Snapped off spark plug - PWC Forum: The best hang-out for Personal WaterCraft enthusiasts
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post #1 of 13 (permalink) Old 07-24-2012, 07:32 AM Thread Starter
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Snapped off spark plug

I am doing an engine tear down and rebuild on my Yamaha FX140. My problem is a broken spark plug. The plug snapped off during a plug change out. Speculation to the cause of the breakage: rust, incorrect installation torque, non use of never seize, ignorance, brute force.

I am learning quite a few things along the way. Was wondering if anyone has had this wonderful experience?
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post #2 of 13 (permalink) Old 07-24-2012, 07:45 AM
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I have not had the experience, but the plugs should be tightened to no more than 9 ft lbs. They are very fragile in this model.

Without a torque wrench, the owners manual recommends hand tight plus 1/4 - 1/2 turn.
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post #3 of 13 (permalink) Old 07-24-2012, 07:27 PM Thread Starter
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oh i am a big fan of using the proper torque specification. i have written torques specs for product i have designed and i have no mercy for those that ignore specifications.

the interesting thing with this tear down is i have found a way to remove the snapped off spark plug without having to remove the head.

another interesting thing i found is the design of the fuel hose attachment on the top of the fuel tank. it is a super simple design, effective, and a cinch to remove and re-install. love finding the often unappreciated genius of others
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post #4 of 13 (permalink) Old 07-24-2012, 07:38 PM
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Well please share on how to remove the plug. Easy out? Left handed drill bit? What is your trick?
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post #5 of 13 (permalink) Old 07-28-2012, 09:24 AM Thread Starter
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Removing broken spark plug and fuel from FX140

i am still struggling with removing the plug. My eventuality is removing the engine and head. (which is what the local professional jet ski mechanics advise)

But for now, i am attacking the left over ceramic and electrode that remain in the center of the broken off plug. I noted a posting online that claims you can use the combustion chamber pressure to "pop" the ceramic and electrode out of the engine. I have studied the sectional drawings online of the spark plug design. The claim makes sense because friction appears to be the only thing holding them in place.

I tried it. I used the battery to spin the crank for 10 revolutions. The ceramic and electrode have not come out yet, but i believe the process has merit.

Next, I will be using the proper size (and material) drill bit to remove half of the ceramic and electrode and hopefully break the frictional bond.

My plan is to use the combustion pressure to blow out the last bit of ceramic and electrode. I will then use a common extractor to remove the remainder of the plug. (the threaded metal)

Something worth noting in my opinion: During this process I found that removing the fuel by way of the top of the fuel tank, using a hand pump, is a very easy way to remove practically ALL of the fuel from the fuel tank.

On the top of the fuel pump is the fuel line connection (top left). The black plastic box is a snap on piece. Underneath is a "flexible" plastic tab, which when flexed, allows the fuel line to be easily slipped off.

Disconnecting the wiring harnesses will prevent the fuel pump from operating when you spin the crank.

i found this helpful photo on the internet

Last edited by Lee Taylor; 07-28-2012 at 09:27 AM.
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post #6 of 13 (permalink) Old 07-29-2012, 10:09 AM
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the ceramic insulator must be dislodged from the steel body before an extractor can be used, a drill bit will not cut ceramic, if you first dislodge the ceramic you can then use the engines compression to blow it out, if any part of the ceramic gets into the combustion chamber and traps between the cyl and piston it will like cause severe damage, engine will have to come out then.
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post #7 of 13 (permalink) Old 07-29-2012, 10:17 AM
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Quote:
Originally Posted by Lee Taylor View Post
the interesting thing with this tear down is i have found a way to remove the snapped off spark plug without having to remove the head.
I must have misunderstood this part as I thought he found a new trick.
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post #8 of 13 (permalink) Old 07-29-2012, 05:58 PM Thread Starter
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the trick i read about was to use the battery to spin the crank and in turn use the combustion chamber pressure to "pop" the ceramic and electrode out of the head.

Well, my ceramic proved much too tight of a fit for this. I spun the crank 20 times and the ceramic and electrode remained in the engine.

So, I started cutting away at the ceramic with a diamond tipped hole cutter i found at Lowes. It just happens to be the right dimensions ID and OD wise. The image says 3/16" but the one you want is the 1/4" OD. (note: I had to cut off the thick part)



I coupled the bit with an Irwin Auger Bit Extension I found at Northern Tools.



So I have been grinding away at the ceramic with the above tools mounted in a variable speed drill motor. Every now and then I stop and use compressed air to blow the residue out of the well and check the progress with a very bright flashlight

I am currently about half way through the ceramic and I noticed the electrode had moved outwards about 1/16". I checked the location of the pistons and noted that the one I am working on is at half stroke. Apparently it is on the compression stroke because during the next cycle of cutting away at the ceramic the electrode pushed up into the center of the diamond tipped tool. I was very happy to feast my eyes on its entire length

The electrode was the first obstacle. The ceramic is the second, and the broken spark threads are the last.
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post #9 of 13 (permalink) Old 07-30-2012, 07:27 AM Thread Starter
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I found this bit of genius in a car forum:

I once dropped a small screw into an intake port while the intake manifold was off the head. Of course the valve was fully open and the screw fell into the cylinder. I removed the sparkplug, and placed a long screwdriver down the sparkplug hole. Slowly I cranked the engine over by hand with a socket wrench on the crankshaft end. Once the screwdriver started to raise, signaling the piston was close to TDC. I stopped turning the engine over before the piston reached TDC. I didn't want to squash the screw with the piston, and I needed to have the intake valve open 100%. I removed the screwdriver from the spark plug hole. Got a shop vac and emptied the dust bucket so I could easily retrieve the screw. I placed the shop vac hose on the intake port, and could hear and see the screw swirling around in the piston by looking down the spark plug hole with a flashlight. After a few seconds, it was sucked up through the intake port. That saved me from having to remove the timing chains and head.
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post #10 of 13 (permalink) Old 07-30-2012, 03:43 PM
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This happened to me once on my boat engine. I was lucky enough to get the ceramic to break off clean. The electrode and the remaining ceramic came right out and all that was left was the threaded part of the plug. I went to the auto parts store and bought brand new easy out set. Chose the appropiate one and tapped in in with a hammer and put the wrench on it and it came right out. It was rusted in there prettyy good, definately not and easy task. I almost had to tear off the whole top end...

Good luck!
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