Mounting engine to irregularly shaped tube

[J Omega]

I have an 80cc engine from ebay which I am trying to mount to my Specialized Hardrock 2010. The down tube is large and irregularly shaped. It appears that the general solution to this is to use a muffler clamp or a u-bolt. However, neither of these will work for me because the tube is not round. On the other hand, clamping two plates on either side won't work because the tube is not square. After several days of thinking and searching the web, I'm at a loss. Any suggestions? My power tool selection is limited (i.e. drill and circular saw) and I have no welder.

The tube cross section is detailed below.

 

[2door]

Here is an old but very informative thread that might offer you some helpful advice.
http://motorbicycling.com/showthread.php?t=6427
Good luck.

Tom

 

[Dave31]

Hey Kyle welcome to the forum,

When I was assembling my Hard Rock it was late at night and I just used what I had on hand laying around.

I found a piece tubing, some clamps and part of a muffler clamp. And with that, I made a front mount for mine.

Cutting the tubing in half to the correct size I needed, then spending the time shaping both pieces one for the top and one for the bottom the exact shape of the down tube.

Then for the top piece I just welded the part of the muffler clamp to it. Thats what the motor bolts too.

Then I just bolted my motor to the top piece that the muffler clamp was welded to, mount the motor in frame, add then the bottom piece and tighten everything up.

Probably took me less then an hour and years later and thousands of miles its been flawless.

 

[J Omega]

So I have made several mounts so far, most of which utilized the water bottle mounting screws in the frame. Needless to say, none of them have stayed together for over 50 miles.

I have finally decided to do this the correct way and purchased a MIG welder. Now I just have a few questions about your mount, Dave.
1) What thickness is the steel from the tubing?
2) How did you shape the fence post correctly?
3) What diameter is the muffler clamp?
4) Where did you find those clamps for the tube?

On a brighter note, the bike has been super fun. It's funny to watch cars try to pass and then realize that you're doing the speed limit.

 

[Dave31]

I have finally decided to do this the correct way and purchased a MIG welder. Now I just have a few questions about your mount, Dave.
1) What thickness is the steel from the tubing?
2) How did you shape the fence post correctly?
3) What diameter is the muffler clamp?
4) Where did you find those clamps for the tube?

On a brighter note, the bike has been super fun. It's funny to watch cars try to pass and then realize that you're doing the speed limit.

1) I used 16-gauge It was a scrap piece I had but this is what it was http://www.homedepot.com/p/YARDGARD...-Corner-Post-328944DPT/100322502#.Ubox-_nryzY

2) Body hammers, ball pin hammer, dead blow hammer, some 2x4, the seat cushion off my stool chair and using the back of my massive Wilton vise that just has the perfect shape for doing stuff just like that. It just takes practice and I have had lots of it. You just got to keep working it until you get the shape you need. I dont know how to explain how to do it?

3) Its been a while and i did not measure it but I believe it was 2 1/4".

4) Hmmm? Either I made them or they are left overs of straps for the muffler that comes with the engine kits.

 

[fatdaddy]

A flat plate and a u-bolt or two. You can see if this one fits or you can make one yourself that will fit perfect.
http://www.ebay.com/itm/80cc-gas-bi...&prg=1005&rk=1&sd=160946810864&#ht_3107wt_930
If you make your own I recommend using the two u-bolt system. It helps keep the engine from twisting.
fatdaddy.

 

[J Omega]

I finally did things the correct way and bought a welder. Last night, I whipped together a mount similar to Dave's. Pictures later today.

 

[fatdaddy]

There ya go, Thats how ya do it. Most people don't have a welder though and have to suffer with just bolting it on with the clamps in the kit.
Looking forward to the pics.
fatdaddy.

 

[J Omega]

Final solution! It's lasted several months now. The welds are embarrassing but they work...

 

[Evil]

Needing mount info for a spoiler..