I fear the worst (see pics!)

[misterguru]

My "new" 1986 60HP Mercury seemed great for this last week... it fell off on power a couple of times, but throttling down and easing back up seemed to fix it.

Today it was missing, then ok again until I was about 6 miles down river.

Then it missed a lot. We could only get 7mph in my little bass boat (16' Skeeter) and it normally runs 40mph.

Well... here are the pics: I am sure I need to check compression to be certain, but what does this tell you experts?

 

[achris]

Re: I fear the worst (see pics!)

Dearly beloved, we are gathered here today..... You know the rest.

That stuff on the end of the plug is aluminium. It should be still on the piston crown. The fact that it has come off, in a process called 'detonation', usually points a to a few 'usual suspects'. The most common is the prop being too big for the engine/boat combination. What RPM were you getting at Maximum throttle? Other possibles cause are bad fuel, or over advanced ignition timing.

Once the engine is stripped and that piston replaced and what ever work needs to be done to the cylinder bores is done, you REALLY need to find the cause of the problem. If you don't, I will guarantee it will happen again.

Good luck,

Chris............

 

[misterguru]

Re: I fear the worst (see pics!)

Ouch! OK... well the boat does not have a tach. It is a 14P prop and it runs 40MPH... about right for a 16' Skeeter w/60 HP right?

Well here is the compression check:

#1 120 lbs
#2 125 lbs
#3 125 lbs

120lbs with a hole in the piston? Wow... maybe it's a small hole. haha

I know you know, but I have to ask... from that pic you are sure it's a piston?

Avg ballpark repair bill? ...is this a $500 thing or a $3000 thing?

 

[achris]

Re: I fear the worst (see pics!)

It's not a hole in the piston, it's metal that has shed from the piston crown. If no damage to the cylinder walls and all that's needed is a new piston, then about 10 hours strip and re-build, a piston and gasket set... Oh, and a tach. Given that the compression readings aren't too bad you may be lucky, very lucky. If the cylinder needs a bore, then that's going to add quite a bit of labour, maybe another 5 hours.

I haven't run the numbers on the 14 prop, 40 mph ect... Will let you know when I do....

Chris............

 

[misterguru]

Re: I fear the worst (see pics!)

Thanks achris... 40mph on GPS is tops... 38 is typical at WOT.

 

[AMD Rules]

Re: I fear the worst (see pics!)

That's #1 piston .... I suspect it might be in better shape that mine was, but could be headed for disaster. Probable causes could be poor cooling and/or ignition timing. Time for a close inspection.

Here's a story you might want to read.... a similar experience I went through back in 2005: 1988 60hp cyl uh-oh

Hope that helps.