Not a lot, actually.

Had it not said "DO NOT OPEN" and "NICHT ÖFFNEN" I probably wouldn't have bothered, but, as I had a knackered damper, well............  

I first milled a bit off the side of the top cap to see if there was evidence of a thread.....nothing. So then I milled two flats on the top cap to be able to grip it in the vice. With some heat and a lot of leverage the top cap moved and came off. It appears to be a pressed fit with some sort of glue.   

Once that was out of the way, I was greeted with another "DO NOT OPEN" "NICHT ÖFFNEN" on the top seal holder. This required some pressure to squash the seal that's situated below the holder so that I could release the spring circlip; a bit tricky, but by putting the body in the lathe chuck and using a tubular spacer over the damper rod, I was able to apply enough pressure from the tail stock. Once the circlip is out of the way, the bump stop (that red thing) gives enough free play to push out the seal holder.

Another wire circlip which locates the lower seal holder comes out easily which then allows the piston assembly to be withdrawn.



One point worth mentioning is that, as there is no separate 'air pocket' to compensate for the damper rod volume, the damper will only work properly when it's fitted the right way up; ie, with the alloy fitting at the bottom.

So, what now: maybe I'll make a new damper rod (the old one is worn through the plating) and re-assemble it just for the fun of it. Can't imagine using it though, there are better dampers around.

I liked getting past BMW's instructions though,    why shouldn't it be opened?

Paul.

I liked getting past BMW's instructions though,    why shouldn't it be opened?

My sort of thinking and as for don't open they are afraid that you will then be able to fix it for sixpence and not buy a new shock for $6XXXX

I was the sort of kid who hadn't even thought of going down to the river till my parents told me not to go down to the river

Good work Paul thanks for opening.
My '86 K75C has an aftermarket damper but the PO gave me the "origional" Koni.
I assumed that they came with Koni, is that not so ?
Perhaps very early ones had BMW dampers?

If anyone can make that "shock" work again it's you Paul, please try.

If you have a KONI then get it rebuilt but no BMW ever came with a KONI to my knowledge.

Ghost who rides wrote:
I assumed that they came with Koni, is that not so ?

Bilstein.

When I bought my K75c it had a Koni on it, I adjusted it to suit me and rode it everywhere, all was good, so one day decided to send it to Rad shock repairs in brisvagas and have new oil and a recharge of the nitrogen in it, when I got it back it was an effort to set the damping up again and 1000ks later a bump was felt everytime the shock worked, so bought the spare bike to use the shockie off it and sent the Koni back to rad to have it fixed, got it back and the same problem appeared when I adjusted the variable damper, so I sent it back again, got it back same problem, so took the K100 shock to the bmw centre and bought an exchange unit that is still on the bike today, works fine but only 110mm travel. Many people have told me to send the Koni back again, but I think if you bump your head on a low hanging branch every time you pass under that tree, how many times do you do it before you learn not too. so havent. but will take it to the Koni place in Sydney one day when the bike is heading that way, one day. I will make sure they can do it properly this  time. The stock rebuilt shock is good so far. I however would be interested to know if our shocks are nitrogen filled and if so was yours full of air of nitrogen as I had thought. Also that shock shows a linear damper setup and I do wonder how it could be changed to increase damping with bump speed or depth of travel just so it can be set up for progressive springs, so have a fiddle if you will and give us your opinion. I will be asking Koni if travel can be increased to 130mm to mimic the generous and good ride experienced on the R100's I have ridden in the late 80's.

geez your over thinking that one keith

bilsteen made some well designed shocks (many held in great esteem these days and for all sorts of applications ) ...but are we kidding ourselves that anything rubber lasts past 25 or so years

good luck with the koni hope you find a fix - resolution,  they always worked well for me ...although I have to say ..that the design - application might be better explained to the rebuilder so that he can rebuild to what he knows work ...not what the shock was designed for  ...I have seen some terrifically mismatched fitups ......from the wrong references ..just lack of knowledge  in many cases ..like wrong springing for load and all that stuff ...
hope that helps


thanks for the insight paul...great work ...yet again

No KONI motorcycle shockie ever came with pressurized nitrogen they were all straight forward oil damped and any that I ever rebuilt were just put together with the normal air that was surrounding me.

