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  • Re: Rough running, 3500 - 4500rpm, Rotax 912

    by » 11 years ago


    Andy, sorry for taking so long to reply, I didn't see you asked me a question. We discovered the casting pin hole by warming up the engine with the rad cap loose, then shutting down and pressure testing the coolant system. With exhaust pipes removed and looking into exhaust ports, the leak was discovered, a very slow drip of coolant in exhaust port near exhaust valve stem! Very tough one to find and have never seen the problem since!

  • Re: Rough running, 3500 - 4500rpm, Rotax 912

    by » 11 years ago


    Thanks Ralph.

    I got the aircraft back a couple of days ago and what a difference! Smooth throughout the rev range and the coolant seems to be behaving itself as it is going into the expansion bottle when hot and returning to the header tank and engine as it cools (which it did not do before). I have only flown it for 2 hours / 4 flights, but so far all is good.

    So...what has been done on it?

    The aircraft manufacturer checked things themselves and then returned it to the Rotax importer who has spent 17hrs working on it. The gearbox was removed to check crank alignment, crank angles were measured, the prop was slightly out of balance and a couple of washers added (but an alternative prop had been previously tried), differential compression test on cylinders, coolant system pressure tested hot and exhausts removed to check for the leakage Ralph has described, one carb flaot replaced as it was slightly 'heavy'. carbs rebalanced....the engine was then run with an accelerometer fitted and that showed no abnormalities. A lot of checks, nothing particularly significantly doneexcept changing the carb float ....yet it now seems to work fine.

    I was anticipating that some 'fault' would be found and rectified but apart from the carb float this does not seem to be the case - and that would obviously not effect the coolant issue.

    I would like to thank the aircraft manufacturer (P+M) and Rotax importer (Skydrive / Conair) for their help and patience in rectifying this problem.

    Andy Buchan

  • Re: Rough running, 3500 - 4500rpm, Rotax 912

    by » 11 years ago


    Fantastic Andy I bet your a happy bunny now,

    Out of interest...what method did they use to balance your prop.

    Nick.

    Thank you said by: milo avram

  • Re: Rough running, 3500 - 4500rpm, Rotax 912

    by » 11 years ago


    That's why Rotax went to the spring type clamps they have.Standard screw type clamps will do exactly what you described over time.Very good catch as heads are very expensive (approx $2000 bare).

  • Re: Rough running, 3500 - 4500rpm, Rotax 912

    by » 10 years ago


    Ok, here is something to remember now. If you ever take your prop off make sure you mark it and the prop hub and put it back on in the exact same clock position. Because the engine is a boxer type and has various harmonics there are times when there will be some slight harmonic in tune with the prop. This can cause the type of vibration you first experienced. The first thing I do with prop vibration is move the prop around the hub to each clock position to find where it is the smoothest. Then go for balancing. It just may be the MFG and importer found the sweet spot on the hub.

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