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Thread: Circle-S Drive tensioner question

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    Circle-S Drive tensioner question

    I've got a question regarding the tensioner system on a circle-s redrive unit. By the looks of things, the drives use a gates poly chain drive belt(cogged timing belt). For a tensioner, it looks like a pulley is pressed to the back side of the belt between the drive and driver sprockets, taking slack from the set-up. Please let me know if this is in-correct as I'm only going from pictures.

    My question is- How durable is the belt in this set-up? And how well does it work overall? I guess two questions....

    I ask because the manufacturer does not approve this type of tensioning system (pressure on the back of the belt), but if it works, I'm all about breaking rules.... I have built a similar belt set up as the Circle-S but currently have no tensioner, and obviously, I am anticipating issues.

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    Re: Circle-S Drive tensioner question

    You are correct as to how the tensioner operates. I have about 35 hours on mine since new and I now have my tensioner set so that it runs lightly on the backside of the belt. I'm not entirely happy with this setup since the backside of the belt is ribbed and this produces a noticable whine when above an idle. Conversely, with the tensioner backed off all the way there is considerable belt slap at idle, especially when everything is cold which leads me to believe that the belt may be jumping cogs so I'm running it at a point where the slap is reduced but not too much pressure on the belt.

    A word of caution ... however you adjust your tensioner, make sure that there's nothing to vibrate loose and go through the prop! They forgot to put a locknut on my tensioner bolt and it vibrated loose and went through my new prop (which is now being repaired by the manufacturer).
    11'6" Marty Bray Hull
    4A084 Continental
    Circle "S" 1.69:1 Reducer
    67" Whirlwind Razor X Prop
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    Re: Circle-S Drive tensioner question

    Here is a picture of what I have. I've progressed past this point, but I haven't added a tensioner yet. I was thinking to install a smooth idler pulley, spring mounted, pushing on the outside of the belt toward the camera. (does that make sense?)reduction drive picture

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    Re: Circle-S Drive tensioner question

    If the Circle-S redrives are considered reliable, I will adapt that configuration to this set-up. I spoke to Chuck, from Airboat Pros, this afternoon and he seemed pretty happy with them. He also was very happy to pass along information on the Gates website on some of the design calculators they have. He was very helpful and it's always nice to speak with someone in the industry.

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    Re: Circle-S Drive tensioner question

    Just a thought about belt tension. After looking at the above photo, could shims be installed (equal thickness) under the two bearing pillow blocks to raise the prop shaft thereby taking up slack in the belt. (or does the belt slack differ from cold start to hot running conditions? thereby requiring the tensioner idle.)
    kent

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    Super Moderator Corky's Avatar
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    Re: Circle-S Drive tensioner question

    Kent, I've watched some in-chasis cameras on a dragster with the big, cogged blower belt and you would'nt believe how much belt stretch/harmonics are present through the whole run..The belt stretches/retracts with different levels of RPMs and torque...That's why there needs to be some type of tensioner with a positive{as in spring loaded} pressure applied to the belt...Since the introduction of the serpentine belt most all equipment has one regardless of horsepower or torque...

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    Re: Circle-S Drive tensioner question

    I was initially going to adjust through shims as Kent suggested but after the first couple test runs I realized something more dynamic is required. To follow Corky's comment, on the blower belt I was surprised to see the amount of "belt slap". It's just to figure what the "best" way to do it is. I'm open to suggestions. .....

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    Re: Circle-S Drive tensioner question

    There's no doubt that belt temperature and torque affect the belt stretch and I think that having a spring loaded idler might be a very good idea but the challenge would be to choose the right spring strength. With the Circle-S, the slack side belt movement is quite violent (laterally, in and out) when power changes and it would require a very stiff spring ... IMO.

