The article for Model Engine Builder is copyrighted so I don't feel free sending it out. Back issues should be available from the site. The article is a guide to building the mechanical part of the dyno but doesn't have detailed drawings. It contains a detailed description on how to setup and run the software. I found the Performance Trends manual hard to use at first. The software is not intuitive bu today's standards. Once you get past the initial learning, it works very well. We can easily do 40 to 50 dyno runs in an afternoon to test various engines and component combinations. The graphing software makes comparisons easy.

Lohring Miller

David Johnston wrote:
Torrington Company Roller clutch is only $15.00

I can imagine that ratchet singing at 18,000 rpm.

Actually I shouldd have said Timken instead of Torrington co. I beleive Timken owns them now.
Heres some tech info:
www.pacificbearingsales.com/pdf/rollerclutch.pdf

Bob DeCortin wrote:
I had a set screw behind the spring to adjust tension and it was easier on parts than originally thought... I built the Dyno in 1996 experimenting with the 23cc reed inducted motors (torque Monsters) made by the Italian Bergonzoni company... only had to re-place a key way once in 2000 after thousands of runs .... I could not find a clutch bearing to work at both the load & high RPM rate back thenB)

They seem kinda borderline to me when you look at RPM overrun limit and torque capacities. FCB-10 would probably be the best choice with torque rating of about 4.2 lbf-ft and overrun RPM of 23700. I myself would feel much better with a higher safety margin. Something for example that could take 30k RPM and still 4.2 lb torque. But I guess that one there could work.

Marc, I know what you mean.
but a 260 or other 26cc piston port engine you probably won't see more than 2.5 ft lbs and over 20k rpm.
Engines like the billets and CMBs are another story.

I don't believe you need a one way clutch. We use the Zenoah clutch, a resilient coupling, and a soft steel square key connecting the engine to the dyno wheel. Engine torque can twist the square key and the Aeromarine square bushings wear fairly rapidly with normal testing. We have had to replace the Zenoah clutch shoe holder with a billet one after the stock one broke. Understand that a stock Zenoah is a 4 hp engine turning around 10,000 rpm and we test engines with nearly 12 hp to 25,000 rpm. SAW Zenoah engines can over rev to 25,000 rpm. Despite this, we have only needed to replace 2 ball bearings after hundreds of runs.

In the one really sudden engine failure we have had, the clutch released before the key twisted more than 90 degrees. I doubt the engine completed more than one revolution after the piston seized around 20,000 rpm. The engine was completely destroyed and the ignition flywheel key sheered. There was no damage to the dyno.

Lohring Miller

I heard there were guys running without the roller clutch.

From what I understand the procedure is to make a run then ride the brake and "burp" the throttle while decelerating keeping fuel/oil going to engine until the centrifugal clutch disengages.

Does this sound correct?

That is what I do, as my dyno uses only a Zenoah clutch, no one-way bearing clutch. It works just fine and most of the dynos I have seen run this way, but I still think it would be nice to have the one-way clutch if it could be reliable. I agree that it is not required however.

The roller clutch has never given me any problems, but I wasn't running over 18,000 rpm.
I have a plan now in case I start having trouble.