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

  1. #151
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    Quote Originally Posted by Michael J Gwaltney View Post
    Unknown: Jim Wagner, Race Team Supervisor. Jean & Jim Wagner formerly managed Lake X for Mr. K.
    The guy on the right was a European distributer. I don't remember which country.
    John

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    Quote Originally Posted by Rotary John View Post
    The guy on the right was a European distributer. I don't remember which country.
    John
    Note Posey's hand. He is covering up the Evinrude logo on Goats jacket. It was cold that day and we all had on all the sweaters and jackets we had. Kukla was turned away from the camara so his Evinrude logo won't show. Funny the things you remember when you see the old pictures.

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    I'm glad you cleared that up John. I kept wondering what that was all about. I thought maybe it was a Scottish thing, but then I didn't think Posey is Scotch.



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    Default OMC Rotary History

    The History of the OMC Wankel Rotary Program
    by John Sheldon
    former OMC project engineer on rotary engines

    Part 1; Oil Cooled Rotors

    In 1958, Curtis Wright signed an exclusive agreement with Wankel GMBH giving them exclusive manufacturing, marketing and sublicensing rights for North and South America as well as a portion of the same worldwide. In 1966, OMC signed a sublicense with Curtis Wright and Wankel GMBH to develop, manufacture and sell Wankel engines for the recreational market worldwide. The original Wankel engine had a stationary crankshaft with the housings rotating around their own centers. This allowed for dynamic balance without the use of counter weights, but had the added complexity of a moving sparkplug and a complicated induction system thru the crankshaft. Max Bentle of Curtis Wright is credited with the kinematic inversion of the engine allowing the housing to remain stationary with a rotating crankshaft. This simplified the engine immensely, but required the addition of counter weights on each end of the crank to achieve dynamic balance. Curtis Wright developed single and twin 60 ci per rotor engines. These engines were both water and air cooled externally and oil cooled internally. The pressurized oil system allowed the use of conventional babit bearings and with the addition of an oil cooler to maintained internal temperatures adequately. I believe Curtis Wight was more interested in selling licenses than producing engines. Curtis Wright went on to develop several different engines from a small lawnmower size to enormous oil field engines.

    OMC started their development work at their Research Center in Milwaukee. They took the basic Curtis Wright 60ci engine and started development work on trochoid coatings and apex seals. Research changed the original CW engine by reducing the displacement to 50ci/rotor and using 2 main bearings instead of the 3 used by CW. The target was 80 HP using side porting. Curtis had use “D-Gun” tungsten carbide from Linde as their coating, which was very effective, but extremely expensive. OMC hired 2 Curtis Wright Engineers, Harry Ward and Mike Griffith. Harry was a former Chevy engine engineer, having worked on the Corvair engine and Mike’s background was in the ag business. Less Foster was named manager of the rotary engine group. OMC also hired Ralph Treadway from GM. Less’s group started a production design of a 2 rotor 100ci engine in hopes the research guys could develop a suitable coating/seal combination before production started. The engine was initially designed as an outboard with it’s own new midsection, gear case and motor cover. The engine was designed to produce 200hp at 6500 RPM. It had water-cooled housings and oil cooled rotors similar to the Curtis Wright engine. It had an oil to water heat exchanger, was peripheral and side ported, 2 oil pumps and used the midsection as the oil reservoir. The engine produced 210 hp. The one difference to the Curtis Wright engine was the oil seal. Curtis had a highly loaded scraper type oil seal and OMC followed Mazda with double oil seal with wave springs and o-rings. This reduced friction hp, provided lower temperatures for the O-rings and was more compliant to side housing distortion.

