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Pitchlock problem


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Have a prop on a -16 that will not pitchlock. Prior to us getting the plane for ballistic foam install, the squadron had the same problem. They changed pitchlock reg., valve housing, then the gearbox sh*t the bed and the prop was seized on the shaft so they r2\'d the tq meter, gearbox, prop/dome. Sooo. They had a good pitchlock after all of that...once...so it could get here.

We have tried all manner and techniques IAW pubs, and otherwise without success. It will overspeed without a problem, but does not even think about locking.

Re-Indexed about 6 times (1x=2 then 3 master).

Tried getting low/ref tq at about 97% then going to 1077 before locking and hitting gov switches...no dice.

Tweeked fuel topping to the high limit 105.6/1600pph. The beta is at 6.0.

Syncrophaser was R2 for a different problem on a different engine.

Thought that it may be in mech gov the whole time, but droop checks from the new sync are good both as master and slave (problem is on no.2)

It has been suggested by the prop guru at PPI that we try to pitchlock in auto. Fuel topping has been confirmed at 105.6 (autotach) so there is not 110 worries. Thinking was that TD had to put above xover, and that coming back to ref. rpm was below lights out. Xover checks have the TD taking as normal, and the sucker is about 45rich.

Any takers.....?

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I had one last year doing the same thing. After second (zero time) PLR we started seriously examining the prop, and found the seating area in the barrel nut to be worn. We changed the barrel nut and problem immediately went away. Basically, the barrel nut had been reworked too many times and the seals couldn\'t hold pressure any more.

About 6 weeks ago another one refused to lock. On investigation we found the PLR index rings to be badly placed. The real reference mark was almost invisible, and another had been made one tooth away ......

As a rule, I always use 98% rpm as minimum torque reference. First attempt from 850TIT, second attempt from 925TIT, last attempt from take-off/1077TIT. I have had successfull pitchlocks as low as 103.4% rpm on first attempt.

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With already changing the prop and verifying the fuel toppings, you already eliminated pretty much everything involved. There is one question though. You mentioned it would overspeed. Is that overspeeding with a throttle burst, or is it when you advance to a certain power setting and let it stabilize before you hit the switches? Many times I have to advance to maximum power before I even hit the switches. If you don\'t see an rpm increase just from hitting the pitchlock switches, there is a wiring problem (since valvehousing was eliminated.) If you already did that and it checked good, I would suggest you may have a bad propeller from your supply which happens to be bad in a similar way that the old one was. Just to verify, I\'d remove the prop from the engine and put it on a test stand (if that\'s possible.)

Possibly whoever installed the prop forgot a seal or cut one on the way on. We also had some crazy problems from the pitchlock regulator either not being installed correctly, or having the externally threaded ring back off. It sounds like something in the prop, since the engine is doing its simple job by overspeeding. Good luck.

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Fixed...sort of. Went back into the dome today. PLR was indexed correctly, but the top half of the barrel was not correct. PPI guru told me to check to see that the dome alignment slot was between #2 and #3. Our was not, it was between #3 and #4. I have never paid any attention to its orientation before, but if it is put together incorrectly at overhaul/buildup then it will work fine all accept for pitchlock. It will never pitchlock if the barrels are mismatched. So I can only assume that it did not lock prior to coming here.

Anyway, good one for the memory bank, and thanks for the help...goats and all.

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