Fork Seals

[azcycle]

Well, I noticed a pronounced "clunk" coming from the fork on brisk acceleration shifts when it topped out at it's full extension.  The right leg looks good but the left definitely has a leak... dirty ring around the stanchion and some oil/dirt residue under the seal cap on the lower leg.

So I called two local shops for prices. Iron Horse BMW quoted $225 in labor and $50 in parts.  The generic shop just down the street quoted same parts price and $175 in labor.  Good deal or no?

Is this something a basic shadetree mechanic can do?  I've GOT to get a repair manual, I know.  I've disassembled/cleaned/replaced seals on my mountain bike forks no problem but I know this is certainly a different animal.  I can't imagine it being done without having to mess with the front brakes. (Which actually need to be drained/refilled/bled anyway).

[Barry]

No need to do anything to the brakes other than tie up the caliper so as not to stress the hose. New seals are cheap and replacement is straight forward enough. There is also precious little to replace inside the fork dampers. Usually just a topping out bush and a good clean up is needed.  Your manual should describe the process and a search should find you quite a few posts as several members have done this job in recent years and will be able to help if you get stuck at any point. One thing that might not be obvious is the top plugs are held in with a circlip but you'll find this has ben well covered on the forum.

[ukzknos]

As long as you have the right tools and a bit of technical nous you can do the whole job for about $15 and a couple of hours!
Check the forum you will find plenty of good advice and somewhere a step by step guide  

[azcycle]

Thanks... that's good to hear!  I did a search but must have done something wrong as I didn't turn up any results. I'll try again.

[Rob Valdez 79 R65]

Oh, double that $15 quote by ukzknos - a quart of BMW 7.5w fork oil cost me $15.


And about those brakes - I rebuilt mine a few years ago, and I am glad I did!  The pistons in the caliper were rusty, and the inside of the caliper had this really nasty sludge.

There are a lot of places to play on these old bikes!

[ukzknos]

Rob

Even doubled still a bit cheaper than $225 + parts quoted!

[montmil]

Fork Seal Replacement
 
1.  While the soft metal "crush" or "wave" washers can fairly often be reused, they are supposed to be replaced with new ones, and they are inexpensive to order along with the seals.   These washers are on the drain bolts on the back of the sliders and there are also similar (but different size) washers used on the allen bolts in the bottom of the sliders.  I've reused these washers numerous times, but sometimes they decided that they don't quite want to hold oil anymore.  They usually make this decision while you are out exploring a twisty back road and dump fork oil onto your front brake rotors just when you might need some front wheel braking power.   Also, note how far the tubes are inserted into the upper triple clamp before you remove them - you can put a mark with a felt pen or something on each to help get you back to close to the right spot and even/equal on both sides when reassembling.
 
2.  The small 10mm drain bolts on the back of the sliders thread into soft alloy - DO NOT TORQUE THEM very tight.  The manuals state approx 10 ft-lbs, I think, which I think we'd all agree is an absolute upper limit.  It is VERY easy to strip the threads on these buggers, so use a small wrench and use your "delicate" touch when doing this.
 
3.  When reassembling - and sometimes when disassembling the slider from the tube one has to tighten/loosen and allen-bolt through the bottom of the sliders that screws up into the damper in the slider.    Sometimes one gets lucky, but sometimes one needs to get a looooong extension for a socket wrench to also reach down in from the top of fork tube to hold the bolt on top of the damper and keep things from turning inside the assembly - otherwise you might think that the lower allen bolt has stripped or not mating, but in fact the whole inner mechanism is turning.
 

[montmil]

Fork Seal Replacement, continued

4.  When you remove the top cap and or nut in the top of the fork tube, you need to press down against the tube's spring about an inch or so to gain access to the spring wire "clip" ring that is in a groove in the top of the tube and which retains the assembly.  A small screwdriver or needle nose pliers can be used to pry out the spring - be carefully not to gouge up the inside of the fork tube and SLOWLY release the pressure from the spring so you don't get any parts popping up into your face.   This can be done by one person, but it is what is often called a "3-handed job", so if you have someone to assist you, it can go much easier.
 
5.   When you put the fork tubes back together and have them mounted in the triple clamps, I will put the fender brace, fender, wheel and axle on but leave the bolts/nuts for the fender, brace and axle pinch bolts a bit loose. I'll then push down on the handlebars and let it bounce back up and repeat this a couple times to set the axle and sliders into their natural alignment before final tightening of all the fasteners.   This ideally enables you to get everything tightened up properly in proper alignment, so as to avoid undue stiction and allow smooth, unstressed action of the suspension.
 
Be methodical and take your time and you'll do fine.   IF you get into a jam (but you won't) there are plenty here who can help.

[Bob_Roller]

To answer your question, if the price quoted you was realistic .

My answer would be yes it is .

They charge around $100 per hour of labor, so they are charging you for 2.25 hours of labor .

I doubt if there are many members here, that could do both forks, in 2.25 hours .

Price for parts is not really out of line, when you look at the current prices for the parts .

