‘98 Mercury 225 efi knocking

**Jmham7** · 10-17-2017, 07:01 PM

Was just out tonight running boat.. has approx 550hrs, oil is good...

running on plane about 70, lost power fell off plane, engine was knocking. At first I thought I spun my hub. I shut off immediately. I start 2 times after for just one second to see if it went away it didn’t. . Something is def wrong. Supposed to have a new lower unit when I bought 2 yrs ago. Spun prop and it didnt click or grind.

Whats next to check. It sound like something is broken and slapping around inside power head.

**FORBESAUTO** · 10-17-2017, 07:09 PM

Pull spark plugs and check for abnormal grey or metal on plugs. If find one that looks bad, pull that head. If all look ok run a compression check. If all good pull lower to make sure noise not coming from it. Sounds like piston was trying to stick.

**tux974** · 10-18-2017, 04:57 AM

Any type of knocking is never a good thing either from LU or power head!
Do as suggested above for a quick inspection and do not start it till you can locate the source of knocking noise.

**Jmham7** · 10-18-2017, 07:04 PM

So there’s a hole in bottom left pot side piston. Now what? What would cause this?

**FORBESAUTO** · 10-18-2017, 09:18 PM

Was afraid of that. Time for a rebuild. More than likely detonation, need to get injectors checked, and go over everything with a fine toothed comb, or it could have just been it's time. Take a picture if you could, that could help in trying to determine what happened.

**Varmint** · 10-19-2017, 08:44 AM

Actually a new wsm rebuild kit for that motor is $1200 w/6 slugs. Cheaper than a 225 2.5 pmax. I would do as suggested above and find a good machine shop to inspect crank and weld the block. Or do like i did, bought a 97 mariner 225 efi 25" for $500 with a good rebuildable PH. I would suggest replacing the crap factory reeds and adding a 4 hole front when you rebuild it,in case you didnt know that.