Kohler M20 spark plugs

[duryea21]

Jonathan where did you get that scientific information about the plug? I would like to look that up and read about it, just curious about it

[Sam Mac]

I have never had good luck with Champion plugs dating back to the 60's. I like NGK or Autolite.

[J-Mech]

Originally Posted by ol'George

I'm thinking an old flathead ain't going to be too sensitive to a little timing advance or pre-ignition @ 6.5 to 1 CR.
But I haven't done any scientific work to that fact.

Now take a SBC of the 60's vintage with 10.25 CR and cheap gas, will take the heads off the pistons in a heartbeat.
BTDT and it wasn't pretty.

I really don't know George.... The old K motors were bad about burn pistons, just from normal use and wear, let along when they weren't tuned right. I've tore them down with few hours on them, most everything looking good, and not much machining needed, but the piston was melted to the top ring on the plug/valve side. And I've seen them with little wear and a blue million hours on them. The KT's and Mag's didn't seem to have the same issue even thought they are basically the same design. Difference being spark plug location and head chamber shape. Does make one wonder if the plug coming into the side of the head up above the valves made for a better burn. Seems the valves wear out and fail in the KT's and Mags more often though, so there is always a trade off to a different design. I agree, lower compression and the engine design may take the increase in timing (assuming the plug actually does fire enough sooner to matter) along with some pre ignition and be ok. I still wouldn't risk it..... but I'm also just not going to pay more than $3 for a spark plug for my "lawn mower" when a copper resistor works so well. I haven't even changed the plugs in any of mine in I couldn't tell you how long. 1811 is due.... but it needs more than plugs. I just rolled 2100 hours on that tractor, and this engine was installed at 1175, so I need to pull the heads and check things out.

Originally Posted by duryea21

Jonathan where did you get that scientific information about the plug? I would like to look that up and read about it, just curious about it

I didn't present any "scientific" information. Mostly experience, and knowledge from years of service. Oh, I read some stuff since this posting.... because I'm to the point now I'm starting to forget things that are kind of trivial. Google it. Info is out there. Just watch who and where you get your info from. On the internet, you can literally find people on both sides of the fence. Easy for me to spot the BS.... but if you don't know and understand some stuff, then sometimes you can be fooled. Likely how you came to purchase the plugs in the first place. Sorry if that offends.

Originally Posted by Sam Mac

I have never had good luck with Champion plugs dating back to the 60's. I like NGK or Autolite.

This statement always puzzles me. Kind of like the whole ethanol debate. A lot of people say they have issues with Champ plugs. Most of them people I have a good deal of respect for. (You and Dale Merkle come to mind.) I've never had bad luck with them, except on rare occasion. I've always ran them in the Cubs, and put them in every Mopar engine that I ran through the shop with no issues. I usually chose Champs for the old tractors I used to overhaul too. I often wonder if it's a fuel related issue. I've never had issues with ethanol, matter of fact I have good results with ethanol. But others swear to the end of the earth that ethanol caused them all kinds of issues. Wonder if it's luck of the draw... or fuel... or ???? I'll keep using them until I have an issue. Biggest issue I have with Autolite plugs is that's what Ford runs, and I just can't stand the thought of using a "Ford" spark plug in anything I own. NGK is a great plug and my next choice when I can't get a Champ or an AC Delco. (As a note, I stick to what OEM was on most everything, so like my Chevy truck gets AC Delco plugs.)

[1711Cub]

Per the recommendations of the majority on this site, I switched from the original Champion plugs to the Autolite 26 plugs. Both of my Magnums run better and start better now. I set the gap to .025".