Join Date: Aug 2016
Location: Orlando, FL
Year/Make/Model: 2009 Kawasaki Vulcan 900 & 2014 Kawasaki Ninja 300 ABS
Color: Orange (Vulcan) & Black (Ninja 300)
Repeatedly Breaking Spark Plugs - Why?
You may have seen my recent thread regarding a bad fuel pump in my 2009 Vulcan 900 Custom. I got the fuel pump replaced, and the bike was running well. I just rode it in city traffic for about 25-30 miles two days ago, and had zero problems.
When I first bought the bike, I replaced the spark plugs in both cylinders. During my troubleshooting of the fuel pump however, I undid the replacement and put the (presumably) original plugs back in. Those are the plugs that were in the bike when it was most recently ridden, with no problems.
Today I decided that since the plugs still needed to be replaced, I would go ahead and do that. I got the front cylinder (not sure if it's #1 or #2) just fine, but when I did the rear cylinder the spark plug broke. What I mean specifically is that the threaded part of the plug broke off of the rest of the plug, so that the wrench was just spinning the top part of the plug in the hole, but the threaded part (including the tip of the plug) was no longer connected.
After some swearing and a lot of struggling, I managed to get the threaded part out of the hole (with the tip of the plug intact). I took a tiny stick magnet down into the hole to get any tiny metal bits that might have come off when it broke.
I didn't use an extreme amount of force, but figured maybe I overdid it or maybe it was a faulty plug, so I went back to the store and got another. They were out of the exact plugs I'd bought the first time, so I bought another brand that is identical spec. So I know it wasn't just a bad batch of plugs from the same shipment or something.
I got back home, and went to install the new plug. This time I didn't use a wrench, and just finger tightened it (using a spark plug socket and an extension, but no ratchet). As soon as I felt resistance, I got my torque wrench out and set it to 13 ft-lbs (per the service manual). I started tightening the plug, but didn't even get to 13 ft-lbs before I felt it start spinning in place again (just like before). Sure enough I pull out the brand new plug and the exact same thing has happened to it. This time I know I didn't use excessive force. I've replaced spark plugs before in other vehicles so I have at least a little experience and know not to use too much force or you run the risk of stripping the threads in the block.
I'm at a loss. Does anyone know what might cause this to happen twice in a row? Could it be something about the threads? If they were stripped, I would expect the plug to stay in one piece but spin loosely (or be impossible to tighten down). However since two totally different plugs both broke in the same fashion, that points to either the bike, or me.
EDIT: Okay, I was able to resolve this. The problem was between the seat and the handlebars (user error!)... In the service manual under the spark plug replacement procedures it specifically states, "The insulator of the spark plug may break if the wrench is inclined during tightening." My ratchet extension is just long enough to put the ratchet right next to the frame, which makes it impossible to keep straight when the ratchet (or torque wrench) is attached. Using a longer extension I was able to get a plug in there night and tight, without breaking.
2009 Kawasaki Vulcan 900 Custom
Last edited by kileg911; 01-02-2017 at 05:05 PM.