Small engine testing equipment

in the 70s, when I raced, I lived on the dyno

would be nice now, but not worth the effort for me to get/build one

Hmmm....then you could finally put down some real numbers. See what these little engines can really do stock, then over stock.




I still want a chassis dyno, but that's because I'm a motorhead.

That is a very cool site. A dyno would be great fun. If you could make it profitable even better. I would not call that cheap by any means though.

Seems to me with all the brain power on this site a group could be assembled, at some desirable undisclosed location, and one of those bad boys could be produced in short order.

Kinda like a working vacation. I will buy the beer...

Cheers,

David

A dynomometer could be fabricated out of something like a torque converter from an automatic transmission where the output shaft could be coupled up to some kind of torque measuring device. Or one could use an old brake band and a drum which could be used to make a prony brake; a one foot shaft and a bathroom scale could be used to make accurate measurements of engine performance.

We had a franken dyno at the last Socal Motor Bicycle Race thanks to Ryan.
5 dyno pulls for $5 with results emailed to you.
Several racers including AGK had 3 of their bikes run on the dyno on the 19th October race day.

I think Ryan said he had about $700 into building it. He just got a flat screen monitor and the computer sorted out running on a generator.

We have had the dyno for about 3 races now.

There is a dyno print out of a stock 66 cc China girl in the race forum done by Ryan.

I've had a dyno design in mind for some time. I might get around to building it one day. Or I might not. But I'll offer it to anyone who might be able to use it.

I'll include a simple diagram.

Picture your bike hung up with the wheels free to spin in the air. Now you take something like a 2 x 4 and mount a bicycle rim brake on it. Put this brake on your drive wheel. Somewhere further back the 2 x4, or 'torque arm' rests on a fulcrum. Beyond that is a bathroom scale. Start your bike up and start applying this brake. You can see that the torque arm is going to act as a lever, applying the bike's torque to the bathroom scale. The scale will then 'read' just how hard that bike is pushing against itself.

I really don't know what sort of torque, at the wheel, to expect out of a china girl engine. But let's imagine it is 50 ft/lb. If it were 3 ft to the fulcrum and then 1 more foot to the scale, then that scale would feel a torque of 150 ft/lb. This is right in the scale's most accurate range. So you could get pretty good torque readings.

You'd need a bike speedometer, or some method of measuring wheel RPMs, in this mix in order to calculate horsepower. But this shouldn't be a major difficulty.

I suppose the bike would also have to be fastened to the ground to keep it from bucking around. Also that brake will get hot. But it shouldn't be too hard to rig up a way of running a little bit of water over that brake to cool it.
Which will also smooth out the braking, helping the possible bucking issue.

This dyno might be a bit crude. But any reasonably handy guy could surely get it working without too much trial-and-error. And it would be pretty inexpensive.

While I love the idea, it's far too much effort for me.
Tuning a china girl for max power and dyno numbers is great fun, but, to me, it's not what chinagirl motorbicycles are about.
It's like trying to turn laps at Indy on your riding mower.
Wrong tool for the job.
Now, if I were to come across a Morini or KTM, my opinion would change....

Shane on one of his Affordable Go Karts racing bicycles on the dyno at the Oct 19th race.