New 336° cam from BMW

Discussion in 'Airheads' started by RGregor, Dec 24, 2012.

  1. motu

    motu Loose Pre Unit

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    Revs - I've been lead to believe it's a bit unsafe to rev an Airhead too high, but my R65 loves to spin to 8,000rpm. I use it as an over rev when I have runaway wheelspin on gravel roads, better to let it go than risk an upshift or back off in a powerslide, but also when the red mist is down and shifting by ear, my shift point seems to be 8,000rpm. I've been reading about the Michel 850 kit for the R65, and they say it spins to 9,000rpm. So long as I have no valve bounce, is it ok to run them at these revs ?

    It reminds me of the Honda XLV750 I had - max hp at 7,000, red line at 8,000 and limiter at 8,250. I had that bike on a dyno a couple of times and the power curve was exactly the same a Honda's - it only lost a couple of hp between 7,000 and 8,000rpm. I used the over rev on gravel too, but also to save wasted upshifts between corners on the road - let it spin out to 8,000 and then into the next corner. I'd like to do this with the R65 too.
    #81
  2. bmwrench

    bmwrench Long timer

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    I hadn't though about the fact that you're in New Zealand. Venolia (in California) has made plenty of R65 pistons, so they could make some for an R45.

    I've never had an R45 apart, so I don't know what the chamber or piston dome are like. Got any specs?
    #82
  3. supershaft

    supershaft because I can

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    Exactly! That is what usable over rev is all about. It is very often very handy to reduce lap times! I haven't figured R65 average piston speed per second. The rest of the bikes at a 70.6 stroke are under 4000fps until just short of 9000rpm. IMO there is no need for a shorter stroke than 70.6 since the valve train is the limiting factor at that stroke, let alone a shorter one. Plus the bore to stroke ratio of a R65 is already 1.33:1. The same as a R100. That's already quite the short stroke considering our head design!!!! Any shorter bore to stroke ratio is barking up the wrong tree IMO.
    #83
  4. motu

    motu Loose Pre Unit

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    I just calculated it all out, and then lost it all....should've written it down the hard way. Anyway, my final point was that bore/stroke is about piston speed, and you can't compare a 650 to a 1,000cc engine....better to compare the R65 to a Triumph 650. At 7,250 the 82mm stroke Triumph has a piston speed of 19.8 m/s, or 3900 ft/min. The 61.5mm R65 is doing 14.86 m/s or 2925 ft/min, at 8,000 the R65 is 16.4 m/s or 3228 ft/min, at 9,000 18.45 m/s or 3631 ft/min.

    At 9,000rpm the piston speed of the R65 is lower than the Triumph at 7,000rpm - and the Triumph was considered to be a revver in it's day.
    #84
  5. supershaft

    supershaft because I can

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    At 8400rpm a R100's piston speed matches a Triumph 650's average piston speed at 7250. My point is that the valve train which is almost identical between a R65 and a R100 is at its limit well before piston speed is on a R100, let alone a R65. The valve train is the limiting factor in both engines. Since piston speed is really not the issue with airheads, why not run as much stroke as you can for more torque. IF piston speed was an issue before the valve train, I would be looking to run a shorter stroke than 70.6mm but . . . .
    #85
  6. motu

    motu Loose Pre Unit

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    Valve train has always been the limiting factor with pushrod engines, that's why ohc is now the prefered option. But plenty of pushrod engines can be made to rev well, some even stock. I used to rev the unit 500cc Triumph twins to over 10,000rpm, completely stock. So if it's happy at 8,000rpm with no valve float issues, that's still safe on these engines - the bottom engine is up to the task ?
    #86
  7. Voltaire

    Voltaire Titanium and Ceramic Hipster

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    Was thinking the same thing ... lighter stronger materials are now being used in Triumph valve trains, the Trident owner at the track was horrified when I told him BMW ones were nearly a foot long..... he gave me some places that make custom ones in the States that don't flex.....mind you how long is Triumph one...4"....?:huh
    #87
  8. pommie john

    pommie john Long timer

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    The main issue with high RPM in airhead engines has been cavitation at the oil pump. Essentially, the pump is trying to suck too much oil from the sump and it has so much suction that it causes bubbles to form in the pick up tube. The traditional way around this was to drill the pick up out bigger. ( I think it goes from 10mm to 13mm but one of the other guys will correct me if I'm wrong).

    After doing this to my racer, it's happy running to 8500 with no problems. I have an oil pressure gauge just in case.

    I believe some people have machined the pump thinner so it draws less oil.

