the DR650 thread

Discussion in 'Thumpers' started by sleepywombat, May 1, 2006.

  1. Albie

    Albie Kool Aid poisoner

    Joined:
    Mar 31, 2004
    Oddometer:
    10,056
    Location:
    NWA
    According to physics, more power has a direct correlation to more heat :D , but as you said, the larger area should help offset that. I know given my propensity to pin the throttle on pretty much everything I ride, I'd be running it hard. :lol3
  2. procycle

    procycle Long timer

    Joined:
    Jun 7, 2007
    Oddometer:
    2,495
    Location:
    Center of the DR650 universe
    All things being equal, yes, a longer stroke will increase compression. I will modify the dish in the top of the piston to compensate.

    This will never be a kit. In any case it would not work with the stock piston because the stocker is too long below the wrist pin. With the stock piston you could only increase the stroke a couple of millimeters before the bottom of the piston hits the crankshaft. The 790 piston is a much more modern design and has the necessary clearance under the piston.

    As far as what is an advantage - It totally depends on what the goals are for the end result. Longer stroke makes more torque at the expense of rpms and vibration and depending on the motor can be more difficult or expensive than just a bigger bore.
  3. procycle

    procycle Long timer

    Joined:
    Jun 7, 2007
    Oddometer:
    2,495
    Location:
    Center of the DR650 universe
    Sure, plenty of interest until we start talking about the cost. A bare minimal 900 kit - custom built crank & rod, modified 790 kit, gaskets, etc would run at least $3000. Add a cam, 3rd gear and whatever will be necessary to keep the clutch hooked up and it would easily go $4k-$5k or more.

    Nope. Never going to be a kit but if someone else besides me is crazy enough to want to do this I'll be happy to help point them in the right direction.
  4. Rusty Rocket

    Rusty Rocket Life behind "Bars"

    Joined:
    Dec 22, 2005
    Oddometer:
    9,894
    Location:
    Trying to leave CT
    Reminds me of the 750cc 2 stroke Maico single that Rick Sieman and DirtBike magazine built back in the last century:eek1
  5. Mongle

    Mongle Knuckle dragger

    Joined:
    Dec 4, 2009
    Oddometer:
    3,385
    Location:
    North Carolina Y'all
    Your thinking is a little confusing. Using the same rod and piston would make the piston HIGHER in the bore.

    Most stroked engines use a shorter compression height on the piston (distance from piston pin centerline to top of piston) to make up the diffrence so the piston doessn't hit the head. A 10mm stroker would have 5 mm more at TDC and 5 mm more at BDC. So- all things being equal you would make the compression height 5 mm shorter so the piston top ends up in the same location. By doing this you increase the stroke but the piston TDC height from crank centerline ends up being the same.

    You can use shorter rods but that often leads to piston to crank counterweight clearance problems.

    And yes, increasing the stroke increases the compression. More "swept volume" with the same compression volume = higher compression ratio. Compression ratio = Swept Volume + Compression Volume / Compression Volume.
  6. procycle

    procycle Long timer

    Joined:
    Jun 7, 2007
    Oddometer:
    2,495
    Location:
    Center of the DR650 universe
    You can't do it that way with most modern motorcycle engines because the wrist pin is already as high in the piston as is practical. There just enough room between the wrist pin and the cylinder head to fit rings with no extra distance available to make a shorter compression height.

    Which is how this one is done with a 5mm shorter custom made Carillo rod. The thing that made it possible is the 790 piston which has a lot of counterweight clearance with the stock crank.
  7. trailrider383

    trailrider383 867-5309

    Joined:
    Jan 12, 2008
    Oddometer:
    3,415
    Location:
    NP, ID
  8. Mongle

    Mongle Knuckle dragger

    Joined:
    Dec 4, 2009
    Oddometer:
    3,385
    Location:
    North Carolina Y'all

    Yes, when we stroke the pin ends up being into the oil rings. No biggie though, you run a shorter pin with a support rail. Like so:

    [​IMG]


    Two diffrent ways of getting the same tamato juice! We often go this route to keep rod length longer for geometry and because custom rods are more expensive then the pistons. Of course, you only need one rod...we need 8:lol3
  9. Albie

    Albie Kool Aid poisoner

    Joined:
    Mar 31, 2004
    Oddometer:
    10,056
    Location:
    NWA
    What's the big deal, I use Rotella in my DR. :lol3
  10. RichBeBe

    RichBeBe All Hail Seitan!!!

    Joined:
    Mar 13, 2004
    Oddometer:
    6,330
    Location:
    NYC
    You could also run the stock length rods and use a cylinder spacer on the DR. Just another tomato juice.
    We would do that on some bikes that could run stock rods on stroked cranks (two piece rods with plane bearings made it easier)Though somewhere i have a cylinder spacer for a stroked RZ350 laying around.
    Not gonna work on your V-8's though
  11. YnotJP?

