Slight motor knock

[mcgreavster]

My 1988 Evinrude XP150 developed what I would describe as a knock when on the water today. Would only do it between 1000-1500 RPM, other than the noise the motor ran perfect. No loss of power at idle or full throttle.

Kinda seems like this is the beginning of the end for this old girl. Any ideas what it could be? I’ll check the compression to start but didn’t know if anyone has any experience with something like this.

Thanks!

Video for reference-

 

[oldboat1]

sounds like a miss. could be a lean miss (air/fuel mix needs to set a bit richer). Check compression, and spark. Run with a timing light and test each cylinder (check for miss -- light will go out).

 

[racerone]

Check gear oil first.

 

[clemsonfor]

If it's a knock from rods it would get louder with RPM or show up also at higher RPM but that's my opinion as what I think you would see.

 

[mcgreavster]

Checked compression and it seemed fine, all 6 within 80-85 PSI. I drained the lower unit oil and the top vent screw had what I would consider a higher than “normal” amount of metal on it. The lower screw barely had any, I ran a high powered magnet through the lower unit oil I just drained and didn’t really get any metal from it. The oil itself still looked really good, no signs of water in it.

Vent screw attached-

 

[clemsonfor]

Seems like more metal than I'd like to see. How long since you last drained and refilled to have cleaned that magnet? 85PSI seems a little on the low side to me. I wonder if that's piston slap and it's just like you said worn out?

 

[mcgreavster]

Seems like more metal than I'd like to see. How long since you last drained and refilled to have cleaned that magnet? 85PSI seems a little on the low side to me. I wonder if that's piston slap and it's just like you said worn out?

I drained and refilled about 20 trips ago in March. I thought this model motor was 90psi from the factory but I could be mistaken.

 

[clemsonfor]

I drained and refilled about 20 trips ago in March. I thought this model motor was 90psi from the factory but I could be mistaken.

Well if your correct about that 85 is great. I do not know personally. I just would of thought it should of been north of 100psi. If there all similar and it runs and you think 90psi was factory I would say it's perfectly healthy that way

 

[racerone]

Remove bypass covers to look at pistons and rings.----- Motors with 85 PSI are likely ready for surgery.