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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10974
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 2000 150hp mod#rj150vxsss. when I'm cruising there

Customer Question

i have a 2000 johnson 150hp mod#rj150vxsss. when I'm cruising there is a nock it has stayed the same all summer. it sounds like a cross between a bearing and a rod nock. the compression on the cylinders are between 95 to 100 psi. i have dropped the lower unit and checked the shaft bearing which looked good and the carrier bearings spins smooth. i have also put new plugs, wires, coils, power pack, optical sensor, fast start temp sensor and new starter with new gear drive, pinion & shaft, pinion hardware and bushing. What is this noise?
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.

Hello. My name is Tan.

This will take more than one reply to find your issue.

Noises are hard to diagnosis when you can hear them yet harder when you can't. Can you do a recording of the noise and post it on Youtube and send me a link?

Does the engine knock at idle in gear, neutral or reverse?

Did you run the engine without the lower unit on with a hose connected to the water tube to supply water to the engine? This will eliminate the lower unit as a cause for the noise.

What was the color of the lube in the lower unit?

Have you used a mechanic stethoscope to isolate where the sound is coming from?

Typically a knock is a bearing failing on the crank or a wrist pin. Now it could be a bearing failing in the lower unit or a gear with a broken tooth. If the lower unit has ever had water init this can cause bearing or gear damage causing the noise.

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