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Hello,
I dig into my notes and saw that I was using Motorex 2.5W fork oil for ages.
Can't find the reasons and the rationale for switching to Bel-Ray and changing weight.
The nearest shop sells Motorex oil and has the whole range available (as he serves a lot of makes and a lot of enduro bikes).
So maybe I was told that 2.5 was too thin for the seals to function properly ?
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BMW Technical Q&A, Primarily R65 / Re: r65 mono upper fork leak
« Last post by skippyc on January 25, 2025, 12:54:40 AM »
The steel washer is never going to seal unless the surface is perfect. They must have thought that little or no oil would get this far up.
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A 50/50 mix of 5W and 10W will give you 7.5W. 
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Bob,
I spent some time examining the fork stanchions (and I *also* used a magnifying glass).
They are fine and "pristine" (given the age they have ...).
The only defect I can see is a slight discoloration (the chrome colour going to a shade of gold ??? ).
No bump or crevasse I can sense or see.
I've also checked my notes. Last oil change was done using half 2.5 W and 5 W Bel Ray fork oil (someone suggested this could lead near 7.5 W grade... )
This oil change took place after replacing the left fork seal which failed ..... My notes do not specify replacing the right one, though.
So the plot thickens...
As I've no fork oil left, and no new fork seals, I'll ask the local BMW guru about the proper oil to use and ask for an expert exam of my stanchions...
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BMW Technical Q&A, Primarily R65 / Re: r65 mono upper fork leak
« Last post by Burt on January 24, 2025, 01:17:30 AM »

Don't ever use PTFE tape on a fine thread on a motorcycle as it's not designed for that. 

If you are using a Loctite based thread sealant, then use a thin line on two or three threads only.  Don't drown the thread in the stuff.  That was how a company Rep. explained to us how to use it many, many years ago.  Always put the cap back on after use and keep it in the fridge to prolong its life. 
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I was discussing this with a friend who does suspension stuff for a living.  The only thing apart from replacing the seals is, have you cleaned up the chromed stanchions sufficiently?  By this I mean rubbing or applying pressure equally with about 400 grade Aluminium Oxide sandpaper in a way that covers the wear areas adequately (criss-cross pattern) to remove any high spots from stone chips, insects, etc.  This is what we used to do on small aircraft when replacing leaking undercarriage struts.  Obviously a lathe would make this easier.  The only other thing could be a low spot spot on the stanchion. 

Generally speaking, I believe the BMW OEM seals are the best.  Is there any chance that the seals have gone hard, as in old stock way past its use by date?  I'm thinking of the very small amount of thermal expansion/retraction that occurs between dissimilar materials during extreme temperature variations combined with wear. 

Is it possible the stanchion is sticking and the leak occurs when you start riding and is still visible at the end of the ride? 

I'm not criticising anything you have done but just trying to suggest possible causes. 
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I don't know if in real world application this makes any difference or not .
I used OEM fork oil 7.5 wt for decades.
It's now not available.
I started using Bel Ray 10wt for a few fork oil changes and had no issues.
The temps here in the Phoenix area usually don't get to the freezing area .
Low temps in the garage are around 60 F, 16 C when I leave for work around 4:45 am.
Air temps on the road upper 30's F to low 40's F, 4 to 6 C.
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Can't find the old oil bottle. But it was Bel Ray low viscosity. Something like 2.5 or 5W.
It was something an old timer BMW mechanic suggested, I think.
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I've got some general questions .
What weight oil are you using ?
What quantity of oil do you put in each fork ?
Any rough spots on the fork tubes ?
I've started putting gators on the forks when I replace seals .
They didn't look right when I put the first set on but I've accepted it since .
Weight oil : Don't remember the exact value but very light. I bet I've the bottle on the shelf, though
Quantity 190cc always put this exact same amount since 1984.
Rough spots : No I checked them more than once and they are more smooth than a baby's ass.
This is why I asked, as I can't find any reason for them to leak. (and as I do not use the bike that often, this increase the cost per km tremendously  !)
20
I've got some general questions .
What weight oil are you using ?
What quantity of oil do you put in each fork ?
Any rough spots on the fork tubes ?
I've started putting gators on the forks when I replace seals .
They didn't look right when I put the first set on but I've accepted it since .
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