Bad piston, rod, wristpin, other?

[avagrace]

I have a 1995 75hp Mercury Serial OG 254565 that has started ticking/clicking. It can only be heard at up to approx 1/4 throttle, but I just cant hear it past that point because of the increased engine noise when I throttle up further. The sound is not in the lower unit. The engine starts great, idles great, top end speed is fine. I just took it in to be tuned up for the summer and the repair man seems to think the sound is coming from the front of the motor and believes it is a bad piston, rod, or wristpin. But of course he can not be sure until the motor is completely torn down. Any ideas on what else the problem could be would be greatly appreciated.

 

[remmer38]

Re: Bad piston, rod, wristpin, other?

Do a visual inspection your self. Some problems are obvious. So you have never been stuck out with this motor? That would denote good running for me. Hmm. Unless a compression check shows different, maybe somethings vibrating in the engine compartment. Catastrophic failure usually means a motor wont start. Is yur mech like mine who drinks not enough coffee?

 

[avagrace]

Re: Bad piston, rod, wristpin, other?

Thanks for the reply remmer38 This engine has not quit on me. It has good compression. So I am at a loss on if I should have it tore down and looked at closer. Hate to spend the 400.00 it would cost to have this done though.

 

[Dhadley]

Re: Bad piston, rod, wristpin, other?

If the wrist pin is starting to pound out or either of the bearings is starting to give up you will be able to tell that by removing the spark plug and turning the motor over by hand.<br /><br />It could be too much skirt to wall wear. It could be a collapsed piston skirt.

 

[avagrace]

Re: Bad piston, rod, wristpin, other?

Dhadley, thanks for the ideas. I am not very schooled in fixing engines, what am I looking for/hearing for when I remove the plugs and turning the motor over by hand?

 

[avagrace]

Re: Bad piston, rod, wristpin, other?

Dhadley, thanks for the ideas. I am not very schooled in fixing engines, what am I looking for/hearing for when I remove the plugs and turning the motor over by hand?

 

[Dhadley]

Re: Bad piston, rod, wristpin, other?

With the plugs out, move the flywheel clockwise so the piston moves past top center. Somewhere just after center (not critical) take a screwdriver or anything and while holding the flywheel, gently push on the top of the piston. It shouldnt move unless the flywheel moves.

 

[avagrace]

Re: Bad piston, rod, wristpin, other?

Dhadley, let me make sure I understand you before I do more harm then good. 1. Take out the plugs. 2. Move flywheel so piston moves to top center. (would top center be closer to the plug hole or further away from the plug hole?)3. Use a screw driver and insert in plug hole and gently push on the top of the piston. Thanks for your help again.

 

[remmer38]

Re: Bad piston, rod, wristpin, other?

Yes Dh. Even though my mariner ran like a top to halk throttle, I finally did a compression check and found 0 on the lower cylinder. After removing the exhaust plate cover, I found I could move the piston by hand in the sleeve. But I have to tell you, this motor even with that problem started on one try and ran at 3000 or so RPMs without any noise or problem. Strange.