Broken off Spark Plug into cylinder head

[Fish for Dinner]

Just an update: The problem was my spark plugs. The boat was misfiring by skipping, loosing power and wouldn't accelerate past 30mph , so I changed all but one of my spark plugs because unfortunately it broke off into the head. I attempted to remove it with an easy out and my easy out ended up breaking off into the same area as well. Im convinced that one plug was either torqued too much from the manufacturer or it was cross threaded when they put it in or when the plug went bad, it rusted into the the spark plug thread and wasn't coming out no matter what. So now I'm forced to remove the head, and possibly rethread it after removing the spark plug. I have the service manual and my neighber is a mechanic and will be helping me through this. I'll give updates after I start.

 

[lazergeek]

Just an update: The problem was my spark plugs. The boat was misfiring by skipping, loosing power and wouldn't accelerate past 30mph , so I changed all but one of my spark plugs because unfortunately it broke off into the head. I attempted to remove it with an easy out and my easy out ended up breaking off into the same area as well. Im convinced that one plug was either torqued too much from the manufacturer or it was cross threaded when they put it in or when the plug went bad, it rusted into the the spark plug thread and wasn't coming out no matter what. So now I'm forced to remove the head, and possibly rethread it after removing the spark plug. I have the service manual and my neighber is a mechanic and will be helping me through this. I'll give updates after I start.

Starboard Motor #1 Cylender by any chance?
The same thing happened to me $1200 buck for the dealer to remove, they claimed they had to remove the head. YES wont cover as spark plugs are a maintenance item. @FSH 210 Sport had told me rumar was Yamaha had a bunch of engines with cross threaded spark plugs in the #1 cylender.

 

[TeenGee]

Bummer.

 

[Cobra Jet Steering LLC]

Bad situation one of the things I have always done to these engines is never seize the plugs and dielectric grease in the plug boots If you ever encounter a plug that refuses to loosen don't force it put some wd 40 or similar penetrating oil in the plug recess and work the plug in and then out a tiny bit at a time usually that will let you remove it slowly but way better than snaping it off in the head, now you need the head removed

 

[drewkaree]

Since your mechanic friend is going to help you out, have him help pull the pump and remove all the 30lb braided line that's still on your impeller.

Since you have a spark plug broken off, I'm wondering how you've been able to accurately determine that the spark plugs are the root of your slipping and lack of acceleration. You also failed to mention previously that it was misfiring.

Good luck, it sounds like there's a lot at play here, not the least of which is troubleshooting and/or tracking down root issues. With so much going on, and the hodgepodge drip of info, I wonder if a bridge is involved somewhere in this saga

 

[Fish for Dinner]

Starboard Motor #1 Cylender by any chance?
The same thing happened to me $1200 buck for the dealer to remove, they claimed they had to remove the head. YES wont cover as spark plugs are a maintenance item. @FSH 210 Sport had told me rumar was Yamaha had a bunch of engines with cross threaded spark plugs in the #1 cylender.

Yes it was cylinder #1. I do believe it was cross threaded. There’s no way it should have been as torqued as it was. The others came out effortlessly.

 

[Cambo]

There has been some debate on anti seize on the thread plugs. NGK says it’s not needed I completely disagree they are putting general info out for regular motors. What makes these engines different is the water cooling, water sits in the exhaust manifold and the water box/ muffler. Have you ever started your motors before heading out for the day and a puddle of water gets pushed out? That moisture makes its way back into the exhaust chambers causing rust on the exposed threads this helps the plug seize. The anti seize prevents this especially the copper hi temp. I went to look at yamaha boat for my brother that sat for years knowing the plugs could be seized that was one of the things checked. All the plugs were very hard to remove and #3 would not come out. I put a lot of leverage and warned the owner it could snap. He offered an impact gun to me it seemed like a great idea as you push with a regular ratchet wrench and extension it puts sideways torsion that I feel helps to snap the plug and easy outs. This impact wrench was the most powerful ryobi that has three different settings and the top puts out some serious torqure about 300lbs. Setting one and two wouldn’t break it free setting three got it turning once it was slowly turning I went back to the hand ratchet and socket and i still could not get it to turn, back to the impact and it slowly backed out.

 

[TeenGee]

I agree with @combo on using anti-seize on spark plugs.
I over torqued a spark plug to the point where the threads sheared from the remainder of the plug leaving the threads in the head. I FREAKED OUT. Fortunately, I had applied anti-seize. the threads came out easily with the help of an easy-out.
I always assemble all bolted joints with anti-seize.

