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Thread: 84 R100RT rebuild questions

  1. #1
    Rally Rat
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    84 R100RT rebuild questions

    Closing in on coming home and finishing the rebuild of my 84 R100RT. Is it worth the time and $$$ to have the crankshaft balanced? I'm installing lightweight wristpins and balancing the pistons and conrods.

    My goals are to make it smooth, more reliable and some modest improvment in performance and handling. I'll be asking more questions about other areas as it progresses. Suggestions are more than welcome. Thanks.

    28 days and a wake up.

  2. #2
    Grammarian no, Rider yes ISAMEMON's Avatar
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    unless the crank is out, then I would just leave it at the rods and pistons, as it can never stop with just the crank, for example, are you doing the flyweehl and clutch assy also ? supposedly, if those are not balanced, you wont know the difference in just doing pistons and rods. The factory balances the flywheel and clutch assy, or so Im told, but when you get replacements, how balanced are they to the rest of the bike ?? how much weight does lightweight wrist pins save ?

    28 days and a wake up sounds like your overseas fightin for freedom
    keep your head down

  3. #3
    Rally Rat
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    Most of the responses I've gotten have been along the lines of don't bother. It's the same crank as the 75s, so I don't think it needs it. I'll balance everything else.

    As soon as I find a post office on this dump, I'm ordering Oak's top end book. I'm sure that'll have enough advice to keep me confused for days.

    Not much fighting this trip. Quite a change from the last one. Thanks.

  4. #4
    keelerb
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    Good luck with your build. And thank you for your service. Stay safe.

  5. #5
    Rally Rat
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    Piston rings

    Moving right along....

    I have rooted around on various sites (engine rebuilding, engineering, MOA, etc.) and as near as I can tell:

    Iron rings for Nikasil cylinders.
    Chrome moly for iron cylinders.

    I can't recall who on advrider and MOA has used Volkswagen rings from Deves, but they seem pleased and report no problems.
    (Update: New post in this forum seems to like total seal.) This would be good, as a set of v dub rings would do both my bikes. Deves, IIRC, has a gapless (?) compression ring. The ends overlap, it that makes sense.

    As always, suggestions appreciated.

    R

  6. #6

    Rebuild Questions

    Total Seal is the company who offer gapless second rings. I have used the gapless rings with about a 50% success rate. Total seal also sells a "classic" ring set, which uses a standard second ring.

    Your bike should have Nikasil cylinders, which uses all cast iron rings. I would reccomend you use OEM parts in this application.

    FWIW, the iron bore bikes also use iron rings except for the top ring, which is a hard chromed steel ring.

  7. #7
    Rally Rat
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    Max BMW doesn't sell rings. I'll check Bob's later. Otherwise, it looks like Goetze (Fed Mogul) is the preferred choice, with an aggressive break in.

    What were the problems with gapless rings? My research shows several failures related to break in procedures with all types of rings in Nik bores. There were several on this site.

    The Nik bores are in great shape, IIRC. It's been awhile since I've seen them. I'll give them a light scrub with a green pad and soapy water and stop thinking about it.

  8. #8
    Grammarian no, Rider yes ISAMEMON's Avatar
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    oh oh
    had not heard to use all cast iron rings with nik cylinders, when I was doing a rebuild, and could not get from Max, I went with Deves, hope I wont have a problem, have not fired it up yet, havent had time to finish

  9. #9

    Rebuild Questions

    The gapless ring consists of a taper faced cast iron ring with a portion of it's underside ground to accept what looks like a rail from a three piece oil ring. The iron "main" ring is installed on the piston, then the secondary is wrapped underneath it just as one would assemble a three piece ring. According to Total Seal, this generates so much negative pressure (vaccum) in the cylinder that oil is sucked down the valve guides on engines with less than perfect valve stem seals. Our motors have no seals there, and I have had problems with aftermarket seals.

    Frequently, even though the rings appear when removed to have seated, smoking and oil consumtion exist and do so with the classic ring symptom of smoking under light throttle.

    When a gapless ring works, it works extremely well, giving superb oil consumtion and leakdown numbers, keeping the oil clean and giving long life. But when they don't, just the opposite is the case. I plan to try these rings again, but I'll need to see consistent results before I can endorse them.

  10. #10

    Rebuid Questions

    BMW's OEM rings are made by Goetze. Why doesn't MAX sell rings?

  11. #11
    Rally Rat
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    Considering the combustion chamber and piston face looked like a coal mine when I pulled it apart, sounds like gapless rings are out. I'll go with Goetze iron rings and run them in hard.

    I don't know that Max doesn't sell rings, they're just not on the fiche.

  12. #12
    Grammarian no, Rider yes ISAMEMON's Avatar
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    recent update on my other post.....Max does sell them
    for some odd reason when the fische came out for both the 100 RT and the 80RT the diagram for the rings and pistons were left out,
    but if you go to a different model, say a 100 S of the same year, you will see the rings listed
    with the R80RT same thing, no rings shown, go to an R80 same year and rings are shown and we know they ae the same motor

    but intersting note, the last R80 I rebuilt was a 78, according to the microfiche it is the same rings as an 85. However for the 78 it says only one set needed, I bought one set, that was all that awas needed, did both pistons, for $57. The newer bikes it lists 2 sets needed. My local dealer confirmed it that says yes it takes 2 sets. when I asked him why I only needed one set a few months ago for a 78 ...his answer was.....I dont know.

  13. #13
    Rally Rat
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    Here we go....

    I finally bought a scale and started weighing the parts.

    Pistons have a 3 gram difference.
    Lightweight wrist pins have a 1 gram difference.
    Conrods have a 5 gram diff, with that coming from the conrod end caps.
    Conrod bolts all weigh the same.

    I switched the pistons and wrist pins around and was able to balance total reciprocating mass to within 1 gram. That leaves the big ends 5 grams different, but with total weight still within 1 gram, if that makes sense.

    If I balance the big ends, then total weight goes out of whack, possibly resulting in more filing. I really don't want to do that, unless someone has a reasonable procedure.

    I do really want this balanced correctly. Should I relax and go with the current weights or grab a file and balance pistons, small and large ends and conrod total weight? I expect I am overthinking it.

  14. #14

    Rebuild Questions

    I think it's worthwhile to go the extra mile when balancing pistons and rods. I usually put the light pin in the light piston and remove weight from the heavy piston until they are within .5 grams. You can balance the rod ends with a belt sander. If you don't know how to do this, ask someone in your local balancing shop. They're usually eager to show you how, and they may even offer to do it for you for a nominal fee. You only have to this once, and it makes an amazing difference in the way a motor runs.

  15. #15
    Registered User lkchris's Avatar
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    Unlike mass-produced Chevies, etc. these engines are handbuilt and BMW is a way different company than GM and you can expect the crank to be balanced.
    Kent Christensen
    21482
    '12 R1200RT, '02 R1100S, '84 R80G/S

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