Author Topic: Mk fork seals  (Read 3692 times)

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Offline Dougiethenoo

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Mk fork seals
« on: 18 Feb 2016 at 03:13 »
The seal housing that holds the leading link face oil seal on one side of my forks is loose and can float more than the seal thickness back and forth between the fork leg and lip of the bushing.
Should this metal housing for the oil seal (item 24, Plate 24) be fixed to the fork leg, if so, what distance set back from the edge of the bushing?
I did not want to damage the bushings by attempting to extract them - so am preparing to mask up and paint the fork tubes with the seal housing in place.
In order to achieve any kind of pressure for sealing, between this oil seal and the leading link face, I am assuming I will need to weld that cup in place.
Any advice on achieving sealing?

Thanks!

Offline eddie

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Re: Mk fork seals
« Reply #1 on: 18 Feb 2016 at 07:43 »
The seal housing should be an 'easy' fit on the boss of the leading link pivot housing - the flange of the bronze bush prevents it falling off! The seal housings often get stretched/distorted if owners try to remove them without first removing the bush. If you are concerned about it moving, clean the area and glue it in place with 2 part epoxy. If you have problems with a persistent leak from the seals, try wiping dry the face of the link and then apply a smear of thick waterpump grease to the face before reassembly - this dodge has worked on my Comp for the last 30 years!
  Regards,
              Eddie.

Offline Dougiethenoo

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Re: Mk fork seals
« Reply #2 on: 18 Feb 2016 at 11:39 »
Thanks Eddie.
I am going to try to persuade the inner bushes to come out before painting, so I can examine the seal housing, condition of sealing surfaces etc - and figure out why there is such a big distance between the inner bush flange face and the "floating" seal housing on one side only.
I suspect the bush is not seated all the way in and some shimming will be necessary on the front wheel spindle when the leading link sits where it should, to remain parallel.
The existing seals and seal housing had been "glued" in place with some silicon rubber sealant but some new seals and a more positive location of the seal housing to keep the seal pushed against the linkage face appears to be necessary.
Thanks for the tip on water pump grease also. That should make a difference.
Do you know how deep should the seal section be? They appear to be a squareish section, with very shallow ridges on the inside face. Having read somewhere this seal is meant to be a U - section, I suspect the seals are quite worn.





Offline eddie

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Re: Mk fork seals
« Reply #3 on: 18 Feb 2016 at 12:38 »
Attached is an exploded view of the forks. You will see that there is a shouldered steel bush on the splined shaft, then the inner link, and finally the leading link that carries the wheel. To get a good seal, the combined length of the bush, the inner link and the boss on the leading link should be about .005" longer than the dimension over the heads of the 2 bronze bushes in the fork leg. Any adjustment to the bushes or the faces of the leading link will adversely affect the operation of the seal. If the face of the link is badly scored, you can attach a steel shim to the face with 2 part epoxy glue (to regain a good sealing surface) - if you do this, fit a similar thickness shim onto the splined shaft between the inner link and leading link (to maintain the original clearances).
  As you say, the seal is basically square in section, with one outer edge radiused to suit the housing. The operating face has a shallow groove to aid the sealing and also make the seal a little less rigid.

  Regards,
              Eddie.

Offline eddie

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Re: Mk fork seals
« Reply #4 on: 18 Feb 2016 at 13:05 »
Hi,
     Sorry about the last attachment - I'm doing battle with a new scanner that has a mind of it's own!
   Attached is the view I intended to send!
  Eddie.

Offline Dougiethenoo

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Re: Mk fork seals
« Reply #5 on: 18 Feb 2016 at 13:30 »
Thank you, that is a much higher resolution exploded diagram than I have in the parts list.

The problem I am seeing with the seal housing on one side is that it will slide easily back toward the fork leg on the bushing housing, allowing no seal contact at all with the link face - I think the seals are in good shape based on your description - and the link face is smooth, so the housing will either need to be glued/welded in place on the fork leg and micro-adjusted with levers to ensure it is aligned parallel to the link face with just enough compression of the seal when the link is seated against the bushing.
I have not checked dimensions over the link, bolt & splined bushings compared to the fork leg bronze bushings but did not discern any lateral play or float on the pivot bolt before dismantling.
The design of that seal is perplexing, it appears that the seal housing ring must be a very tight fit on the fork leg in order to make the seal work.
Ah well, another challenge!

Many thanks for your help!

Offline eddie

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Re: Mk fork seals
« Reply #6 on: 18 Feb 2016 at 13:58 »
You will find that the forged lug on the back of the fork leg has a machined register for the seal and housing. The housing should sit against the step at the end of the register. There is no need for the fit of the housing to be oil tight as the I.D. of the seal should be small enough to prevent oil escaping between it and the register.

  Eddie.

Offline Dougiethenoo

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Re: Mk fork seals
« Reply #7 on: 18 Feb 2016 at 14:58 »
You will find that the forged lug on the back of the fork leg has a machined register for the seal and housing. The housing should sit against the step at the end of the register. There is no need for the fit of the housing to be oil tight as the I.D. of the seal should be small enough to prevent oil escaping between it and the register.

  Eddie.

Thank you - that makes sense. I guess my problem is that the ID of the seal housing now exceeds the OD of this step. When the forks come back from painting I will investigate further.