Rear engine mount help

S

steakeater10

New Member
After receiving my 66cc Skyhawk engine kit, I immediately realized that I had measured wrong and that both my down tube and seat tube were about a quarter of an inch too big for the standard mounts. I bought a universal front mount from SBP, thinking that I would make my own rear engine mount, but unfortunately that is proving to be a little harder than I thought. The people at Spookytooth recommended crimping my frame with vice grips, and seeing as I have an aluminum frame, I figured it would be best to get a second opinion. Would pinching the seat tube ruin the integrity of the frame? Thanks
 
I'm not comfortable with squishing the seat tube. Some might be, but aesthetically it would be bad and structurally questionable.
If your measurement is correct, "a quarter of an inch too large", then you could easily take that much material out of the mount to make it fit your seat tube. 1/4" would only be an 1/8" on each side. You could use a sanding drum in a drill motor or if you have access to a die grinder the work would go faster. A Dremel tool would work but that's a lot of grinding for a little tool. But that's just my opinion; there'll be others, I'm sure.
Tom
 
steakeater10 said:
The people at Spookytooth recommended crimping my frame with vice grips, and seeing as I have an aluminum frame, I figured it would be best to get a second opinion. Would pinching the seat tube ruin the integrity of the frame? Thanks
Click to expand...

You were wise indeed for questioning this. With a typical aluminum frame the best you could hope for is a crushed & cracked tube - bad enough by itself but add in the stress of an engine and it'd be over in a hurry. Even a steel tube wouldn't like it much better - while it wouldn't crack, tubing gets it's strength from it's shape. Put even a small kink in a tube then try to bend it, guess where it'll bend every time?

Now - it's true you could probably get away with it on a steel seatpost tube... but still... who the heck would want to do that to their nice new ride? o_O

I had to do what Tom suggested for my first build (aluminum mountain bike) and it worked really well... still working actually - 5000 miles later lol
 
Thank you so much for the responses. I ended up having to use a dremmel to shave down the mounts, as my tool selection is quite limited, but I think it worked well. There is still a lot I have to do before I will start riding, but the solving of the mount situation takes a lot of weight off my shoulders. I will be sure to tell how it works and post pics. Thanks
 
There is not enough meat in the stock rear mount to go a 1/4" bigger I don't believe. My seat tube is 1 1/4" and the stock mount is for a 1 1/8" tube. I set the rear mount halves up in my mill and bored them to 1 1/4". My clamp rear half is cast not a strap and it is pretty thin now.

Put a SBP shift kit on it and their rear mount will work (-:

Jim
 
The mount seems to be working fine for me, but now I have run into yet another problem. When I put my throttle on the handlebars, it does not allow the right downshift to pull all the way. The only way I can give the shifter (which is as far left on the right handlebar as I could get it) clearance is by sliding the throttle about an inch off the handlebars, so that the tip of the throttle is not slid all the way with the tip of the handlebars. Is it safe to have the throttle like this (an inch too far to the right), is there a way to allow the shifter to have more room, or do I need to by a twist shifter? Thanks
 
Is the right side shift lever on your bike for the front derailleur? If so?, I usually remove the front derailleur! (With a engine on the bike, I've never had a need for that many gears!!) ;)
 
I agree on getting rid of the front derailer control. My front derailer control was on the left side so I took it off and made a short wire to hold the derailer on my center front sprocket. I then moved the 7 speed rear control to the left bar. Jim at Sick Bike Parts recommended doing that when I added the shift kit. Even when I was single speed with the motor and even before the motor I only used the center front sprocket. I don't ride offroad. With the shift kit all of the stock front sprockets and derailer come off.

The Sick Bike Parts shift kit with seven speeds and the extra big first gear chain ring really makes the engine package SO much better.

Jim
 
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