GP460 Engine On Friction Drive

Discussion in 'Friction Drive' started by 5-7HEAVEN, Apr 25, 2009.

  1. 5-7HEAVEN

    5-7HEAVEN Guest

    Has anyone done this swap yet?

    I'm doing it, will probably mount on my Raleigh men's cruiser w/7-speeds as a test bike.

    I could use some helpful hints, especially about roller size, possible weak links and exhaust options.


  2. fetor56

    fetor56 Guest

    Can't help much 5-7 cos i havn't got a GP460(yet) but i do have the BMP's kit.
    My first impressions are that you'll need to fab a stronger(possibly even longer) U-bracket to take the power,even then the rest of the setup will no doubt need additional strengthing.
    I did my U from 6mm steel instead of the standard 5mm,i know it's only 1mm diff but it's a handy improvement & i'm reluctant to go crazy adding weight.
    Were u thinking of using the standard 1.25" one-way drive roller or swapping?

    PS....sorry about the mud,it's been raining on & off here for the last 5 days.
  3. DetonatorTuning

    DetonatorTuning Active Member


    .02 worth

    build a deeper, longer "u" channel so that you can can put 3 rollers in it.

    one higher in the middle and 2 lower more toward the front and back. all of them touching to the same degree at once. tie the outer 2 to the center one by a chain loop on the far side ( opposite the engine)

    i really think the sticking point is going to be getting enough contact without using so much down pressure that the resultant tire deflection just eats up the power anyway.

    you're going to want to use a small enough roller to let the engine spin up to rpm easily to avoid long periods of high torque present at the roller/ tire. you are going to want to get to 22:1-23:1 for that engine and it's GOING TO BE FAST.

    can't wait,
  4. 5-7HEAVEN

    5-7HEAVEN Guest

    fetor, I believe the front U-bracket will be the weak link. The thinner BMP front mount's strength has been questioned before and I don't particularly care for all front brackets' tendencies to pivot and twist. For additional strength I'm gonna triangulate this mounting position ala Staton gearbox, using additional struts.

    Detonator Tuning, believe it or not I'm trying to keep this project as simple as possible. I will try controlling this engine's power with the standard engine channel and a single friction roller. To harness the power I'll use a small-diameter spindle. Then I'll keep speeds below the projected 40mph maximum until all systems are "GO!"

    Other braces of 5/16" X 5" bolts are to be used front, midship and rear should add more than enough strength to the 1/8" steel engine channel.

    I'll start off with a secondhand 1.25" Staton friction roller from "The Dragon Lady's" front drive. It only has a few hundred miles use with no wear on its contact surface. Surprisingly, the ends which ride inside the bearings wore its plating off. That slight wear allows the new bearings to SLIP-FIT!!! onto the spindle.

    The BMP engine channel also allows a slip-fit for the outer diameter of the 1.375" bearing. It makes for a very freespinning roller. This is strange; the other vendor's press-fit bearing arrangement had always made the roller feel slightly tight and resistive after swapping in a new spindle.

    There were other subtle reasons I decided to swap in another vendor's spindles. The BMP's driveshaft is only .50" diameter; its threaded end protrudes .125" into the clutch bellhousing area. I'm not saying the shaft might contact the crankshaft. For overkill, its diameter would worry me that it's not strong enough.

    The Staton roller looks as tough as a grenade. Its diamond-hatch grip surface is very aggressive and the .625" ends are larger than BMP's driveshaft.

    The GP460 I'll be using is Zomby Builder's old engine. It has limited miles and thanks Dave for a great price. It has Trevor Simpson's headkit/piston/cylinder w/15:1 compression. Dave ran the engine with racing gas due to high compression. I'm detuning to 13:1cr; then I can use 91/92 octane pump gas. Racing gas costs $120/5 gallons which is too rich for me. A $23 compression dome should make this beast streetable.

    The only other high-performance parts will be the Dominator pipe from like this one:

    Other builders on this forum have used this exhaust system affter modifying the pipe for clearance. Careful research predicts that the Dominator SHOULD clear all obstacles without modifications, just mounting bracket onto the engine channel. I will figure out the kit's front brace and goped tank location after this powerpipe is securely fastened.

    fetor, I'm using Staton's rollers because they have more sizes to choose from. If a 1.25" spindle does not allow this modified 460 engine to rev high enough, then a 1.125" or 1.00" can be substituted. An online calculator has engine speed at 12,155rpm/13,500rpm/15,200rpm at a speed of 40mph.

    That cross-references to gear ratio comparisons of 23.5:1 for a 1.25" roller, 26.1 for a 1.125" spindle and 29.4 if a 1.00" friction device is used.

    Steve, I might try the 1.00" roller first. According to other people's testimonies this engine produces its maximum torque at 8,000rpm. That's sky high compared to Hondas, Subarus, Mitsubishis and others. Even though clutch engagement might be at 3000rpm, power might not be there unless gearing is very low.

