Primary Drive Belt Interchange/Compatibility

Discussion in 'Norton Commando Classic Motorcycles' started by lcrken, Nov 1, 2017.

  1. lcrken

    lcrken VIP MEMBER

    Joined:
    Mar 15, 2009
    We've had some good information lately in a couple of other posts on belt drives, but I thought I'd post this one separately to address a question I've had for a while. I'm particularly hoping for answers from folks who've used the Gates Poly Chain Carbon or Polygrip GT3 belts, like G81 Can Cycle (John) and comnoz (Jim).

    I've used HTD belt primaries for decades, and been very happy with them, but they do have some disadvantages. From my standpoint, the principle one is that I need at least a 40 mm wide belt for the higher horsepower Commando engines, and that doesn't allow easy fitting of the stock alternator. I never cared much on the race bikes, which don't use a alternator, but now that I'm more involved in street bikes, it's a real disadvantage. The newer belt designs, i.e. Gates Polygrip GT3 and Poly Chain Carbon, need to have pulleys with the GT2 tooth profile, at least according to Gates. I've seen at least one Commando primary drive using HTD profile pulleys with a GT2 profile belt, and it seemed to work OK.

    So, my question is, does anyone know if it is practical to use the newer profile belts with the older HTD pulleys? The reason I'm asking is that I suspect that Gates might be guilty of telling us they aren't compatible for business reasons, not engineering ones. And I could be wrong on that. Anybody with experience in this area willing to offer up some real world data? If we can use the newer belt technology on existing HTD drives, that would be a real plus.

    FWIW, I'm not interested in the alternate trapezoidal belt drives. I tried them decades ago on a race bike, and had disastrous results.

    Ken
     
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  2. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    My take is the polychain belt will run on an HTD pulley with reduced life and power capability.
    Now the bad part -there is not a Polychain belt available in the proper length needed to gear up the transmission so it will handle the power. Jim
     
  3. marinatlas

    marinatlas

    Joined:
    Nov 4, 2007
    Hi, Doug Mac Rae had good feedback few times ago with his RPP gold, may be he could chime about the tooth profile ??
     
  4. dero

    dero VIP MEMBER

    Joined:
    Jan 22, 2010
    Some body else commented on their opti belt a while ago and how good it had been , I purchased 3 of them instead of the usual Gates belt & so far am still running the first one .
    It has outlasted the Gates belts by far . The bike is a 920 road bike & I have a fairly spirited riding style .
    Does not answer your question , but if you are looking for a better belt I would recommend them .
     
  5. marinatlas

    marinatlas

    Joined:
    Nov 4, 2007
    Hi Dero, I had also Optibelt in two of my bikes as it's the belt that Steve Maney supplied his kit with........so far , all is fine!
     
  6. lcrken

    lcrken VIP MEMBER

    Joined:
    Mar 15, 2009
    Optibelt is a good brand. I've used them in the past, as well as Gates Synchro-Power and PowerGrip GT, Uniroyal PowerGrip, Bando Synchro-Link, Fenner, Speed Control, UNITTA, and probably some other off-brands. I had good results with all of them on the race bikes, but they were also replaced regularly, so I can't say much about long term durabilty on the street. When Steve Maney was racing with us here in the US, he used both the Optibelt HTD and the Optibelt Omega interchangeably on his bike. The Omega has a modified tooth profile, but is compatible with HTD pulleys. In fact, the Omega tooth profile looks a lot like the Gates PolyGrip profile. The fact that Optibelt says it is compatible with HTD pulleys is one of the reasons I'm curious about whether the PolyGrip and Poly Chain belts can be used with HTD pulleys.

    Ken
     
    Last edited: Nov 2, 2017
  7. lcrken

    lcrken VIP MEMBER

    Joined:
    Mar 15, 2009
    Thanks, Jim. That is kind of a catch, isn't it?

    I've just found a Gates interchange guide from 2004 that addresses my question with more detail, although it doesn't address the PolyGrip belts. It has drawings of how well all different belt teeth fit the different pulley grooves. It's available here

    https://www.gates.com/~/media/files...belt-sprocket-interchange-brochure-102005.pdf

    Their recommendations say that a PowerGrip GT2 belt can be used as a replacement for an HTD belt on and HTD pulley, but new designs should use the GT2 pulley design. They also say that the Poly Chain GT2 belt can be used as a replacement on a Poly Chain GT pulley, but that for new designs the GT2 pulley should be used.

    No mention of the Poly Chain Carbon back then. It does say that the Poly Chain GT2 belt (in the 8M size we use for Commandos) should not be used on an HTD pulley, because the belt tooth is deeper than the pulley groove, and the belt will not wrap the pulley properly. That would seem to support your conclusion that the Poly Chain belts could be used on HTD pulleys, but that it's not really a good match.

    Ken
     
  8. G81 Can Cycle

    G81 Can Cycle VIP MEMBER

    Joined:
    Mar 6, 2012
    Ken

    I think you answered your own question on the tooth profile. The Poly Chain Carbon does have a unique profile. We were fortunate to have our gear and spline cutting tool vendor stock this profile. We are new to the belt drive market with our offering through CNW. So I have limited experience in how a HTD pulley would handle a Poly Chain Carbon belt. Ours was a new design' and we designed and manufactured the CNW Electric Start Conversion to use the Poly Chain Carbon belt.

    I concur with Jim's comment above. We wanted to produce a different ratio primary drive for Kenney at NYC Norton to put on my Seeley build, but the Poly Chain Carbon belt was not available for this non stock ratio.

    John
     
  9. lcrken

    lcrken VIP MEMBER

    Joined:
    Mar 15, 2009
    Thanks, John. I think my questions are pretty well answered now. For me, the good news is that the carbon belt is available in 896 mm length, which is the size I'm using for the pulley combination on my MK3 build. The bad news is that I have HTD pulleys. I think what I'll have to do is try it out with the best HTD compatible belt I can find, and see if it holds up. The only reason I'm a little nervous with it is because the widest I could fit and still get an alternator on is 30 mm, and my previous experiences with trying that on a large engine weren't too good. I'm hoping modern belts are a bit better. If not, I'll have to come begging to you for a clutch basket and front pulley to fit the carbon belt profile.

    Ken
     
  10. Kvinnhering

    Kvinnhering VIP MEMBER

    Joined:
    Feb 16, 2011
    +1
     
  11. G81 Can Cycle

    G81 Can Cycle VIP MEMBER

    Joined:
    Mar 6, 2012
    Ken

    We would be happy to help The Poly Chain Carbon belt we use on our system is rated for 100 HP. As I have said before, we ran this stock ratio belt system on Stan Keyes Commando race bikes for 2 years. They are 750's run in AHRMA Bears class. They put out in excess of 60 HP. Same belts were run on both bikes for 2 years, no belt replacement, and no failures of the belts. Stan won the Bears National Championship both years. I would like to work on different ratios for primary drive for performance application, and would like to develop a final drive Poly Chain belt system, and have had talks with Comnoz about this.

    I will have to put that on the schedule. The schedule for development is pretty full right now. We are working on casting Ducati heads (Am I allowed to speak Italian on this forum? LOL). We have 3D printed the designs and are flow testing the prints. Next is to print the patterns and core boxes and we should have performance heads for Ducs by spring. And, no, I am not working on Norton heads, Full Auto does too good of work on that product to compete with them.
     

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