Engine Performance

[Capt. Debbie]

Gerry,

I'd vote elsewhere given his symptoms. Hub speed this consistent?

The more times it spins free of engine-to-prop the less friction the hub has left for the next time it happens. And progressively slippage gets worse.

And during a hub slippage it emulates cavitation where prop thrust speed would drop off to near 0. He's maintains consistently 3 knots slower?

Could it be as simple as his GPS was knots v mph on the read out? Perhaps.

I think we both agree it's not the powerhead.

Originally Posted by Gerry Zagorski

As suggested above, the first thing I would check for is a spun hub. If you're not familiar what a prop hub is, it's a insert in the prop. When there's an impact the hub breaks free (or spins) within in the prop so the sudden impact of something stopping the prop doesn't ruin the prop shaft and or your gears...

The symptoms of a spun hub is an engine that races but does not get up to speed... The hub breaks free and spins within the prop instead of spinning the prop. It's kind of like spinning your car tires on ice... The engine will race, but you won't go anywhere...

This video will help to explain https://www.youtube.com/watch?v=d7Lz7cI-srQ

I were you, I would take the prop off the engine and take it to a reputable prop shop and have them see if the hub is spun... If it is they can re hub it for you and it will likely be around $100 or less to re hub it.

If that's not it, you have something else going on.