    Please share your experiences. At what gearing was your 460 engine most responsive in all your experiments?

    to be continued...
    Last edited by a moderator: Apr 27, 2009
  5. DetonatorTuning

    DetonatorTuning Active Member


    the 1.25" will be the ticket. 41.1mph @ 12500.

    23.5:1 reduction thru a tranny like i'm using gives FANTASTIC accel. and you'll have MUCH less loss. my current "low" gear is 22.79:1 and i only go there for extreem headwind, 25mph and up. accel. is brisk to say the least. if wind is 5-10mph i can easily pull all hills etc. @ 19.29:1 running 40-45mph right around 11,000rpm.

    you'll be above the HP peak of 11,000 but if 40's all you want then you're done. it will not be much over 50-60mpg but it will be a riot as long as it's hooked up.

    best of luck, keep us posted


    after thought, what's the ratio on the 1.5" ? is there a 1-3/8" ?

    as a point of interest, 21-21.5:1 is the best compromise ratio for me at the present time.
    Last edited: Apr 27, 2009
  6. 5-7HEAVEN

    5-7HEAVEN Guest

    Steve, the 1.5" friction roller is equivalent to 19.6:1 when crossreferenced with two popular online calculators.

    At 40mph, 10,100 rpm with this big spindle.

    A 1.375" roller is equivalent to 21.35:1; at 40mph, 11000rpm.

    I'm starting off with a 1.125" roller, which is like 26:1 gears.

    13,500rpm at 40mph. With stiff gears, Dominator pipe, 13:1 compression and custom headkit, I believe this engine should still be producing hp at this speed.
    Last edited by a moderator: Apr 27, 2009
  7. DetonatorTuning

    DetonatorTuning Active Member

    in a perfect world the 1-3/8" roller is the ticket.

    you'lll have all the power you're going to get at 11,000rpm, the CR and pipe are just going to make that # higher in pretty much the same spot.

    you will still have "over revs" available though, mine see's 13,500 regularly just not at speeds i want to maintain. you are not going to like the sound of that motor sustained over 11,000rpm and that takes getting used to.

    ps, 26:1 will feel "thin", what i mean is it will be hard to tell if it's completely hooked up because it will turn thru and rev real free.

    Last edited: Apr 28, 2009
  8. 5-7HEAVEN

    5-7HEAVEN Guest

    Detonator, I have roller sizes of 1.00", 1.125". 1.25", 1.375" and 1.5". I'll start off with 1.25" spindle instead of the 1.125" spindle and see what works after that.

    Steve, can you explain your last statement "At 26:1 , will feel "thin", what I mean will be hard to tell if it's completely hooked up because it will turn thru and rev freely"?
  9. DetonatorTuning

    DetonatorTuning Active Member


    by "thin" i mean that there will be very little sensation of resistance, it will rev real easy and move on up in speed but there will be little "torque" pulling feel.

    this sensation will be unsettling and you'll find yourself wanting to look to see if you are really hooked up.

    it's odd enough that even with chain i was looking to see if i had derailed and running on a flange or something.

  10. 5-7HEAVEN

    5-7HEAVEN Guest

    Well, my Staton parts arrived. Dave sent me a 1.25" roller instead of the 1.125". I also ordered a 1.00" roller so I'll try that smaller one first.

    Hmmm, this GP460 engine is weak on torque, huh?

    :idea:I have a sneaking suspicion I'll be running TWO engines on my bike in the near future!!!:devilish:

    Yesterday I rode to work on "the Dragon Lady". The front engine died a mile from my building so I "limped" along on the rear engine until I got there. It was a fuel delivery problem I was able to correct after work.

    I absolutely HATE to get stuck on the road and pedal home.. My way of justifying having twin engines on my projects.:jester:

    No, I don't think it's too much power for a bike. Centrifugal clutches and sensible, disciplined throttle control will tame the beasts.

    First things first. Single engine install.
  11. DetonatorTuning

    DetonatorTuning Active Member

    ah......................... no, i'd not say 2.3#'s/ft @ 8,000rpm is particularly weak torque for a 46cc 11:1 2 stroke.

    i'm just not getting the explanation across in an understandable way.

    what i mean to say is that 26:1 and above this engine revs very fast and easy, because of that, coupled with the fact that the gearing is only going to let you go 32mph @ 11,000rpm, the sound that the 460 will be making, compared to the speed, will make it seem like it must be spinning loose.

    Last edited: Apr 30, 2009
  12. 5-7HEAVEN

    5-7HEAVEN Guest

    Not to worry, Detonator. I have all the spindle sizes; it should be no problem to swap rollers to match engine rpm and speed.

    Since the engine channel is only .125" thick, extra "meat" might need to be added near the outboard bearing for more support.

    The Dominator pipe arrived today. Removing the mounting bracket allows the pipe to bolt on and clear everything. Rewelding the bracket at a 90-degree angle permits the exhaust to be secured to the top of the engine channel.

    Extra support struts will be added to triangulate front mounting U-bracket.

