Prop overhaul - how frequently?

[Ernie Martin]

In a normally aspirated 337G, how long should one go between prop overhauls? I know the SB says to service at 500 hrs, but for Part 91 operations, in real life is there a fixed time or is it "on condition"? In short, if blades have been inspected and are within spec and properly balanced, if there are no cracks visible when you remove the spinners, and if there are no leaks and the units are operating fine, do you keep flying even if it's been 1000 - 2000 hrs since last OH? What's your field experience on how long do they normally go between overhauls?

Ernie

[rick bell]

my poh says 5years or 1500 hours wich ever comes first(73p)
oh both of mine with new engines, one blade was way out of tolerance, both gov.s way out of wack (couldn't keep sync)
this was about 7yrs and 1400 hours
rick

[GMAs]

Props for part 91 useage are usually done at the time interval stated in the service manual/manufactures manual... which says 5 years or at overhaul... which ever comes first... but, that is only a advisory which can be ignored and is most of the time...

But.....

You may not want to.. as the prop will start to corrode down inside by different metals... and once it started you can't stop it when it gets too deep... these are collarless hubs... and if the corrosion is bad engough.. you can pitch a blade... but, most of the time you will start to feel a lot of play in the prop.. as well as it will start to leak... but, that is not the norm that is the exception....

More the reason that they want you to have it serviced is that its a spinning oil filter up their in the hub and piston area... by the prop turning and the crank spinning.. you can centrifically throw stuff out of the oil.. with the clean stuff going back to the engine and the junk staying to the outside... and we have taken them off and looked into the crank... which is supposed to be hollow... and its full of junk and small metal parts (filings) which will cause pitting inside the crank (we once felt this might be a reason why the cranks were breaking in this area) as well as inside the hub... of the prop... this stuff keeps building up to the point where the O ring inside the piston assembly which moves the props position... starts to become a problem and the O ring starts to get worn or cut... and then you have a leak into the rest of the prop assembly which has greases that get washed out and things become from worse to worser... and you oil showing on the prop shanks... making them little streaks... (not good)...

So the limits on the prop are really the times that it needs to be checked and cleaned out...

Again its a toss up... if you mess with it.. you get the took it appart factor... if you don't you get the replacement factor... clean engine oil... and frequent changing... is the best for the prop here... if you don't want to take the advisory... but, I wouldn't let it go much past 5 to 7 years... You can specify that you only want it cleaned and re-sealed... and notification of parts out of limits... for this the prop shop will only charge about 800 bucks... for each prop... which is really cheep insurance... but, most will find the piston cup.. the thing on the front of the prop.. will be scored... them things cost 500 bucks... most of the other parts will be most of the time within limits... and they will check the balancing and re-balance if needed after they assemble the prop... Good prop shops are the ones that have a lot of props in them... and you have to wait a week or two ...

as to prop gov's... send both in at the same time... so they can set them togeather... else your mechanic will have to dink with them to make them act the same... most of the time they will be within limits... unless you ran dirty oil... of got metal in them... they have a little oil pump that boost the pressure up... which we have found is the only part that seems to wear in it...

Hope this helps.. GMAS....