73 johnson 115.. piston hits spark plug.

[naturallysmashed]

Hello I'm 21 and just bought my first boat for 400 bucks with my buddy. It's a 19' fiberform with a 73 johnson 115. We did all the basic tune-up things and got it running mint. What was done to this engine by the previous owner is a story for another day.

The engine ran and sounded great in the driveway, everything seemed to work properly so we took it out!

While idling up and down the river it seemed fine.. maybe a little burst of exhaust here and there.. I didn't really think much of it. So I decide alright, lets take it into the bay. It got up on plain but quickly started misfiring. Not enough of a misfire to take it off plane but it was noticeable. So I shut it off, switched gas tanks, checked out a few things.. no change. I took the boat right back in.

When I got it home I decided, okay lets pull the plugs. The first plug I pulled out was messed up. The ground electrode was bent all the way into the middle electrode. So basically there was no gap left.

Since I refused to believe there was something wrong with the engine I worked so hard on, I re-gapped it, ran it in the yard. Ran great plug looked great.

I took it out again, but the waves were way too rough. I took it out and took it right back in because my bilge wasn't working properly and we were taking on way too much water. But for that short time it ran great, felt as if all the power was there.

When back at the house I decided to inspect the plug again. The gap wasn't completely gone but the electrode was hit again. Now I know I can't just take it out before something really serious happens to the engine.

I'm thinking its a worn bearing, but I don't know much at all considering this is my first boat. It's pretty disappointing to work on something for so long, spend every cent you have on it... then this happens. But I still want to fix it, I need to.

If anyone has a better idea what happened to it or what I need to check or anything I can do.. your insight would be appreciated.

[SparkieBoat]

first off you need to find out exactly what plugs go into your motor, could be that you are using the wrong plugs..post the plug #s maybe someone will know which ones to use on that motor..or you can look it up or call a dealer with your model # and they can tell you. If you have the correct plugs the you either have piston slop or the heads have been shaved a couple of times..in either case you can add a compression ring or 2 to the plug to back it up a bit or try to find a shorter plug or one that has no electrode protruding ( some auto plugs are like this ) I am curious how this type of plug would work on a boat motor anyway..I may try a set that I have laying around just for fun.

[R.Johnson]

What plug's are in the engine, and are they all the same make, and model?

[naturallysmashed]

Thank you, I'm almost positive they're the right plugs but you're right.. I could have got the wrong ones.. I'll pull one in a little bit and post the number on it.

Also, I did take a washer ring off another plug and put it on.. but before I ran it I took it off because I wasn't sure if I was doing the right thing. That would save me a ton of trouble if that's all it is. But I'd think the other piston on the same side would also be hitting, none of the other plugs are being touched. Just the one cylinder is getting that.

[SparkieBoat]

sounds like piston slop then..Put on an extra ring and keep your RPMs to a minimum..I would stay under 4500..it may last you a while..unless you now how to do a piston rod repair..or have a friend that does..run it till she blows then find a good used motor.

[crxess]

You bought new plugs?
They were in separate boxes?
Pull the bad one and a good one and compare numbers/electrode length.

If it was a bearing and allowed that much movement, you would hear the Knocking and then the explosion.

SPARK PLUG, Champion ul-77v
ALTERNATE SPARK PLUGS FOR SPECIAL APPLICATIONS; 386143-AC-M4OFF; 386144 CHAMPION - L2G; 386145 CHAMPION - L77J

[gazza2007au]

have u stopped and thought about looking at the old plugs to see if any of them have touched the piston? also measuring the old spark plugs with the new ones would be ideal and the washers are on the spark plgs for a reason u should no remove them as the thread length has been takin into account to suit your engine!

[naturallysmashed]

sounds like piston slop then..Put on an extra ring and keep your RPMs to a minimum..I would stay under 4500..it may last you a while..unless you now how to do a piston rod repair..or have a friend that does..run it till she blows then find a good used motor.

I might try the extra ring for now because fishing is just about here.. I could probably do the rod repair between working on car engines, the johnson manual, and my dad could help.. seem's like he's rebuilding one of his every few years.