    Goped tank will bolt onto the outboard side of the engine channel. It needs to be drilled to accommodate its petcock, and a fuel line to a reserve tank.

    Happy time teardrop reserve tank will mount on the bike frame's top bar.

    So maybe a 1.25" roller at 23:1 gearing might be a better starting point, Steve.
    Last edited by a moderator: May 1, 2009
  13. fetor56

    fetor56 Guest

    It's going to be interesting to see how loud & powerful this engine is with the pipe & also how much torque......imagine it's going to rev pretty freely. :ee2k:
  14. DetonatorTuning

    DetonatorTuning Active Member

    much is going to depend on the total weight of bike and rider in full gear, added to the terrain, how much you're willing to pedal away from stops, and the yet unknowable issue of keeping the contact constant without excess downpressure and tire deflection losses cancelling out the power available.

    i'd go with the 1.25" as a starting point.

    when i was using the GEBE, i could beat traffic across the intersection on the pedals then throw in the gas and STAY ahead. that was at 19:1 and just 11:1 CR.

    i gained a noticable amount of midrange torque just replacing my base gasket.

    5-7's engine at 13:1 is going to be pretty stout and have the topend advantage of the Dom. pipe. most people are surprised that the Dom. is quieter than the stock muffler.

  15. 5-7HEAVEN

    5-7HEAVEN Guest

    I just bought a 2005 Giant Rincon bike in mint condition for this project. The original wheels will go for my exercise bike at work. New high-performance rims and tires need to be built by Eki Cyclery. It's a bike shop three blocks from my workplace that I give mY business to. If my bike needs work I strip the motorized components before taking it in.

    The bike weighs under 33 pounds, which is 12 pounds less than what "The Dragon Lady" started out as, I think. Total motorized bicycle should weigh about 50lbs. That is 41 pounds less than my twin-engined girlie cruiser.

    If and when this Giant bike uses two engines, its total weight would be under 70lbs.

    That'd be more than 20lbs LESS THAN the "The Dragon Lady. Well, maybe with heavier wheels this bike might weigh 55lbs/single engine or 70lbs/twin engines.

    Rider in full gear would weigh about 215lbs.

    I PRESUMED that davesmotors would send me the lower compression dome, but it's outa stock. My engine has 15:1 cr which is too high for 91octane gas. I might just order a GP460 with stock compression from this vendor to finish this single engine install. When the 13:1 dome becomes available I might do the twin engine project.

    Steve, with my motorized bike I pedal my single-speed bike furiously and throttle both engines simultaneously. Then around 27mph it's all engine.

    With 21 speeds I'll probably be pedalling at 30-something mph with the engine.
    Last edited by a moderator: May 2, 2009
  16. DetonatorTuning

    DetonatorTuning Active Member

    the TS heads, domes, reed cages etc. have been "out of stock " for some time.

    you might try simpson racing direct but i think he got out of the loose parts end.

    gopednation's "for sale" forum would be my first stop, you might be able to make a trade.

    when i was running the GEBE i found i never used the gears on my bike. just left it 42T- 17T, .40:1. this low enough to get the jump on traffic and enough to still pedal at about 20mph if i ever wanted too, which wasn't often, 12mph and engine ON.

  17. kerf

    kerf Guest

    One thing I've noticed on the 460 is the torque curve is flat at low RPM. The engine doesn't get into the power till you get over 6K, where most are topping out. 7 - 8K things start getting interesting. I still believe the friction drive will be the weak link although, I've seen Honda 50's on them.
  18. DetonatorTuning

    DetonatorTuning Active Member

    me too saddly, but the experiment is interesting and important in that it could lead to some interest in providing an enhanced friction configuration to handle this kind of power.

    a stronger more efficient friction system would be good all the way around.

  19. 5-7HEAVEN

    5-7HEAVEN Guest

    Detonator, thanks for tips on finding that compression dome.

    kerf, time will tell if the friction drive will be the weakest link. Personally I feel the clutch and roller will withstand the torture. As you've pointed out, this engine produces power at a very high rpm. A low-winding engine produces its torque at the low end. This is where power engagement components would be placed to the test. Parts fail when the clutch grabs and tries to put the power to the ground. However, centrifugal clutches engage gradually, there is less stress to break parts. This is especially if the rider pedals vigorously from a standstart.

    It's like doing a rolling start instead of a standing start at the beginning of a dragrace.

    It would seem to me that the only weak link would be friction roller and tire engagement. Since this engine is not noted for its massive torque I don't foresee any problems at all.

    :idea:Disciplined throttle control will be the key to success.
  20. kerf

    kerf Guest

    I hope all works out. My experience with friction drives, of which I have three, is the tire becomes the weak point. Optimum roller tension, per my experience and David Staton's recommendation, is just enough tension to prevent slippage while holding the bike @ WOT. With the TLE43, this is a good range as it doesn't induce excess drag. You will need a lot more tension to achieve that standing lockup. Don't sell the 460 short.