Yamaha YM1S with Lifan single...need suggestions!

[makenzie71]

I just picked up a 1964 Yamaha YM1S for a song. No seat and motor is partially broken down (no carbs, no head, no side cover, and probably needs full rebuild). I'm not up for putting it back stock so I'm going to swap in another motor.

I picked up a 200cc Lifan engine from Katoranger a while back that I've been eyeballing. After I get new rings on the piston it should be good for about 18hp at the crank. I'm considering porting, polishing, shaving the head a bit, and finding a higher compression piston. Then a full exhaust and a proper carburetor...hoping I can get the thing to make 20whp. Don't know, though.

I'm thinking a 250cc top end would be a better decision. But even that leaves me wondering what I can do?

I want to go as big as I can, but I really like this kcik-start single. I would be stoked if I could manage to get in the 22~28whp area. What do you guys suggest?

My only other real option I'm considering is an air-cooled 250~400cc 2-stroke single...but that might be way over my power expectations lol. I'm not trying to make a hot rod...just a little bare bones racer.

[Weldangrind]

I'd love to see pics of your new bike.

Which type of Lifan do you have? Pushrod or OHC? I have a few pushrod engines around, and they need to remain at a relatively low compression ratio, or you're likely to break the kicker gear; there is no compression release device.

The 250 top end is actually around 230, IIRC. I stuck a pushrod 230 in Son of Weldangrind's XR200R, and it rips! The kicker feels like it will come apart when we start it, so I'm going to enable the electric start and save the kicker for backup.

I presume that the OHC version has a decompression device, so you could certainly shave the head and find a higher compression piston for that.

If the Lifan you have is a pushrod motor, I'd just install it and enjoy it for what it is. You can still optimize the intake and exhaust for maximum flow.

[FastDoc]

I just Googled the bike. Nice looking model. According to wikepedia, FWIW they sell for over $1,500 depending on condition. It MAY be worth considering rebuilding the stock motor, unless the bike is just a rat you want to have fun with. :wink:

[katoranger]

It is a pushrod engine from my 200cc lifan. The rings had siezed to the cylinder in the GA humidity.

My concern would be if the bike can handle the power.

[makenzie71]

All it really "needs" is to have the cylinder honed...there's a little rust in it. But i would like to get a new set of rings, though.

Will the 230cc single cylinders and pistons swap straight in on this 200cc? I have a pushrod 230 in my quad that's running strong...I could swap them around.

The stock YM1S engine made about 29hp at the crank...old school 2-stroke twin meant about 20 on the ground. I don't want a whole lot of power. 25-ish is dandy for me. Plus it'll be lighter. I don't it'll over-power the bike, but should be a bit more peppy.

[Weldangrind]

I only presume that the 230 jug will fit on the 200 bottom end. You're in uncharted territory. Please take many pics.

[katoranger]

I had freed it up after it sat for nearly two years. When I got it loose it didn't have much compression and I lost interest in my project then.

Like you I try to work with what I can trade or sell and use the money for my projects. Right now lots of other things need to be done before I can work on a bike or anything.

[makenzie71]

You don't happen to have a push rod 250 top end laying around, do you? Even a bad one I would consider. I don't want to drop $100~150 on new parts that may not work. I think I'll only need the piston and jug, but I may need a head, too.

[katoranger]

Not right now and I don't really plan to get any more until I move some of the stuff I currently have. My shed is full of stuff and so it the yard around it. I have a 2003 Golf GTI that I need to finish parting and then move on to some of the bikes and tractors.

I had one of those yamahas here at one time.

[FastDoc]

Fun car! :P

[makenzie71]

well hurry up and part the wagon so we can get to the fun stuff lol

[makenzie71]

Dug the stock lump and set a Lifan engine in the frame to see how it fits. I almost don't have room. Just barely clears the backbone.





















That motor is a 150cc equivalent to the final motor...same dimensions, though. I'll be able to use one of the rear mounts in the frame and then I'll cut a set of plates for mounting the front up. It all should go together nicely.

Right now she's shaved 44lb between the lower motor weight, lighter exhaust, and battery box and such gone. Of course I'll gain a couple pounds back with my carburetor assembly and peripherals, but still a significant cut in weight.

[makenzie71]

Once I get the mounting sorted out I'm going to just use the top end off my 250 quad to get my running bike. I would like to buy a new motor but don't have the $500 bleh

[FastDoc]

Great project. It looks like the motor is supposed to be in there. It almost looks like a small Manx Norton. 8)

You may be able to recoup some of the expenses by eBaying the old motor and parts.

[makenzie71]

Thanks Doc!