    I'm not familiar enough with the R65 engine to know if it's a problem with them too.
    #88
  9. Rob Farmer

    Rob Farmer Long timer

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    Moorespeed engines rev to 10,000 rpm and seem to be very reliable. If you look at the website under the 750cc class theres a brief lowdown on the moorespeed short stroke engine.

    http://www.moorespeed.co.uk/classic-racing
    #89
  10. pommie john

    pommie john Long timer

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    I've looked at ways around the pushrod issue and haven't yet found a good solution. The chrome moly steel ones are stiff, but much heavier and with a foot long pushrod, there's significantly less thermal expansion in the rod so valve clearances vary as the engine heats up.

    A friend of mine tried composite carbon pushrods. Very light and very stiff , but they don't expand at all with heat. It was so bad that if he set valve clearances hot, when the engine cooled down there was no compression when the engine was cold because the pushrods held the valves open! The only way he could make it work was either to set the valve clearances every time the engine was cold, and then reset them as it got hot, or never let the engine cool down!
    #90
  11. supershaft

    supershaft because I can

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    Not always. It depends on the stroke. Some pushrod engines run into piston speed problems before valve train problems. For instance, Triumph 650's are going to run into piston speed issues long before BMW 650's or 1000's.
    #91
  12. supershaft

    supershaft because I can

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    I had some custom made at Manton here in Ca. Twice as heavy as BMW steel rods and three times as heavy as BMW aluminum rods which absolutely do flex a lot as evidenced by their rub marks. The big money pushroders (NASCAR and NHRA drag racers) have doubled and tripled their pushrod weights in the last ten or so years for more rigidity and power with relatively little effect on valve float rpm. I think my heavier pushrods did lower my valve float by a couple of hundred RPM BUT I am also running heavier intake valves (bigger) at the same time.

    I forgot to add that I am running into the same issue as pj's friend with the carbon fiber rods with my 4130 pushrods. I am setting my exhaust at zero play and my intakes just slightly preloaded in order to get .004 and .008" when it is hot but it apparently isn't enough to effect starting at all so far.
    #92
  13. supershaft

    supershaft because I can

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    The later models come stock with that mod (and a lot of other mods as well). I don't know when they started doing it. My '92 has a 13mm oil pickup. I would guess my '83 R65 did too. I use to rev it well over its 7650 stock redline ALL the time. My stock electronic tachs top out at 8000rpm so I am guessing up above that. I am guessing my valves are now floating a little before 8500rpm. If it becomes an issue I can always preload my stock springs a bit. Right now they are bone stock.
    #93
  14. Voltaire

    Voltaire Titanium and Ceramic Hipster

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    The R65 has the larger oil pick up.
    SS, I no longer beleive what the BMW rev counter says after seeing the ignition program on the lappy....its spot on...as it has to be...the rev counter less so....I gave up on the electronic one as it wet heywire over 7500.....the mechanical on is better but reads high.
    No longer run one, just change up when the limiter hits :D
    #94
  15. RGregor

    RGregor Been here awhile

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    So your pushrods are ~150 grams?
    And everything stock except your Ti-retainers? What are they? Probably around ~12 grams.

    I believe your observations but I also believe in physics and mathematics.
    Pure mathematics say that you'll need 26% more spring force than stock for the same rpm.
    For 8500 rpm you'd need more than 1000N spring force.
    The stock spring has around 800N max force.
    Preloading 1mm brings an additional 45N only.

    Somethings wrong in that calc.

