New build- Full suspension mountain bike

darkness · Mar 29, 2012

Hey guys. Im a newbie to the site.

My last build was a road bike. It was an older non- descript bike (not even sure of the brand, no labeling) which i chose mainly for its light weight cause i thought it would be faster. Unfortunately, i was riding along an old logging road by my house and i hit a pot hole and somehow the bolt which secures the handlebars snapped, sending the front wheel completely sideways, and me flying ( i was going downhill probably 25+ mph) into the gravel road. I sprained my wrist, bruised my legs very badly, skinned both my hands down close to bone practically, hit my head really hard (even with a helmet) and havent thought about putting a new bike together for over a year now.

But seeing a full suspension motorized mountain bike online got me thinking. Looks like a lot fun. I have a lot of nearby trails to ride, through the forest.

Due to the fact that my motor was not damaged at all by the wreck, i think i will make my new project a full suspension mountain bike. So i was just wondering, what are some things i need to know about installing an 80cc (66cc) RAW motor on a fully suspended mountain bike? Is there anything i should be concerned about? is it even feasible without major alteration? and i was thinking about converting to a single speed, to get rid of the shifter .bf.

(less clutter on the handlebars), is that a good idea?

rustycase · Mar 29, 2012

Welcome aboard!

Gosh, glad you made it through the wreck...
I've only taken 1 spill, so far, and it was at very slow speed, right in my own driveway!

There's a few full suspension mabs here. It's definitely more work, but well worth it if you really need it.

Time well spent to read through a bunch of the threads to get information.

Best
rc

darkness · Mar 29, 2012

Thanks Rustycase,

I just think of a hardtail as not being suited to any serious trail riding, obviously there is a clearance issue for a non- friction drive motor on most full suspension bikes.

I just wonder, would it be worth the money to seek out and buy a seemingly rare full suspension bike that is compatible?
or would a hardtail suffice for some trail riding?

mind you its not like a rocky mountain trail, just some dirt paths with a lot of hills and banked curves.

Goat Herder · Mar 29, 2012

Welcome to to forum Darkness. You will need to put the rear sus pivot point right at the motor cogs output sprocket. Doing other wise will only cause grief as the chain will loosen and tighten with bumps causing derailment..

16v4nrbrgr · Mar 29, 2012

I was looking around on craigslist with the same intention, and some older suspension MTB's have the shock outside the frame behind the seat, so there's room for an engine inside. I was also thinking that if you could get or make a spring tensioner that works reliably and has sufficient tension, possibly crank sprocket placement wouldn't be as critical. Sorry to hear about your spill, I've had a few and they suck, good luck with your build.

darkness · Mar 29, 2012

Thanks,
and thats what i was thinking as well, the only bikes ive seen, the pivot point is down by the pedals and the spring is up and behind the seat kind of.
I wonder, would this type of bike work if you installed a spring loaded tensioner with it?

Goat Herder · Mar 29, 2012

I had a friend that did one. He gave it the best college try ever. In the end it was too much grief. While he got it to work. IMHO The problem is the distance from where the pivot point needs to be and the amount of potential chain slap was simply too much. This had been acheived with a nice long very sturdy throw sweep travel spring teinsioner as well.

I definitely do not want to discourage you. When the pivot is right at the out put the chain will stay the same as slack and tightness gos when the swing arm moves.

When you start a china motor by letting out the clutch the big surprise here will be the way the chain behaves when it goes to slack out way from the natural load of simply driving it. This is something too consider besides swing arm movement.

He even made nylon guide blocks for this right behind the motor that proved problematic for this as the block would wear over a short period of time from start ups.

If his chain had been right on the pivot point it would have worked perfect.

NunyaBidness · Mar 29, 2012

If you get the right mountain bike you can install a motor and use a shift kit to do away with any motor chain tension issues.

darkness · Mar 29, 2012

I have a mountain bike with front suspension, and the motor will fit.
I was just concerned that a hardtail might not handle things too well off road.

