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Thread: Special order oversize pistons for 1980 R100. Anyone in?

  1. #1
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    Special order oversize pistons for 1980 R100. Anyone in?

    Hello,
    Firstly, this is my first post here, and I look forward to being a member. I love my airhead, I loved the first airhead I saw, I'm excited.

    But, my airhead had some issues with the exhaust valve guide: it became unseated. Someone put on Bronze guides, and the machine shop says those fall out with the extra heat from the ethanol (always with the ethanol, right?). Luckily I found it before engine destruction occurred, but one thing led to the next, I decide to do a whole top (side?) end rebuild, and my pistons are out of spec and I need to do a first over on the cylinders and get new pistons. First over pistons from BMW are $370 each. That's crazy.

    So the guy at the machine shop called a company, and they can do forged (higher quality) custom pistons, rings and knuckles for around $450. Then I called a company in California, and they gave me a similar quote: $450 for two, OR, I could get four new ones for around $650 (four is normally the minimum order).

    So, if I hear from someone that needs a first over pair of pistons on a 1980 R100 (I'm not sure what else it'll fit, but I can get the specs), or the guy said I could order the second pair at .5 over the first pair for a second over at the same price, we could stand to save each other a lot of money. I'm looking to put the order in within the next week. Maybe someone else is in a similar position, or maybe someone will read this and say "well, now's my chance!"

    Here's to overdoing maintenance, eh?

  2. #2
    Administrator 20774's Avatar
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    On the Airheads listserver email list, the concensus from the BMW mechanics is that the R100 is not a cylinder you want to consider going 1st over. It is so close to the minimum liner thickness that trying to bore it will likely result in a cylinder that will not hold its pure shape. I think the issue will be that the areas where the head bolts run around the outside will warp, creating seal problems in the long run.

    You might want to do some research along those lines.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
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    So what do people do if the pistons are out of spec? I'm 5 thousandths out of spec, and the max tolerance is 3.2, plus the rings are blowing by past the first and second... I'm not sure what else to do.

    I know '81 on can't be done, but BMW offers first over pistons for the 1980 and earlier; surely they wouldn't offer if it wasn't safe, would they?

  4. #4
    Administrator 20774's Avatar
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    It's still something you can try but I'd be ready for the downside of it not working. The options are to find good used iron cylinders...but that might be a crap shoot. Can a cylinder be resleeved? I don't remember if that's a real possibilty...probably dicey as well.

    On a related note, I'm having work done on my R25/2. The cylinder will be sent off the Bore-Tech to have a carbide impregnation treatment done. Vech at Benchmark Works has the engine now. When I dropped off the parts, he mentioned that the Bore-Tech process does add some dimension back to the cylinder...I don't recall what the amount was. In my case, the R25/2 rings measured right at the upper limit of spec. I'm not sure about the measurements I made of the bore and the feeler gage I slipped between the piston skirt and the side of the cylinder. But if I am right at the upper range, it might be that the carbide treatment will bring me back inside the range a bit, enough to be OK. I have no clue or experience...I'll wait to hear back. Something to check on though...

    After that, the only way to go seems to be Nikasil. It's an expensive proposition initially, but the long term is good because with no wear, the cylinder should last much longer with only rings needed at usual intervals.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    I'll have to check out the info on damage as a result of boring, and make a decision.
    I'll need new pistons one way or the other, so the offer stands: if someone else is interested in going in on a pair, I'm game.

  6. #6
    Registered User PeoriaMac's Avatar
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    Or, another po$$ibility

    Flatracer.com sells the following....

    The big daddy! Increase your 980cc Boxer to 1070cc, adding lots of power and torque in the process. It includes new alloy Nikasil plated cylinders, stainless pushrod tubes, lighter forged pistons offering 9.5:1 compression ratio, piston rings, lighter forged con rods, big end shells, gudgeon pins and circlips, asymmetrical camshaft and all the necessary gaskets and rubbers to fit it on your engine. Increases the real power to over 80BHP with a noticeable increase in the torque available.

    Pice 1,790 British Pound$
    Mac
    1986 R80RT, 2005 R1200GS
    Livin' Large On The Lake

  7. #7
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    Quote Originally Posted by 20774 View Post
    Hmmm...they say don't trust anything on the Internet. Now your opinion is that if you can't find anything to support your theory on the Internet, then Internet must also be wrong.

    I'd agree that there's not much on the Interent. My opinion is that your average machine shop probably doesn't know the particulars about BMW motorcycle engines. And talking to Tom Cutter didn't provide valuable input? Ted Porter and Tom are too busy to create a website. As I mentioned earlier, this very topic was discussed by Tom and Ted in the February timeframe on the Airheads email list. Both of their opinions were that boring to 1st over on a 1000cc bike didn't make sense and they felt there were definite downsides in doing that. So, I guess it is on the Internet!!

    Anyway, I think you've done a good job of asking around, even going to independent places, and forming your own opinion. I applaud you for that. Me, I don't think I have enough pelotas to think "too far" outside the box...I would go with the known experts in BMW motorcycle engines.

    Good luck...I think in the end, it sounded like you were going to rering and hone and give it a try. Maybe I missed the final solution...
    IMHO the most accurate place for detailed technical information ... Anywhere... is found on forums.

    reason is quite simple ... peer review .. if someone posts something even remotely wrong. someone will drive by and point it out. most times a GANG of folks will point out the tiniest of errors.

    for peer review to work, two major points must be valid.

    1. forum must be specific to technical info sought.
    2. forum must have enough traffic to make peer reviews valid.

    generally the most accurate information gets posted on specific to desired topic forum with the most traffic.

    for instance, ADV has 287K+ members with possibly largest BMW motorcycle following on WWW.

    post an error on any technical topic on ADV.... odds are a gang of folks will happily point out those errors. Peer review is VERY powerful. results in very accurate data.

    BMW MOA overcomes low traffic by being specific to BMW. with some very knowledgeable BMW folks known to drop by.

    another low traffic forum with valuable specific data is HUBB. Horizons unlimited's traffic is tiny compared to ADV. but it's populated with lots of folks committed to long distance travel. if one is prepping to go RTW. HUBB would one of the best resources on WWW despite it's relatively low traffic.

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