R65 bumped up to 850cc

Discussion in 'Airheads' started by Wirespokes, Jul 3, 2010.

  1. Wirespokes

    Wirespokes Beemerholics Anonymous

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    I'm looking for data concerning an R65 hop-up that involved re-sleeving R65 cylinders to 94mm bore with Venolia pistons.

    I've got a bike that outwardly appears stock (ignoring the 34mm flat slide Mikunis), but after pulling the head to repair a nicked fin, discovered the Venolia and larger bore. The head has had work done also as evidenced by a cup shaped washer between the springs (yep, twin valve springs) and head.

    I've heard of cutting down R80 cylinders to match the R65's shorter stroke, but wouldn't have imagined an R100 sleeve fitting into the barrel, much less the block. Evidently the block would have been bored as well. The barrels and head are R65 as evidenced by the 6.5 at the cylinder bases and the numbers on the heads.

    Any of you know anything about this modification?
    #1
  2. jdiaz

    jdiaz .

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    Didn't San Jose/CC used to advertise an 850cc "Tiger" kit for the R65? Maybe it was Lufty.
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  3. bmwrench

    bmwrench Long timer

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    CC Products/San Jose BMW offered this kit as well as am earlier 720cc (?) kit. They used a standard R65 cylinder bored to accept a sleeve available from several sources.

    The crankcase on an R65 has the same size bore for the cylinder spigot as the '76-on big twins.

    The only real problems that I am aware of with these kits was that the boring shop often finished them with too much clearance, resulting in piston slap when the motor was cold.
    #3
  4. Wirespokes

    Wirespokes Beemerholics Anonymous

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    Thanks Bud. I was wondering if that was piston slap - but it isn't noisy on first start up, but a half minute later. And then it goes away. I guess I could always get them plated to match the pistons if it bugs me too much - otherwise I'll just consider it "racing" tolerance. :evil

    Another question - would you happen to know what the jetting should be for this kit? I'm assuming the 34mm Mikunis were part of it?

    Reason I ask is because a major rejetting ocurred when the two-into-one Luftmeister was added - which I've just replaced with a stock system.
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  5. Hawk Medicine

    Hawk Medicine Coyote's Brother

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    Wireworker might be a good inside track for info on this conversion.

    I think that he might know someone at SJ.:wink:
    #5
  6. bmwrench

    bmwrench Long timer

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    Surprisingly, big-bore kits rarely require much in the way of re-jetting. I assume it is because the bigger piston gives he jets a stronger signal. The bigger piston also often makes for a better combustion chamber configuration-squish clearance is often tighter, and the dome smaller.

    Regarding your (probably) loose clearance: Check with your local automotive machine shop as to whether they can knurl the piston skirts. Or, send a piston to Venolia and ask them to duplicate it in a slightly larger size. Venolia is very easy to deal with,and they'll make as few as one. If you do this, check with Total Seal about the rings. What is available for rings changes constantly, so you might have to use different rings.
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  7. Lornce

    Lornce Lost In Place

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    Maybe measure the clearances before you go too far. :brow

    Venolia race pistons are forged while stock BMW pistons are cast.

    Cast pistons have much lower expansion rates and subsequantly run much tighter piston-bore clearances.

    Forged pistons expand at a higher rate and are fitted much looser in the bore to allow for the expansion. They should quiet down at operating temps.

    Measure the Venolias and you should find a 0.007" taper between the skirt and the head of the piston. Another mfgr'd detail to permit expansion of the business end of the piston.

    blah blah blah...
    #7
  8. bmwrench

    bmwrench Long timer

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    "edit: Anyone ever hang a stock 1000cc top end on an R65? Oughta' make for approx 850cc, no?
    Will the pushrod tubes fit the R65 block?
    If so, will the pushrods work without scraping?"

    It would be an interesting thing to do, but since the R65 stroke is 9mm shorter, the pistons would stop a long way from the top of the bore. You could cut the cylinders down in length, but because of the short stroke, you'd have low compression. The pushrods would be a problem since the lifter angle is different, too.

    I built a short-stroke (R65 crank) R75 for Bob's parts manager using R75 heads and an 88mm piston a few years ago. It required a huge dome to get the compression I wanted. It wasn't real fast, but it was the noisiest thing I've ever stood beside!
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  9. Lornce

    Lornce Lost In Place

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    While on the topic, do any of you guys know a good source for suitable iron liners to accomodate 1050 Venolias? I've about had it with overbored '77 barrels that're too thin to stay round...

    :twitch
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  10. bmwrench

    bmwrench Long timer

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    I got mine from LA Sleeve. Tell them what you're up to, and they'll advise.
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  11. Lornce

    Lornce Lost In Place

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    Have you had good success with them? How thick are the walls? How many miles, how dimensionally stable, etc. ??

    :scratch
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  12. bmwrench

    bmwrench Long timer

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    The bikes I sleeved have been out of my hands for years. Several of them had covered upward over 30,000 miles the last time I saw them, and one was over-revved often enough to wreck it's rod bearings on a regular basis!

    I can't remember how thick the liners were. I went with LA's advice. We put a thick flange at the top to stabilize it as much as possible and (unfortunately) turned the bottom of it to fit in a standard case.
    #12
  13. Wirespokes

    Wirespokes Beemerholics Anonymous

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    Thanks Lornce and Wrench! Good data!

    I probably won't worry about the piston slap - it goes away pretty quickly and isn't even very loud.

    I wondered why stock 100 cylinders hadn't been used, and it's possibly the pushrod tube angle that scotches it. I'd think that if the pushrod tube issue was resolved, cutting down the cylinder base would bring the piston crown where it should be to have proper compression.

