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TERMINE und FORUMSTECHNIK => International discussion forum in english language => Thema gestartet von: Studsgaard am 21 Juli 2017, 12:15:54

Titel: Front suspension oil leak.
Beitrag von: Studsgaard am 21 Juli 2017, 12:15:54
Hi Guys.

My BMW R25/2 left hand front suspension started leaking a drop of oil once in a while. Now the rubber boot is FULL of oil and it pours out the small cracks...
A seal obviously needs attention. I haven't been able to find any step by step info on how to proceed. Any advice?
Wheel off, remove boot, top cap, remove the whole inner suspension or hopefully an easier solution?

Titel: Re: Front suspension oil leak.
Beitrag von: Old Bob UK am 23 Juli 2017, 13:01:02
Hi Studsgaard,
                       I'll try to keep this as simple as possible!
Unlike "normal" fork legs the boot SHOULD be full of oil. There are no internal seals.
So all you need is to change the boot. You are on the right track regarding method.
However:- a couple of points to note.
Remove wheel.
Remove both hose clips on boot. Somehow drain remaining oil, even by cutting old boot.
Be prepared for a gush of oil !!
Remove top chrome cover under which is an aluminium 'boss'
Inside boss is a 10mm thread and nut. Undo the nut using a cranked 14mm ring or box
spanner so you can use a screwdriver to hold the threaded part from turning.
The whole leg c/w spring can now be pulled out downwards.
I did mine on a bike lift so had plenty of room but you might have to arrange to lift the
front up to get it all the way out; but the spring is fairly flexible so it might wiggle out.
A parts list shows various bushes/spacers/circlips etc. But these all stay in place.
The spring can now be unscrewed from the leg, for convenience.
'Simply' clean up, remove old boot and fit new boot.
Being plastic the boot can be very tight to stretch over it's fitting but warming up in hot water
helps a bit. Refit spring to leg.
Secure bottom boot clip and offer back up into position. The top spring retainer will find it's own way
into the top boss.
An afterthought to my job:
While at this stage try to check if the top of boot can be fitted to fork shroud BEFORE retainer enters boss!
This will make the extreeemly tedious oil replenishing much easier.
If so secure boot clip on carefully pour 150/170 cc engine oil into fork via top boss.
Jack up leg and secure top nut and refit top cover with gasket.
If this is not possible:-
push leg in and fit top nut loosely for support.
Before securing boot top clip try to introduce some oil into boot, pump action oil can etc.
Secure boot clips and try to put rest of oil into fork through top boss. There are only 2 very small
holes in this, one lets oil in, other lets air out. This process is most annoying and can get very messy!
It seems like about 1cc /minute!!
Secure top nut and fit top cover and gasket.
Refit wheel, check over and away you go.
Think that's about it,
Have a nice day or two
Titel: Re: Front suspension oil leak.
Beitrag von: Studsgaard am 24 Juli 2017, 10:28:32
How very very informative and nice of you Bob - excellent reply, thank you!

One question comes to mind before racing for my tools:
Is it necessary to completely dismount the spring?
I am thinking: Wheel off, boot off, new boot on and refill oil from the top or is this not possible with the spring attached?

Thanks again.
Titel: Re: Front suspension oil leak.
Beitrag von: Old Bob UK am 24 Juli 2017, 12:57:41
I looked into that initially but realised the boot will not stretch over
the axle mounting lump at the bottom of the leg. The leg must be
removed, sorry, and the boot slid on from top to bottom.
As mentioned the new boot is so stiff and tight it is a struggle to even get it
to fit where it's supposed to. Even warming up only lasts a few seconds.
It,s not as daunting as it might seem, in fact it takes longer to write it than do it.
Regards, BoB.

Titel: Re: Front suspension oil leak.
Beitrag von: Studsgaard am 24 Juli 2017, 19:48:58
Thanks again Bob - I'll take your word for it and save the hassle of trying to 'shortcut'. I'll order the parts and get on the case next weekend.
Titel: Re: Front suspension oil leak.
Beitrag von: Jollyjester am 25 Juli 2017, 08:40:04
I agree with all that has been said. replaced the rubber boots on my 1951 R25. basically the same, refilling can be speeded up by squeezing the boot, bit like milking a cow, pushes air out and sucks oil in. After 3 years still oil tight. They last time was in the 1960's using BSA Bantam parts, because, I did not know where to get originals.

They were disposed of when I pull it all apart in 2012

If your R25 is in the UK, and been here all it's life, it may well be listed in  my records /archives from AFN ltd and BMW Club UK&I indexes. Send me a P.M. and I will give a direct contact. even if an import still interested. I am the archivist for the classic / vintage register of the BMW Club

I go on holiday Wed 26th - 5th Aug.
Titel: Re: Front suspension oil leak.
Beitrag von: Studsgaard am 26 Juli 2017, 10:44:21
Hi Jester, thanks for your input.
My bike was originally with the police here i Denmark before it went 'civil'. Unfortunately it doesn't have matching numbers and I guess it won't be in your records.
Have a nice holiday.
Titel: Re: Front suspension oil leak.
Beitrag von: Old Bob UK am 27 Juli 2017, 21:29:48
Hi Studsgaard,
                      I've been thinking about this a lot.
Regarding oil filling it seems to me that, after removing the top 10mm nut,
and providing none of the fittings related to the steering head/yoke assembly
have been disturbed, it will be possible to completely unscrew and remove the
top aluminium boss. This will allow a measured amount of oil to be poured into the leg, 
after, of course, the boot and inner leg have been inserted and supported by loosely slipping
the axle into place. Refit the boss using a smear of thread sealer. Keep the axle in place
until everything is secured.
Worth a look I think, unless anyone can come up with a reason against.
All the best BoB.
P.S. a good exploded parts diagram helps to explain a lot.     (I hope)
Can't get the link to work but you shouid be able to find it!!
Titel: Re: Front suspension oil leak.
Beitrag von: 4Taktix am 27 Juli 2017, 22:23:27
How about a big syringe (let's say 20 ml) to get the oil through one of the two small holes ? (injection-needle removed)
Not sure, which size the wholes are on an /2, but I do it this way on my R25/3, works OK for me.
So you can measure the amount of oil very simple (has to be equal left and right, at least on a /3)
and can also accellerate the filling by applying pressure.
Just my 2 cent.
Titel: Re: Front suspension oil leak.
Beitrag von: Old Bob UK am 28 Juli 2017, 15:15:22
Thanks for your input, all ideas are welcome.
Regards, BoB.
Titel: Re: Front suspension oil leak.
Beitrag von: Studsgaard am 28 Juli 2017, 15:29:31
Many thanks to all of you!
Excellent advice.