Fork rebuild

[Soeren]

Hello my guys

I'm standing before a fork rebuild because of a blown forkseal and the fact that I have no idea what state the fork is in, but judging by how the rest of the bike was maintained by the previous owner I am suspecting the worst.
I was hoping there was a complete rebuild kit available for the R65, but this dosent seem to be the case.

My situation is like this, my bike is my only means transportation and I need it for work, so I want to make sure to get all the parts that potentially could need replacing, and do the rebuild all in one go without having to wait for a part.

Parts list:

Forkseals
Front fork boot / dust cap (I have one that is split)
Fork boot inner felt strip
Fork oil
Springs (I'm thinking of getting Wilbers Progressive springs)

I have read about the damper piston rings but dont see them at motorworks or motobins, whats the deal with that?

Am I missing something?

And lastly, my steering head bearings seem slightly worn, I can feel the grooves in the cup ever so slightly. Should I replace these when I'm already in there. Or can this easily be done later on?

[Barry]

Hello Soeren,

You missed out the part most likely to need replacement which is the topping out bush. They are often found to have broken up or dissolved into mush.

If the bike is an early 78-80 model it might benefit from the damper valve body and washer being replaced with the later version. At the very least ensure there is no axial play when the valve body is installed in the stanchion.

Personally springs would be the last thing I'd think of replacing unless laden sag measurements have shown the springs to have insufficient rate for your weight. The stock springs are dual rate and the spring rate is already high enough for most riders. Fitting anything stiffer will make controlling rebound without a clunk even harder. If you do need to change springs at a later date it's an easy job that requires only the top plugs to be removed.

I wouldn't replace the damper piston rings. It's usually unnecessary and there are stories of replacements being too big.

While it might be good idea to do the steering bearings at the same they could be done later without any dismantling of the forks other than removing each fork leg as a whole unit.

[georgesgiralt]

Hello
As far as I know, the later piston and spring is not available from BMW.
Last but not least, the rings are to be taken from another bike as they are not listed for the R65. If you do a search on this very website, you should find them and see a picture of the packet I got from BMW. I can't reach my notes with the P/N now as I'm not at home.
The bumper stop also can be sourced from another bike than the R65 but the others P/N are very hard compared to the correct part for the R65 which dissolves in the fork oil in a very short time. I think BMW is slowly searching for a replacement done by another maker...
Do not stock the orange R65 bump stop as they transform themselves into goo on the shelf.

[Barry]

The harder topping out bush that Georges refers to is this:

[Soeren]

Thanks a lot, seems like I'll stick to changing forkseals, front fork boot, boot felt, top out bushing and oil for now.

BTW I think the damper ring kit is this one 31-42-2-333-753, can you confirm?

And should I go with the harder clear rubber bumper rather than the red/orange one thats specific for the R65?

Sorry Barry, I forgot to mention its a 1983 

[Barry]

An 83 should already have the updated damper valve.

The choice of bumper bush is a choice of durability. I have had the hard bumper in for 10 years without any sign of deterioration while recent stocks of the red rubber bumper have failed very quickly as Georges advised. i would prefer the softer bumper if a more durable one could be found.

[Tony Smith]

In addition to the very sound suggestions from others I would also order damper piston rings - the reason is that people insist in trying to force them in from the top of the fork leg and every R65 forkleg I have ever pulled apart has been missing piston rings (they go in easily from the bottom of the fork leg). I would also fit gaiters rather than a dust cap - my on the ground experience is that fork seals protected by a gaiter last much, much longer than those that are not, besides gaiters look cool! Buy the "good" ones from Motobins and not the cheap imitation ones.

Fork fluid - I use a 50/50 mix of Castrol fork 5 and fork 10, but then I weigh north of 125kg so if you are lighter you would want to t3.5"rim back the amount of fork 10.

Because of my weight I inevitably end up putting spacers on top of the springs, check the free length of your existing springs and if they are within spec, you might want to go the same way - I use bits of alloy round bar I bought from a salvage yard, I currently have 3.5" spacers on top of fitted new standard R80ST springs. Oh, one more thing. If you do not own a rattle gun you are going to need to borrow about 1 yard's worth of socket extensions so that you can use the 13mm castellation on the top of the damper rod to undo the bottom damper rod retaining bolt.

Finally, buy new alloy or copper (I prefer copper) crush washers for the damper rod bolt and the drain bolts.

Have fun

[Soeren]

Damnit, the order was already shipped last Tuesday, and I chose not to buy a full set of rings, I bought two just in case one was dammaged or missing. Now after Tony's relpy I feel I should have bought a full set of six, oh well you live and you learn

[Barry]

I've had the forks apart half a dozen times and never broken a piston ring. Given care there is no reason you should break them.

[Speyman]

Give a call to Rubber Chicken Racing. Tom Cutter will assemble a kit for you that will contain all the necessary part.

[Tony Smith]

I've had the forks apart half a dozen times and never broken a piston ring. Given care there is no reason you should break them.

I quite agree, in fact you would have to work hard at damaging a piston ring when inserting the rods from the bottom of the forks.

However it has been my experience that very few people know that is how you are supposed to do it and that they insist in inserting them from the top, which frequently, or perhaps usually, results in one of more of the rings becoming  "kinked" and therefore useless.

[georgesgiralt]

May I add that I use a foil of aluminum from a beer can to act as a "cone" to insert the piston with the rings.
The sheet metal is sufficiently thin to accept to pass between the cylinder and the piston and, this way, you are sure the rings will stay at 120° interval as you put them.
Just my 2 ¢