Oil leak at front wheel

[BEESY]

Do you think that if the leak was caused by over filling then the leak would have shown itself straight away?

By wiping the oil away without tracing where it came from, you removed the best way to find the leak.

You could refill with oil and see where it's coming from, but that only gets you back to where you were originally, or you could take the wheel off to see what that might reveal.

Barring a crack in the fork leg itself, there are only really three or four places it can come from, the drain screw, the shuttle valve stud (if fitted, not 100% sure on your model), the oil seal and the top nut.

[AdrianS]

Oil leaks from overfilling don’t always show up immediately unless a large excess was introduced which takes the level to or above the oil seal holder. The oil seal will stop splash oil but probably wont stop pressurised oil when the forks are in use. You are also relying on the seal of the oil seal holder threads to prevent oil leaking down the fork leg.
If in doubt, it is not difficult to remove the leg, strip and rebuild it and fill with the correct amount of oil.
You only need to buy a seal for a couple of quid if the bushes are ok. Very often the seal holder can be unscrewed without the use of the special tool but I’m sure someone will loan you the tool if necessary.

[Phil C]

The bike is a 1965 B40F, so the forks are Heavyweight.  I don't think there's a shuttle valve (whatever that is!)
I think I'll probably remove and strip down the leg (never done it before, so will be learning as I go along.) Looking at Rupert Ratio, vol 2, p.60, it appears the only must-have tools are an oil seal holder fitting/removal tool, and a stanchion puller (fork leg fitting/removal tool.).   Phil

[chaz]

if you dont have the special tool, and are intending to do the job when the specialist shops are closed, you might try
https://www.eurocarparts.com/p/masterpro-rubber-strap-oil-filter-wrench-6-inch-538770251?gclid=Cj0KCQiA2ZCOBhDiARIsAMRfv9LR2NMqmpLHzd3d5ms8Mr41MHhGYtO2mNQkjn8y8rlA-JgVHUD78dgaAgo4EALw_wcB
40% off on first order
or
https://www.eurocarparts.com/p/amtech-oil-filter-wrench-with-strap-553774870?gclid=Cj0KCQiA2ZCOBhDiARIsAMRfv9KHrpQnvldSgboSKjiLogQsp1Z8O_C0pywfd8TC-ED6LXhVVxgrNvUaAqlqEALw_wcB
which uses sockets
as for the reassembly, a wooden broom handle tapered down has been known to work, for many years

[Phil C]

Thanks Chaz, but I don't think I'll be attempting it this side of new year, esp as I've just this week moved house and am still getting things sorted.   Phil

[Phil C]

Anyone who has no patience for stupid questions, please look away now.

To strip down my forks, in order to check them over and service them, do I need to remove them from the bike (in which case I guess I would need to disconnect the wiring and cables etc), or is it possible to leave the forks on the bike and strip the innards out? The forks (see pics) are, I think, the Heavyweight type.  Bike is 1965 B40F. Phil

[chaz]

normally, loosen the top clamp bolt, loosen the top chrome nut, remove the front wheel and loosen the bottom clamp. the leg should then drop out.
only do the one side and you will not have trouble lining it all back up. service, then reassemble leg into yokes tighten up then you can do the other side . finally re insert the wheel.

take them both out together and you have fun re lining and threading everything back again.
unless. you intend checking the head bearings.

should be re looking at mine this week, sprang a leak from the drain screw and damn bike has not been on the road ,or even off the ramp yet¬¬

[AdrianS]

You can remove them both together but put them back individually.
To remove in one piece and then strip for dismantling, just remove the brake cable from the cam lever, slacken off the clamp bolts at the bottom of the trousers, loosen the chrome top nuts a few turns then tap them with a mallet and the forks should drop a little. Then remove the chrome nuts so the forks can drop. Support the wheel when doing this to avoid too much strain on the chrome nuts. You will have to put the centre stand on some blocks of wood to give enough clearance to remove the forks.
Alternatively, remove brake cable, from wheel, remove mudguard, loosen of clamp bolts and remove each leg individually. There is a special too to screw into the fork leg if it is very tight in the yokes so you can hit with a hammer. This tool also helps reinstallation but the job can be done without it.
As previously said it is a simple fork and relatively easy to service but can be a bit messy!
They are quite a crude fork with not many components. Unless you can feel a lot of play in the fork legs on the bike, the bushes should be fine. I’ve never had to replace fork bushes but am sure others have.
You just need a couple of oil seals, a bit of string, possibly some PTFE tape and some new oil. I use 10/40 oil which I find fine but agains you will get advice to use different grades.

[Phil C]

The string I guess is to act as an oil seal. What kind of string?

[JulianS]

The string is used in the recess - indicated with screw driver in photo - below the threaded area of the fork bottom. BSA said number 5 twine. Good luck with finding that. You could use any suitable size string.

I use a length of PTFE tape twisted from flat into a thread - also a concentric carb O ring can be stretched over the thread and seated in the recess if you prefer.

[JulianS]

BSA fitted the same basic heavyweight forks from 1945 - 1965, varying in mudguard and wheel fitting and fork shaft lengths. The below is from the B31/33 Instruction manual and describes how to remove and dismantle.

I suggest that the battery is disconnected and that the headlamp unit be removed from the nacelle.

Make sure that you safely raise the front of the bike as you would have done when you removed the front wheel to do the brake some time back.

The fork shaft can be a tight fit in the top yoke taper and can also be difficult to pull through the bottom yoke especially if the shaft is rusted and/or dirty. You can very carefully use a wedge in the split in the bottom yoke to open it slightly - not too far or it may fracture. A spray of WD40 can help.

With the fork leg removed the oil seal holder can sometimes be very tightly screwed on and if this is the case the proper tool is needed.

If you replace the oil seal the easy way to fit it in the seal holder is to push it in with thumbs as far as you can the screw the holder onto the fork bottom (before you assemble the leg) and this wil push it all the way in.

[Phil C]

Just to wind this up: after removing the forks, stripping and checking them, renewing the oil seals, checking the brake over, and putting it all back together again, the leak hasn't recurred. So although I'm not absolutely sure where the leak was, I've serviced the forks, had fun, learnt a lot, and - hopefully - cured the problem. Many thanks again to all those who answered my many questions. Phil