2003 200 HP Mercury Knocking / Losing Power

[fedpo]

I have a 2003 200 HP Mercury Saltwater motor (not EFI, just the basic motor). While cruising down the river yesterday, about 4000 RPM and 35-40 MPH, I hear a "pop" in the motor (sounds like a small rock was thrown at the motor), and the motor starts to lose some power. It drops to 3000 RPM and 20-25 mph. When I put the motor in neutral, it sounds normal. When I put it in gear at idol speed, there is a definate "knocking" noise. It almost sounds like something is loose in the motor or maybe the lower unit. It starts fine; it idols in neutral fine; it "knocks" when in gear and it has less than normal power. Any help would be GREATLY APPRECIATED!

 

[fedpo]

Re: 2003 200 HP Mercury Knocking / Losing Power

I did a little work on this motor last night. I pulled the plugs which have only been in the motor for about 35 hours of operation. The first 5 looked normal, no obvious issues. The last plug I pulled (#1) was completely "closed" (no gap). It looked like the tip was hit and "mashed" all the way down. I know the plug was gapped properly when I put it in. Any thoughts / suggestions / comments? I plan to get a new plug today but I'm afraid the same thing will happen.

 

[Jeff_G]

Re: 2003 200 HP Mercury Knocking / Losing Power

Don't even turn the engine over. Something has gone bad in the powerhead and hit/closed the plug. You may have detonated the piston, broken a ring etc. You can pull the cylinder head and look at the cylinder to see what is wrong.
If the rod has broken or other internal problems running the engine can cause more damage and may tear up the engine to the point of not being rebuildable.
Get it to a good shop for diagnosis.
Good luck

 

[fedpo]

Re: 2003 200 HP Mercury Knocking / Losing Power

This turned out to be a MAJOR problem! I pulled the head cover last night and the piston in question looked like a waffle. It had dents and dings all over it. Something hard was in there and created all kinds of damage. I now have to decide: rebuild or buy new motor? Either way, it looks like I will be doing my part to help the economy!

 

[Fuzzytbay]

Re: 2003 200 HP Mercury Knocking / Losing Power

Check out the cylinder walls, if they are not scored/scratched, it might be a "mild" rebuild, of just the piston/wristpin/ crank bearing, and maybe rod. Plus the associated things that go with this. Be best though, if you do tear it down, to check out all the other piston etc. too.

 

[Jeff_G]

Re: 2003 200 HP Mercury Knocking / Losing Power

You most probably broke a ring.
You can have it rebuilt or have a replacement powerhead put on.
I have found very few aftermarket reman. replacement powerheads really up to quality. Mercury does have a replacement reman. powerhead.
If you have a very good shop with experienced techs that could be a way to go. What ever you do check out references first. Don't just go by the low bid, get detailed estimates.

 

[fedpo]

Re: 2003 200 HP Mercury Knocking / Losing Power

THANKS FOR YOUR INFO! Couple follow-up questions: While I'm fairly mechanically inclined, I have very little experience working on boat motors. Having looked at the motor, I THINK I can break it down. Will I need special tools? Will I likely get in over my head and do more damage than good? Is it possible to romove what needs rebuilding, have someone do the repairs, then replace the parts myself? Anything to save a few bucks. I enjoy the work as long as it's possible for me to do.