The BMW (Bilstein) unit is just oil damped.......and the remaining oil that was left in the damper was black!

How does it get black in a sealed chamber?    

Paul.

I think we have seen something similar on some fork oil exchanges paul ...given that they do have some element of air exposed to the oil

I would suggest as the seals deteriorate , air , water etc does infact get in and aids in the corrosion effect of the piston assembly working constantly up and down the bore . I recon there is a slight reaming effect over the years mixing cylinder wall particulate and other metals  with the remaining oil - now gunk

I recall that my rear shock got to the stage of latching itself in the fully compressed position after a somewhat large road surface deviation , periodically ....on the way to our first get together down in Urunga a few years ago now . 

the "rad shockie" guy often mentions  hard chroming the piston rod for all rebuilds
 he has a stack of them in his workshop ...almost crates of them each week from all sorts of machines

Keith,

From what I have seen the only time you will see nitrogen in a motorcycle shockie, is in the top of the line Ohlins or similar. Usually it will be a race team, after that extra little edge.  Unless of course you work in the aviation industry. 

I have even seen compressed air, used in aircraft nose undercarriage shockies on things such as small Cessna's, Pipers, etc.  Not exactly the industry standard but GA is full of cowboys. 

All of your Regular Public Transport (Boeing, Airbus, etc), and military jets will have the oil/nitrogen combination.  Why, because regular compressed air contains water molecules, which can cause corrosion, and can be compressed.  Nitrogen is an inert gas and not susceptible to compression like regular air.  Regular air will also generate heat more easily which can cause problems.

Throw in say 5 psi to set a set of motorcycle front forks and you should be able to feel the effect.  What in effect is happening compared to a jet aircraft, is that the motorcycle forks are supporting a few hundred kilos, whereas an airliner is supporting a hundred thousand kilos. 

You could say that performance is more import for an airliner compared to our small by comparison K bikes. Nitrogen is also a bit more expensive    than regular air.

   If you are still awake, that's all folks.

There are quite a few shocks that have pressurized nitrogen in them but it doesn't last long, maybe 12 months, but I suppose from the manufacturers point of view it's the ultimate shock.

sidecar paul wrote:The BMW (Bilstein) unit is just oil damped

According to the sales brochures and owners manual from those days the shockie was gas filled....I asssume that it was nitrogen and not air.

But on the other hand nothing mentioned about this in the shop manual....

Hi there, I always thought that the "do not open" warning was regarding the high pressure gas contained. My current, progressive 465 shock, claims to be "state of the art in high pressure gas monotube shock design" and from literature you could think that by gas they mean nitrogen, them also suggest that springs are progressive rate type.
Any case the shock looks and feels good.
Best regards
JAP

Well, I couldn't resist it,.....with all those bits lying on the bench. I made a damper rod today.

Because I don't go with convention, I decided to make the new damper rod from stainless steel.

The original rod is 10.5mm diameter, so, as I was going to use the existing seal, I've opted to use 7/16" bar. That's a little over ½mm bigger in diameter and I'm expecting it to compensate for any wear on the old seal. At least it will apply more pressure on the seal.

The thread at the piston end is 8 x 1, that was straight forward enough to replicate, but the thread in the alloy bottom fitting is 9 x 1, so the easy option was to open that to 10 x 1. Who keeps 9mm taps & dies?   

If I ever use this damper it'll go on the outfit so I've shortened the rod by 30mm. Yes, I know sidecarists have some funny ideas, :geek: but I like to be low.
Note also the flats for tightening the rod to the alloy fitting.


[url=https://servimg.com/view/17238339/370][img]https://i.servimg.com/u/f58/17/23/83/39/sam_0814.jpg[/img][/url]

The wear on the old damper rod can be seen and I think that is where the rod has been rubbing on the cast iron seal holder and top cap. To avoid this happening again I made a PTFE bush to isolate the (soft ss) rod from any metal to metal contact.
[url=https://servimg.com/view/17238339/371][img]https://i.servimg.com/u/f58/17/23/83/39/sam_0815.jpg[/img][/url]


It was a bit tricky compressing the seal assembly  to fit the top circlip and I had to machine the groove in the top seal holder a bit deeper. Using a larger diameter rod meant that the two seal components don't mate as deep as before so the seal holder sits a bit higher.
[url=https://servimg.com/view/17238339/372][img]https://i.servimg.com/u/f58/17/23/83/39/sam_0816.jpg[/img][/url]

So there it is, all assembled, filled with PJ1 30 sae oil and, actually, it feels rather good. A bit more work on the spring mountings, a coat of paint and I'll give it a whirl on the outfit to see how it goes.
Just think, had it not said 'DO NOT OPEN', it would have gone in the bin.   Thank you Bilstein.   