    I joined OMC in the summer of 1968 and was put in the OMC 1 year new hire training program. At that time OMC was totally integrated, from melting their own aluminum, die casting their own parts, carburetion, electrical, gears, painting and machining. In fact OMC was the largest aluminum captive die caster in the world, casting 250,000-300,000 lbs of aluminum a day. The training program assigned me to every department in the plant for 6 months and than 3 months each in 2 of the engineering departments. My second stint was with the rotary group where Ralph Treadway too me under his wing. I was assigned to the oil seals, as what we had at the time didn’t work very well; very high oil consumption. Ralph was also assigned to lay the engine down for a stern drive. Without the midsection for the oil reserve, the housings had to be modified to include an oil pan ala automotive along with a high rise exhaust. The engine turned out really neat as it was so small a complete rear seat could be built in the boat eliminating the big box common to stern drives with automotive engines. Being dynamically balanced, there was virtually no vibration felt in the boat. It was also hundreds of pounds lighter than the V-8 being used and as such would out accelerate them even with 100 less hp. My seal work went on with some successes and some not so successful. The seals were being made in Japan, so the iteration time between design/development changes took some time. Oil consumption finally was under control and both the outboard and stern drive versions performed very well. Remember at the time, 125 hp was the largest engines available. The outboard version pushed a 23’ Wellcraft cuddy cabin at 52 MPH. Quite an accomplishment for that period. OMC was in the boat business, so the stern drive version was in an OMC boat, known for its heavy weight and lack of performance. The rotary allowed a full rear seat and performed well against the V-8 in the same boat. Both versions meet the design requirement of 100 hrs @ WOT. Less Foster kept pushing to release both units to production, but the powers to be insisted on a true manufacturing costing vs Less’s estimates. The result was disastrous! The true manufactured cost was twice what Less estimated; opps! Less left the company and George Miller took over as head of the group. Mike Griffith and I were assigned to a major cost reduction design of the oil cooled engine program, while Harry Ward started work on a snowmobile engine. The original oil cooled engine was made from all sand cast parts from an outside source. The trochoid coating was still “D-Gun”, as research hadn’t developed a lower cost suitable coating yet. The first step was to redesign all the housings as high-pressure die-castings. We even explored die cast aluminum rotors and 2 piece center housings glued together. After several months of work, it became apparent an oil-cooled engine could not be made cost competitive with a 2 cycle and work on oil cooled engines stopped. I believe stopping work on the stern drive version was a mistake, as it was lower cost than the Detroit V-8 being used, offered performance advantages and allowed the removal of the “dog house” in the back of the boat. It was about this time Ralf Treadway left OMC and returned to GM to work on their rotary program.

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    Default Part 2, the Snowmobile Engine

    The History of the OMC Wankel Rotary Program
    by John Sheldon
    former OMC project engineer on rotary engines

