Mysterious oil leak

[RogerSB]

Hi all, thought I'd share this:-

For a few weeks I've been seeing a small puddle of oil the size of a small coin on my garage floor directly under and slightly to the left of the steering head. Searching with a torch and mirror didn't show anything.  I know I've pumped plenty of grease in there and my thought was that maybe the grease was melting and leaking. This puddle has been appearing again and again but on checking I still couldn't fathom out where it was coming from.

Last week I was sitting on my garage stool, puzzled by the oil that didn't seem to come from anywhere, when my wife came into the garage with a cup of tea for me.  On mentioning this phenomenon to her she immediately felt under the back of the mudguard stay, showed me oil on her finger and said 'Well, it's obvious it's from here'. What 

Running my finger under the length of the stay it dawned on me that it was from the fork. My immediate thought was a leaking fork drain bolt and oil making its way slowly under the stay to drip from its back corner. On further investigation I discovered it wasn't from there at all but coming from the oil seal holder and running down the outside (but hidden inside) of the fork leg.  Then my conclusion was that it was from the oil seal, but no, it turned out to be from the threaded joint to the fork leg.

Reply no. 25 here may explain it:-
https://www.a7a10.net/forum/index.php?topic=14235.msg118560#msg118560

I’ve just ordered a decent quality strap wrench and my plan (to avoid a strip down) is to first try and turn the oil seal holder to expose a couple of threads and seal it with locktite. If I can’t undo it against the pressure of a sidecar spring I’ll try tightening it.

Anybody had any success with this method?

Rog.

[rayjay]

I wouldn't use locktite on those threads, BSA Recommended two turns of No5 cotton twine (still available) around the bottom threads. I did that with a smear of hylomar sealant,1200 miles so far and no leaks

[bikerbob]

When I did my front fork overhaul some years ago I used PTFE tape just twisted it to form like thin string wrapped it arund the bottom of the threads then tightened seal covers down no leaks for at least 5 years now.

[Swarfcut]

 Roger.  The more I think about how the damn thing leaks, the more it perplexes. Oil can work its way down the threads of the seal holders, coming from below the seal if there is a gap between the seal lower edge and the top of the slider. Any oil that passes the seal on the stanchion will pool above the seal and can then either stay there or somehow work its way back down the threads. Sealing the threads could result in the seal holder full of oil? Suppose it all depends on the quality and function of the seal and its performance on the stanchion.
 
 Ever the cheapskate, I'd only worry when the leak stops, the forks clank and the oil has gone. Check the level from time to time, spread the rust inhibiting fluid as and when, stop worrying. Revisiting the fork assembly thread there was a lot of care and expense involved. A proper job will involve a complete strip to assure perfection, not strictly a worthwhile prospect for a minor irritation. Seem to remember a drain hole was suggested.....

 Swarfy.

[RogerSB]

Thanks to all.  When I overhauled the forks mid 2019 I wrapped twine around the bottom of the threads as recommended by BSA. I did wonder at the time if I'd be better using something more modern but having owned carvel and clinker built boats I knew that caulking works well. Both the forks were treated in the same way, the other leg's oil seal is fine. I'm putting this one leaking due to the threads being opened up a little too much.

Swarfy, The oil seal being fitted above the threads in the bottom section of the holder will get flooded by oil with fork depression.  Simon (at Barleycorn) told me the bottom section of the oil seal holder (the piece that holds the oil seal and with threads) is machined out of a more solid piece, so it's made separate to the top half and both pieces are very tightly screwed together.  To open up the threads in the already finished holders he had to separate the two halves, machine the threads to open them up slightly and then fit the pieces back together again. Quite a job without causing any damage to the finish - and he said he had hundreds to do.

[RDfella]

Have a similar problem with my A10. I just let it leak. Fitted many BSA fork oil seals over the years - mainly when replacing rusty oil seal holders. Never had this problem before I fitted stainless holders. If ever I can be arsed to strip the forks again (got a zillion jobs waiting my attention without re-visiting the A10 forks) I aim to measure the depth as shown in the bottom picture as I reckon the recess is too deep and not clamping the oil seal to the slider. If it was properly clamped, how could oil reach the threads? Sealing the thread seems to me a bit like thinking one can cure a leaky roof by blocking the downpipe.

[orabanda]

To ensure oil doesn't leak past the static surface of the seal, it's best practice to put sealant (loctite 569 is a good choice) on the OD of the seal when fitting it into the seal holder.
Because the seal is rubber backed and the fork holders are often stainless, Primer T needs to be used to prepare the seal and the fork holder surfaces.

A couple of turns of PTFE thread tape on the slider threads will seal the fork seal holder, which can be easily unscrewed in 15 years time when you replace the seals.
Make or buy the factory style seal holder assembly tool (piece of pipe with a Tee bar at the top, and lugs that engage into the slots inside the seal holder).

Richard

[Colsbeeza]

Roger,
 Perhaps your wife should become a Forum member.? She could become a go-to problem solving consultant. Very impressive.!!
Col

[Joolstacho]

Yes Mrs Roger obviously has very handy fingers.

[RogerSB]

Thank you all for your input, maybe I am being a fussy b*****.  It niggles me because the only other leak I have is from the gearbox speedo drive.

When assembling the forks, as an experiment, I didn't use the circlips but A65 fork bush retainers (pic). They are self centralising for clearance around the stanchions but I did need to shim between the top bush and retainer to take up free play between it and the oil seal when the holder is screwed down. One fork needed a 0.010" shim, the other 0.020". I have the correct oil seal holder tool, as suggested by Richard, so I would have screwed it down tight.

It's obvious that BSA expected oil to be able to seep down the threads otherwise they wouldn't have recommended caulking the bottom joint with twine.

I'll give it tweak with the strap wrench and if it doesn't work I'll join RDFella and put up with it. I don't fancy a fork strip at the moment, especially with a sidecar attached.

Col, my wife (Shirley) has helped me with my bikes and cars since we first met. Here she is in 1966 while under training  .

Rog.

[RogerSB]

I used this strap wrench on the leaky oil seal holder yesterday. The rubber strap is about 1/8" thick and only just went between the mudguard bracket and oil seal holder. I made sure it was around the more solid part at the bottom where the oil seal would be and I was able to turn and tighten the holder by about a 1/2 millimetre.  Not a lot but it must have been enough to squash the twine a bit more and on testing it today happily there's no sign of any oil from that joint.

After being able to tighten the leaky one, out of curiosity, I had a go on the one that wasn't leaking, but that one didn't budge.

Rog.

[KiwiGF]

When I did my front fork overhaul some years ago I used PTFE tape just twisted it to form like thin string wrapped it arund the bottom of the threads then tightened seal covers down no leaks for at least 5 years now.

Thats the method I use (on several different BSA’s using the same design forks)  and I have not had a leak yet, I don’t do the fork seal holders up too tight, using a home made tool, actually little more than hand tight, so I can get them undone again when it comes to it.