25cc Robin Mini 4 & Aluminum frame bike


Blue Coupe

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.




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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
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
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.
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!
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
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.
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 !!
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!
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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!!!