    Part 2; the Snowmobile Engine
    With the demise of the oil cooled rotor engine program I was reassigned to Harry Ward who was working on an air-cooled engine for snowmobiles. Harry knew from his experience at CW, an oil cooled engine could not be hand started at –40. Ficthel and Sachs from Germany had developed a charged cooled rotor engine where the incoming air-fuel mix passed thru the rotor to cool the internal parts. Roller bearings were used instead of the babitt bearings of an oil cool rotor, which required oil to be mixed with the gas ala 2-cycles. Unlike a piston engine, the rotor is a captive heat source with very little heat rejected to the housing walls. As such most of the cooling had to come from the incoming charge to cool the rotor. The result is a significant reduction in volumetric efficiency, the actual amount of air going thru the engine vs its theoretical capacity. This is due to the significant heating of the charge as it passes thru the engine. A rotary engine is unique in that only one section of the engine is exposed to combustion. The down side is that it always hot, not like a piston engine, as combustion occurs almost continuously in that section. Harry had done some work at Curtis Wright with partially air-cooled housings. Unfortunately he had designed a 2 stage axial blower running at 30,000 RPM and took 35 hp to drive to cool the CW design. Ficthel had used an axial fan on their engines, but they had cooling fins all around the engine and had reduced performance to be able to cool the engine. Harry decided a partially cooled engine was possible if an adequate fan could be developed. I developed a computer program to predict airflow required vs. fin design. We produced rotor housings without any fins and machined various fin designs into them. We then had an external variable speed blower to blow air thru the fins measuring air velocity at each fin. Harry developed an ingenious method of measuring heat flux thru the engine. A pair of accurately spaced spring loaded thermocouples measured temperatures allowing us to calculate heat flux. Testing various fin configurations and measuring the air velocity required to cool the engine, we verified my computer predictions. Using the computer program and manufacturing constraints for casting fins, we were able to predict how much air and at what pressure would be required to cool this engine. One of the design constraints for the engine was it had to run at +90 in addition to -40. With the fin design fairly well set due to die casting restrictions, the challenge became to design a fan that would provide sufficient air flow at a given pressure to cool the engine. Very little has been written on centrifugal fans. We knew an axial fan could not generate sufficient pressure that would result in the velocity required to cool the engine. We ended up with a two-piece fan that was die castable in magnesium including a pre-swirl inlet section. Research had developed a sprayed tungsten carbide from Metco that would meet the durability requirements when coupled with tool steel apex seals. A durability cycle of 55 minutes WOT, followed by 5 min idle, for 100 hrs. was established as the minimum life requirement. More details on this engine can be found in the SAE paper written by Harry Ward. The snowmobile engine was released for production and in the winter of 1972. 150 engines were built on a production line in Milwaukee. 100 of these engines were installed in the new snowmobile designed for this engine. The 100 units were given to various dealers throughout the snow belt with instructions to loan them to their customers for no more than a week at a time. No service was to be performed on these engines at the dealer level. They were instructed to call OMC if they had any problems and OMC would send a service technician with a new engine. For the entire season, no one reported any problem with an engine. Not even a sparkplug was replaced. The units were returned in the spring with the plan being to tear all the engines apart for inspection. The 6 units with the most hours were torn down and the engines looked so good that the remainder were never disassembled. Production started for the ’73 model year. Approximately 15,000 engines were produced for the 73 & 74 season. OMC went out of the snowmobile business after the ’74 season. Because of the high maintenance of the die cast die fin sections, one of the last changes was to change the rotor housing from high pressure die cast 380 alloy to permanent molded 356 alloy. This not only reduced the costly die maintenance, but also gave the added benefit of better thermal conductivity, lowering temperatures. Many of these engines are still running today, 35 years later. With no home for an air cooled engine, attention turned to water cooled versions of this engine.
    Because of the availability of production parts and the severe environment of the air cooled engine, the snowmobile engine continued to be the workhorse for component development. One of my responsibilities at the time was all the rotating components of this engine, bearings, seals and rotors. The rotor bearing was the weak link of this engine. Being inside the rotor, it is completely dependent on the incoming charge for cooling and lubrication. The bearing was already pretty special. It had a silver plated retainer and a high temperature temper of the outer race. Steel grows; get larger, as it gets hotter. That is until it exceeds the temper temperature where in it gets smaller. As I figured out after 100’s of tests, there was a lubrication breakdown between the retainer and the outer race. The result was steel running on steel at very high speeds generating extreme heat. The result was the bearing shrinking onto the crank eccentric stalling the engine. It took a hydraulic press or a sledge hammer to get them apart. I took several samples to SKF Research and talked to the chief metallurgist. He told me this was impossible to do. When I suggested he come to Waukegan and see for himself, he said the bearing had to be reaching 1800 F for this to happen. This type failure was self-destructing. When the bearing got near its thermal breakdown temperature it would self generate additional heat causing further oil breakdown, causing additional heat, etc, etc,etc. The end result was a shrunk bearing and a stalled engine. Dozens of bearing designs and modifications were tried before a successful solution was found. Interesting enough, none of the snowmobile engines in use showed any bearing problems. Part of the reason is it was very difficult to maintain WOT for extended periods of time and by nature, snowmobiles ran at much colder ambients. The apex seals were a second area where thermal breakdown of the oil caused problems. Similar to the bearing, it was a snowballing failure; generating addition heat as failure started. Wear was so severe the seals would look like horseshoe nails after only a few hours of running. Many, many, many, iterations were tested with varying results before a better seal was developed. Less than .0005 in wear was measured in 100 hrs WOT testing. Unfortunately, these never saw production. One might ask why all this testing and development when there was no home for the air-cooled engine. Part 3 is on the water-cooled engines based on the snowmobile design.

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    Default Part 3

    The History of the OMC Wankel Rotary Program
    by John Sheldon
    former OMC project engineer on rotary engines

