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Thread: Odd Exhaust

  1. #1
    --Tony AnnapolisAirhead's Avatar
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    Odd Exhaust

    I set out to sync the carbs on my '71 R75/5 and it dawned on me that it has no exhaust cross-overs. I thought all '70-95 boxers had at least one cross-over.

    Here is a picture. The picture isn't really all that clear, but the headers are smooth. Not like they were cut off and welded.

    Has anyone else seen anything like this or know if this was stock or production numbers?

    A friend who has another '71 R75/5 and who rode mine for a year or so told me that my bike feels like it has better mid-range power--so I was wondering if this could be the result of no cross over?
    Seems to me that the balancing of the carbs would be even more critical.
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    Last edited by AnnapolisAirhead; 12-12-2010 at 06:36 PM.
    1971 BMW R75/5 | 1975 Moto Guzzi 850T Cafe | 1983 BMW R100RS | 1988 BMW R100GS
    1988 BMW K75 | 1998 BWM R1100RT | 2000 Moto Guzzi Quota 1100ES |2002 Moto Guzzi V11 LeMans

  2. #2
    #4869 DennisDarrow's Avatar
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    That is strange and yes syncing is even more critical.....Something happened and am sure you will hear all about it from the "know alls".........Surely IS NOT a carry over from the /2's as they have one even though it's in the rear........HMMMM, one wonders.....Dennis

  3. #3
    --Tony AnnapolisAirhead's Avatar
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    That's what I was thinking Dennis, the /2 carry-over....but I seem to recall cross-overs there too. One other thing, the Bing 32mm carbs didn't have a vacuum port, but I've seen that before. The vacuum port kit was installed last year to make balancing easier.

    The bike is pretty much stock except for the repro seat, lower bars and headlight mirrors (so you can confirm that your knees still exist). Runs like a top, but the mufflers are getting a bit long in the tooth. I like the stainless exhaust systems, but thinking that I may now keep the existing headers.

    Here's another pic.
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    1971 BMW R75/5 | 1975 Moto Guzzi 850T Cafe | 1983 BMW R100RS | 1988 BMW R100GS
    1988 BMW K75 | 1998 BWM R1100RT | 2000 Moto Guzzi Quota 1100ES |2002 Moto Guzzi V11 LeMans

  4. #4
    Liaison 20774's Avatar
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    My R69S has no front cross-over, just the aft one. I don't recall if the R69S and the early R75/5s exhaust diameters were the same. If they were, I could see where stocks might have been used up with the first few '70 models, but hard to believe they would still be doing that for the '71 models.
    Kurt -- Forum Liaison ---> 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!

  5. #5
    --Tony AnnapolisAirhead's Avatar
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    Kurt, this bike doesn't have any cross-overs. Maybe the picture doesn't show it very well, but its a clear shot straight to the silencers. The nubs you may see in the picture are just the motor mounts.

    It looks to be stock BMW headers, just wondering if it is stock or not. European maybe?

    There's is a URL to check VIN numbers, but I'll have to dig that up.
    1971 BMW R75/5 | 1975 Moto Guzzi 850T Cafe | 1983 BMW R100RS | 1988 BMW R100GS
    1988 BMW K75 | 1998 BWM R1100RT | 2000 Moto Guzzi Quota 1100ES |2002 Moto Guzzi V11 LeMans

  6. #6
    rabid reader dbrick's Avatar
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    I have a very vague memory - CRS Syndrome, anyone? - that I considered buying some aftermarket headers in the mid-70s with no crossover points. Maybe a prior owner installed some; they look pretty shiny for an almost-40-year-old machine.
    David Brick
    Santa Cruz CA
    2007 R1200R

  7. #7
    Liaison 20774's Avatar
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    Quote Originally Posted by AnnapolisAirhead View Post
    There's is a URL to check VIN numbers, but I'll have to dig that up.
    http://www.bmw-z1.com/VIN/VINdecode-e.cgi

    or you can just go to RealOEM and enter you VIN...it will then show you the month/year of build.

    Also Phil Hawksley site lists the VINs by model:

    http://www.bmbikes.co.uk/enginechassis.htm
    Kurt -- Forum Liaison ---> 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!

  8. #8
    Registered User mneblett's Avatar
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    My wife's R75/5 has a cross-over. Myunderstanding is that it is there to improve low-end torque - pressure pulses arriving at the right time to enhance scavenging. I suspect your friend is not so much feeling better mid-range power, but simply noticing the more stark change from poor low-end to normal mid-range.
    Mark Neblett
    Fairfax, VA
    #32806

  9. #9
    --Tony AnnapolisAirhead's Avatar
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    Its pretty shiny all over, 31k on the odom, very little surface rust/bare metal parts. If the headers are aftermarket, they did a nice job.

