BMW K100RS Tech Thread

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    76 of 90
    caveman
    11 months ago
    Yermo,
    The factory rider's manual (pg. 58) list Max. oil consumption at l/100km = 0.15 so you are still well below that. I agree the the recent increase should be investigated anyway. I would have to agree with chicken that change in oil formation that you are running could very well be the cause and very easy to check. I would try 20-50w non synthetic API SE and SF, the engine was not designed for synthetic and fear of developing sprag clutch problems with it's use. Also checking that the crank vent is not blocked is easy too. But in the end it could very well be time to move on to a different bike, I heard riding a K75 will "ruin" you!
    Cheers
    77 of 90
    Yermo
    10 months ago
    Crank vent!! I had not considered that. If that vent is clogged it'll create back pressure, no? 

    The crank vent had come unattached and I reattached it at the same time as the last oil change. I wonder if maybe I missed some crud in the line since it was quite challenging to get the thing back on. 
    78 of 90
    caveman
    10 months ago
    I would unattach the vent again! If I'm not mistaken the original vent (crankcase) goes through the fuel tank vent with a check valve that can ether hang up closed causing crankcase pressure or hang up open causing fuel vapor (or raw fuel if full tank) to be drawn into crankcase; nether being good for the engine. So I would ether vent it to atmosphere or to intake track.

    BTW I know you took a short ride on a 75s (in NY)... maybe that did not move you to explore the other option? 

    Cheers
    79 of 90
    Yermo
    10 months ago
    I will check that out. Thank you for the pointers. 

    The K75S is an impressive machine but I still like my K100RS. :) 
    80 of 90
    Yermo
    10 months ago
    I came across this document today:
    81 of 90
    Yermo
    9 months ago
    I'm building up the motivation to start delving into the oil consumption issues on the Beloved Blue Oil Burner. With 125,000 on the clock, valve stem oil seals are the likely culprit. It's burning oil mainly on deceleration which implies oil is getting sucked past the valve stems because of the vacuum that's generated while decelerating off throttle.

    82 of 90
    Yermo
    8 months ago
    There's a K bike owners group on facebook. A question was asked about the Laminar Lip I have on mine when I realized that I not posted the link here:

    Link #63532
    Yermo
    8 months ago

    Laminar Products for BMW K100RS-K1100RS

    This makes a huge difference in the buffeting these bikes generate.

    https://www.laminarlip.com/k100rs.p...
    83 of 90
    Yermo
    8 months ago
    Link #63535
    Yermo
    8 months ago
    84 of 90
    Yermo
    8 months ago
    So instead of riding, buffalo and I started to tear into the oil consumption issues on my long suffering oil burner. We managed to pull off the top of the airbox which houses the "cyclonic separator". It at first appeared that it could be taken apart but it looks like it's installed before the part is glued.

    We found some pictures of it here:

    85 of 90
    Yermo
    8 months ago
    Diagram of a modification to the crankcase breather system in the middle of this page:

    86 of 90
    Yermo
    7 months ago
    A description of the valve check procedure of the K100RS:
    Video #65241
    Yermo
    7 months ago

    BMW Service - BMW K75 & K100 Valve Clearance Check

    Checking the valve clearances on a 1985 K100RT. This applies to all K75 models (1986 ~ 1995), all K100 models (1985 ~ 1990) and is basically the same for the...
    87 of 90
    America.Rides.Maps
    7 months ago
    Are you swapping engines?
    88 of 90
    Yermo
    7 months ago
    America.Rides.Maps, yea, that's the plan. To do a rebuild on the engine I have is silly expensive. 

    I have two parts bikes. One runs. One has been sitting too long. Sadly, both have compression numbers that give me serious pause. I've been doing some reading to convince myself that I'm not misinterpreting the numbers or making some mistake.

    Ideally, I'd like to do the engine swap once. On this bike, the engine is the center stressed member so it's more like you swap bikes around an engine. It's a pretty big job. 
    89 of 90
    Yermo
    28 days ago
    It dawns on me that I haven't posted anything here about the massive Oil Burner Engine Swap Project of 2019. 

    After a lot of soul searching and upon strong recommendations from experts, I decided to swap engines instead of trying to fix/rebuild my engine.

    My best guess is that the increasing oil consumption and fouling of plugs is due to valve stem seals failing and this may all be due to running the engine with a failed open thermostat for way too long. The problem was obscured by a temperature gauge that wasn't reading properly.

    The donor bike has only 38,000 miles on it. The question was asked as to why I don't just run that bike instead? 

    Blasphemy!! If I were to do that then it wouldn't be my bike.

    So where we sit now is that both my bike and the donor bike are disassembled off the frame. The frames are hanging like carcasses in my garage. My engine and the donor engine are on the workbench and I'm starting to slowly clean and re-assemble things.

    A smattering of photos, sadly not in chronological order:

    Photo #69806
    Yermo
    2 months ago

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    Yermo
    8 months ago

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    90 of 90
    Yermo
    21 days ago
    The fuel lines on the donor motor are rock solid and the factory BMW lines are no longer available. Asking in the K100RS group on Facebook I was told to look for "Sae30r10 fuel line" which is apparently the spec for submersible lines in the fuel tank, which will also need to be replaced. It's an 8mm interior diameter.
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