    Part 3; Water Cooling the snowmobile Engine

    As mentioned earlier, with the demise of the snowmobile business, rotary work turned to water-cooling the basic snowmobile engine for outboard use. The earlier oil cooled rotor engines followed CW and Mazda in using multi-pass axial cooling of the housings. The water flowed parallel to the crankshaft in three passes. The end housings acted as plates to cover the water passages of the rotor housings and thus had to be sealed to prevent water from leaking out. This was accomplished by using spaghetti O-rings on both sides of the cooling passages. O-ring grooves were milled in the rotor housings to fit the seals. This was a costly operation and caused assembly problems; the O-rings would fall out of the groove and get pinched resulting in leaks and tear down. OMC was starting to investigate lost foam die-casting. This process allows the use of closed passages while still maintaining the advantages of die-casting. Kind of like a sand casting. With this in mind, it was decided to use circumferential cooling of the rotor housing. Heat transfer is a function of the velocity of the water so by varying the width of the water passage, the cooling of the housing could be tailored to the required heat load of the engine while maintaining a constant volume of water. The air-cooled engine demonstrated partial cooling was feasible. The end housings were cooled by taking water from a high pressure point on the rotor housing and exiting to a low pressure point. They were also only cooled on the hot section. A simple round O-ring sealed the transfer points. We new from previous work on the oil cooled engines a dual spark plug gave an addition 10% power, but also lead to housing cracking due to the heat load imposed. Therefore the decision was made to maintain the single leading sparkplug location from the snowmobile engine. I’m frequently asked why we used a 12mm plug vs the conventional 14mm plug. We used a surface gap plug with the end .010 away from the trochoid surface. If a J-gap plug would be installed, the J would protrude into the engine and the rotor/apex seal would be destroyed as it tried to pass by. Thus to prevent this from happening, a new 12mm surface gap plug was made by Champion. One of the concerns was the exhaust system. Aluminum melts at approx 1060F and the exhaust from the rotary was approx. 1800F . While the snowmobile used a steel exhaust pipe mounted directly at the exhaust, the outboard version had to turn 90 degrees and then travel thru the mid section and out thru the prop. A stainless steel deflector was used to deflect and turn the exhaust and the rest was water-cooled. The exhaust pipe thru the midsection was surround by water and thus wasn’t a problem. With the housings designed, prototypes were sand cast and machined. All of the internal parts were directly from the snowmobile engine. Even the snowmobile crank was used for the initial builds. The spline extending from the flywheel on the snowmobile engine was inertia welded on, so it was just left off for the water-cooled version. The engine produced approx. 50 HP initially, and with further development increased to 60 HP. The biggest problem was carburetion. OMC made their own carbs and the calibration continued to give problems. More on this a bit latter. A two rotor version was designed by adding a center housing and a new 2 eccentric crank. Different counter weights had to be used as only the bending couple had to be balanced. The eccentrics were 180 degrees from each other. The exhaust system again was a problem. The first attempt was a stainless steel casting where the top rotor had the deflector to turn the exhaust stream 90 degrees, but the bottom rotor exhausted straight out into the exhaust stream from the top rotor. This caused problems with exhaust blow down pulses causing scavenging problems. Later iterations split the exhaust into 2 streams until it entered the mid section. This eliminated the bad pulse problem. The engine produced approx 115/120 HP at 7000 RPM. It also fit under the 70 HP 2-cycle motor cover. Carburetion continued to be a problem, only doubled. After much consternation, the Japanese company Keihin was called in to help. Within 30 days, they had a calibration that was so good it would cycle with the thermostat opening and closing. This is the engine we showed to the board of directors. The Keihin carb also did its magic on the single rotor engine. The twin rotor was the bases for the 4-rotor race engine. That story has been told in a previous article. With the 4-rotor entering the picture as # 1 priority for the company, let alone the rotary group, resources for the single and twin were diminished. Some endurance running was done with apex seals and rotor bearing continuing to be occasional problems. The new parts developed in the air-cooled version fairly well solved these problems. Work also was done on emissions. While the rotary was significantly better than a comparable 2-stroke, lean air reactors were tested. While they reduced hydrocarbon emissions by a facter of 10, they also raised the exhaust gas temperature to 2400 F. One unit running outside had its exhaust aimed at the concrete, which puckered and exploded. So much for running on the dock. Turbo charging was also tried, but the increase in temperature caused all sorts of issues and was never really pursued.
    In ’76 OMC decided to curtail its rotary program and the water cooled engines were put on the shelf.

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    Default OMC's rotary

    will there be a part 4 ? or has the 4 rotor racing powerhead story been told , completely , already ? This is SO fascinating to me . it seems to me that , w/turbocharging a 4 rotor could put out over 500 H.P. but, that might be monstrously large &heavy ? Not to mention EXPENSE.

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    Quote Originally Posted by Roy Hodges View Post
    will there be a part 4 ? or has the 4 rotor racing powerhead story been told , completely , already ? This is SO fascinating to me . it seems to me that , w/turbocharging a 4 rotor could put out over 500 H.P. but, that might be monstrously large &heavy ? Not to mention EXPENSE.
    Yes there is a part 4 and maybe even a part 5. I don't know yet as I haven't written it. You know, ambition & time must coincide.

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    Quote Originally Posted by Roy Hodges View Post
    will there be a part 4 ? or has the 4 rotor racing powerhead story been told , completely , already ? This is SO fascinating to me . it seems to me that , w/turbocharging a 4 rotor could put out over 500 H.P. but, that might be monstrously large &heavy ? Not to mention EXPENSE.
    The story of the race engine started this thread, but there are some many tidbits I forgot in the story. Like the time we got thrown out of the hotel in Belgium for dropping water baloons on the girls walking by, or the time we rebuilt a powerhead in the hotel room using the sink to wash out the carbs. As Ken Finley tells me when I talk with him, there's lots of these tidbit I forgot to tell. The thermal load was too high at the time for turbo charging. The one time we tried it on a single rotor, we we pulling 60 HP at 3000 RPM before it let go. I suspect with some of the advances Moller has made it would be more feasable today.
    John

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    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.



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