mercury 110 9.8 hp low thrust drive underpowered

[rob.s.uk]

I have I mercury 110 9.8hp. When the engine is used on the water the engine rpm doesn't match the speed. I was wondering if it's propeller slip the boat moves just slowly. I think I may have found a problem with the gearbox. When the engine is in reverse and the propeller is turned by hand it doesn't matter if it's turned clockwise or anti clockwise it turns the engine. If the engines in forward and the propeller is turned by hand anti clockwise turns the engine but clockwise there's a clicking coming from the gearbox. So I was wondering if something is wrong inside the gearbox. Hope I make sense and someone can help.

 

[GA_Boater]

Welcome aboard.

You described normal operation of a Mercury lower unit, Rob. The clicking in forward is caused by a dog clutch used to protect the motor if the prop hits something.

What boat is the 9.9 mounted on? Small/large or light/heavy boat.? When in reverse and the engine turned, were the spark plugs still in?

 

[Scott Danforth]

Welcome Aboard.

yes, normal. Just swapped power heads on a 9.8EL and 9.8M and the prop acts the same as you described.

however what condition is your prop, you may have spun a hub.

 

[rob.s.uk]

Thank you for your replys. The engine is on a 3.2 meter inflatable tender lightweight but rated at 15hp. the plugs were in when I turned it by hand plenty of compression I only turned it a tiny amount not a full rotation. I have just been reading a thread on here which said the clicking is normal. The hub inside the prop looks ok no sign of a problem but that must be what the problem is. If I turn the drive shaft and hold the prop it doesn't slip but I read a thread that said you would have to be as strong as a horse to make it slip. I think as it's an old engine I will get the prop rehubbed as I don't think I will find a new prop.

 

[Scott Danforth]

they make new props every day for that motor.

 

[rob.s.uk]

I have found it difficult to find parts for this engine in the UK as it's so old. Unless you happen to find a marine workshop who is breaking older engines.

 

[rob.s.uk]

When the prop hub spins is it obvious to see (chewed up). Or can it spin in its housing.

 

[rob.s.uk]

propeller hub

I've just bought an engine when testing it for the first time I found the speed of the boat doesn't match the rpm. It's very underpowered. I suspected the hub was spinning in the prop so I removed the prop and it looks fine. When the prop hub spins is it obvious to see (chewed up)?. Or can it spin in its housing inside the prop?. I would of thought it was quite obvious to see if it was damaged with bits of rubber missing ect.

 

[GA_Boater]

The easiest thing to do is draw a line across the prop and hub. If the hub is spun, the line won't be straight after using the boat.

 

[Scott Danforth]

Rob, try to keep everything to one thread post.

 

[Scott Danforth]

and no, if the hub simply came unbonded, there would be no missing chunks.

 

[Sea Rider]

Need to make a prop test to confirm hub is already shot, visual hub inspection or even fingering it won't say a thing about its condition.

Happy Boating

 

[Chris1956]

Mark the hub and the prop with matching marks. Install the prop and test boat speed. Now examine match marks. If not longer lined up, the hub is bad.

 

[rob.s.uk]

Marked a line across the prop and hub they still lined up after a run so it's not the prop. I got the boat on the plane but it's revving and looses drive when I throttle back and try again it seems ok until the revs pick up again. I just can't seem to work out what's up. It's like pushing the clutch pedal down in a car as your underway.

 

[steelespike]

Tell us about your motor and boat. Tell us your wot rpm and gps speed.

 

[rob.s.uk]

The engine is a mercury 110 9.8. It's on a 3.3 meter inflatable tender. I couldn't tell you the rpm or gps speed as there are no electronics or instruments onboard. It seems to loose drive at higher rpm maybe it's prop slip or cavitation?. I have tested the prop and its not the hub.

 

[Sea Rider]

If hole shot is awful you can blame the engine to be under powered, but could be due to excesive hull drag, poor inflation on tubes and keel, badly trimmed, weight is not even distributed on deck or engine sits too low, too much lower tail drag due to water splashes ? Assume you made the prop test as suggested by Chris, right ?

Happy Boating

 

[Scott Danforth]

take a picture of the motor and boat from the side.

if the motor is reving up and you are loosing thrust, its either prop blow out/cavitation or a blown hub or stripped gears in the gear case

you have eliminated prop hub.

from the crankshaft output splines to the pinion gear splines - the driveshaft is a single shaft
from the ring gear splines to the prop splines is a single shaft

if you drain the gear case oil and find metal shavings, you could have lost your gears.

the fact that you can still hit the holeshot and get on plane makes me believe its prop blow out.

 

[rob.s.uk]

Yeah I've done the prop test and its fine marks still line up. The boat was empty when I tried that boats inflated correctly ect. Engine has plenty of power takes a while to get on the plane but when it dose the engine revs like it's out of gear. If I throttle back and try again it seems to engage again. Can't be a gear selector problem because it would stay out of gear. It's like something's slipping.

 

[GA_Boater]

Plus 1 ^^^^^^ A pic as Scott suggested could help us figure out the prob.