Fork Disassembly - yikes!

[AlfromNH]

I took apart my forks. I don't know the history of this bike, but I know this isn't good






The last shot shows the "Support for Damper Pipe", which is mangled from bottoming out I guess. Likely from lack oil causing lack of damping? It's a replaceable part, is it pressed onto the damper pipe?

[montmil]

Ah, yes... the disintegrated rubber baby buggy bumper.

At least you know where the replacements will be located. The rubbery rings on my '81 R65 were nothing more than a very fine sludge sitting atop the Damper Pipe Support.

Which, BTW, just pulls off the damper rod... Although the mushroomed shape of your 'support' bit may require some judicious application of force.

[nhmaf]

Yup - that what those disintegrated rubber bushings do!
Go to the other thread in here where we are discussing George's fork problems, or find the link to my thread, "does my damper rod assembly look odd..." and on the 2nd page of that you'll see pictures of the parts you should order.

If you were gentle and carefully clean those (3) thin "piston rings" and they aren't bent or overly worn, you can re-use them.   New ones are about $7 apiece and the new ones have a slightly different cross section - not as good as the originals if you originals are OK.   But, do get the new (red) topping out bushing, and while you're at it, a new white plastic valve washer, and possibly a new drilled damper valve top plate.   Looks like you've got the older 1 piece damper valve.  You *may* need a new circlip with spring teeth (like Georges).   Also, BE SURE to get new crush washers for the forks for the drain bolt, bottom big allen bolt, and for the top filler plug - they are cheap and you REALLY don't want to reuse one only to have it leak on your new brake pads after you're taking her out for a shakedown ride - I've been there and would have happily paid the 59 cents to have avoided the 2-hour tear down again!

Call up MAX BMW over in No Hampton NH and ask for Rusty in the parts department (or Rose Marston can also help, but Rusty is DA MAN when it comes to airheads and part numbers).   Tell him Mike Fugere sent you and that you need parts for your R65 forks - you can give him the parts numbers from my package pics in the other thread, or you can have him open my order from June to get numbers for some of the stuff you need.

I've got stuff lined up for this weekend already, but if you get in a jam let me know and maybe I'll find an excuse to ride down your way sometime.

[georgesgiralt]

Hello AlfromNH,
I'm also in the process of restoring my fork.
You need the stop rubber (the one which disintegrated) 31 42 1 237 215 (2 pieces), the plastic bushing (white) 31 42 1  242 645 (2 pieces).
The bottom centre bushing (the mushroom) 31 42 2 301 015 which is expensive, do not forget a couple of seals for the fork tubes : 31 42 1 242 646 and all washer :
Top filler plug 07 11 9 963 072 (the less important) drain plug 07 11 9 963 037 (difficult to get outside BMW) and the most important, the one on the bottom 8 mm bolt : 07 11 9 963 130
If it is worn out, new Circlips which are 31 42 1 242 646 (Check the part number for your bike's serial number)
Then maybe the rings 31 42 2 333 753 which will cost you around 35 € the set
Of course a litre of fork oil (between SAE 5 to  SAE 15 weight depending your taste, I would suggest the lighter side for a start) and you've got everything needed for a busy week-end ! .

The rubber bushing goes right at the top of the piston, then the perforated washer, then the white plastic washer, then the valve housing then the circlips, then the centring bottom.
Do not forget to measure the springs to ascertain their state. It would be silly to renew the fork and open it again in a few weeks because the springs are weak.
And you're done.
Bear in mind that the parts number I give you are the one I ordered for my European R65 (1982) and that yours may vary a little. But the guy at the parts department should address that.
You can see my progress at "Nothing goes as planned" thread.

[Barry]

On 79 forks if original you will not have the the sprung seeger circlip like Georges. Look at the parts. You will have the full length valve body and circlip and possibly not even a shim. If there is no shim check the axial play of the valve body inside the stanchion recess and fit a shim if you can detect any play, We are talking anything more than say 5 thou. Shims  come in vaious thicknesses.

[AlfromNH]

Hey guys, thanks for the detailed explanations, I appreciate the help.

