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Old 01-29-2013, 07:29 PM   #1
jgas OP
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Trials motor for trail bike?

I have a totally beat up KDX 200, think it's a 97 model. Motor is beyond fixing, pipes trashed, etc. Not worth fixing up. I was beating around the idea of stripping it down to bare bones and putting a Trails motor in it, using it for a homeade Trails/Trials combo bike. Just a playbike, not competing. I also do alot of singletrack trail work and sometimes an easy to ride slow bike that would crawl around with a low seat height would be perfect. My GasGas XC is just too racy and I hate to make it go that slow. I think I hurt it's feelings.

What older Trials bike would be reliable, cheap, easy to find parts for, etc. I was thinking of just buying an older bike, using the motor and whatever else I might need, and selling or parting out the rest.

I know almost nothing about Trials bikes except they are really fun, and you have to stand up. I can't stand up for long due to a bum leg and bad back. Sure, I could buy one of the newer do it all Trials type bikes but I really can't afford another bike with all my other toys unless I keep it cheap.
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Old 01-30-2013, 06:32 AM   #2
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Why don't you put a heavier flywheel, smaller carb. and modify the exhaust valve (if it has one), and lower the gearing on the KDX? That should give you what you want.
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Old 01-30-2013, 07:30 AM   #3
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Yes, a KDX is already ultra mellow anyway..... Open the Pvalve earlier, 26 mm carb, gearing, Steahly flywheel. A lot cheaper and easier than trying to find a trials engine that will fit, work and have any parts availability. If you could get parts a Montesa from early in decade would make a nice trail engine though.
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Old 01-30-2013, 08:00 AM   #4
lamotovita
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Quote:
Originally Posted by buls4evr View Post
Yes, a KDX is already ultra mellow anyway..... Open the Pvalve earlier, 26 mm carb, gearing, Steahly flywheel. A lot cheaper and easier than trying to find a trials engine that will fit, work and have any parts availability. If you could get parts a Montesa from early in decade would make a nice trail engine though.
I think you have the power valve operation backwards. It should open later.
I think the five speed Montesa would not make as good a trail bike as a six speed.
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Old 01-30-2013, 11:25 AM   #5
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I think you missed the part that he has a completely trashed motor. A heavy flywheel on trash is still trash.

Back to the hybrid concept. The key is finding a motor that is still good but the rest of the bike is gone. Chain on the correct side. And cheap enough to actually be an option. I doubt you will find a good, plentiful, easy to get parts for engine cheaper then just buying a whole bike. Neat idea, but the supply of parts does not exist to allow it to pan out.
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Old 01-30-2013, 11:36 AM   #6
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No shortage of used KDX200 parts around....Whole engines, whole bikes....all a lot better option than trying to engineer a trials engine from another make in there." Trashed "is a useless generic term. It could likely be fixed BY SOMEONE just perhaps not by the OP.
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Old 01-30-2013, 01:09 PM   #7
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You would never find one,but a super sherpa motor would be cool! Air cooled single of some type.On second thought a yamaha ttl or honda crf 230 might be a better package.I don't know where you would find such an engine short of a totaled bike though
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Old 01-30-2013, 01:44 PM   #8
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+1 on a Super Sherpa. a neighbor's son ran his into the back of a car last year, so it's possible. I'd almost trade my KLX250S for my stepdaughter's Sherpa. neat little bike and very simple....
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Old 01-30-2013, 04:12 PM   #9
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I have been interested in hybridized bikes in the past, specifically putting a DR650 motor in a DRZ400 chassis. Thought better of it as I measured and realized how much frame rebuilding it would take. Ended up buying a XR650R, which in a way is what I would have ended up with, only engineered by Honda.

Trials motors are small, you could probably fit one pretty easily. But, trials bikes tend to die at the engine, not in crashes etc. I think to get the motor you are going to have to buy an entire trials bike. At which point, go ahead and buy and old trials steed, and add a seat to it. Would take just a bit of fabricating, and you'd have what you're talking about, just coming from the other side. If you haven't ridden a trials bike on trail, you should borrow one. You might be hooked, and inclined to sell what remains of the KDX.
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Old 01-30-2013, 05:38 PM   #10
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Or, it might be a good time to try to develop your own electric bike
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Old 01-31-2013, 08:52 AM   #11
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Quote:
Originally Posted by buls4evr View Post
Or, it might be a good time to try to develop your own electric bike
This really isnt rocket surgery!...

All a trials bike is, a normal engine, tuned to run from 0 RPMs to say 5-6000 RPMs at peak torque below 2500 RPM, where as street and or dirtbikes work the opposite, max RPM exceeding 8000, torque and HP moved up the RPM ranges to facilitate SPEEDS, which is desired in Racing.

How they accomplish some of it, is Porting, carbs, exhaust, flwheels and gearing. Problem is a trials engineered modern bike (say for instance, since watercooled trials bikes have been around) carburetors and Exhaust have been tied to porting of the cylinders for slower speed riding. This tends to make a trials engine less than suitable to ride to go get groceries, for example, other than the ergonomics of the trials frame. above 50% RPMs a trials tuned engine with trials exhaust will over heat the exhaust a LOT.

So when everyone said better detune a dirtbike engine than repurpose a trials purposed engine, is VERY SANE advice.

FWIW, in the early 70's we took all the crap off enduros, like DT250's that was not needed (lights, cut down seats) and modified the final gearing (sprockets) because we no longer desired speed. But due to porting, exhaust and internal gearing and designs, they were NOT competitive in trials, versus trials bikes by design. Even so, chasing my brother on his 185 suzuki, while I was on my sherpa-T, I stood no chance keeping up, while running at higher speeds on twisty single track or woods riding, like you find in public riding areas... He had no chance in hell following me through rocky creeks either.
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Old 01-31-2013, 01:48 PM   #12
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Get a Harbor Freight motor and put a centrifugal clutch on it .
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Old 01-31-2013, 02:49 PM   #13
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CR500 engine
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Old 01-31-2013, 04:01 PM   #14
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I think the KDX mill is still the better bet here in that you aren't going to gain much overall trail ability with the trials motor. you will get better grunt off the very bottom which would be good if you plan on riding it aggressively through very technical conditions and wanted something better than your gas gas in those spots. In that case, the kdx chassis isn't the best choice.

for your trail maintenance bike, go tw200 which loves to go slow, stop/go, low seat estart, quiet etc.

If you were thinking ty yamaha engines, maybe those would make more sense and actually be available?
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Old 02-04-2013, 03:44 AM   #15
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water cooled rotax

I always felt the motor from my 94 Aprilia would have made a great transplant motor. The motor is used in other applications ie carting so parts may be available; watch for kick starts. Chain is right side of motor, I think it was only a 5 gear;

What a great motor though, I still miss it.
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