    YnotJP? Long timer

    Joined:
    Dec 26, 2007
    Oddometer:
    2,653
    Location:
    Philippines and Seattle
    We got many rods from Spade Carillo in the mid 1960's, for small block Fords and Chevys. Never had a rod problem.
    They are a thing of beauty. Needing only one is nice. But, you should buy two, just to have one to hold and look at.
  12. trailrider383

    trailrider383 867-5309

    Joined:
    Jan 12, 2008
    Oddometer:
    3,415
    Location:
    NP, ID
    Say what?
  13. procycle

    procycle Long timer

    Joined:
    Jun 7, 2007
    Oddometer:
    2,495
    Location:
    Center of the DR650 universe
    Yeah, but if you're after 10 mm more stroke there are multiple problems to overcome after spacing up the cylinder. Cam chain length, upper motor mounts, fitting carburetor and exhaust pipes, oil lines, etc. It's certainly a lot easier with a 2-stroke.
  14. canoli

    canoli human

    Joined:
    Jul 26, 2008
    Oddometer:
    1,811
    Location:
    Not from round these parts.
    So the ongoing struggle to get my Safari tank dialed in continues. When I last checked in you guys told me to fill it up and see how far I can get before it craps out. Seemed like the logical thing to do so I filled it with 33 liters (still had some in the tank when I rolled up to the gas station) and rode it for 275 miles. Then 5 miles from town in 108 degree heat, it stopped. It looked like I still had a lot of gas left so the only thing I could do was shake the bike a bit and luckily got some gas into the engine. Once at home I let everything cool down and I sprayed the carb inlet elbow with ALOT of WD40 and proceeded to empty the remaining gas into another container. When the Safari finally ran dry I found that it still had an additional 4 1/4 liters of gas remainingÂ…and I was pissed. So I stripped the tank off grabbed a set of vice grips and cranked the elbow over to the 90 degree position. Was pretty happy that nothing snapped off and after I put the tank back on I re-routed the lines and removed the cheap inline filter I installed.

    [​IMG]

    This is what it looks like now.
    [​IMG]

    Does this look right to you? How bad is that bend in the hose? :ear

    Going out for a ride tomorrow and hopefully I can get another 50-60 miles before it goes dry. If not, I might be putting the Safari in the flea market and picking up a Acerbis. I really need the range and don't want to carry external containers if I don't have to.



    Stay tuned and thanks again for your help.
    Canoli
  15. Rusty Rocket

    Rusty Rocket Life behind "Bars"

    Joined:
    Dec 22, 2005
    Oddometer:
    9,894
    Location:
    Trying to leave CT
    Easy on a 2 stroke, but with OHCam, you'd need a longer camchain. That was how I immediately thought it would be accomplished, but the more I thought about it, the more confused I became.:lol3
  16. RichBeBe

    RichBeBe All Hail Seitan!!!

    Joined:
    Mar 13, 2004
    Oddometer:
    6,330
    Location:
    NYC
    Agreed, I was more stating another option. The shorter rod is the way to go since you have the skirt clearance. The engine mount is the only real problem that I see on a DR.
    We used to do it on a lot of 4-strokes, some you needed a new cam chain and some you didn't though rarely were the strokes 10mm. Though we did make and sell a few .250" spacers for Suzuki GS1150;s, which would be a for a pretty big stroke
  17. amk

    amk Been here awhile

    Joined:
    Jun 27, 2007
    Oddometer:
    497
    I cannot pinpoint you to the exact cause of the problem, but the theory of problem solving is simple enough. DR does not have a gas pump, i.e. gas flows free to the carb by its weight and atmospheric pressure.
    So the first one is to make sure the carb's inlet is below the petcock. The last usually has a pipe of 5 cm. height inside the tank, so everything under the the pipe is stayed there forever and cannot be used.
    Second, make sure the gas inside is under the atmospheric pressure, the breather is not blocked etc. Just take the gas cap off and depress start button again.
    Third, remove all barriers between tank and carb's inlet, i.e. filters, here I am not sure, but there probably is a small oem one right in the tank petcock or in the carb. Take the petcock out, open it, disconnect the hose from inlet and blow into petcock, should be no resistance to the air flow.
    It is one of three reasons, which one is yours? It actually may be all 3 of them simultaneously.
  18. Kommando

    Kommando Long timer

    Joined:
    Nov 28, 2006
    Oddometer:
    7,403
    Location:
    Spacecoaster FL
    Not quite right. The DR and other carbed bikes are primarily fed by gravity. There's a bit of suction/siphon going on too, but the primary method of getting gas into the carb from the tank is by gravity feed. As long as there is no kink or blockage in the line, you basically just want the fuel to NOT have to flow uphill to get into the carb. Suction will overcome a little bit, but it can also allow air-bubbles to get into the line and affect fuel flow. The flow from my petcock to my carb is all either down or sideways. There is no uphill flow. As long as my tank is venting ok, I have no flow issues. I can run my tank pretty dry. Route your fuel lines so that there is NO uphill flow. If you can't do that, you may want to install a fuelpump.
  19. TRAVELGUY

    TRAVELGUY Old Traveler

    Joined:
    May 20, 2008
    Oddometer:
    725
    Location:
    Georgetown, In / Costa Rica
    I had a temporary problem with emptying my safari also. Was getting a vapor lock at the aftermarket filter I had installed. Changed to a different filter and all went well. When the vapor lock happened I could just blow into the tank vent and clear the vapor lock then tank would empty. When I disconnect my fuel lines from the carb to drain my safari the tank totally empties.

    Hope this info helps.

    TravelGuy

  20. Mambo Dave

    Mambo Dave Backyard Adventurer

    Joined:
    Oct 7, 2011
    Oddometer:
    5,929
    Location:
    11 ft. AMSL
    Do Acerbis tanks have this much of a problem emptying fuel?