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Bit of a puzzle to think about on non-flying days

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Bit of a puzzle to think about on non-flying days

Postby PKnight » Mon Jan 15, 2018 10:01 am

I have a 6 cylinder engine 33A1336 early hydraulic lifter with hollow push rods. Good compressions, 1170 hours, always been stiff when hot. Installed in a J430. It has a cold start kit and starts first time in cold with choke.
The starter motor, starter relay, earth connections, battery have all been checked/swapped and are AOK.

Symptoms:-
If I land away and wander off for 30 to 60 mins when I return to the aircraft I am never certain how it is going to start. Most times, perhaps 4 out of 5, I turn the key, the prop spins as normal and the engine fires on almost the first revolution.
However, occasionally I turn the starter and it moves very slow, almost failing to turn the prop. Usually if this happens I curse a bit, stop and try again. The prop still turns slowly but almost always catches after a couple of blades and off we go. This event does not seem to correlate with anything simple like how long the aircraft has been left standing after flight (although generally if it is more than 1 hour the problem is less frequent), or the outside temperature. The electrical systems seem to be fine.

Questions
Has anyone else experienced this behaviour? Has anyone got a bright idea about what might be going on?
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Re: Bit of a puzzle to think about on non-flying days

Postby Steevo » Mon Jan 15, 2018 11:28 am

A friend of mine with a J160 has just had exactly the same issue with a 2200A. The problem turned out to be a battery. Most of the time everything would work fine but other times the prop would hardly turn and he struggled to start it. Battery was holding 12.3v but it was only when an intense battery test was done that the problem was discovered.
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Re: Bit of a puzzle to think about on non-flying days

Postby PKnight » Tue Jan 16, 2018 10:24 am

Thanks Steve.
I would be a bit miserable if it was the battery as it is only 2 years old. A full discharge test may be a good idea.
The other thought I had was whether or not the nature of the approach to an airfield affected the likelihood of the failure to start properly.
I was thinking that a long approach with the landing light and fuel pump on and the revs at less than 2000rpm will probably be discharging the battery as there will be insufficient charge current. A long taxi in will also contribute to the discharge. So a re-start will already have a battery slightly below optimum as well as a tight hot engine.
As I have a voltmeter on the panel I should note the displayed voltage and see if that correlates with a poor start. If it does then that at least confirms that the problem is primarily in the electrical system, most likely the battery, rather than the engine having some exotic behaviour that makes it harder to turn than usual.
Peter
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Re: Bit of a puzzle to think about on non-flying days

Postby Sonex w CAMit » Fri Jan 19, 2018 2:18 am

Do you have a good heavy gauge ground wire from back end of starter motor to engine frame and or battery ?

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Re: Bit of a puzzle to think about on non-flying days

Postby PKnight » Sat Jan 20, 2018 7:31 pm

David
There is a very solid ground from the starter to the earth point. There is also an extra ground from the engine frame to the same earth point to eliminate a bit of noise that was affecting the reading on the EGT and CHT gauges. I have got a new battery (Odyssey PC625) and I will post the voltage reading for reference as soon as we get some decent flying weather.
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Re: Bit of a puzzle to think about on non-flying days

Postby PKnight » Wed Feb 07, 2018 10:46 pm

Conclusion.
All the evidence points to a poor earth connection from the battery to the starter. The earth cable had started to fray just after the ring terminal that attached it to the battery. The fault was hard to spot as insulation partly masked it. First evidence that this was where the problem lay was that the wire got very hot at this joint. A new earth cable and terminals seem to have removed the problem as the prop now spins fast on start-up even on a stiff and hot engine.
Many thanks for all the comments and suggestions
Peter
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Re: Bit of a puzzle to think about on non-flying days

Postby Garyo » Fri Feb 09, 2018 10:07 am

Good result and 1 to remember
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