How much CHAIN BINDING is OK - Grubee Stage III Rear Mount

Discussion in 'Rack Mounted Engines' started by highcap56, Jul 11, 2010.

  1. highcap56

    highcap56 New Member

    Trying to finish my project. The Grubee Stage III Rear Mount kit came with no clear instructions on how to properly mount the rear mount for the engine, so using photos I was able to do it and get it leveled out. This is being installed on a Diamond Back Response 18 speed mountain bike with no rear suspension.

    Minor adjustments had to made and extra spacers and a temporary threaded piece of stock had to be used to replace the quick release axle due to the installation of spacers on the left side that were needed to give clearance so the chain would not hit the frame... really need a stronger, longer axle but that is another question....

    I trued the sprocket and got it NEARLY 100% even left-right-top-bottom with just a little bit of out of round motion up and down when I spin the wheel. No side to side wobbling at all.

    No matter HOW MUCH I mess with the rear mount (about 7 hours yesterday... yes.. I want to finish and ride!!) I get a small amount of chain "popping" or binding when I back the bike up, but not as much when I roll forward... sometimes not at all, but always a little when I roll it backwards.

    Chain tensioner (sp) seems to make it worse and I'm wondering if I can do with out that.

    Question - How MUCH chain binding is acceptable? My goal is to be able to spin it back and forward with no popping at all, but no cigar to this point.

    I'll post a photo later so you can see the install.

    No matter how I adjust the rear mount the motor seems SLIGHTLY leaning to the right, so perhaps I need to make spacers for it on the left side to move it up a little.

    Suggestions greatly appreciated.

    Thanks! :dunce:

    EDIT - How many posts are required before you can post a photo? I do not see an option. Would be easier to get help if I could do that.

    Attached Files:

    Last edited: Jul 11, 2010

  2. highcap56

    highcap56 New Member

    I also wondering if I have even mounted the rack to correct points?

    Already have figured out that my master link needs to face the other way.

    If I am just doing something plainly stupid, don't be shy!

    The clearance problem with the chain is my biggest worry.

    Are other installations this tight in that area?


    (no one in Burbank/LA that I know has a clue or I would bother them... :whistling: )
  3. ocscully

    ocscully Member

    In your post you say that the motor leans to the right?, but in your photos it appears to me that it is leaning to the left. You need to do what ever it takes to get both the output sprocket from the gearbox and the driven sprocket on your wheel in the same plane. Use washers on one side to shim up the motor. You are also fighting your frames design ( the bent seat stays) to get chain clearance. You might need to flatten the left chainstay to get the clearance you need or go to a smaller driven sprocket on the rear wheel (50t or 48t). You also appear to be using the engager. You might want to do a search here for "engager", and read about how this coupler causes alot of problems and breakage when used incorrectly. I find that the best thing to do with it is set it up permantly engaged. The tendency is to use it as a clutch and it is not a clutch. Its sole purpose is to allow you to start the motor without the bike taking off. It you engage it at any rpm above idle things in the gearbox will start breaking. As for the popping noise I think that it is probably coming from your alignment issues.

  4. highcap56

    highcap56 New Member

    Had considered everything BUT flattening that frame section. Great idea! Now I have to figure out how to do that.

    You are correct that it was leaning left, not right, and I put a single spacer washer on the left front and rear of the mount and it straightened up.

    Getting very little binding now except I know when the master link goes through as I get a little pop. While it is not hitting the frame, with just a little play I could see that happening tho... really need to flatten that frame.

    On the engager, I can see what you mean. It is a piece of junk. Since I'm not riding yet (serviced the motor today and it cranked right up) will it idle with the engager in at a dead stop? If so, I have no problems leaving it engaged at all times.

    I'm finished with everything now except the chain issue and will post more pics tomorrow.

    I think it will be a blast once I get this all behind me and I have enjoyed the project in the meantime.

    Thanks for your reply! :arabia:
  5. highcap56

    highcap56 New Member

    Re: Flattening that frame tube......

    I'm thinking vise grips. :evilgrin:

    Tube seems pretty thin but I did not want to throw the bike geometry out of whack. Also a little gun shy out of worry that the tube will split and not just bend.

    No choice if I want to ride.
  6. ocscully

    ocscully Member

    If it were me I'd take the time to make a form to support the outside of the tube and also a smaller one to use on the inside of the tube, and then squeeze the tube between them using a large (hefty 6in. or larger) C-Clamp. You just want to ovalize the tube a bit to get the additional clearance you need. Using the larger form on the outside and the smaller on the inside most of the bending should happen from the inside edge of the tube. The C-Clamp will provide more control over the bending process as well. No guarantees with any of this but it should work.

  7. highcap56

    highcap56 New Member

    Makes perfect sense. As you can tell, I'm not a metal worker or engineer. :)

    Thanks - couple of pieces of flat steel stock with a clamp on either side should do it.

    Really appreciate your advice. Hopefully I'll be riding soon.
  8. ocscully

    ocscully Member

    Notes on the Engager

    The stall speed on the clutch as it comes from Grubee/Birddog is to close to the rpm of the motor at idle. So with the engager permanently engaged the bike will want to take off on you when it fires, if you don't have a good hold on the bars or a good center stand to lift the rear wheel. Grubee/Birdgog do not offer any stronger clutch springs, but you can get some extra rpm buffer by lightening the clutch shoes. Lightening the shoes is accomplished by drilling several holes in the recess around the outside edge of each shoe.

  9. highcap56

    highcap56 New Member

    Thanks - I read the other thread you mentioned.

    Now for the rest of the story...

    That frame is hardened steel. Two 8 inch c-clamps would not budge it.

    Reluctantly, to avoid any more lost time building that one, I pulled the kit and put the bike back to normal.

    Looking for a cruiser (cheap) with caliper brakes front and rear. Saw a couple of threads here.

    Whatever I get, the kit will go on fast. I think I know every part inside out that has to be taken on, off, or adjusted.

    I'll show you the new bike in a couple of weeks.

    Really appreciate your help.