Buying used 1991 K100RS with 50K miles: what to look out for? - - Excellence in Motion
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post #1 of 5 (permalink) Old May 29th, 2013, 12:07 pm Thread Starter
Join Date: Mar 2013
Location: Boulder, CO, USA
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Buying used 1991 K100RS with 50K miles: what to look out for?

Hello, folks,

I'm looking at a 1991 K100RS 16-valve "flying brick" with about 50K miles on it. I'd appreciate any advice on mechanical issues, etc., that I should be looking out for.

I'm not all that familiar with these models. My one and only bike was a 1971 R75/5 workhorse that I sold to my brother-in-law last year.

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post #2 of 5 (permalink) Old May 30th, 2013, 11:16 am
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Location: Austin, Texas, USA
Posts: 190
I would look at two items first-

Look at the bottom of the engine- front part for any signs of coolant leakage in the water pump/oil pan area. At the rear/bellhousing for any sign of oil leakage at the drain hole there. Remove the bellypan if installed to see these areas.

Rebuilding the water pump can get expensive. An oil leak from the rear "main seal" is more labor than parts cost intensive.

These are not reasons to pass on the bike, just be aware of potential expenses.


'17 R1200RS, 2 yrs. 27,000 mi.
'16 R1200RS, 18 mo. 28,000 mi. (gone)
'03 R1100S Boxer Cup Replika 6/200
'85 K100/1100RS, 34 yrs. 326,000 mi.
'05 R1200ST, 8 yrs. 57,400 mi.-3rd deer killed it.
'11 R1200RT, 2 yrs. 30,000 mi. (gone)
'99 R1100S, 2 yrs. 15,000 mi. (gone)
'96 Ducati 900SS/SP, 12 yrs. (gone)
500,000+ BMW miles
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post #3 of 5 (permalink) Old May 30th, 2013, 12:39 pm
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Join Date: Jun 2009
Location: Burton, British Columbia, Canada
Posts: 1,650
Yes to the above and if the pump is leaking it may also show in either the oil or coolant. My earlier bike sure showed an oil slick on top of the coolant in the overflow tank and the radiator. They had a few updates on the seal/shaft over the years....ugly mess I found back then in my 85.

Bike sitting for a while or regularly ridden? Could make all the difference as to what you could find in the tank as the fuel pump dampener and other rubber parts may have turned to goo.Open the gas cap and sniff for sure, if that doesn't smell like fresh gas don't start it like that could just cause problems with the fuel injection.

Inspect all the rubber bits/hoses,BMW rubber doesn't do too good over the long term if it hasn't been protected/lubed over the years.

If a running bike,make sure you run it until the cooling fan comes on. Looks like many of them have seized,may depend on where the bike was ridden mostly as they almost never come on riding highways so can seize from not being used often enough.

Brakes??? Considering how much BMW wants for some of their brake parts I'd make sure they function properly and that the fluid isn't some ugly mess that has been sitting there for years corroding the MCs and calipers. And rubber brake lines, if original they probably should be replaced, hard to see they could degrade internally. That's getting all too common on even newer BMWs.

Take some pics and post them,some of us can be good at spotting them details.

Benelli 50cc at 14
Yamaha RD 200 at 16
Yamaha RD 350 at 17
Honda CB 750 F at 18
Honda V45 Sabre at 24
BMW K100RS at 27
BMW R100GS at 34
BMW K1200RS at 53
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post #4 of 5 (permalink) Old Jun 1st, 2013, 8:26 am
PsyKotic Waterfowl
Join Date: Aug 2006
Location: Seattle, WA,
Posts: 1,328
If it's only got 50K on it then just buy it if you can get it for a reasonable price. Yeah, there may be some issues due to age but on the whole they are good, reliable bikes. JMHO but if you're worried about every little detail of what might be wrong with it then you should just buy a new bike.
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post #5 of 5 (permalink) Old Jul 14th, 2013, 4:42 pm
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Join Date: Aug 2012
Location: london, london, uk
Posts: 20
My 75k mile 16v k100rs had a leaky gearbox rod seal(had to take exhaust off but easy cheap fix), wobbly rear paralever bearings, wobbly front discs (new bobbins, pain but not to dear), clutch and throttle cables both snapped(had been off road for two years) and a leaky fork seal (local shop fixed it and now front end bottoms out).

I gave it a full service including balancing the fuel injection.
I used carb balancers for fuel injection.
This improved my fuel economy from 100 to 180 miles per tank riding round town.

I cant think what else was wrong but I paid 840 for it and I love my K.

I never owned a BMW before and I am very pleased and surprised by how good it is.

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