Worries about fitting

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benutne

New Member
Apr 22, 2011
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Spfd
I have a Specialized Stumpjumper (no idea what year but I've had it for about five and my brother had it before then) that I would like to install one of the 69/80cc kits from GasBike.com onto. Though I worry about the thickness of the lower bar. What does the "universal" mount do differently than the standard clamp styles? How big is too big for the lower bars? The seat post looks a little thicker than most too.

I also have a 15 speed Roadmaster Mt. Fury I could use but I'd really much rather install a kit on the Specialized.

I'm pretty certain the kit would "fit" in the frame, but I'm just concerned the mounting brackets might be too small for the tubes.

Any thoughts or advice to offer?
 
biknut

biknut

Well-Known Member
Sep 28, 2010
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Dallas
Welcome to the forum.

There's thousands of ways to mount the engine. One you get started it'll be easy to see what you need to do.

Learn how to post pictures and we can help you mount anything.
 
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benutne

New Member
Apr 22, 2011
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biknut said:
Welcome to the forum.

There's thousands of ways to mount the engine. One you get started it'll be easy to see what you need to do.

Learn how to post pictures and we can help you mount anything.
Click to expand...
Sure thing. I just didn't have any pictures of my bike handy. I'll take some when I get home and post them here.
 
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benutne

New Member
Apr 22, 2011
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Here's another question: How do I measure the tubes? Do I measure circumference or diameter? I can measure circumference using a cloth tape measure. But how does one measure diameter? Just eyeballing it dead on?
 
timboellner

timboellner

Member
Apr 1, 2009
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Towson Maryland
Don't try to eyeball tubing diameters.
Everything is measured in diameter, not circumference.
You can pick up a set of calipers like these at Harborfreight or anyplace that sells handtools.
They measure inside diameters of tubing also.
6" Utility Caliper

Like the guys already said. There is a solution to mounting your engine to any bike out there.
The Specialized is absolutley the better way to go in my opinion.

Get building, summer is on the way !!!!!!!!!!

TiM
 
forrman

forrman

New Member
Mar 5, 2011
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Canyon Country, CA
I have the same problem too: the lower frame tube on my mountain bike has a diameter greater than the diameter designed for the engine mount. I heated up the frame (using a propane torch) and hammered two dings to help the engine seat better, but the threaded bolts inside the block are still too short for bolting on the clamps. I tried looking for longer threaded shafts to replace the stock ones, but they are metric (close to a #10-24 standard thread), but I haven't found any that will work (I only have Lowes and Home Depot as my sources for bolts, buts, shafts, etc.) So that's where I'm stuck. So I either find the right metric shafts, re-thread the block to standard size thread and install standard shafts, or maybe find some long nuts that will extend the length of the block mounting shafts. Your thoughts? I have pictures I can post, once I figure out how and where to post them.
 
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matthurd

New Member
Dec 13, 2010
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manchester NH
if you can't measure the diameter, measure the circumference and divide it by 3.14, bike tubing usually is done in pretty standard sizing (1 inch, 3/4 inch and such) so with a little math you can get close enough to what it is and make a reasonable assumption.

the universal mount is basically just a big U bolt, you use a mounting plate, mount it to the standard mounts, and then mount the U-clamp to the plate. thats how mine worked anyways (i didn't use it in the end though).
 
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benutne

New Member
Apr 22, 2011
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OK, I borrowed a digital caliper and took some measurements from my bike. Being digital, it gave me some really specific measurements. My seat post is 1 25/64" (see what I mean?) Down tube is 1 3/4". And I
m not sure what the third tube is called, the one you rack yourself on when you stop too fast, is 1 13/32".

I also measured the bike from the center of the crank to where the seat post stops and measured 19".

No pictures yet but it looks exactly like this.
 
Pilotgeek

Pilotgeek

New Member
Apr 6, 2011
403
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Green Bay, WI
My bike is almost exactly like that, but in silver. It will fit fine, except I had to mount the carb a little to the side. I used an adapter as shown in matthurd's post. It works great and I have about 150 miles on that build so far.
 
mixxmilkk1

mixxmilkk1

New Member
Apr 30, 2010
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Mpls Minnesota
Just get online, and buy a universal setfrom sbp.com theyy have the best ones to use for that size tube. Mine is the same way. And I have to say one thing about Mr. Forrman!. Yoy should be taken off the streets for destroying your frame!. You should never compermize the strenght of your frame buy doing that!.. You should get another bike now, before you get hurt by it folding on you. (I wouldn't want to be behind you when that happens.
 
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steampunk

Member
Mar 10, 2011
440
0
16
lakewood co
forrman said:
I have the same problem too: the lower frame tube on my mountain bike has a diameter greater than the diameter designed for the engine mount. I heated up the frame (using a propane torch) and hammered two dings to help the engine seat better, but the threaded bolts inside the block are still too short for bolting on the clamps. I tried looking for longer threaded shafts to replace the stock ones, but they are metric (close to a #10-24 standard thread), but I haven't found any that will work (I only have Lowes and Home Depot as my sources for bolts, buts, shafts, etc.) So that's where I'm stuck. So I either find the right metric shafts, re-thread the block to standard size thread and install standard shafts, or maybe find some long nuts that will extend the length of the block mounting shafts. Your thoughts? I have pictures I can post, once I figure out how and where to post them.
Click to expand...
dude! go to allen bolt in burbank...all the hardware you need
 
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matthurd

New Member
Dec 13, 2010
817
2
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manchester NH
benutne said:
Where can I get the universal mount from a reliable vendor?
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mine came from kingsmotorbikes, and in reality it's a pretty simple part and imo there isn't really much that can go wrong, so if you like the style of the one i showed you (there is 2 U bolts btw, just didn't know where the second one was off hand), go ahead and order from them.
 
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