Are these forks compatible with the bmw 1991/2 k100rs 4-valve with ABS?: http://www.ebay.com/itm/261242822729?item=261242822729&viewitem=&vxp=mtr

I made the mistake of buying some forks from a '91 k75 off ebay and they're not right. My right fork was leaking oil fairly badly and my seal replacement process went all wrong and I basically completely destroyed the fork. If those are compatible, it solves all my problems.

Your fork legs will be .7mm bigger. If you got the tripple clamps with the forks then you will have a better chance of fitting them although not a good chance. The wheel axle spacers will be different and so will the caliper mounts.

Those eBay forks look exactly like the ones on my 4-valve k100rs. The 1991 k75 forks I got are indeed a little bit smaller and have the caliper mounts in a different spot (ugh!). However, the forks in the link I posted look exactly the same, with the ABS sensor mount and all. But they are different and will not work?

So you got forks that were different to the ones in the picture.
Check the addvertisement and if it doesn't say that the forks may not be the ones pictured get onto ebay and get a refund of all the price and postage both ways. Ebay don't like people that are fraudulent.
I took a guy to the cleaners a few months back and he had to pay me the purchase price plus postage before I sent the item back and that included return postage.

No no no, sorry. I bought forks from a completely different auction and it was my fault they don't fit. I didn't check compatibility, blah blah. Just saw it said K75 K1 K100 and assumed a fit. Can't get a refund on the ones I already bought.

I'm simply asking if the forks in the auction I posted above would fit my bike. They look exactly the same as the forks I originally had, but are from a '93 k1100.

Sorry total missunderstanding there.
Those forks will fit as they are 41.7mm dia. They look well used the hard chrome is rusting in pinholes and there is a slight brownish discolouration on one leg just above the slider which shows that there is some wear. I honestly dont think you would be any better off with those as they will give trouble.
I would be inclined to get the ones Pinwalls have on there http://www.ebay.com/itm/96-BMW-K1100RS-K1100-1100-FORKS-W-TRIPLE-TREE-/130927361804?pt=Motorcycles_Parts_Accessories&hash=item1e7be0ff0c&vxp=mtr
Might be twice the price but having dealt with Pinwalls a few times I would feel that at least you are getting good gear.
There are quite a few around that part the Ks out Higland motorsports often has K parts but I reckon you will pay around the $250 mark for a good pair where ever you go.

You should get about the same for the K75s forks as they are good forks to put on a K100RS 8v

Cool, thanks Rick.  I didn't want to make another $200 mistake.

By the way, the smaller diameter forks did actually seem to clamp down okay, it was just that the calipers didn't match up with the mounts.

Forgive me if it looks like a thread hijack but what Rick said about the K75 forks for the K100 caught my attention.
The original forks on my '84 K100RT have been playing up and have been looking for an alternative.
The right leg has a few small pits but no matter what I've tried, they are still weeping quite badly. Today I notice the left one is starting to do the same.
I'm not so particular in keeping it 100% original and have just bought, what I assume is, a pair of K75 forks on eBay.
http://www.ebay.co.uk/itm/290945554348?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
Think I got a good deal on them and they sound ok.
My question(s) is are they a straight swop for the K100 or any mods needed? 
And are they an improvement over the earlier ones?
I know that I'll need the 2 piece front guard and bridge. Think I may have sourced them already.

No worries, this thread was done anyways.  I believe the forks only changed diameter on the later model K100s (90-92).  As such, they should fit, but the main concern is going to be whether or not the calipers line up with the mounting spots on the forks.  Again, I think it should be a direct swap, although you say you'll need the bridge plate?  I think there are some differences between either the RT or LT (can't remember which) and all the other models (referring to overall bike rather than just forks).

Either way, it sounds like you bought em already, and at what looks like a steal.  So we'll find out when you try to put em on!

Think the main changes in forks and brakes came with the introduction of the 16v engines.
Anything with the 'Y' pattern wheels seems to be fairly interchangeable.
I had an '89 LT before my present '84 RT and the differences are minor and don't affect brakes or forks.
The two piece front guards came towards the end of the 8v bikes certainly on the K75 and, I think, some K100's.
All of the 16v bikes had the slightly wider fork tubes and no, you can't make them fit the 8v yokes.
Ask me how I know...
The K1100 LT has the same rim size as the 8v and both of the 16v RS's has the wider rims for radial tyres.

There are 3 different fork diameters 41.0mm, 41.3mm and 41.7mm.
Basicly K75, K100 and 16v K100 or K1100 in that order.  There are some differences with the K75 but I am not sire of which is which but fairly sure the K75RT had the 41.3 which is the same as K100.  Those forks there are either K75RT or 16v K because the forks had a bridge at the top.

