use the Jim Comstock/CNW breather, Faultless.

I fitted 2 O rings to mine years ago and they have not leaked since. The groove in the shaft is twice as wide as it needed to be in mine so the O ring flattened out too quickly. 2 O rings was a good quick and easy fix.

PM999S said:

Thanks yes that might at least make it more difficult for engine oil to get pushed up the cable. I've also installed the reed valve from Holland Norton Works that cured much of the crankcase leaking so a bit surprised there's still enough pressure to push oil that far up the cable!

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+1 for HNW reed breather & dead simple to fit

Norton Heavy Twin Single Chain (20M3S +)
Tach Drive
left to right
1. housing-big V counterbore (allow easy insertion?) \Have seen these with a big fat oring in the V to augment the small one on the shaft.
2. tach drive gear/grooved7mm shaft - 7mmx5mm oring high up shaft-this shaft used in #1
3. 10mmx7mmx1.5mm nitril- for use in #4 housing
4. housing- small counterbore for metric oring- bottom housing has installed tach drive coupler
5. Tach drive gear/plain 7mm shaft-used in #4
6. tach housing modified for 14mmx7mm lipseal-
top seal has flat face inserted in hole most resistant to crankcase pressure
bottom seal flat face is thrust surface but easier for crancase pressure to over ride seal
7. 1/2"x1/4" CR2450 seal in calipers
8. Tach housing modified for CR2450 with flat surface showing outward
9. Tach housing modified for CR2450-shown empty my choice with the seal cup face side in and gives a broader thrust face for the gear being pushed UP
10. 06-3056 gasket
11. CR2450

I have only heard of and seen the spiral grooved shaft in pix on the internet-never heard of them before this thread...and now on AN site
To me crank case breathers are OT for tach drive oil leaks.
IMO the cure is right here in front of you.

I thought it was a given that with any sprung seal the spring faces that which is being contained.... or are there gaps in my education??
My old Sunbeam had a scrolled crankshaft pulley, hence my advocation and support for the AN solution..

EstuaryBoy said:

I thought it was a given that with any sprung seal the spring faces that which is being contained.... or are there gaps in my education??
My old Sunbeam had a scrolled crankshaft pulley, hence my advocation and support for the AN solution..

Click to expand...

EstuaryBoy said:

I thought it was a given that with any sprung seal the spring faces that which is being contained.... or are there gaps in my education??
My old Sunbeam had a scrolled crankshaft pulley, hence my advocation and support for the AN solution..

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When I first bought my '73 850 in around 1975 it had this problem and I replaced the 'O' ring with, from memory a Ford valve stem seal which I had around and it's still in there now, no leaks!

I have a 1973 850 with the standard tachometer drive, speaking to Andover Norton when rebuilding the engine they advised and supplied the Mk3 version which they said would not leak. It's fitted and does not leak.