 

[Cambo]

Just to show you how susceptible to corrosion the combustion chamber is, this boat was at copart and was about 1 year old it sunk and then must have been taken apart

the rust was thick, built up in the cylinders and had more rust than any other part by about 200%

 

[FSH 210 Sport]

Starboard Motor #1 Cylender by any chance?
The same thing happened to me $1200 buck for the dealer to remove, they claimed they had to remove the head. YES wont cover as spark plugs are a maintenance item. @FSH 210 Sport had told me rumar was Yamaha had a bunch of engines with cross threaded spark plugs in the #1 cylender.

I was told that bit about the cross threaded #1 cylinder plug by an engine salvaging place. I’m also somewhat confident there is a stainless steel insert in the head where the plug goes.

I run the old school copper based anti seize on the spark plugs, I apply a light coat and use my finger across the threads as I turn the plug to get it into the bottom of the threads then use a paper shop towel to remove the excess so it it doesn’t pile up in the spark plug well. I use a torque wrench and set it per the service manual to tighten the plugs.

When I work on the jet pumps all of those bolts get Loctite 572 low strength thread sealant which is what the service manual specs out. I apply it the same way as the anti seize on the plugs. Its a bit of a pita when R&R’ing the pumps as I clean it all off with taps and dies, but(!) everything comes apart easily with no corrosion on any of the fasteners.

If it was me I’d be taking it to the dealer, Vallely Sport and Marine in Bismarck North Dakota, and have them do the work, $1200 while nothing to sneeze at would be well worth it to have them take care of that.

 

[Murf'n'surf]

Been there.....done that. It sucks but it's repairable.

https://jetboaters.net/threads/well-sh-t-spark-plug-fail.27911/post-459356

 

[adrianp89]

Anti-sieze will cause you break it as welll…. Ask me how I know. Easy out worked for me though

 

[FSH 210 Sport]

Anti-sieze will cause you break it as welll…. Ask me how I know. Easy out worked for me though

Okay how do you know?

 

[adrianp89]

Okay how do you know?

Previous owner used it on old plugs. I put in new plugs without any seize, put torque wrench to spec, snapped it before even close to clicking.

 

[TeenGee]

The plugs I use have a crush washer. The installation is finger tight plus 1/2 turn. No torque wrench needed. When I broke mine, it was after several reinstallations had fully crushed the washer. The additional 1/2 turn broke the plug.

 

[anmut]

The plugs I use have a crush washer. The installation is finger tight plus 1/2 turn. No torque wrench needed. When I broke mine, it was after several reinstallations had fully crushed the washer. The additional 1/2 turn broke the plug.

Yes, my NGK's have that as well and I use the same procedure: hand tight them in with the socket extension only, then 1/2 turn with the socket

 

[Fish for Dinner]

Why are people using torque wrenches on spark plugs?? They are suppose to barely be hand tightened. This is one of the reasons why they break when changing them.

 

[adrianp89]

Why are people using torque wrenches on spark plugs?? They are suppose to barely be hand tightened. This is one of the reasons why they break when changing them.

Because there is a spec on them… They don’t break at spec if you don’t lube it up. Some of us prefer our boats as intended and not driving around for a year with fishing line on the impeller.

 

[Ronnie]

Why are people using torque wrenches on spark plugs?? They are suppose to barely be hand tightened. This is one of the reasons why they break when changing them.

I just do what the illustrated instructions state on every single spark plug box.

that is: gap to spec. If necessary, insert by hand, the crush washer will compress up to 1/16”, tighten with a socket wrench another 1/4th to 2/3rds turn, don’t use on flying vehicles.



Wow you have a lot going on with this engine.

Here is my two cents based on experiences with Yamaha’s 1.8L motors.

REMEMBER, this is free advice so use it or discard it at your own risk.

1. if you can remove the head yourself you can pull what’s left of the plug out by yourself.

2. if you are going to DYI this buy all of the seals as well.

3. also install new spark plugs for the remaining three cylinders as well

4. I recommend putting anti seize on the plug threads and dielectric grease in the ignition coils.

5. once the engine is up and running, if the rpm’s are lower than the other engine conduct a compression check on all cylinders of the repaired engine to see how much damage the broken parts of the plug did leaving the cylinder.

evaluate your options (leave it be as is or take it to a shop for a top end rebuild).

 

[Fish for Dinner]

Because there is a spec on them… They don’t break at spec if you don’t lube it up. Some of us prefer our boats as intended and not driving around for a year with fishing line on the impeller.