Planet Minis

slimbo

Have a sl70e 4spd, manual motor that was given to me minus carb and intake. Would like to build a bigger displacement motor to put in my crf50, is this thing worth building up? If so what are some motor combinations? Not just looking for displacement, but more in the line of faster with being reliable, if thats possible. One other thing, this motor project is something to tinker with and is on a budget. What do I need to do to wire this thing up? Will the 12v cdi udate wire right up to my crf harness? Can these old style heads be bored to accept a bearing type cam? What about a roller bearing top end? Custom connecting rod? Has anyone ever modified the stroke of a stock crank? Is it possible to plug crank pin hole, weld it and machine it on the location you want? That doesn't seem like it would be too much of a big deal or would it. I have a crank pressing fixture laying around from the karting days to put the crank back together. Cutting some weight off the crank pin and crank?I am a machinst/tool & diemaker for 16 years with some time on my hands and thought it might be fun to tinker around with this thing. The shop I work at has pretty much all the tooling you could ever ask for to make just about anything. There are some guys on here that are really sharp with what parts go and fit with each other. It would be great to get some input from you guys. I am not an engine builder and do not consider myself one, just looking for something to do. Once again fellas not just looking for a bolt on bore kit, that wouldn't be any fun.

arlindsay1992

I guess your the kind of person who likes building the bike almost or maore than riding it. Nothing wrong with that. But if your doing something custom, there are no rules. If it was up to me, I'd throw it in my bike and ride it. It's really up to you.

kane

I read a post about how those trannies lock up when built into a high hp motor. It was posted by fatcaat, search the archives in the ct forum and you will find it.

davez

Check out Powroll for getting your stock crank stroked

davez

or a good massage parlour, ha ha. just kidding

slimbo

dave, as long as there is a happy ending.....

fatcaaat

I've been building these engines for many years and have found some issues with some of the older trannies when placed under stress.

First, I wouldn't recommending building things for these engines, such as stroker cranks, etc...they are readily available and cheap from dratv.com so go have a look over there.

Second, I have build a few engines based off the older ct70h, sl70, xl70, and s65 engines. They ususally go well on the street, but there have been two instances of grenading the trannies.

The build was a 52mm stroker crank and a 52mm bore with a lots of bells and whistles putting down an estimated 10-11 hp. On almost full throttle in 3rd gear the tranny blew apart (geared about 40mph) and threw me off the bike and down a ravine. On a 4th gear run on a similiar build, my buddy had his lock up at about 50mph in the street and laid a strip of rubber about 40 feet long.

My recommendation is that unless you are absolutely sure that the parts are in excellent condition and within honda factory specs, I wouldn't go big with it.

Also, your wiring harness, coil, and complete electic system is not compatible with the xr50, so you have to get all those parts too.

My final recommendation is to do the following:
1. Find a junked ct70 3-speed motor with good tranny
2. Bore the cases to 56mm
3. Install a dratv 52mm crankshaft, with CDI
4. Port the heck out of the head
5. Install a 54mm piston and cylinder using a gb0-piston
6. Transfer your clutch from your sl70 and install hd clutch springs
7. Install the Monster Cam from dratv into the ct70 head alsong with HD springs
8. Replace the rubber rollers for the cam
9. Install a hv oil pump and drill the oriface to 2mm
10. Get a bigger intake manifold and a tm24 flatslide carb
11. Get a cdi system from ebay

Now you've got 120cc's...and estimated 12hp. Hang on.