R65 1982. Fork seals failling when riding on cold outside temperature .

[Burt]

George, 

What was the turn around time from the date you ordered the forks, please?  I understand that things in Europe are a little quicker. 

The exchange rate for me in Australia is favourable but the postage will be some thing extra and I have the option of having them shipped to the UK and carried out for me. 

Cheers, Burt. 

[georgesgiralt]

Hello Burt,
I ordered them on Feb. 12th (and paid them by instant European wire transfer, something which could normally take time) and the parcel was scheduled for delivery on the 18th. Which I had to postpone to the 19th because I was not home on the 18....
The seller, Moto-point.pl said he is speaking English, but you'd better ask Deepl.com to translate into Polish ;-) I can't tell for the maker, Acribyus because I did not contact them (and I doubt they will sell to individuals ? ).

These tubes are sold in France  by a reputable pattern part seller (Bihr). I bet they are from the Polish maker. And the price is greater than the Polish one but far less than the BMW tag. So maybe some pattern part maker will/could sell them Down Under .... And the price may be reasonable if you think of the shipping costs...
I've to get the reassembly going ! Have a nice day !

[Burt]

Thanks George, 

A quick turnaround was what I was after, instead of weeks.  That is good to know and most helpful. 

I shall contact them and explain my options, in Polish as well.  They are for a K series BMW and I can borrow another set of forks as an interim measure.  I have someone travelling from the UK to here in two weeks with a few parts already, so that is one of my options. 

The price of two of them is still less than the price of one here.   

Cheers, Burt. 

[georgesgiralt]

So perfection is not of this world...
I can't install the stanchions on the bike.
The hole on the yoke is a bit too small (around 6/100 of a millimeter)  because the new stanchions are a bit nearer of the nominal 36 mm diameter than the BMW supplied ones.
I've to remove this material on the aluminum yoke hole because I will not be able to remove that amount on the stanchions (hard chrome, and the thickness of the chrome deposit may well be less thick than that... ).
So I'm looking for a smooth way to do this on my garage... And keep things straight and perpendicular in order for the fork to have no stiction...
Any ideas ? Tricks ?
Thank you for your help !

[Barry]

I can think of ways of removing material with a suitably sized flap wheel but the problem is keeping the holes parallel and truly perpendicular to the yoke. Only machining can do that. 

Another thought, if the old stanchions are scrap how about applying grinding paste to them and using them as a lap by rotating inside both yokes at the same time to maintain alignment. 0.06mm is quite a lot to remove that way so it will be a slow job.

Whenever I remove my stanchions and replace them they are a tight fit and I need to insert a hardwood wedge in the gap of the yoke to gently open them up a little.

[georgesgiralt]

Barry, good thinking. I'll give it a try if I've to machine them. Someone in France, suggested to heat the yokes at 80°C and that should do it. So i'll try this first...

[skippyc]

I've used heat from a heat gun to remove and replace stanchions

[Burt]

I was discussing this over the weekend on a motorcycle trip and the suggestion was to use 80 grit sandpaper on the stanchion.  It will dull the chrome finish but may solve the problem.  Kerosene was recommended as the lubricant as it can be a bit abrasive as well but I have not heard of that before.  The usual criss-cross pattern to even it out and don't use Carborundum sandpaper.  A lot of work though and I just don't like the idea of removing material from the yoke.  Unless it is the last resort and done in an engineering workshop. 

If you are planning on using heat then you may want to find a large enough freezer to throw the stanchions in for a while.  Alternatively, is there any snow outside?  For my way of thinking, I would only be using heat if something is designed as an interference fit and it is recommended as an installation procedure. 

As I am still considering a set of those stanchions, I have the option of access to a lathe.  However you mention you are carrying out the work in a garage, so not an option for you as that would be my preferred method in this situation. 

[georgesgiralt]

Some progress and success.
My set up :

I used the old tube to make the fork geometrically correct and the whole is tightened properly with the correct torque. 
and after heating up to 70°C ~ 80°C here I am :

There is even some play (I can't measure it)
And the yoke is not forced open by any mechanical method. Only some heat...
So I bet I won't need to grind the yokes, after all...
Some more pictures when the bike is reassembled...
Thank you all for your insight and help !

[georgesgiralt]

Starting to look the part ....


I heated to 50°C ~60°C  and it was enough to slide the tubes.
The difficulty was to set the proper 190 mm measurement and clamp the tubes in the same time. The tubes slide very very well when the yoke is heated...
Today challenge is to put the fork on and install the upper yoke. ....

[georgesgiralt]

An update.....
Searching to prove me right into the BMW Maintenance manual, I stumped on the dimensions and tolerance for the fork tubes and stanchions.
The new Polish ones are only 1/100 mm above tolerance and the old ones are between 2 to 4/100 mm under tolerance.
I bet that this smaller tube make the wiper's gasket job very difficult...
As the fork is assembled and on the bike, I can't measure the inner diameter of the fork tubes but ....
It is funny to note that the hard chromed stanchions which are very very hard are the parts wearing the most !

[Barry]

An update on the depth measurement...


I've just dropped a thin steel rod down through the spring and I get 470mm to the top of the stanchion plug.

[georgesgiralt]

Thank you Barry, I've got the same measurement.  Do you get the rod wet ? And if yes, how many mm got wet ?

[Barry]

Yes rod was wet. 

I aim for 35mm which is the the middle of the recommend range of 20mm - 50mm above the damper piston top.

I have run as low as the 20mm level and the forks still work fine but with a softer feel and more dive.

My understanding is that 190cc should give a 35mm level.  Where there is some confusion is that the BMW information says 190cc for both an oil change and a dry fill after the forks have been dismantled. That can't possibly be correct. I can recall members here recommending more oil for a dry fill perhaps 205cc but I'm not certain.  It doesn't take much oil to increase the level. Many years ago I calculated the internal volume of the stanchion and subtracted the volume of the spring which gave a result  of 3.6cc per 10mm increase in level.  I predict that if you were to add only 15 cc more oil you will see an oil level on the dipstick.

[georgesgiralt]

Thank you Barry for the follow up. I actually removed the oil on one side because I was thinking I may have omitted to put some in... So, now I've the remaining oil from the first fill an 190CC on top.
If I've some time tomorrow, I'll put my dipstick in and check...
Will report back.

Edit : So, I used my dipstick to check the side where I changed oil. You are right. 190 CC is good for a change of oil but not for a dry fill. On this side the level is at around 5cm on the dipstick. The other side is, as I told you dry... So I added some oil to get to approximately the same level (it is difficult to read the oil level as this oil is near transparent ).
I've learned a new trick.... Thank you.