Paul.

These are the pictures that should have appeared on my last post!

sidecar paul wrote: Who keeps 9mm taps & dies?   

Almost every Norwegian   .





Congrats with the close to new shockie.   .

I have some too

OK, almost every Norwegian and some Aussies   .

They came with a very comprehensive set I bought many years ago and to be honest they probably haven't been used or at least I don't remember using them.

And your back.....rehab moving in the correct direction?

And even some Americans have them.  My dad had a 60 VW bug convertible that he kept until 1985. He went through three engines (36 HP) and several hundred thousand miles and did all of the wrenching on it himself.  The metric tap and dies he bought for the bug come in very handy when I F up threads on my Ks.

Inge K. wrote:And your back.....rehab moving in the correct direction?

I have ended up with an infection but that now seems to be clearing up and the physioterrorists have me doing all sorts of painful things. Surgeon said that it was a real mess but he had managed to fix it so a good outcome can be expected.
Its still a day by day thing and still gets painful but I was under no delusions about that and that it is a long term recovery.
Surgeon didn't seem to see the funny side when I said I wanted to go to the Alpine rally in June and am working towards that as a goal.  Maybe maybe not but no harm in aiming for the stars and better than aiming for the roof.

Good discription of a physio person, If I was ever to threaten some one I would allude to them that when I finished with em they would then go to physio where the nice nurse would set about tearing you apart "for your own good"
30mm shorter for a chair, good to know but does that mean you have less travell at front, the reason I consider adding to the back length was to catch up to the front, The fronts 185mm travell is great here in the Cessnock shire, pitty the back didnt match, as did the trailbikes I started riding on years ago, now they were designed for my shire. Yep having read most local mags from 1975 onwards I thought gas was nitrogen in the shocks based on the adds in the mags, but air is a gass and so is carbon dioxide or monoxide, both probably able to be used, The blacking of the oil may be caremalisation of the oil, repeated heating and cooling perhaps, either that or it leaked heaps before you pulled it down and on every down stroke if sucked in all the spare soot from the diesels you follow on the highways over there

Duck and Rick, I can tie your posts together.

Every year at the Alpine Rally Henning, the organiser arranges for an early VW engine block for the festivities.  You dont need a torch when that magnesium engine block is burning.

Al

Keith,
I'm also using shorter front units in my Wasp leading link forks, I like the front swinging arm to be pointing up at the front and I've always found that too much suspension movement on an outfit makes them a bit squidgy in the twisties.

Maybe if we had roads like the ones in Saxon's recent post, I might have to rethink my ideas.   

But, of course, ask 10 sidecar people the same question and you'll probably get 10 different opinions.

I wonder why everyone's 9mm taps and dies are so pristine?

Paul.

BTW, that original (scrap) shock was bought from a breaker just for the spring, but it turned out to be a K75, so I the spring wasn't any use to me after all. 

I bought my 75 in 1995 and 6mths later a mate John bought a used gpx750, I took it for a ride and found it fitted like a glove, perfect ergonomics and 130mm suspension travel front and rear, on our roads it sat and rode the bumps superbly, from that ride I figured that the rear on my bike needed that extra 30mm travell to allow me to fine tune it to be perfect like the front, haven;t done it yet but maybe this time round I will get it done and know for sure if it can be the answer to my suspension feel. On a side note John asked if I had an article on that bike as I kept heaps of mags in them days, went home and found it after a hour of so's search, checked the mag and saw the rego plate on the test bike, and recignoised it as John's bike, took it to work and gave it to John who came back to my desk an hour later absolutly stoked as he picked up on the rego also, never seen a happier bloke, It was like a prise to him. Good for him. I was happy for him even though his bike could not carry half of what I could, with panniers topbox and r series fairing pockets.