    This is all hypothetical for me since I don't plan on making such modifications. I think these things are plenty powerful just as they are. And if I want more oomph, ride the 100S instead. But I do enjoy the 'what ifs'.
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  14. Wirespokes

    Wirespokes Beemerholics Anonymous

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    Today I put the bike on an exhaust gas analyzer and found out it's running very rich. I'd suspected that not only because of the carbon build up, but because I got rid of the two into one Luftmeister and returned to stock exhaust. I knew the bike had extensive tuning with the two into one.

    Suspecting this is a CC Products kit I called San Jose hoping to get the specs on what jets and needles came with the kit - assuming the 34mm flat slide Mikunis were part of it. The reply was that Chris no longer has any data on that build and I'm on my own.

    Would any of you happen to have that data?:wink:

    Barring that, I'm guessing that jetting for an R80 should be close. I've heard that these hop-up kits didn't really need much in the way of jetting changes so it's possible the stock R65 jetting would work.

    But there's another problem - I don't know how to transfer Bing data over to Mikuni data. Are there interchangeability charts available? Suggestions?

    I'd rather not go through the guessing game of figuring out jetting if I can help it!
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  15. bmwrench

    bmwrench Long timer

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    My experience with flat-slides and BMWs has been that if you want them to work right, they have to run a bit rich. When I tried to jet a set of them down on 1050 kitted bike it would occasionally lean backfire and blow the carbs off the heads! The flat-slides were probably sold by Luftmeister, who were very excited by them at the time. The Carb Parts Warehouse is the place to go for jets and good advice on those carbs.

    My advice is to ebay the Mikunis and get a set of Dell'Ortos.
    #15
  16. Wirespokes

    Wirespokes Beemerholics Anonymous

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    That's funny - I've been hankering for a set of Dells on this bike, but figured the Mikunis might be more 'state of the art'.

    Which Dellortos would you suggest? Any particular size and style you'd recommend?
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  17. BMW851

    BMW851 Piston Broke

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    The party trick with twin shock R65's in the mid to late '80's in Aussie was to fit 1000cc barrels machined down to the shorter stroke, yes they fitted straight into the R65 crankcase's, if you had the money a set of I think Miele piston's or venola's can't remember, I just had the 1000cc one's skirts cut down to stop them hitting the crank, make your own pushrods by cutting down the long stroke ones, get the crank rebalanced, slap on a set of 38mm Pumper Delorto's, add an RS cam, throw it all together and Bob's your father, or uncle or whatever. (The R65 Mono Shock Block is the same as far as I know)

    And a free breathing exhuast system helps it should sound like a bevel drive Duke with open mouth Conti's.

    Swept volume ends up around 850 & 70 odd hp, in a short wheelbase frame with short gearing that loves twisties and they won't scrape the heads, unless you fall off it of course.

    The engineering types will be going but, but, but...........

    It worked, was raced for awhile then road registered, as for engine life, well umm err.

    So you well may have a butchers special, and a very rare special at that as well.
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  18. Airhead Wrangler

    Airhead Wrangler Adios Mexico

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    IIRC, Scheck or HPN used this engine configuration on their ISDT bikes in the late 70s. R65 bottom end with R90 top end for a displacement around 800cc.
    #18
  19. supershaft

    supershaft because I can

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    How did you set up the push rod tube seals? I remember the seals fitting very poorly one time I did that.

    I have set up a couple of R65 850 kits. Chris did all the work in house. You can tell if it is a 850 kit because the ENTIRE cylinder wall is bored away for the sleeve. You slide just a ring of fins around the liner. The setup was COMPLETELY savage. There was JUST enough cylinder left to not cave in when you torqued the head bolts.

    Having bored and honed more than a couple of cylinders for 1050 kits myself, I know that for it to work even close to right you have got to get the interference fit for the sleeve/cylinder JUST right. As most of you know, I do not recommend boring those cylinders out more than BMW did. The R65 is a hogged out 450 and the R100 is a hogged out 750. They stopped both at a bore/stroke ratio of 1.33:1 for GOOD reasons! The main one being cylinder wall stability!

    On four strokes, I don't think forged pistons need any more room to speak of. Forged pistons in two strokes do! They are often just a BAD idea in two strokes. It's not so much increased expansion for more mass but the localized expansion that results from not being able to control high concentrations of mass during the forging process. It's the same reason how forged rods can sometimes be SO off end to end.

    I like Dell's mostly because the airbox snorkels fit right but they all work real well IF you can manage to get those independent floats on the flat slides to not constantly flood the carbs. I don't think the flat slides need to be rich at all. I run my dells with no acc. pump for a LOT more midrange as do a lot of other tuners I know.

    Being around three different dynos in my life, it was rare to see a stock or rodded bike that wasn't too fat on top! It is a real power KILLER. Even good tuners jet kits and over the phone jetting is on the safe (fat) side of really ripping! Jetting those Mikuni's takes buying sets of jets and slides besides some time and experience. Get your wallet out! Ron wood, Chris at San Jose, Dyna Jet, what have you, I take no ones word for gospel and jet to what works. That takes buying jets and slides among other things! A lot of jet kits are really just a very conservative STARTING point.

    The main advantage of flat slides is the more concentrated low pressure over the main jet for whatever that is worth.
    #19
  20. supershaft

    supershaft because I can

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    I was thinking that EXCEPT for cornering clearance, I don't understand why anyone would want to run shorter than a 70.6mm stroke in an airhead. That is unless you have got a from the factory hogged out 450 (a R65)! IMO, piston speed is not a limiting factor. It's mostly a combination of volumetric efficiency and valve train. As long as both of those are limiting my rpm more so than piston speed, I am going to run as long of a stroke as I can. If I had an airhead set up to make GOOD power above 9,500rpm, I might think about running a shorter stroke.
    #20