Kohler K301 Head

[Benh8975]

I began rebuilding a Kohler K301AQS which was on a 1250 Cub. It appeared that the exhaust valve was hitting the spark plug and had knocked it sideways. The motor has been completely rebuilt with help from this forum and others.

I attempted to put a helicoil in the head, but when I went to start it last night the plug came out with the helicoil. I'm guessing that when the last spark plug had gotten knocked sideways it messed the threads up enough to where the helicoil did not have anything to hold on to.

I have found a couple possible options and would like to get some other people's opinions.

1. Tap the head out to 18mm and use a champion D-9 plug. I've heard that this is not the best option for the 4th Generation head, which I have, that places the spark plug straight over top of the exhaust valve.

2. Take the head to a machine shop where they can weld and machine new threads into the head. I believe this and option 3 are the best options.

3. Get a new head. From what I have found online, most machine shops would charge around the price of a brand-new head for the engine. I could also search for a used head on Ebay and possibly save a few dollars from option 2.

4. Another possible option that I have thought about is trying to find a helicoil with a wider outer diameter and the same 14mm thread sizes. I have not been able to find one yet, but someone may know of one.

I would love to hear other people's input about this.

[green407]

I'm partial to just replacing the head with a known good one.

I'm also curious why the exhaust valve was striking the spark plug?

Was it the wrong plug that was too long?
Was the head cylinder head shaved down too much?

[West Valley G]

If it were me I would go with the new head as well. With a
good used one you eliminate multiple variables. Get on with
enjoying your new rebuild.

Ken

[DSarow]

I agree with getting a new head,its possible that after doing all that machining and the work you won't get the proper results.Good luck