When I have a closer look I think they are from a K100 8v Special edition which had the 2 piece front guard and a much shorter travel. Have a look at the top plug and see if there is an S stamped into the plug and they are the sport fork which is the same as K75S and will fit a K100 8V.
I hope that has helped. Inge if he is around knows more about that side of them than I do.

The best thing is measure them and if they are 41.3 then they should be ok

Thought:  if the forks have the fork bridge at the top, and do NOT have the slot for an ABS sensor, wouldn't that mean they are 41.3mm and from a special edition k100 8v or k75s?

Thanks Rick. That sounds promising.
Don't think they are 16v as they don't have the same ABS sensor arm in the right place.
The seller was sold them for a K100 and advertised them as such.
Do you happen to know or maybe Inge will, does the K75RT front guard fit or did this model have a special type?

Up till the introduction of the ABSII the ABS was optional so there are 2 left side sliders and If you didnt want ABS then you got the slider without the mount too.
There are 2 fork bridges a cast one from the K75RT and a 2mm plate which I say is quite inadequate, from the 16V units. The guards attach in different ways but I reckon they would be interchangeable.
I dont want to pull anything apart to check at the moment as I now have an infection where I had carpal tunnel surgery about a week ago so the spanners are out of bounds but I will have a look through my reams of digital paper and get back.

Well well there it was right in front of me. Hmmmm now how do I get my cave like that?

The part numbers are the same for same colours in K1100LT and K75RT so I will say yes they will interchange.
I reckon that the 2 piece guards look heaps better too.  I built a bracket to fit one to my K100 that Alby has now and it looked great.

Thanks Rick. That's very helpful.
Good luck with the Carpel tunnel stuff. Think it's something up the road for me too.
Need to get my hands on the forks to know any more but is looking good so far.
The seller is sending them tomorrow so should have them soon. Will keep you posted.

Forks arrived today and I think they must be K75RT. No 'S' stamped on the plug.
They are identical to the K100RT Brembo's with the addition of the lugs for the bridge. The sliders are year stamped 86 and 87.
I picked up a K75RT front guard and bridge from eBay in dark metallic blue for £38 including p&p. Although I did discover that the original guard would have fitted these forks anyway.
I've installed them with the 2 piece guard and bridge though because, as Rick says, the bridge is a pretty substantial fork brace. I can respray the guard at a future time as summertime is running! Being a darker blue, it doesn't look that bad. Think it does look smarter, too. 
Haven't had a chance to try them out yet but looks promising.

According to the parts fiche, the lower triples for the 4V and 1100's are the same.

Would this not mean that the fork diameters are the same?

From 8/91 on, the fork tube #'s are the same for all 100/1100K's.  The 4V tubes  fall in this same size.

I am assuming these forks are 41.7mm.

Tried out the 'new' forks today by doing a couple of hundred miles up the Antrim coast road and back.
What a revelation!
I knew something was different as soon as I took her off the centre stand. Less dip at the front end and the ride height is a good inch (25mm) higher.
No clunks and really nice feel to the front end now. Less dive when braking, too. And no oil leaks!
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Still not sure of the pedigree of these forks bit think they may have uprated springs in them. I think the chunky bridge is a big help as I remember the difference fitting a tubular one to my '89 LT made.
Thought they might be from a K75RT as the bridge and front guard are from that model and fit perfectly. But the K75RT didn't come out until '89 and these forks were made in '86 and '87. Old stock maybe?
Only trouble is that the rear Hagon shock doesn't feel up to the job now.
Dear Santa.
About a RAM shock for my K...

RicK G wrote:There are 3 different fork diameters 41.0mm, 41.3mm and 41.7mm.
Basicly K75, K100 and 16v K100 or K1100 in that order.  There are some differences with the K75 but I am not sire of which is which but fairly sure the K75RT had the 41.3 which is the same as K100.  Those forks there are either K75RT or 16v K because the forks had a bridge at the top.

When I have a closer look I think they are from a K100 8v Special edition which had the 2 piece front guard and a much shorter travel. Have a look at the top plug and see if there is an S stamped into the plug and they are the sport fork which is the same as K75S and will fit a K100 8V.
I hope that has helped. Inge if he is around knows more about that side of them than I do.

The best thing is measure them and if they are 41.3 then they should be ok

OK, so I've got pitted stanchions (is that the correct term for the chrome tubes?) on my 95 K1100LT, and am thinking of taking the same part off my old 85 K100RT to replace them, but from the above it looks like that won't work?

Does anyone know anyone who refurbishes stanchions in Australia?

not sure exactly ....but rad shockies in Brisbane do hard chroming to things that need repairing

there may be specialist folks for the forks though

the k100 forks  will be a backward step in any case ..along with the size issues you will have to use a k100 front wheel and brake calipers as well at a minimum ...have you measured with digital calipers rickety ?

That's right they don't fit. As Charlie said RAD Shocks do a good job, you will find others but I couldnt offer any opinions.