wrong plugs, piston hit plug, am I hosed?

[jpbohney]

I have a 1986 Johnson V490hp and my mechanic installed QL78YC stating it would run better. It ran great several times till a recent trip when I lost power. Inspection revealed a single cylinder with a plug gap fully closed past the electrode and some small metallic debris wedged next to the electrode. The piston appeared to have a single small nick where I assume it hit the plug. A plug look up reveals spec with QL77jc4 or QL82C. I assume the QL78yc is too long, but why did failure occur only after several outings? Is the piston traveling too far for another (bad) reason? I installed L82C which I had available and the motor runs (much more smoothly than with the mangled plug), but I have not water tested it. Thank you.

 

[clint]

Wrong plugs, piston hit plug, am I hosed?

Wrong plugs, piston hit plug, am I hosed?

Ouch! I would not run motor until you remove heads and make sure there isnt any metal bouncing around in the cylinders. That would be first priority. The smallest piece of the plug could ruin your cylinder or lodge on the side of a piston and score the heck out of it.
Clint :$

 

[ob]

Re: wrong plugs, piston hit plug, am I hosed?

Well the YC plug is definately a protruded nose plug.This issue has come up before.Hopefully no damage has occured beyond a nick in the piston crown.A compression test would be a good idea.Otherwise ,always use the specified plug.Your mechanic should have known better.I'd find another one in the future.

 

[itstippy]

Re: wrong plugs, piston hit plug, am I hosed?

If the problem is solely the protruded nose plug then why did the motor run fine for several trips before the piston made impact with the electrode? You'd think it would happen the first time he fired it up.

 

[seahorse5]

Re: wrong plugs, piston hit plug, am I hosed?

Since it was only 1 piston that hit and not all 4 on a 20 year old motor, I would guess that the piston and pin are worn enough to add some "slop" to each stroke.

Check for rod and piston pin wear by pushing on the top of the piston after turning the piston past top dead center. Any slop or free play is usually wrist pin hole wear.

 

[jpbohney]

Re: wrong plugs, piston hit plug, am I hosed?

Incredibly I just ran into my former mechanic. He reports that I likely have a bad rod bearing and need a $3000 rebuild. He advises against running the motor. If the problem is piston slop, can I run the motor (with the correct plugs of course)? What might be the remaining life on the engine? Any feasible shortcuts? Thank you.

 

[Dhadley]

Re: wrong plugs, piston hit plug, am I hosed?

Don't panic but go back and read Seahorse's post. The extended reach plugs will hit at higher rpm's but not at idle. Trust me.

The heads need to come off for a close inspection anyway so it's not a big deal. Most likely all we'll need is a couple of gaskets and 4 water deflectors.

 

[Scaaty]

Re: wrong plugs, piston hit plug, am I hosed?

"1986 Johnson V490hp" ....and "ran into my former mechanic. He reports that I likely have a bad rod bearing and need a $3000 rebuild.".

Just what planet is he from....$3000 will get ya a decent 80's 20 footer with 125 hp. ready to go in this part on the world

I'd pop the head off, quick look, new gasket, stick new plugs in and go for a ride

 

[MASTER Brian]

Re: wrong plugs, piston hit plug, am I hosed?

If it is just worn some piston slop caused by wearing bearings and you know how to rebuild a motor, you could probably get by replacing the worn bearings, gaskets, a hone and a new set of rings for several hunded $$.

Heck, I may even have a gasket kit for a V4 evinrude I'd let go for cheap. They sent me the wrong kit, when I ordered my V6 kit and have never shipped me a way to return it. Problem is I don't know what it fits exactly, but I'm sure someone could figure it out.

 

[itstippy]

Re: wrong plugs, piston hit plug, am I hosed?

Since it was only 1 piston that hit and not all 4 on a 20 year old motor, I would guess that the piston and pin are worn enough to add some "slop" to each stroke.

Check for rod and piston pin wear by pushing on the top of the piston after turning the piston past top dead center. Any slop or free play is usually wrist pin hole wear.

Seahorse, I have heard of this test before but never seen it done. I'm intriqued. Would this be a useful test when evaluating an older outboard with unknown service history? Is there a way to measure the amount of play and determine whether it is "within spec" for that model? Or is any play at all a bad sign? Thanks!

 

[jpbohney]

Re: wrong plugs, piston hit plug, am I hosed?

I have a 1986 Johnson V490hp and my mechanic installed QL78YC stating it would run better. It ran great several times till a recent trip when I lost power. Inspection revealed a single cylinder with a plug gap fully closed past the electrode and some small metallic debris wedged next to the electrode. The piston appeared to have a single small nick where I assume it hit the plug. A plug look up reveals spec with QL77jc4 or QL82C. I assume the QL78yc is too long, but why did failure occur only after several outings? Is the piston traveling too far for another (bad) reason? I installed L82C which I had available and the motor runs (much more smoothly than with the mangled plug), but I have not water tested it. Thank you.

So I pulled the head and found that the whole pisto edge and the head have been moth-eaten. The head and piston have been ripped up although there is not loose metal in the cylinder and the cylinder seems smooth. There is a tiny dink at the lip of one of the ports. What could do this? Where can I get a new head?

 

[seahorse5]

Re: wrong plugs, piston hit plug, am I hosed?

Seahorse, I have heard of this test before but never seen it done. I'm intriqued. Would this be a useful test when evaluating an older outboard with unknown service history? Is there a way to measure the amount of play and determine whether it is "within spec" for that model? Or is any play at all a bad sign? Thanks!

Any well trained and experienced mechanic knows this test, especially when checking out older motors. There should be no slop at all when pushing on top of a piston after it has gone past top dead center. Most of the time any play is from an elongated wrist pin hole, commonly from detonation and overpropping. It is very very rare that the crank and rod bearing is bad and sloppy.

 

[Joe Reeves]

Re: wrong plugs, piston hit plug, am I hosed?

The 1986 90hp Evinrude/Johnson calls for Champion QL77JC4 spark plugs, gapped at .040 .

The 77 is the heat range. The plugs your mechanic recommended (78's) are too hot a plug and could (and usually does) result in piston damage due to pre-ignition. The aluminum melting/flaking off the piston is what smashed into the spark plug. Whether your engine's piston was failing before the 78's were installed or not can only be answered by yourself...... was the engine running ragged before your mechanic installed them and this was the reason it was being worked on at that time?

Bottom line.... The engine requires a major overhaul, usually amounting to approximately $400/$500 in parts and machine work plus labor.

 

[MASTER Brian]

Re: wrong plugs, piston hit plug, am I hosed?

I obviously haven't seen your head, but from what you described it sounds like you have pitting on the head. Take it to a machine shop and see what they say. Normally, it is ok, to just take the high spots out. You can have the pits/dips in the head, but not the pieces that protrude.