[naturallysmashed]

You bought new plugs?
They were in separate boxes?
Pull the bad one and a good one and compare numbers/electrode length.

If it was a bearing and allowed that much movement, you would hear the Knocking and then the explosion.

SPARK PLUG, Champion ul-77v
ALTERNATE SPARK PLUGS FOR SPECIAL APPLICATIONS; 386143-AC-M4OFF; 386144 CHAMPION - L2G; 386145 CHAMPION - L77J

yeah I thought a bad bearing would mean knocking, but my friend kept saying it so I felt like I had to mention it. The plugs I'm using now are NGK BR9HS 10.. the guy at west marine gave me those.

[naturallysmashed]

have u stopped and thought about looking at the old plugs to see if any of them have touched the piston? also measuring the old spark plugs with the new ones would be ideal and the washers are on the spark plgs for a reason u should no remove them as the thread length has been takin into account to suit your engine!

before I threw the old plugs out I inspected them, they all looked fine.. which was weird. I believe the guy before me had no clue what he was doing and it didn't get to high enough rpm's to mess up the plugs because he had the wires on the wrong cylinders so the firing order was messed up.. took me a little while to figure out he screwed that one up, thanks to the book! The thread length was taken into account when the engine was new.. but the heads could have been redone so they might be thinner.. also who knows if the plug was over tightened a few times and stripped into the head deeper. It's hard to tell just by looking. Do these things ever happen?

[gazza2007au]

the washers on the spark plug stop it from going past a certain point

[naturallysmashed]

yeah i guess it would be impossible to twist it in that far. i'm leaning towards needing a new rod

[Shizzy]

so it sounds like you tossed out the old plugs already?

[gazza2007au]

if its hitting the spark plug it will more than likely be the big end or little end bearing not the rod its self if its the big end bearings u will also need the crankshaft repaired as the bearings scratch the crankshaft journals but lets start with the basic things try the correct spark plugs and go from there

[Shizzy]

agreed. is it possible to get your hands on one of the correct Champion plugs and compare to the ones yo uare trying to run?

[crb478]

yeah I thought a bad bearing would mean knocking, but my friend kept saying it so I felt like I had to mention it. The plugs I'm using now are NGK BR9HS 10.. the guy at west marine gave me those.

First get the Champion plugs in there. Then pull the plugs out and press something against the top of the piston as you turn the flywheel back and forth and try to see if you can feel any play or looseness in the piston. Also look inside to see if there is any excess carbon build up. It would not hurt to do a decarb to the motor just to clean things up. This could be as simple as a plug that is silghtly too long, or carbon build up that is hitting the plug, or it could be a rod bearing that is wearing out. Start with the cheap and easy fixes first, you may get lucky.

[ezeke]

Bottom line is that you will probably not have the problem with the Champion Surface Gap Plug UL77V.

[crxess]

I think, if the plugs are proper length, I'd pull the head and do a visual inspection.
Could be a piece of reed valve or other debris in there or other damage.
Head gasket is relatively cheap and not that hard a job. Well worth possibly saving a motor.

Gap type plug for that motor:
Champion QL77J4
Champion QL77JC4
Gap .030

[gazza2007au]

again we are diving in to deep let this guy change the plugs first

[Daviet]

You might try doing a search on this topic. I seem to remember someone having to double ring a spark plug and running it for quite a while with no problems, every thing checked OK on their engine if I remember correctly. Just a thought.

[Faztbullet]

That engine uses perma gap plugs which are flat,

[Willyclay]

Here's a link to the spark plug specs:

http://www.boatsetup.com/SparkPlugChart.pdf

[ezeke]

Here's a link to the spark plug specs:

http://www.boatsetup.com/SparkPlugChart.pdf

That link (chart) is out of date; this one updated to March 2009 is more recent: http://continuouswave.com/whaler/ref...gChart2008.pdf

Boatsetup does have one updated to 2007: http://boatsetup.com/Spark%20Plug%20...2007%20BRP.pdf

[Willyclay]

Thanks for that info but I don't see his 1973 Model 115 listed.

[crxess]

That engine uses perma gap plugs which are flat,

Surface plugs tend to run cold and foul to much. That is why a newer Gap adjustable plug is listed.