spark plug hole in head ... moved?

[justinpittman]

Where is the hole supposed to be for the spark plug in a K301 head? Above the exhaust valve? or in-between the exhaust & fuel valves?

It appears to have moved between K301A vs K301AS. See the photo. LEFT side = new, RIGHT side = original. Notice the hole shifted towards the exhaust valve.

Why did I even bother with a new head? Because when I went to change spark plugs, I found the hole threads stripped, and the hole had already been re-bored once before.

When I searched for differences between K301A vs K301AS before purchasing this new head, the only thing I found was the oil pan had changed ...

 

[justinpittman]

P.S. now that I search more thoroughly, I've found a thorough write-up on the evolution of these cylinder heads, and whoever wrote it up is biased on pulling but still said it should be OK to swap-out:

" NOTE: The fourth generation head will interchange on the K241/M10, K301/M12 and K321/M14 engines. It doesn't matter about the spark plug location, except for pulling purposes. For pulling, it's best to have the spark plug directly over the exhaust valve. The only exception is the very early K241 "LP" head. It has a smaller combustion chamber which will allow the engine to have a higher compression ratio, and shouldn't be used on the K301/M12 and K321/M14 engines for general yard work. It should be used for pulling purposes only using high octane gas, E-85 or methanol fuel. The reason for this is because the compression will be so high, the engine will run too hot for low octane gas, and severe damage to the engine may result. "

http://gardentractorpullingtips.com/cylhead.htm

 

[slufkin]

Dont forget you will need the matching tinwork or to make a new hole in the top tin for the spark plug at the new location

 

[justinpittman]

make a new hole in the top tin

Ah, yup will do. So folks have used new(er) heads with no issue then?

 

[dfrisk]

Yes, I've used new heads with the plug directly over the exh valve on several Kohlers that did weekly mowing on my 2+ acres. I ran good gas with no issues for years.

 

[dkirk]

Proper engine design practice is to locate the spark plug over the hottest area of the combustion chamber - in the case of an L-head engine (flat head), this is directly over the exhaust valve. This allows the advancing flame front to propagate toward the cooler parts of the chamber after ignition, thereby reducing the tendency to detonate.