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Thread: OMC’s 4-Rotor Wankel Racing Engine - The Real Story

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    Preserving OMC Heritage LIQUID NIRVANA's Avatar
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    Wayne
    Some of the "behind the scenes" """MOMENTS""" are death defying to say the least. John is a great storyteller, that for sure. You are in for some interesting reading. Stay Tuned.

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    Default Can't Hardly Wait Ken...

    .....It's been riveting enough that we're getting the fleshing out of the OMC rotaries, but the inside stories are what really brings us at least a little bit into the going's on. When you mention "death defying" it makes me think of how quickly I could redline my little RX2 Mazda in the mud. Is that about grenading a rotary with a turbo? As I started off...can hardly wait for more. I found out that trying to pull up those days from the past and talking with others that were there will also dredge up things I had forgotten about. So we are looking forward to more of your posts John.



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    Default Jack Leek Story

    Quote Originally Posted by Master Oil Racing Team View Post
    Hope there is a part 4 and more John. You write so incredibly well and concise that I can gather the gist of engineering terms I'm not familiar with. You can throw us tidbits anytime while waiting for time and ambition to come back around.
    While at a race in Memphis, Jack Leek and his wife had retired early, while the rest of the race crew partied in the parking lot. Mouse and Ziggy got bored (read tipsy) and noticed a Bobcat where the hotel was building a swimming pool. They hot wired it and started using it as an elevater, giving people a ride in the bucket to the second floor. After a while this got old too, so they took the Bobcat and moved the swimming pool sand pile up against Leek's hotel door ( which just happened to open inward) and then piled all the empty beer cans on top of the pile. After frantic pounding on Leek's door, he arose and opened his door to see what the hell all the comotion was about. Needles to say it took several hours to dig out Jack and clean up the mess.

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    That story is a perfect candidate for Miss BK's thread of Boat Racer's Practical Jokes John. If you haven't found that one....check it out. Somebody needs to link this to that thread.



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    Default another one

    Quote Originally Posted by Master Oil Racing Team View Post
    That story is a perfect candidate for Miss BK's thread of Boat Racer's Practical Jokes John. If you haven't found that one....check it out. Somebody needs to link this to that thread.
    How about the time Mouse stole a kids bike and was having bike races in the pool. Then they decided to go in one door of a room, over the bed, even if someone was in it, and then out the back door back into the pool.

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    Default part 4

    The History of the OMC Rotary Program
    By John Sheldon


    Part 4; Additional Rotary Programs

    In the 70’s, OMC owned several non-marine companies. Among them was Cushman Vehicles. Cushman was using a B&S 12 hp 4-cycle engine in their golf cart. The engine actually produced 9 to 10 hp. I was asked if I could develop a true 15 hp engine for a golf cart application. To expedite things, I used the snowmobile engine, detuned to produce 15 hp at 3600 RPM. This was accomplished by removing the peripheral intake port and using only a small downstream side port. The engine was built, dyno tested and sent to Cushman for installation in a golf cart. The only report I ever got back was, “the acceleration was beyond exhilarating, it was down right frightening”. Seems the detuned engine with a large displacement gave considerably more torque than the B&S engine had. When you nailed the throttle, it picked the front wheels off the ground. Even though Jim Briggs was responsible for Cushman, they decided it was just too much engine for a golf cart and they didn’t want to fund a completely new engine for their application.

