I have 1999 Mercury EFI 150 and the bottom end has clunk when accelerating not every time. Also the rpms have increased from 5200 to about 5800 .

T

tonystas

Recruit
Joined
Apr 27, 2021
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I have a problem with my 1999 mercury EFI 150 hp there is clunk or knock in the bottom end when I accelerate.
- This doesn’t happen every time but most of the time
- Also the RPMS have increased it went from 5200 to about 5800
- I have changed the oil in the bottom end and it was a little low but there was no water in it
- It started when I took the boat off the trailer and the launch the water was low so I had to reverse hard to get it off I heard a grind or clunk and since then I have had this problem
- If anyone has some troubleshooting or info on what this could be I would really appreciate the help
Thanks
 
Texasmark

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,844
The rear of F gear and front of the clutch dog are sawtoothed. The driveshaft drives the F and R gears simultaneously and neither are connected to the prop shaft via the clutch dog in N gear.

The sloping part of this sawtooth is your overrun clutch and allows the engine to run slower than the oncoming water is forcing the prop to turn during deceleration. The vertical part of the sawtooth is where you apply thrust. Over time the (somewhat sharp) corner, aka peak, what have you, gets worn off and as a result the driving force of F gear can and will (BTDT) slip out of the front of the clutch dog, locked to the prop shaft, but being held in the rear of F gear by the lightest of 3 spring pressures of the 3 gears. Since spring pressure is a variable, it can and will yield if enough force is applied, causing your problem.

Being a 99 year model and 150 HP, if you had a lot of hard use this is entirely possible......since your prop is not slipping and you are absolutely sure of that....rubber hubs like to play games when they are going out and sometimes it's hard to tell. A strobe mark from the prop shaft out to the hard metal that makes up the prop "tube" is how I test for a slipping prop. Scribe the line, take it out and run it hard and check the line. It won't lie.
 
T

tonystas

Recruit
Joined
Apr 27, 2021
Messages
4
Texasmark said:
The rear of F gear and front of the clutch dog are sawtoothed. The driveshaft drives the F and R gears simultaneously and neither are connected to the prop shaft via the clutch dog in N gear.

The sloping part of this sawtooth is your overrun clutch and allows the engine to run slower than the oncoming water is forcing the prop to turn during deceleration. The vertical part of the sawtooth is where you apply thrust. Over time the (somewhat sharp) corner, aka peak, what have you, gets worn off and as a result the driving force of F gear can and will (BTDT) slip out of the front of the clutch dog, locked to the prop shaft, but being held in the rear of F gear by the lightest of 3 spring pressures of the 3 gears. Since spring pressure is a variable, it can and will yield if enough force is applied, causing your problem.

Being a 99 year model and 150 HP, if you had a lot of hard use this is entirely possible......since your prop is not slipping and you are absolutely sure of that....rubber hubs like to play games when they are going out and sometimes it's hard to tell. A strobe mark from the prop shaft out to the hard metal that makes up the prop "tube" is how I test for a slipping prop. Scribe the line, take it out and run it hard and check the line. It won't lie.
Click to expand...
The rubber hub that you are talking about is the spacer in the prop right
 
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