another sparkplug ejected

[RJR49 129]

Several years ago the sparkplug of my K341 ejected from the cylinder head. I screwed up the Helicoil, so I bored out the sparkplug hole and welded in a threaded bushing. you'll notice on the lower right corner of the picture of the head that there is a shiny area. When I lapped the head to insure that it was flat, there wasn't a ridge in that area for the gasket. But  when I pulled the head everything was pristine. This time the bushing blew out. I blame myself for machining to much of the weld but I'm concerned. One, that there is that much pressure from the compression, and two, that this time there is a lot of carbon. As soon as the gasket arrives I'll put it all back together but I would appreciate any thoughts you guys might have. BTW the picture shows oil in everything. I did that after I took the head off to avoid corrosion 

[squonk 41,067]

I would get another head

[ranger 1,750]

Clean it very well, bolt the head down to a thick plate, (if you have one). If not bolt it back onto the block, without the gasket. Then fill the hole with weld. Drill and thread for spark plug! Or avoid all the hassle, and find another head, as suggested by @squonk!

[RJR49 129]

I've thought about getting another head. Kohler doesn't make them anymore. used ones are cheap enough but who knows if they're any better than the one I have. there is a new one on EBay but it's around $350.00! Someone mentioned a Chinese copy in a derogatory way but I haven't seen one advertised. As an aside I've had good luck with Chinese parts. My Carb was cheaper than a Kohler rebuild kit and works great. I'm pretty sure that my starter and coil are probably Chinese too.

[Rick3478 428]

That looks like a pretty big hole.  Couple thoughts on saving the head:

 

I think Wisconsin used to use larger thread plugs on some of their older engines, S-8D/S-10D maybe, and might be close enough heat range.

 

Unless the hole is already too big for that.

 

Might be able to countersink or back-cut the inside and machine a bushing to fit through the head with big nut on the outside, not have to rely on weld.

[ebinmaine 67,420]

With the amount of literally explosive pressure put on these heads it's no surprise to me at all when a repair doesn't last. 

Aluminum welding and repair is a science all its own. 

 

If a larger spark plug thread is available and -IF- your cylinder head has enough material around the plug hole you might consider going that route. 

 

There are garden tractor puller outfits that could sell you a new head. 

 

10 hours ago, RJR49 said:

used ones are cheap enough but who knows if they're any better than the one I have

 

Contact one of our own Redsquare vendors. 

K & B Horse Parts 

 

Or

 

A to Z Tractor in PA. 

 

I'd be perfectly comfortable installing a used piece from either one. 

 

 

 

10 hours ago, RJR49 said:

As an aside I've had good luck with Chinese parts. My Carb was cheaper than a Kohler rebuild kit and works great.

 

For your own sake I'm glad to hear this but it hasn't been the experience of a growing number of people. 

I've personally had at least a half dozen garbage carburetors go through our shop. 

I will no longer use or advise them. 

 

If you still have your old Kohler carb hang onto it. They're extremely easy to clean and rebuild. 

 

[ranger 1,750]

I’ve just had a thought 🤔🙀 the Ford pinto engines, Capri, Escort, etc, over here, use an 18mm spark plug. I’m sure that I’ve seen advertised a screw in adaptor for using smaller diameter plugs in these engines? Might work if the existing hole can take an 18mm thread? Another option could be to thread the hole with a fine thread and countersink the underside, then machine an adaptor, in aluminum / aluminium to fit. After fitting the adaptor, from the underside, then put a couple of weld ‘tacks’ on the topside to stop it unscrewing when you fit the plug. If you can obtain a long reach plug in the correct temp range, the adaptor could be made longer to suit the longer plug? The countersink on the underside should then give mechanical support to the adaptor and reduce risk of it blowing out. Also with a longer adaptor, the weld can be all the way around the adaptor to head joint, meaning no need to grind, sand, machine any of it away?