Spark Plug Thread Problems

[90GTVert]

Thanks to Speedy for posting this info.


In my almost 20 years of automotive service I never saw what just happened to me a few minutes ago!

Bear with me.......

It is important to make sure your valves are adjusted properly in order to do a proper plug read for carb tuning. Too loose and your plug will give a false rich, too tight and you will see a false lean (and it will most likely run like a turd especially if they are too tight).
I just installed a 50mm kit and have been fiddling with the carb to get the right tune. The 88 jet was too lean for sure, the 105 was way too rich but the 95 was about right, it still feels a little rich on the low end. I got a 92 to put in but before I put it in I wanted to re-adjust the valves. I have gotten pretty good at valve adjustments after owning VWs for so many years. I Put the valves on a good snug .0025 (they we just a little loose), went to put the plug back in and....OH SH!T, I felt the threads give way!
Visions of doing a plug insert went racing through my mind. Ok no big deal, I have been here before on heads that were wayyy more difficult to work on than this for sure. Once I got the plug out I looked at it to see how much debris was on it, assuming that it was the threads of the head that let go and was expecting to see lots of aluminum shavings to confirm what I suspected. I also thought, wow what a crap head since I have only done and in/out with the plug just a few times since this build 100 miles ago.
I looked at the plug and didnt see a thing. No shavings at all.
HuH?
My eyes must be getting bad but upon much closer inspection, the spark-plug actually broke and started to pull apart! This has never happened to me in all the gazillions of plugs I have changed. I have never seen it happen and have only heard of it happening once. I have seen the boot end of the plug break off, I have seen the porcelain crack due to over tightening but never this. Once I felt the plug suddenly get loose upon tightening I stopped quick and backed it out.

It was VERY difficult to see where the plug broke, I had to inspect it several times to see that it was actually broken. I cannot see down in the spark plug hole at all but I know for sure that if it had been the threads of the head that had pulled out, the plug would have been covered in shavings.

I am rather ashamed to admit that I only have...um...zero spare plugs on hand
Autozone is just up the street so no big deal there really.

This experience got me to thinking, When doing a sparkplug thread repair make sure to use the right type of insert. Especially on a little high compression 1 cyl. engine like these.

I am pasting the following from another site for 2 reasons...
1) Because I feel they explain it better than I can.
2) In-case the site I found it on goes poof.

"Inserts for aluminum heads are made of aluminum and are hard anodized to prevent them from ever stripping again. It is very important to understand that all coil inserts are made of stainless steel which simply transfers heat to slowly to transfer heat fast enough to allow the plug to cool and operate at the prescribed heat range. If a steel insert is used in an aluminum head it will fail to maintain metal to metal contact with the head as the engine heats up. Aluminum expands at a rate of 2.8 times more than steel. The aluminum will simply expand away from the insert and the plug will begin to loose its ability to transfer heat. If the spark plug overheats, pre-ignition and detonation can occur."

www.locknstitch.com/sparkpluginserts.htm

Also, using the proper heat range of spark-plug very important...

www.google.com/#sclient=psy&hl=en&source=hp&q=spark+plug+heat+range+comparison+chart&aq=1&aqi=g5&aql=&oq=&pbx=1&bav=on.2,or.r_gc.r_pw.&fp=2ec23705adf4e555

I hope this helps someone who runs into the eventual stripped spark plug hole!

Cheers friends and be safe among the scoot hunger cagers!

[motorhead]

So I finally got around to looking at my new (to me) scooter to run it to get some baseline performance data. Checked the oil, carb, fuel and went to check compression, then uh oh! The adapter is just spinning, and then i tried the plug again and the spark plug goes all the way in and keeps spinning. Plug hole was stripped! So, After 2 hours I was able to repair it, here's how. This also works on GY6 since it uses the same plug.

Your are going to need your standard plug, m12 x 1.25 tap and a plug with the same thread as the tap and washers. I had a DPR8EA on hand so I used that.



First remove the head from the bike. Drill through the plug as squarely as you can with a 25/64 drill bit. Then tap the plug hole. Make sure you clean off all the aluminum powder.


Then line up the old plug and your new plug together and use washers or what ever else you have on hand to keep the plug from going all the way into the head. I used this nut here. Obviously the piston will hit the plug if its threaded all the way in without some form of a washer.


Last step, thread in the new plug before installing the head. Why? If the new plug hole isn't drilled correctly the plug may be leaning near the valve cover part of the head and you can't get a socket to fit. So tighten the plug up first with a wrench if you have to. then put your bike back together and order a replacement head. At least with this method, you can use the bike indefinitely while the new head is in the mail if you feel like you want a new one on there.


I never bothered with helicoils in all my years because you still have to drill into the head and you have no room in your scoot to fit a drill. Head, still has to come off the bike with helicoil. Besides, the tap, drillbit, plug and washers all cost the same or less than a helicoil set. With this method, your plug is threaded into freshly threaded aluminum and you wont have to hope the helicoil doesn't get blown out, word on the street is it happens! This method may not elegant but if you strip the plug hole, you gotta pay the piper.