    Edit: these are the according data
    <table border="0" cellpadding="0" cellspacing="0" width="400"><colgroup><col style="width:60pt" width="80"> <col style="width:60pt" span="4" width="80"> </colgroup><tbody><tr style="height:15.75pt" height="21"> <td class="xl66" style="height:15.75pt;width:60pt" height="21" width="80">Masses</td> <td style="width:60pt" width="80">
    </td> <td style="width:60pt" width="80">
    </td> <td class="xl66" colspan="2" style="mso-ignore:colspan;width:120pt" width="160">Masses, reduced to valve side</td> </tr> <tr style="height:12.75pt" height="17"> <td class="xl67" style="height:12.75pt" height="17">Part</td> <td class="xl67">Stock</td> <td class="xl67">mod</td> <td class="xl67">Stock</td> <td class="xl67">mod</td> </tr> <tr style="height:12.75pt" height="17"> <td class="xl67" style="height:12.75pt" height="17">Lifter</td> <td class="xl68">60,0</td> <td class="xl68">60,0</td> <td class="xl68">43,2</td> <td class="xl68">43,2</td> </tr> <tr style="height:12.75pt" height="17"> <td class="xl67" style="height:12.75pt" height="17">Pushrod</td> <td class="xl68">54,0</td> <td class="xl68">150,0</td> <td class="xl68">38,8</td> <td class="xl68">107,9</td> </tr> <tr style="height:12.75pt" height="17"> <td class="xl67" style="height:12.75pt" height="17">Rocker</td> <td class="xl68">30,0</td> <td class="xl68">30,0</td> <td class="xl68">30,0</td> <td class="xl68">30,0</td> </tr> <tr style="height:12.75pt" height="17"> <td class="xl67" style="height:12.75pt" height="17">Screw</td> <td class="xl68">15,0</td> <td class="xl68">15,0</td> <td class="xl68">10,8</td> <td class="xl68">10,8</td> </tr> <tr style="height:12.75pt" height="17"> <td class="xl67" style="height:12.75pt" height="17">Valve(in)</td> <td class="xl68">86,0</td> <td class="xl68">86,0</td> <td class="xl68">86,0</td> <td class="xl68">86,0</td> </tr> <tr style="height:12.75pt" height="17"> <td class="xl67" style="height:12.75pt" height="17">Spring</td> <td class="xl68">54,0</td> <td class="xl68">54,0</td> <td class="xl68">18,0</td> <td class="xl68">18,0</td> </tr> <tr style="height:12.75pt" height="17"> <td class="xl67" style="height:12.75pt" height="17">Retainer</td> <td class="xl68">17,0</td> <td class="xl68">12,0</td> <td class="xl68">17,0</td> <td class="xl68">12,0</td> </tr> <tr style="height:12.75pt" height="17"> <td class="xl70" style="height:12.75pt" height="17">Keys</td> <td class="xl69">3,0</td> <td class="xl69">3,0</td> <td class="xl69">3,0</td> <td class="xl69">3,0</td> </tr> <tr style="height:12.75pt" height="17"> <td class="xl67" style="height:12.75pt" height="17">Sum</td> <td class="xl65">
    </td> <td class="xl65">
    </td> <td class="xl68">246,8</td> <td class="xl68">310,9</td> </tr> <tr style="height:12.75pt" height="17"> <td class="xl67" style="height:12.75pt" height="17">
    </td> <td class="xl65">
    </td> <td class="xl65">
    </td> <td class="xl65">
    </td> <td class="xl65">
    </td> </tr> <tr style="height:12.75pt" height="17"> <td class="xl71" colspan="2" style="height:12.75pt;mso-ignore:colspan" height="17">Rel. Change to stock</td> <td>
    </td> <td class="xl67">100</td> <td class="xl68">126,0</td> </tr> </tbody></table>
    #95
  16. RecycledRS

    RecycledRS Along for the ride

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    RGreger what type of spring material are you using to get 18 grams?
    #96
  17. supershaft

    supershaft because I can

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    Pure mathematics? Mathematics is pure until we associate values to the numbers. Therein lies possible imperfection! I couldn't care less about the physics of it since all kinds of tuners have noticed since the early sixties that I am aware of that weight on the pushrod side of the rocker for some reason effects valve float rpm very little just as the tiniest differences in weight on the valve side of the rocker arm effects valve float rpm a great deal. Try to work that out on paper if you can but I still won't care much sense I am mostly interested in what works, not math. Especially bad math since, if some math predicts something won't work and it does work, it's not good math. There is no need to 'believe' in good physics! It's the bad physics that takes a leap of faith. You don't have to believe just me. Do some reading on the subject. My experience was just what the experts predicted. That's the kind of experts I listen to! I am sure some would have predicted that it wouldn't work at all but here I am and it works. It's great when things work out! Now I am not completely sold on the idea as of yet with only 2000 miles experience but so far so good.

    I don't remember the exact weights. They are real close to three times the weight of the aluminum rods and twice as heavy as the steel ones. The retainers are only grams lighter but they really do increase any setup's float rpm by around 500rpm just as some experts predict. Predictions that can be duplicated. Now THAT'S good science!
    #97
  18. RGregor

    RGregor Been here awhile

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    The spring has a weight of 54 grams. But as only parts of it are moving you don't count the whole weight.
    Usual numbers are 50% or 30% of the spring weight.
    54/3=18.
    #98
  19. RGregor

    RGregor Been here awhile

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    I did some reading on the subject and the way to calculate masses is the result of it.
    Still it's a very primitive model as it does not take into account any flexibility.

    Now, obviously your practical results and my theory differ. At this point asking questions way reveal some information not mentioned yet. Not the case here.
    Good practical results beat bad theory. Any hints where to find the information you refer to in literature?

    Happy New Year to all Adventurers here!
    #99
  20. supershaft

    supershaft because I can

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    I think I googled pushrods? I think Manton has links to sites? Tons of tuners are just recently running way heavier rods for rigidity. Circle Track magazine might be a source? Sprint car racers are the other cutting edge pushrod sport!