View Full Version : Cross Threaded Spark Plug Hole
gaillarry
08-13-2010, 12:19 PM
My son decided to change the spark plug and cross threaded the hole. He got the plug about 3/4 was in and of course it won't go any further. I got it out but what's the best was to fix it???
alantf
08-13-2010, 12:58 PM
If he didn't put too much pressure on the plug spanner (wrench?) & bugger it up completely, you MAY be able to just screw the plug in correctly. Have you tried that yet? :??:
gaillarry
08-13-2010, 01:04 PM
If he didn't put too much pressure on the plug spanner (wrench?) & bugger it up completely, you MAY be able to just screw the plug in correctly. Have you tried that yet? :??:
Yes I tried that but it keeps going into the threads he screwed up. I was thinking of getting a thread chaser - what size would I need?
alantf
08-13-2010, 02:01 PM
Unfortunately, I don't think it's that simple. You may already have bits of thread (metal) in the cylinder, that could bugger the piston rings, & a thread chaser may only add to the problem. You'll probably need to remove the cylinder head to assess damage & carry out a repair.
Is there anyone with more "hands on" knowledge who can come in at this point? :sad:
Easy Rider
08-13-2010, 02:34 PM
Is there anyone with more "hands on" knowledge who can come in at this point? :sad:
I think you are basically correct but it depends..........
On how old the bike is and how willing you are to take a chance.
If a new plug won't follow the original threads, chances are that the thread chaser won't either.
That might be a good solution IF you could start it at the other end where the threads are good.
Alas, I think on the GZ, you need to take the cam off to remove the head......so it isn't a real easy job.......and if you're going that far, might as well heli-coil it for a proper fix.
IF the bike is OLD and/or you really don't have the skill or the money to do it "right", a thread chaser from the outside....with lots of grease on it to catch the filings....probably wouldn't make matters any worse and you might luck out. Any filings produced will PROBABLY blow out without doing any real damage.....maybe.
Someday maybe I'll tell my "rock through the plug hole story" but not today. Sufice it to say that one needs to be VERY sure that the base of the old plug is absolutely clean before you unscrew it. :roll:
The second big question IS: Does the boy now know to use FINGERS ONLY when threading in a plug ???
patrick_777
08-13-2010, 03:42 PM
Someday maybe I'll tell my "rock through the plug hole story" but not today.
That is a pretty good story, though.
blaine
08-13-2010, 04:39 PM
[quote="Easy Rider":r4gysxrt]Someday maybe I'll tell my "rock through the plug hole story" but not today.
That is a pretty good story, though.[/quote:r4gysxrt]
:plus1: But a hard way to learn a lesson!
Easy Rider
08-13-2010, 04:51 PM
[quote="Easy Rider":1fuxym20]Someday maybe I'll tell my "rock through the plug hole story" but not today.
That is a pretty good story, though.[/quote:1fuxym20]
Oops. Have I told you the story about.............
Yes, Gramps, we heard it before !!! :roll:
emory70
08-13-2010, 08:46 PM
that was one of the first lessons my dad taught me... "whenever possible, start a bolt, nut, screw... with your fingers." that was followed closely by "don't tighten anything until all fasteners are started."
that was one of the first lessons my dad taught me... "whenever possible, start a bolt, nut, screw... with your fingers." that was followed closely by "don't tighten anything until all fasteners are started."
Same here! The thread size is 12x1.25mm 98.9% of auto engines use 14x1.25 threads & all thread chasers that I have seen are 14mm/18mm so you will need a long reach tap. You may be able to blow out most of the shavings if the piston is at TDC on the exhaust stroke.
gaillarry
08-14-2010, 07:07 AM
Going to pull the cylinder head and take it to a machine shop and have it done right. I have the manual, any tricks getting the head off?
Just follow the manual, stuff a clean rag under the cam shaft gear so you dont drop any bolts into the crankcase. Also be sure to replace the cylinder base gasket.
gaillarry
08-22-2010, 08:05 AM
Got the head off and here's a pic of the piston top, lots of metal shavings and carbon buildup. New gaskets came in yesterday (base and headgasket) now to put it all back together. Local machine shop re-tapped the spark plug hole and the plug fits nicely.
http://i6.photobucket.com/albums/y217/gaillarry/GZ250Piston2.jpg
Water Warrior 2
08-22-2010, 03:44 PM
Got the head off and here's a pic of the piston top, lots of metal shavings and carbon buildup. New gaskets came in yesterday (base and headgasket) now to put it all back together. Local machine shop re-tapped the spark plug hole and the plug fits nicely.
http://i6.photobucket.com/albums/y217/gaillarry/GZ250Piston2.jpg
Looks like you are half way there.
Don't worry too much about carbon build up, it will increase the compression a tiny bit. :lol:
Don't worry too much about carbon build up, it will increase the compression a tiny bit. :lol:
Maybe .001%
gaillarry
08-22-2010, 04:51 PM
Since I had the carb off to remove the head I decided to clean it. The bike has been fouling spark plugs for years.
The cap was on the mixture screw from the factory. I drilled out the cap and to my shock the mixture screw was completely closed !!!! The tip of the screw is about 1/4" into the carb throat. Someone was asleep at the factory when the carb was assembled.
No wonder plugs were fouling and the piston was full of carbon. Whats the proper setting for the mixture screw!!
blaine
08-22-2010, 05:31 PM
About 2 1/2 turns out to start .Once you have engine started,adjust for smoothest idle,about half way between lean & rich.
:2tup: :rawk:
Easy Rider
08-22-2010, 07:39 PM
No wonder plugs were fouling and the piston was full of carbon.
I think you may still have that problem.....because the screw being all the way IN would have made it more LEAN, not rich. If you have another problem actually making it rich, you may find that the idle mix screw has no effect.
:cry:
P.S. Be **REALLY** careful not to overtighten the plug. You may be missing 1/3 of the original threads.......or more.
gaillarry
08-22-2010, 08:29 PM
I'll find out tomorrow when I start the bike. Have to let the gasket sealant on the valve cover set for the night. The machine shop did a good job of rethreading the spark plug hole, but advised me next time it'll need a helicoil.
I've read posts here - IN - Rich , OUT - lean...... or is it the other way around??
blaine
08-22-2010, 08:39 PM
I've read posts here - IN - Rich , OUT - lean...... or is it the other way around??
The other way around "In-lean,Out-rich". As EASY said with the mixture screw all the way in it would not be causing your rich mixture.But would definitely affect your idle.
:cool: :roll:
gaillarry
08-22-2010, 08:48 PM
I'll set it at 2.5 turns out and go from there, I'll post back the results.
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