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Thread: High cyl head temp

  1. #1

    Join Date
    May 2012

    High cyl head temp

    I have a. Io 360 a1b6 in a glasair with 550 hrs on it. Recently when I run above 65% power the #2cylinder climbs dramatically and the engine starts to run rough. I did a compression check,fuel flow check per cylinder, borascope, cleaned injectors, and all appear normal. Any suggestions?

  2. #2

    Join Date
    Aug 2011
    Marietta, GA
    Look for an induction leak on that cylinder. Perhaps a fitting backed out or cracked. Maybe you have a blown induction gasket, a loose induction tube, a loose hose clamp on an induction tube, or a cracked rubber hose between the sump and the induction tube.

    I've never done it, but I'm told that if you'll carefully spray all of those areas with WD-40 with the engine idling on the ground, engine rpm will increase enough to be noticable when you "find" the leak with the WD-40.

  3. #3

    Join Date
    Oct 2011
    New Hampshire
    An IO-360-A1B6 is a 200hp angle valve engine with 2 magnetos. The #2 cylinder is the front left. Induction leaks generally are worst when idling and get better when the throttle goes forward and the induction air flow from the fuel control overwhelms the smaller flow through the leak.

    Does switching mags to run on just one mag help? If you have Bendix mags has the 500hr internal inspection been done? I understand that misfiring mags can create high cylinder head temps although I have fortunately never experienced that.

    Exhaust leaks leave white staining so if the exhaust stack was cracked and blowing hot gas on the CHT probe and the intake riser, you would see the trail.

    If the nut that connects the fuel injection line to the fuel injector body were leaking, you would see blue stains. Has the entire fuel injector body been unscrewed from the cylinder and cleaned? There is a screen around the lower part that lets air in around the business end of the internal injector nozzle so as to get a nice spray pattern from the internal nozzle. Upper deck fuel pressure rises from < 1 psi at idle to about 5psi at full throttle. If the screen near the bottom of the injector body is plugged up with dirt or maybe bug guts, the injector would not work right.

    Best of luck,


  4. #4

    Join Date
    May 2012


    I looked for obvious signs of induction leaks and found none. Also pulled the line from the spider to the injector and it looks fine also. I am running out of ideas

  5. #5

    Join Date
    Jul 2011
    So, smooth and cool at idle, and hot and rough under power and not an injection nozzle? And Wes,, it doesn't seem like a bad mag would show only on one cylinder?

    Try switching plugs with another cylinder or even a new plug or ignition wire and fitting. A plug can be marginal , runs ok until under pressure.
    It seems you have covered most anything else, except maybe an excorcist?

    Really reaching for straws; a high performance car engine can have a weak exhaust valve spring, or hydrauic lifter problem that can show up as a leak at the valve at power and high rpm; really never heard of it in a Lycoming.

    Any chance your engine was built in Kenya rather than Williamsport?
    Last edited by Bill Greenwood; 05-31-2012 at 05:29 PM.

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