And like i said, im not looking to jump it or boulder hop down a mountain,
but some people on here swear that a hardtail wont handle anything more than going down the street, others say the ride isnt that bad if you take one off road.

So Im almost to the point of saying, F it all.
Ill see what works for myself.

killercanuck · Mar 29, 2012

Best of luck then. But like Nunya said, a shift kit will avoid any tensioner/pivot point hassles. Check out SBP(Sick Bike Parts) on the sidebar ads, they have vids you can check out too. As long as your motor will fit in the frame, rear suspension is achievable.

gl.

KCvale · Mar 29, 2012

I don't think you will have much luck direct-driving a soft tail, but with the right bike you can Jackshaft one like this one I built a few months ago.

One thing you can count on with a soft tail bicycle is the angle of arc movement of the wheel to the pedal sprocket maintains an even chain distance, and therefore no chain problems.

Trying to mount a second drive chain line on a different vertical axis to that pedal crank center will be a chain tensioning nightmare and really not the worth the trouble considering the advantages of just using a jackshaft.

Velodrome · Mar 29, 2012

I have an OLD Specialized Ground Control Ive been thinking about doing somethnig with. It looks alot like this but in grey. Room for a 4 stroke and I think with some creative chain tensioning and / or a belt drive It would work. Its just sitting there in the garrage tempting me...

darkness · Mar 29, 2012

thanks everyone for the input.

16v4nrbrgr · Mar 29, 2012

Hardtails are great off road, that's what I use for my regular pedal mountain bike, If you want avoid bruising your taint you can always get a suspension seatpost, and your bike will be simpler and lighter, as well as not needing a shift kit or careful placement of the engine. I plan on just getting a suspension seatpost for my mountain bike since a hardtail is more efficient when you have to pedal it uphill unless it has a lock on the travel for climbing, and softails are still heavier and more expensive.

If you wanna get riding ASAP, I say seatpost and a Dax kit and you should be on your way.

darkness · Mar 30, 2012

yea?
you think so 16?
I think i might just do that. I have a decent 26" mountain bike with front suspension, im thinking i wont be sitting down for most off road rides.
But it might be a good investment.
The thing is, with motor bikes, you can drop a crap load of money on one and have a sweet ride, but in the end, its still not a dirt bike.
So might as well save a little, and just have one that works fine and does what you want it to do. right? ha.
thanks for the suggestion.

16v4nrbrgr · Mar 30, 2012

I hear you, I struggle with the balance of whether to just bite the bullet and get my M2 endorsement and get a motorcycle, but I figure this is a good learning step on something I can wrestle first. I think hitting jumps on a motorized mountain bike would be great fun!

Easy Rider · Mar 30, 2012

KCvale said:
I don't think you will have much luck direct-driving a soft tail, but with the right bike you can Jackshaft one like this one I built a few months ago.

One thing you can count on with a soft tail bicycle is the angle of arc movement of the wheel to the pedal sprocket maintains an even chain distance, and therefore no chain problems.

Trying to mount a second drive chain line on a different vertical axis to that pedal crank center will be a chain tensioning nightmare and really not the worth the trouble considering the advantages of just using a jackshaft.

Nice LTS!
I have the same frame and like you said: The best way is to use a shift kit.
I gave up on my LTS and put it back to a regular bicycle.

Len455 · Mar 31, 2012

Darknes, just use your hard tail like 16 said. I have one to and yesterday we were flying threw the desert going 20mph on dirt roads. Just stand up and use your legs like shocks!

Len455 · Mar 31, 2012

And my mountain bike for serious trails is a hard tail to

darkness · Mar 31, 2012

Thats what im thinking too.
Seems like some people say you have to have shocks on both ends,
to truly enjoy off road.
I think it might be harder on your engine, but hardtail would be fine.
Thanks for the input.

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