Author Topic: Bell Cranks  (Read 3969 times)

Offline PaulR

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Re: Bell Cranks
« Reply #15 on: May 13, 2026, 05:21:29 am »
I just found a pic of an engine I built in 2012 to test a design published on the internet, but with modifications. I added adjustable valve timing and stroke mechanism, a toothed pulley power take off for driving accessories via a toothed rubber belt, and one of the snap on / off type ball joints Chris mentioned, to drive the bellcrank. Pic attached. Just FYI, hope the ideas help.
Yes, the 'McCabe Runner' is what I was basing my idea on and you obviously had the same concerns as me about the forces affecting the bell crank connections! How did it run?

Offline cnr6400

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Re: Bell Cranks
« Reply #16 on: May 13, 2026, 01:58:00 pm »
Hi Paul, It didn't run all that well in stock form as built from the published drawing, but it did run. After endless guessing and messing around  careful scientific experiments adjusting the valve stroke and timing it ran fantastic, I checked it with a tachometer and it was doing 2600 rpm on 15 psi air! It was a lot of fun. One thing I found was that the valve needed to be a bit sloppy in the hole for it in the cylinder block, and oiled well. The fit was probably about .002" / 0.12 mm clearance. As you can see it had a fairly big disc crank with lots of inertia to keep it turning. I belted the engine to some experimental loads like a tiny Baker fan and a grinding spindle. They worked, but the engine did not make quite enough power to run these accessories. Hope this info helps.  :cheers:
"I've cut that stock three times, and it's still too short!"

Offline PaulR

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Re: Bell Cranks
« Reply #17 on: May 13, 2026, 06:09:55 pm »
After endless guessing and messing around  careful scientific experiments...
:lolb: Sounds familiar!

 

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