Stripped spark plug in head

[Ben Morong]

I went and did it -- putting the spark plug back into a K161 in an Original and I stripped the threads. Had another head on the shelf, took it down and cleaned off the old carbon (still gooey after 3 or 4 years), and started checking for flatness. Got the sheet of glass, put a piece of 600 sandpaper on it and found the high spots. 600 didn't seem be doing much at all, changed to 320 and got a little better results, then finally wet it and it worked better. Got the head down to flat, removed some carbon from the top of the block, put on a new gasket (Stens was all I had), put on the head, torqued it down following the sequence and the torque in the book. Started the engine and it runs, and I shut it off right away.

Questions: Should I have put NeverSeize on the gasket? The old one seemed to have it on -- aluminum colored and actually felt kind of wet. And I know I should get the engine hot, then let it cool down and retorque the head, but how long do I run it? Just long enough to get it hot, or for 1/2 hour, or what? And do Helicoils work?

[Jeff in Pa]

I run mine for a hour but people have said 15 minutes for the first time. I retorque after an addition 4-5 hours run time.

Heli coils will be fine for the repair if they are installed correctly. For a thru hole like a spark plug, a self locking heli coil would be better. They have a small flat on some of the coils to help keep it in place.

Jeff

[Tom Scott]

Heli-Coil makes a special kit for spark plug hole repair, and the shop I worked for liked them. Should be readily available at any good automotive or equipment repair shop. A Heli-Coil repair is generally considered to be a correct and proper repair.

[Jlaws]

Years ago I stripped the threads in the head of my 122 . The plug I was using only threaded about halfway into the head....
I found another brand of plug that had deeper threads ( was probably the wrong heat range ) but was able to get down to the good threads . I eventually changed the head when I rebuilt the engine , but I got a couple more years out of it..
I have noticed that different brand of plugs don't always have the same thread depth , even though they cross to each other .
Anybody else ever notice this ?

[Farmallgray]

Jess,
That is why all the plug manufacturers recommend to go by their application listings rather than cross referencing.
Sometimes when you cross-reference they can jump heat ranges because some companies don't offer the same heat ranges as others.

Ben,
I know a lot of guys warm the engine, then let it cool off before re-torquing. I have had better luck re-torquing while they are still hot.

[mgonitzke]

Todd-

That's interesting. I have never retorqued hot because the aluminum head expands more than the steel bolts, so theoretically the torque on the bolts would decrease when everything cools back down again, and the bolts may not be torqued enough.

[Farmallgray]

Matt,

We had a K161 in a 71 that we used to work on for a guy. He used it really hard and mowed like 2 acres and this little 71 was his only mower. It may even be the 71 that my Dad now owns.

Anyhow this guy was bringing this tractor in every couple months with a blown head gasket. Each time we sanded the head on a piece of glass to make sure it was flat and used a new Kohler gasket. We even checked the block with a straight edge. We were following normal procedure of warming it up then letting it cool and re-torquing. I think we even replaced the bolts and chased the threads in the block. After doing this a half dozen times, We didn't know what to do. In desperation, we decided to try re-torquing it hot. It never came back again with a blown head gasket. I think it ran for a good 7 or 8 years then the guy traded it in. By that time the engine needed overhauled.

Ever since that, I always re-torque them hot and have never had a problem.