25cc Robin Mini 4 & Aluminum frame bike

Discussion in 'Rack Mounted Engines' started by Blue Coupe, Jan 8, 2008.

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  1. Blue Coupe

    Blue Coupe Guest

    I started to install my Golden eagle 25cc Mini 4 on my Aluminum frame bike and ran into a few issues.

    The small frame tubes that angle down from the seat post to the axle will not allow the engine mount to be attached straight up and down. I could angle the engine mount back, however I would rather not since the engine would be significantly over the back of the tire.

    Even if I could clear the frame tubes, the axle is bolt is too short. Does anyone make longer axles for a Shimano FR RM40 hubs? The other concern is that the axle bolt is tiny in diameter.

    Also, the derailer is attached to the frame with small screws that will interfere with the engine mounts. I intend to shorten the screws and mount them from the inside of the frame, it might work.

    Attached are a few photos.



    Attached Files:

    Last edited by a moderator: Jan 8, 2008

  2. JemmaUK

    JemmaUK Guest


    Re the problem with the short axle - all you need to do is buy a new one which is a solid axle and longer than the usual - any bike shop can supply those for relatively cheap money - around about $15 or so probably...

    The axle in the picture looks like a quick release spindle. GEBE advise that you do NOT use these with engines - a rear axle collapse at 30mph can really hurt....

    The issue with the frame dropouts is only really an issue when it comes to the forward mounting strap which connects the engine mount to the brake mount on the frame - it might be too short as the throttle cable might be as well - those can be solved relatively easily by a sympathetic bike store... in fact the engine being mounted further back might actually improve the weight distribution over the back wheel...

    Alternatively you can make up some spacers on an extra long axle and then gently bend the mount - although that will induce stress in it - a better way is frame mounting although its a sight more complex.. involves fabbing your own mount and shortening the GEBE one accordingly..

    hope that helped

    Jemma xx
  3. kenspice

    kenspice Guest

    Very good explanation Jemma, however, mounting the engine farther back lessens the fuel capacity and also puts more strain on the lower mount through leverage. Mounting on the frame is a bit more difficult but worth the time. It also makes a wheel removal MUCH easier as you don't have to mess with the engine mounts. Ken
  4. larymor

    larymor Guest

    Do a frame mount....just type in frame mount robin subaru in the search box....I did a simple frame mount on my r/s35 and it works fine...make sure you get your measurements right.
  5. Blue Coupe

    Blue Coupe Guest

    Agreed, I won't use the "Skewer" quick release axle.

    I seached for the Robin 35 frame mount tech and it looks like it will work.
    Here is the link;

    Larry do have pics of the inside of the frame where you attached the bolts?

    I'll have to take another look at my frame, I might be able to use something like cable locks on the frame. i.e. u shaped bolt with nuts.

    Are the replacement axles just bolt in? Or do you need special tools? One bike shops I spoke with today said that I need cone wrenches to change the axle.

    Thank you for the suggestions!
  6. kenspice

    kenspice Guest

    Every bikes frame is somewhat different. Be VERY careful when drilling the frame mount holes. You can easily weaken it. I have not heard of anyone using the u bolts. It might work. These engines are lightweights and it does not take much to hold them in place BUT they vibrate and things loosen fast. Put a locknut, lockwasher or locktite on anything you fabricate and everything else too. A good set of bike tools and thin / open end wrenches is a must. Read, Read and Read some more. Stay up late and read everything on this web site. You will be surprised how many things you can modify before they break. Ken
  7. Scottm

    Scottm Guest

    I get such a kick out of watching everyone help each other. I don't even have a rack mount but I've learned so much.
  8. larymor

    larymor Guest

    Blue Coop
    Sorry no pics of inside..I just drilled through the flat part of the frame near the axle and as you can see in the pic, I inserted the bolt from the inside and attached the locking nut to the outside...VIOLA !!
  9. Blue Coupe

    Blue Coupe Guest

    Ken, Thanks for the tip on the loctite, will do.

    Lary, turns out I too have a flat part of the frame that can be drilled. Not in the same location as yours but it should work.

    The mounting bracket from Golden Eagle is mild steel and it is relatively easy to bend (if you have a vise). I made a few bends to clearance the engine mount around the frame, holes are drilled in the frame. The clearance between the gears and one of the mounting bolts is going to be very tight.

    I'll post a few pics when I'm done...I expect that the mounting bracket will need to be bent again to ensure the belt runs true. Hopefully there won't be to many more snags to overcome.

    Thanks again for all the help!
    This place is GREAT!
    Last edited by a moderator: Jan 10, 2008
  10. larymor

    larymor Guest

    make sure to get your measurements right !! I think starmann and bamabikeguy have the measurements all figured out.....do a search b4 u cut the bracket ! This is of utmost importance!!!
  11. Blue Coupe

    Blue Coupe Guest

    The total length of the engine bracket is 14 3/4 inches top to bottom. I actually did not cut the bracket, I bent it. It probably is a little shorter from the bends. One of the bends needs to be adjusted to ensure it doesn't rub the frame.

    Installation is complete ! I forsee a few minor adjustments. The belt seems to be running true.

    I went for my first ride tonight! The little Robin started right up with just a couple of pulls.

    First impressions
    1. The Robin engine is only 2.8 KG, however you will feel the extra weight of the kit if you lift/carrier your bike allot.
    2. Engine noise is tolerable since the 25 cc engine is a 4 stroke. I believe 84db flat out. It definitely is not whisper quiet.
    3. Once I'm past 3/4 throtle I need to modulate the throtle to ensure the engine does not bog or I guess overfuel. You need to match your speed with the engine speed. I live in Calgary at 3500ft so the carb might need to be leaned out.
    4. Without the engine running I would estimate the drag on the rear wheel is double of normal. This means you really need to run the engine or remove the belt for medium or long rides.
    5. Performance seems to quite good, the set-up runs about 90% of what I could peak for top speed on my own. Now for the good part, top gear, lite pedalling and she REALLY moves. I tried a small hill and with a little pedal assist it was effortless.

    It was definitely good fun! :grin:

    Attached are a few pics of the installation. Everything fits quite well, the exception is the bolt near the smallest gear. All gears are useable and so far they have not rubbed.


    Attached Files:

    Last edited by a moderator: Jan 10, 2008
  12. sabrewalt

    sabrewalt Guest

    Thanks for the PICS and the ride report. Very helpful. We don't see many Robin 25's.
    Last edited by a moderator: Jan 11, 2008
  13. larymor

    larymor Guest

    Cool beans blue !! Enjoy!
  14. kenspice

    kenspice Guest

    Good pic.s and report. One small tip.. Take the black knob off of the tensioner, and put a small nut on it then screw the black knob back on and tighten the small nut up to the bottom of the knob. That will keep you from singing the " I'm always chasing little black balls" song. Enjoy the ride! Ken
  15. Blue Coupe

    Blue Coupe Guest

    Thanks for the black ball tip, I'll install a nut so that I'm not chasing this ball down the street!