[caci]

I had mine done last month by Bushong.  I had a cir-clip come loose in the left leg (that means it could fall off!).

Monte's spot on the procedure (I watched).  

A couple of things to be aware of are:

1. The clunk may be either the "top out" bumpers or the limit may have been reached with displaced retainer cir-clips - these are at the bottom end of the tubes - not the spring retainer clips at the top.

2. Make sure they/you check the piston rings - 3 wavy rings on the shaft that make sure the fork oil passes through the metering orifices and not around them.  One of mine was damaged, again, due to the retainer coming loose.

3.  I'm not sure where you are having them done, but like so many other "features" of our bikes - the forks are different.

4.  The bottom allen is a lot less of a hassle if you use a 3/8" impact to remove it (before the inside can start spinning).

5.  Like Monte said, Clymer has step by step instr. - the most tricky part is re-inserting the valve assembly - getting those piston rings past the sharp step in the bottom of the fork tube - beer can, feeler gauges, factory beemer tool, etc.

I'm contributing to this thread because I watched a guy whom has probably done a LOT of these and he had to think about a couple of things on my forks, because they are a little different.  

The top out bumpers are polymer and evidently deteriorate over time (spring top outs are more common).

Regards,
Chris

[Rob Valdez 79 R65]

You might want to read through this thread of mine, recently.
http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1254093089


If you do this yourself, you will want to get a set of 3/8" drive allen keys for your ratchet wrench.

For your OTHER ratchet wrench ( ), you will want about 18-24" worth of extention, and, a 13mm socket.  That goes down in the fork leg from the top after you have removed the oil and spring.  (see link)

WARNING: the drain plug screws will easily strip the soft, aluminum threads in the fork legs.  Take care.

[Barry]

he most tricky part is re-inserting the valve assembly - getting those piston rings past the sharp step in the bottom of the fork tube - beer can, feeler gauges, factory beemer tool, etc.

The method I used was to insert the damper rod from the top. The circlip groove at the top of the stanchions has a tapered lower edge which guides the rings in nicely. You can even just about do this with the valve body already in position at the bottom of the stanchions.

[Barry]

The clunk may be either the "top out" bumpers or the limit may have been reached with displaced retainer cir-clips - these are at the bottom end of the tubes - not the spring retainer clips at the top.

Interesting comment caci what year is your bike?  I found that the valve body had .040" play and had to make shims to eliminate this. Mine is an early model though and by 81 the valve body should have been modified either shimmed at the factory or will have a shorter valve body and spring retainer fitted.

[caci]

The clunk may be either the "top out" bumpers or the limit may have been reached with displaced retainer cir-clips - these are at the bottom end of the tubes - not the spring retainer clips at the top.

Interesting comment caci what year is your bike?  I found that the valve body had .040" play and had to make shims to eliminate this. Mine is an early model though and by 81 the valve body should have been modified either shimmed at the factory or will have a shorter valve body and spring retainer fitted.

Mine is an '84.  
Remember the part where the bottom cir clip had come loose?  It was "dished" a little bit - instead of being flat, it was slightly cupped, like it had ben forced out of its groove.
When "we" were reassembling, we could not get that clip to fully seat and discovered that a thin (about .010") shim could be left out and the clip snapped right in.
Maybe mis-fit from the factory?  My bike has 14,000 documented miles and I'm pretty sure this is the first time the forks have been apart.  I would have not even fooled with them, as the seals weren't leaking.

I had already drained and refilled the fork oil.  I had removed the front wheel to paly with the brakes and noticed that the forks were no longer in alignment. The fender bracket was the only thing stopping the slider from falling off!  I had visions of a previous frame twisting crash that had left everything in a bind - luckily, that wasn't the case.

[caci]

he most tricky part is re-inserting the valve assembly - getting those piston rings past the sharp step in the bottom of the fork tube - beer can, feeler gauges, factory beemer tool, etc.

The method I used was to insert the damper rod from the top. The circlip groove at the top of the stanchions has a tapered lower edge which guides the rings in nicely. You can even just about do this with the valve body already in position at the bottom of the stanchions.

Good point.  I do remember reading about that method, but as I had mentioned to Perry about the fork coming apart, he offered to re-install the piston, because he had the factory tool (slides in the bottom, has a thin-walled part to allow the rings to slide in without catching the edge.)

I had read on several web pages about installing from the top and had I tried to do this myself, that is how I might have done it.

I'm glad that Perry looked at it, as I would have missed the top out bumper. It was black (originally white) and split (I didn't notice).

Maybe the "normal" (all other R) forks, with their screw-in top caps, don't lend themselves to "from-the-top" installation.

I can confirm - on mine, at least - that you would not be able to install from the bottom withoust some kind of guidw, as the transition is very sharp and piston rig damage could result.

Again, this began as my mentioning to Perry about the left fork "hanging" lower than the right when I attempted to re-install the front wheel and discovering the problem with the cir clip.  

He offered to slide the damper assembly together and after he noticed the bumper and ring, it became a "fork rebuild", with new fork seals and the previously mentioned top out bumpers.

The charge was very reasonable, as I removed the forks beforehand.