Engine Performance

[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.

[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.

[Gerry Zagorski]

Originally Posted by Capt. Frank

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.

Some good observations there Frank although I think I only understood about half of what you said

Definitely not the power head though....

[Capt. Debbie]

Gerry it's funny. We are both throwing our best deduction out there on this. A good thing for the thread.

But I bet we are missing some key fact or two that would make the culprit a "no brainer." Betcha.

Originally Posted by Gerry Zagorski

Some good observations there Frank although I think I only understood about half of what you said

Definitely not the power head though....

[Gerry Zagorski]

Yes sir.... Something's not adding up here.

[Down The Hatch]

I thanks both of you for your advice. I will remove the prop in the spring and get to the bottom of this. Love the site. You have been very helpful