I got the bottom "Support for Damper Pipe" caps off, one is completely destroyed, the other shows some cracking.

As far as the "rings":

There's obvious wear, to the rings and the top cap of the damper rod. Is this top cap removable? It looks like a separate part, but the fiche doesn't list it separate from the rod.

I don't see the rings called out on the fiche?

[Barry]

Yes the damper piston unscrews from the rod.

You have a dilemma with the rings though as the general advice is not to replace them. New stock are not good quality and reckoned to cause stiction.  There is a guy who recently had this problem and solved it in an ingenious way by turning out the ring slot to accept a later type plastic wiper.  I'll see if I can find the picture.

[Bob_Roller]

The top part comes off, but iti looks like the whole damper comes as one unit, individual parts not available .

There are two holes at the bottom of the tube, you can put a punch in the holes and then use A 13 mm socket on the to p to seperate the two parts .

I think the last time I did this on my '82 LS, I put a punch in the lower holes then put some thin pieces of wood in a vise and then put the punch and damper in the vise tightened it up and needed an air impact wrench to get the upper part loosened from the tube .

[georgesgiralt]

I destroyed a couple of punch and an HSS drill bit trying to unscrew the top part of the plunger.
So maybe it's screwed and welded in place which explains why the sell the whole instead of the two separate parts.
As per the rings, if you enter the P/N in RealOem, you'll see that they are listed for about all bikes except the R45/R65... Either it's a mistake or they don't fit the R65...
I've ordered a set so I'll told you if they fit or not.
I've also read somewhere that the poor ring quality has somewhat improved recently but I can't find the thread nor the source. So maybe it's a figment of my imagination or will...

[Bob_Roller]

The top does come off, I had them disassembled on my '81 and '82 bikes .

They usually need a good shock from an air impact wrench to get them apart, I couldn't do it with a socket and a ratchet alone .

The forks are a different size on the larger displacement bikes, it would be nice to know if you can use the parts from them .

[AlfromNH]

So if the damper rod comes with the piston, does it also include the rings?

At this point, I think I won't bother trying to get the piston off the rod. The rings look ok, so I'll replace all the rubber parts and put it back together.

[Barry]

My piston wasn't but I heard later pistons were Red loctited so heat would be needed.

As I said earlier there is recent eveidence at least in the Uk that new rings are poor quality.  A Guy called Charles Newall fitted them and was so dissatisfied he eventually did the mod below. Different model and although the piston diameter will be the same R65 pistons may not have the height.

I think if it was me I'd very carefully polish things up and see how it went.

Puzzle is how they got like that the first place. What's the stanchion bore like ?

[nhmaf]

Al -

Sorry to see but from the looks of that pic, I think you're gonna have to order new damping rod - you can check with Rusty, but I am pretty sure that they sell the rod with the top piston as 1 part.  You do have to buy the rings separately, and those rings are definitely too worn to do their job properly...

The thing we have to be careful of, is that even BMWs microfiches have errors - both of omission and inclusion.   So, sometimes one will see an assembly on the fiche with 15 parts, when there are only 8-10 parts to the assembly in any given flavor - they just included all versions/variants of the parts in the one drawing when they updated, added, or deleted part numbers..

[AlfromNH]

Al -

Sorry to see but from the looks of that pic, I think you're gonna have to order new damping rod - you can check with Rusty, but I am pretty sure that they sell the rod with the top piston as 1 part.  You do have to buy the rings separately, and those rings are definitely too worn to do their job properly...

Well that's certainly not what I wanted to hear :-/

I guess the big question now is the one Barry asked earlier: what does the inside of the fork tubes look like? On first look I thought they were ok, but I guess I better clean 'em up and take a closer look.

[Tony Smith]

Al -

  You do have to buy the rings separately, and those rings are definitely too worn to do their job properly...

FWIIW, Motobins P/N Part No.29000 BMW Part No. 31 42 1 232 059

Recently fitted 1 (At around $AU5 each) due to being a bit too rough feeding them into the stanchion. Seemed to pretty much match the existing ones.
 
I did consider putting the rod in the Lathe and fitting the plastic ring but didn't want to be a pioneer. Next time!