    I've tried to adjust the idler to where it just barely touches the belt but when power is applied it starts rapping against the adjustment bolt in a very destructive manner so my only options are to adjust it to a tight contact or back it off completely in which case you get a lot of belt slap at low power settings when cold.
    11'6" Marty Bray Hull
    4A084 Continental
    Circle "S" 1.69:1 Reducer
    67" Whirlwind Razor X Prop
    SS Rigging

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    Re: Circle-S Drive tensioner question

    I'm thinking about a serpentine belt tensioner arm/pulley from an automotive set-up but I would have to sleeve the O.D. to achieve an acceptable width.... maybe the arm idea won't work due to the pulley being supported from one side only....maybe that's a poor idea....maybe more thought is required here. LOL. Not a new concept I looking for here, Back to Google!! Again, I'm open to suggestions

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    Re: Circle-S Drive tensioner question

    Oh Corky, thanks for your experience here! I appreciate your insight. BTW it seems as our hulls are of similar size, mine is 66 wide before the soft chine begins, tapering to 60 at the bow and 13'-3" form bow tip to top of transom plate. I also used .125 5052 for the floor. I feel a lot better about my build after reading on yours. thanks and keep the pictures coming.

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    Super Moderator Corky's Avatar
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    Re: Circle-S Drive tensioner question

    Go to an automotive site like Summit racing or Jegs high performance and type in supercharger belt tensioner...Most of those seem to be bigger than an OEM auto idler and would need little to no mods for your size belt...Some kits{edelbrock is one} even have a bolt on plate that you could fasten to your framework and in turn fasten the tensioner to that...Those type kits would give you some ideas..... I would'nt see why that type would'nt hold up for your application...Just make sure you have the belt in close working range and use the tensioner for the harmonic/stretching duty...

    As for the hull, I did'nt want to use anything lighter than the .125 floor and sides I know how I am on the hulls with this river...As you know there's a fine line between safe and overkill and the weight adds up quick..I'm going through way more .35 welding wire than I originally planned but I really had no idea how much would be needed but I stocked up again today with 3 more 1 lb spools for the gun...

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    Re: Circle-S Drive tensioner question

    Awesome thanks for the advice on the tensioner, I will add shim to under the pillow-blocks for primary adjustment and look into Summit for a tensioner.

    I've been working on the cage and rudders for mine of late, also both aluminum, and have been burning quite a bit of wire myself. On another topic, what do you figure your boat will weigh when done? and Would you know what an average weight of a mini would be? I've been meaning to borrow a load cell from the plant here so I could get a rough weight on mine but haven't gotten around to it yet. My guesstimate is around 1300#. I'm not sure how that compares to everyone else and i suppose that is what I'm trying to do.

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    Super Moderator Corky's Avatar
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    Re: Circle-S Drive tensioner question

    I've done an estimate on my hull and it looks to be right around 336 lbs...Heck just the 3 sheets of 5 x10 x.125 weigh in at 264 lbs...I'm not sure just how much the stripped down engine weighs in at I'll have to get it weighed...

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    Re: Circle-S Drive tensioner question

    My boat weighs 752 lbs the way it sits with anchor, tools, anchor winch, battery, and about 3 gals of gas in it.
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    Re: Circle-S Drive tensioner question

    Wow Papee, that's light. I'm going to weigh mine this evening. I'll get back to you by morning....

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    Re: Circle-S Drive tensioner question

    Back to the drive tensioner ... Corky ... please post pictures of your Circle-S drive when you receive it .... I'm very curious if there's been any updates to it

    Thanks
    11'6" Marty Bray Hull
    4A084 Continental
    Circle "S" 1.69:1 Reducer
    67" Whirlwind Razor X Prop
    SS Rigging

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    Re: Circle-S Drive tensioner question

    I know we're kinda side tracking the thread here but 1050# is what I'm currently at. I can see another 100-150# going onto it. UHMW for the hull and a floor sheeting are the major pieces left to install

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    Super Moderator Corky's Avatar
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    Re: Circle-S Drive tensioner question

    Our 084s are around 50hp {rounded up} but your turbocharged engine looks like it should put out much more than that so the weight might still be OK for performance...I just reviewed your intro thread and saw you're up there around 200 hp...Holy cow you should have more than enough engine to overcome the extra pounds but I'd still try to keep it light if it's possible...
    Last edited by Corky; 03-06-2015 at 06:16 PM.

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    Re: Circle-S Drive tensioner question

    l'll have to weigh it again when it's a little closer to finished but it looks like the c.o.g. is just behind the drivers seat.(for now) I'd have to fill the tank and set the battery as well which will move it back some. How do think this will affect the handling?

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    Re: Circle-S Drive tensioner question

    Just don't do anything permanent with your battery and fuel tank mounting. Run it and see where it rides and move the two around while testing. When you find the sweet spot bolt them down.
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