    When I plug in the last 7-digits of the VIN into the bmw-z1 site, it tells me that I am riding/driving a 1986 (E30) 320i convertible. hmmm...

    Mark, you may be correct about the mid-range, although he rode my bike nearly daily to the gym each morning on nice day for a year. So I'm pretty sure he'd feel the difference in low-end on the new bike, right?

    Since the Bing's did not come with a vacuum port and the headers without a cross-over, maybe this was just an early model??

    Any thoughts on whether I'd be better off with a cross-over at this point? If not, I'm included to just replace the silencers and leave well enough alone.
    1971 BMW R75/5 | 1975 Moto Guzzi 850T Cafe | 1983 BMW R100RS | 1988 BMW R100GS
    1988 BMW K75 | 1998 BWM R1100RT | 2000 Moto Guzzi Quota 1100ES |2002 Moto Guzzi V11 LeMans

  10. #10
    Liaison 20774's Avatar
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    Quote Originally Posted by AnnapolisAirhead View Post
    When I plug in the last 7-digits of the VIN into the bmw-z1 site, it tells me that I am riding/driving a 1986 (E30) 320i convertible. hmmm...
    Your bike should only have 7-digits, something like 297xxxx to 298xxxx. Anything different than that, you might just have a "beamer"!!
    Kurt -- Forum Liaison ---> 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!

  11. #11
    --Tony AnnapolisAirhead's Avatar
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    Quote Originally Posted by 20774 View Post
    Your bike should only have 7-digits, something like 297xxxx to 298xxxx. Anything different than that, you might just have a "beamer"!!
    Oops, that's what happens when I type without glasses. I was using the title number.

    So the correct info on the bike is that it was manufactured in 12/1970. Catalog model ECE, whatever that means. Anyway, its early. I'll check with the 5United roster to see if anyone has one made about the same time or before and try to contact them.
    1971 BMW R75/5 | 1975 Moto Guzzi 850T Cafe | 1983 BMW R100RS | 1988 BMW R100GS
    1988 BMW K75 | 1998 BWM R1100RT | 2000 Moto Guzzi Quota 1100ES |2002 Moto Guzzi V11 LeMans

  12. #12
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    I have bought stainless headers for /2 conversion from Epco with no crossovers
    for use with R75/5 and R100/7 engines - I just ordered them that way for less
    cost and ease of assembly, tuning idle and balance by ear - suits me fine as a
    tourer not interested in ultimate available performance.

    Maybe I am not the only one with that frame of mind.

    I have a 1970 R75/5 stock parts bike that came with single crossover forward.

  13. #13
    MCM-now MAC-exhaust used to make headers for BMWs without cross-over pipes. Yours were probably made by them.

  14. #14
    --Tony AnnapolisAirhead's Avatar
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    Thanks guys. I've seen complete stainless exhausts for /5 from Epco, he makes a fine set.
    1971 BMW R75/5 | 1975 Moto Guzzi 850T Cafe | 1983 BMW R100RS | 1988 BMW R100GS
    1988 BMW K75 | 1998 BWM R1100RT | 2000 Moto Guzzi Quota 1100ES |2002 Moto Guzzi V11 LeMans

  15. #15
    VANZEN
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    cross

    The cross-over tube is, in fact, designed to improve low to mid RPM torque delivery.
    The second cross-over that was added in '81 (?)
    was intended to compensate for EPA mandates
    that otherwise might have compromised power delivery
    by boosting torque delivery over an even larger (and frequently used) RPM range.
    Placement and number of cross-overs will affect the "shape" of the torque delivery curve.

    In the days of old, high RPM racing machines such as the the RS54 were without a cross-over,
    but it will be interesting to note that Udo Gietl experimented
    both with the number and placement of cross-overs,
    and ultimately got rid of all of them –
    Seems that he favored a tapered header
    claiming that this technique improved torque delivery throughout a wider range of RPM
    than was possible with cross-overs.

    Consequently, when one sees his R90S Superbike,
    one might assume that it is fitted with conventional single diameter headers as stock ...
    but it is not !

    Only recently has Gietls's performance technique been applied to production motorcycles.
    Last edited by vanzen; 12-16-2010 at 04:58 PM. Reason: add

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