    Pioneer Chain Saw was another OMC company. Vibration was becoming a major issue with chainsaws. Long-term exposure to chainsaw vibration caused Reynolds disease in the hands of the user. Some manufactures chose to use vibration isolation to help reduce the problem, but this added considerable cost to the unit. Pioneer wanted to use a rotary as it was dynamically balanced with only torsional inputs. As a side note, nobody figure out at the time that the vibration input from the chain cutting wood was equal in vibration to the piston engine. I was assigned the project to design and develop a 5 hp air-cooled engine for a chainsaw. Pioneer engineering would incorporate the engine into a new saw design. Knowing 1 hp per ci was feasible, I decided on 5 ci for the displacement and copied the snowmobile cooling arrangement. This meant a very high performance fan to be able to cool the engine properly. Normally chainsaws had the starter on the left side, but because of the airflow restriction caused by the starter, I told Pioneer, the starter could not be in front of the fan. The starter on the left was to allow closer clearance from the ground to the bar and chain. Pioneer didn’t want to give up this feature, so they designed a swing arm starter like some of the outboards used. To use this type starter and get back to the crank resulted in a 2 to 1 reduction in cranking speed. I know now this is not something you want to do with a rotary. Many design innovations were used on this engine. The stationary gear, rotor, buttons and apex seals were made with the powered metal process (sintered metal). The trochoid was chrome plated. The side housings were hi-silicon aluminum requiring no addition wear surfacing. Prototypes were made and assembled. Dyno testing confirmed 5hp at 7000 RPM, but cooling was an issue. No failures resulted from the high temps, but performance tapered off as the temps rose. It was felt that chainsaw typically didn’t run at WOT for extended periods and thus this may be acceptable. The day came to install the engine into the new saw. After a couple of tweaks, it was ready to try cutting wood. After pulling on the starter for God knows how long, it became apparent the swing arm reduction starter was not going to crank the engine fast enough to start. We did what all good engineers would do. Cut a hole in the starter housing and get out the electric drill with a socket. The engine started, but threw the socket beyond retrieval. The saw performed well and cut wood like a banshee. That’s when I learned what sawdust coupled with tree sap did to cooling fins. It didn’t take very long before temperatures started rising beyond acceptable levels. We also learned very quickly what saw chain induced vibration meant. At this point in the development, it was apparent vibration isolators would be required to tame the saw chain vibration and thus the advantage of the rotary was diminished because of the cost of the two together. The project was stopped.

    We changed directions and used the same hardware for a water-cooled version. 6 HP was the target. New parts were designed and made to water cool the engine. A cast in sintered metal insert was used for the trochoid surface. The goal was to sinter to size and no addition trochoid machining would be required. The engine produced the target 6 HP but would not consistently idle below 2500 RPM. Idle speed on the 2-strokes was 300/500 RPM. Starting was also an issue. Most of the small 2-strokes would start with a flick of the flywheel. This was not the case with the rotary and a significant pull on the starter rope was required. Many 100’s of hours were run on this engine with no mechanical problems. We mounted the engine to a 6HP mid-section/lower unit and went boating. Idling and start ability continued to be a problem. The guys at research came up with an ingenious invention that took some charge from the compression cycle and put in back into the intake cycle. This solved the idling and starting issues. The engine would consistently idle at 500 RPM and would start with a modest pull of the starter rope. It was at this time the 4 rotor race engine came into being and I was reassigned to that program. The 6 HP engine was assigned to Doug Betts; a relatively new engineer at OMC. The program floundered with redesigns to increase displacement and HP. The demise of the engine was part of the OMC direction to shelve the rotary programs. Ken Finely has my only picture of the engine. Maybe he would be kind enough to post it.

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    Preserving OMC Heritage LIQUID NIRVANA's Avatar
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    Sorry I missed this John. The "Mac" name caught me unawares.

    Ken Finlay.



    ================================================== ===============

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    Quote Originally Posted by LIQUID NIRVANA View Post
    Sorry I missed this John. The "Mac" name caught me unawares.

    Ken Finlay.



    ================================================== ===============
    Ken:
    The picture of the 6 HP outboard, on a slide.
    John

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    The OMC 6hp Prototype Rotary outboard powerheads


    This picture indicates just how much smaller the Rotary powerhead was when compared with a 1971 6hp Johnson/Evinrude or the earlier Johnson/Evinrude 9.5hp

    ================================================== ==============

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    Default OMC rotary engines

    There was a total of 6 race engines plus a ton of spare parts. The 6 were defined by the shroud, bucket and exhaust manifold. The bucket/shroud sold on E-bay was not completely machined and never had a power head installed. 2 units are in a private collection, 1 unit is on display at BRP and 1 unit is on the 100th Evinrude anun. tour. I believe there is 1 more complete unit somewhere. I am told that all the OMC race hardware was scrapped when BRP took over (V-4, V-6, V-8, and rotary).

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