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Thread: Another MMO thread question.

  1. #1
    Richgj3's Avatar
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    Another MMO thread question.

    Many people who run small continentals like the O-200 and O-300 advocate the use of MMO and TCP claiming it reduces the frequency of sticking exhaust valves. I have experienced those problems in both engines I have owned.

    So, if you were running one of these engines in the experimental category and were using MMO would you use the recommended dose in the fuel or would you be more aggressive? Would you also use it in the oil as well as the gas?

    I own a 1963 Corvair which had been sitting a while and had some lifter issues which were cured by liberal doses of MMO in both the gas and the oil. The Corvair, for you youngsters, is a flat opposed air cooled six.

    Thanks

    Rich
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    I’ve used it as specified in certified aircraft as well as experimental airplanes. Way back when, Aeronca recommended it for operations with the E109 and E113 engines, so it has a back door for being “approved”.


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    Cub Builder's Avatar
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    I have, I would, and I do. I have also found a good dose of MMO in the oil to be great for freeing up stuck rings. I have had 2 cases recently where I've seen mid to high time engines with low compressions with the leakage blowing through the rings. In both cases, the owners were ready to tear down the engines for top overhauls. And in both cases, I advised the owners to add a pint of MMO to the oil and and re-check the compressions after 5 hours flight time. In both cases, the compressions returned to passing and with continued use of MMO, the compressions continued to improve. One case (Lyc Angle valve IO-360), 1 year later now checks 79/80 on all 4 cylinders. The other case (Continental IO-360) has flown 400 hrs since starting to use MMO with two failing cylinders and is now 200 hrs past TBO with compressions all in the mid 70s. That is not to say this is a fix every time you have low compressions, but sometimes engines that can be easily cleaned up are being overhauled.

    For my own planes (O-200 and O-320), I add a cup of MMO to the oil. I also premix my own fuel, so use a pint of MMO to 100 gallons of fuel, and my fuel is a premix of 15 - 20% 100LL and the rest alcohol free premium Mogas.

    Some folks will agree, and others will say I'm just using air freshener for my engines. But in my experience, MMO is a useful additive.

    -Cub Builder
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    fobjob's Avatar
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    As I understand it, radial engines under high boost at high altitudes suffered greatly from carbon valve deposits , the B29 certainly, and the B36 as well. The B36 also had a design flaw in its cooling, the exhaust air was dumped into the space just in front of the pusher prop hub area, which was NOT a low pressure area (reverse flow) ...about that time MMO started to be used, and quickly became mandatory. Anyone using large radials has a few drums of MMO in the hanger....
    Kerosine, and stoddard solvent, has an affinity to being absorbed by carbon deposits which are then softened, and fall off the surface that they have been baked onto. It’s more effective in the oil. A friend showed up one day with a fifties vintage Jeep pick up with a used Ford 302 engine (fairly high mileage) shoehorned within on its first run. It had a loudly sticking lifter (or valve) which went quiet before we got the whole quart bottle of MMO into it.
    Last edited by fobjob; 05-08-2020 at 11:45 AM.
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    Richgj3's Avatar
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    “friend showed up one day with a fifties vintage Jeep pick up with a used Ford 302 engine (fairly high mileage) shoehorned within on its first run. It had a loudly sticking lifter (or valve) which went quiet before we got the whole quart bottle of MMO into it.”

    Same thing with my Corvair.

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    Picked up a 195 from a really knowledgable guy in Garden City a decade or so ago. He recommended MMO. I figured he knew more about old engines than I ever will. Used it ever since. My engines go beyond TBO.
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    I had an O-320 stick an exhaust valve at 1200 hours, unstuck the valve and started running MMO religiously - the engine went over TBO with no issues.

    I run MMO in the gas and oil. I dump the MMO in the oil during about 10-15ish before an oil change.

    I follow the MMO quantity recommendations for the gas. For the oil, I bounce back and forth between a full-dose and half-dose per their recommendation.
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  8. #8
    Richgj3's Avatar
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    Quote Originally Posted by bob turner View Post
    Picked up a 195 from a really knowledgable guy in Garden City a decade or so ago. He recommended MMO. I figured he knew more about old engines than I ever will. Used it ever since. My engines go beyond TBO.
    Bob
    Do you use in in the oil too, or only the fuel?

  9. #9
    cubdriver2's Avatar
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    Sat in on a radial engine clinic at Oshkosh 20+ years ago. One of the speakers had run TWAs engine shops for the Connie's. Some one asked about MMO. He said " I don't know if it was ever approved but we bought trucks full of 55gl drums of it "

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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    I always ran it in the R985 in the Howard, both oil and gas!


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    My dad was in air corp ww2 and told me the same story of 55gal drums of MMO by the truck load....

    I was the 3rd owner of the prototype Spezio Tu-holer. The #2 owner had been using Quaker State Av oil back when they had a problem but I didn't know it. I was doing touch and goes while a buddy was mowing the runway. He flagged me down waving his arms. I couldn't hear it but my O290 was back firing pretty bad. He and my other A&P friend told me to put a quart of either "Moto Medic"( probably Kerosine and Stoddards) or MMO in the oil and run it for at least 15 min. Then change the oil and continue to use the recomended dose of MMO in both gas and oil. BTW, the Moto Medic was much cheaper. It worked and I've been a believer ever since.
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  12. #12
    Cub Special Ed's Avatar
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    Recomended use. Fuel only in my c90. Plugs look great every anual and after 500+hrs no valve issues.
    "There are 3 kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves." Will Rogers
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    phdigger123's Avatar
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    Makes me wonder if I should run MMO in my R-680.

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    Cub Special Ed's Avatar
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    I read one time, mabe others on here know where, but when the ol bomber mechanics used to have major engine problems with radials they would drain the oil, fill with mmo then run for a little bit. Then drain and put regular oil in and send them off. Same with fuel. They traveled with 55 gal drums of the stuff. I use it in fuel in everything. Even got the ol 6.2 detroit in my 83 gmc to quit smoking!
    "There are 3 kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves." Will Rogers

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    cubdriver2's Avatar
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    Quote Originally Posted by phdigger123 View Post
    Makes me wonder if I should run MMO in my R-680.
    We did in the mogas

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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