I have run an os 91 in my BVM fan for about 30 flights before it smoked the piston. I know the OS would like to run at a lower RPM. Is there a different fan that can be run on the BVM Viojet that will absorb some additional HP for longer engine life?

Will the Viofan (96 version) fan work and /or is it pitched to throw more air?

Thanks for your response.

Paul

The only solution to your problem is to limit the max rpm of your OS to 22krpm max, via a slightly richer high end needle setting. There is no difference between the Viojet and Viofan rotors.

Peter

Thanks Peter.

I have a OS .91/Bvm Fan setup. Is this a common problem with the OS over-revving in this fan. So far I only have 1 flight on it, and it was way too rich to hit and high rpm's. I will be putting a inflight needle on it when it arrives.

Thanks,

Mark

Yes, I guess it is. They just will not last very long at full throttle with this fan. Just regular running near peak will get about 10 - 30 runs on the rod. If you are careful, maybe 50 + ?????

I had a header come loose, and loose a little muff. pressure. The engine goes a little lean with a minimum of back pressure. Boy, can you get some vertical for about $180 in parts!

If you want it to last -add 6-thats right-6 ozs of castor oil to each gallon of fuel-no more blown engines even at 24k-it DOES help the engine live longer.



Jackjet

I'm curious about your statement as I have the same setup but have not run it yet. You say you smoked the piston. Does it have a hole in the middle? If so does it look melted? Is inside of the head discolored or mottled? Is the rest of the engine ok? I ask this because these are indications of pipe problems not engine overrev. There was an article in RCJI a couple years ago about the time I was having problems with my Dynamax/Webra 80. My problem was the pipe. I saw some of the early indications of what they were describing in my engine. Changed the pipe and it ran fine till the rod let go
Thanks for the input on this fan/engine combo!

A fuel problem is what did my engine in. Engine detonation burned the top of the piston. The OS will run just fine with a good set up. There are more than a few pilots on here that will tell you that the OS engine rod will not last at max rpm. But then I've had a lot of other brands of engines blow a rod too. I like the OS over any of the other brands except BV's.

Give it a try and tell me what your experiences are.

The OS.91 turns more than 24K in a Dynamax fan and I have never lost a con rod. Make sure you use a fuel with 23% oil, a synthetic/castor blend and use only 5% nitro. The Wildcat 5% Jet-A is a good choice. Or you can add the castor like Jackjet mentions. The only damage I have ever had to an OS.91, besides crash damage, was caused by running too lean. The motor I'm running now has several hundred flights on it, and the only parts that I have replaced are the piston and liner.

Hi Chopper, The OS .91 is good engine, but in the Viojett it tends to be made out of glass. The reason that it will not fit in the Viofan is that the carb is offset in the backplate, the same reason that you cannot fit the engine fairing on the back of the Viojett. You might try seeing if you can pick a good used BVM .91 or .96, there seems to be a good quantity for sale right now. That inflight mixture is an engine saver. Bill Harris

I would like to know some more about Larry Wolfe's suggestion to use turbine oil in your glow fuel---his information sounds logical--anyone tried this???

I have NOT used the 91 in a Viofan, but a few people I know have done it, with the same results as yours. They just don't match up very well. Do yourself a favor and get a Violett engine for your viofan and your troubles will go away. Or get a Dynamax fan for your 91.
I think you are reinventing a wheel that has proven to be lousy, here.