Chris Guenther
Just got it firing!
Looks like I cross threaded one of my spark plugs... What should I do now? I think it's just at the start, but I can turn the plug in with my fingers about two turns before it gets stuck.
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Cross Threaded spark plug
- Thread starter Chris Guenther
- Start date
Vagrant
GT Reference
If it goes in normally for 2 turns then starts to stick I doubt it's stripped. New plug or reusing an old one?
I'd make a super sized Q tip from a strip of old cotton sock or similar. then soak it in a lube like WD40 and carefully clean out the hole. next try a different plug using your fingers only. in hard to get at holes I use a short piece of fuel line shoved onto the plug to screw them in. That way the hose will slip on the plug before you strip things. worse case you might need to put in a heli-coil but you might also get by with a tap run through it.
I'd make a super sized Q tip from a strip of old cotton sock or similar. then soak it in a lube like WD40 and carefully clean out the hole. next try a different plug using your fingers only. in hard to get at holes I use a short piece of fuel line shoved onto the plug to screw them in. That way the hose will slip on the plug before you strip things. worse case you might need to put in a heli-coil but you might also get by with a tap run through it.
Chris Guenther
Just got it firing!
Thanks for the reply. I was just done adjusting the valves and was putting the plug back in. I tried the plug from the other side and it gets stuck at the same place. I tried your trick to clean the threads, and pulled out some fine metal filings, but still can't get the plug in. I'm going to try and find a back tap, if not, I'll pull the head off to be safe. Can I reuse the head gasket? It's a V7 III with about 1200km on it.
If you need to re-do the spark plug threads, the head must be removed to eliminate filing going into the cylinder. Helicoils aren't a good way to go for spark plugs. There are inserts that are installed from the inside that are best for this application. Any good automotive machine shop should be able to handle the task. BTW, head gaskets are not re-useable.
Chris Guenther
Just got it firing!
Thanks for the reply. My understanding is that a back tap works from the inside out so you don't get filings into the cylinder.
Good luck with that. I prefer not to take any chances.
kiwi dave
GT Reference
I'm gonna get criticized for this, but I wonder just how much harm will occur if there's a couple of fine filings sitting on the top of the piston momentarily. Not going to stay there long.
You'd be surprised at how much noise a piece of threads the size of a small fingernail clipping can make.
Worked at a Toyota dealer where this happened. Sounded like someone threw a handful of nuts and bolts into the cylinder.
It never blew out the exhaust and just rattled around in the cylinder. Eventually had to pull the head to find it.
Worked at a Toyota dealer where this happened. Sounded like someone threw a handful of nuts and bolts into the cylinder.
It never blew out the exhaust and just rattled around in the cylinder. Eventually had to pull the head to find it.
kiwi dave
GT Reference
I would have thought it would be incinerated almost almost immediately. Same for those who manage to drop a pencil or chopstick into the combustion chamber when chasing T.D.C., and have to whip the head off to retrieve it.
We are talking about the same environment where pistons can melt if the mixture gets too lean?
I learn something every day. Thanks for the enlightenment.
We are talking about the same environment where pistons can melt if the mixture gets too lean?
I learn something every day. Thanks for the enlightenment.
Chris Guenther
Just got it firing!
It ended up being some fine metal shavings stuck in the threads. Used a tap with grease on the end. Working it in and out a few times, cleaning and re-greasing the tap. Only had to go about half way in. Sparkplug goes in fine now! Thanks for the input guys!
I've had this problem with 1 of my bikes many years ago and I've helped out a couple of friends since. I've fed a tap through the threads from the outside each time. After the re-tapping exercise turn the engine over quite a few times with both plugs removed. Even get an air nozzle in there and squirt it all around. It's unlikely that there'll be anything of consequence left in there if you're thorough. 1 of the times I did this the thread was fine. There was just some tiny piece of carbon or whatever that made it impossible to hand thread the plug back in. There was no problem what-so-ever with any of these engines after doing this. If any tiny particulate was left then it would almost certainly find its way out through the exhaust port very soon.
If you do have to install a new thread use Time-Serts ( https://www.timesert.com/ ) rather than Helicoils. Helicoils were great in their day, but some modern alternatives are far superior. As stated above, however, you really should remove the head to do this. I've not come across thread head inserts which you insert from the inside, but I'm sure (if they're out there) that they'd be a great way to go. I've NEVER had a Time-Sert failure.
If you do have to install a new thread use Time-Serts ( https://www.timesert.com/ ) rather than Helicoils. Helicoils were great in their day, but some modern alternatives are far superior. As stated above, however, you really should remove the head to do this. I've not come across thread head inserts which you insert from the inside, but I'm sure (if they're out there) that they'd be a great way to go. I've NEVER had a Time-Sert failure.