M18 engine head milling

[ol'George]

Not to piss on yer parade, but
M-18's are a flat head engine, (and a dam good old one.)
Once you go milling the head other than say .040 you begin to shroud the valves.
Even then I'd clay the head to see what the valve to head clearance is.
As far as 93 or more octane, it is a waste of money and a decrease in power on a low compression engine.
Now if you are wanting to build a competition engine, pop up pistons, relieving the cylinder, special design CNC head, larger valves/ special cam,special flywheel rated above 4000, rpm's special intake/exhaust etc. etc. to name a few things, are a start.
But a flat head engine is not an inherently power house design to start with.
They are made for work & torque.
If you are looking for factory specifications look in the service manual available from kohler free, or here on our site.

[J-Mech]

Originally Posted by Pray-2-miss-rocks

Who said anything about needing 93 now? Lol. Did anyone read my post or was I not clear (I dunno how I could have been clearer)? I'm wondering if there is a "run of the mill" milling (pun intended) amount that will increase compression to run safely on 93 octane.

Otherwise thank you for the info.

Mower is in good shape, have all kinds off attachments as well. Obviously the old man original owner loved it. I think it's perfect for my yard, half the property is woods, other half grass. It's also a mix of flat, hills, and....rocks. a zero turn wouldn't really save me a lot of time

I read your post. And I don't mind pissing on your parade.

You don't need, nor will 93 octane gain you anything. George hit the nail on the head. This isn't a high performance engine. It's a flathead lawnmower engine. Run 89 and be happy. If you don't like that answer, sorry.

[Gompers]

Your tractor. Do what you want.

But if it runs good, leave it alone. You can run 93 in it all day long. It won’t hurt anything, but you’re just burning money. Higher octane rating just means it won’t detonate until a higher temperature/pressure. That’s all. You can always run high octane fuel in a lower compession application, it’s just a waste of money. Go get some 100LL if you’re so inclined.

That being said, I do run 91 no ethanol in all of my small engines just because some of them sit for a long time between uses and I feel better about having 91 in there to start with vs 87, and I don’t go through enough gas for it to be a major difference in cost.

[J-Mech]

You can run 93 in it all day long. It won’t hurt anything, but you’re just burning money.

Maybe. I've never ran any of my small engines on 93 that I can recall, but I tried it in my Honda motorcycles. Actually got less mileage, and ran worse. Engines just weren't set up for higher octane. I'd bet the Kohler would be the same..... and I've been turning wrenches long enough to feel pretty safe with that statement.

[Pray-2-miss-rocks]

You're totally missing what I'm saying, maybe this isn't the place for this particular question?


Safe running on 93 octane is the *compression target*. My goal could be 112 octane as a compression target or c16, requiring more milling to achieve the appropriate compression ratio, but that'd be silly. I'm not talking about pouring 93 octane into my gas tank when I get home.

[Pray-2-miss-rocks]

Originally Posted by J-Mech

Maybe. I've never ran any of my small engines on 93 that I can recall, but I tried it in my Honda motorcycles. Actually got less mileage, and ran worse. Engines just weren't set up for higher octane. I'd bet the Kohler would be the same..... and I've been turning wrenches long enough to feel pretty safe with that statement.

Correct, low compression and high octane will run worse, with timing the same.

[Pray-2-miss-rocks]

Originally Posted by J-Mech

I read your post. And I don't mind pissing on your parade.

You don't need, nor will 93 octane gain you anything. George hit the nail on the head. This isn't a high performance engine. It's a flathead lawnmower engine. Run 89 and be happy. If you don't like that answer, sorry.

I don't mind that answer, just thought there'd be more people on here that would understand my question. No worries.

[Pray-2-miss-rocks]

Originally Posted by ol'George

Not to piss on yer parade, but
M-18's are a flat head engine, (and a dam good old one.)
Once you go milling the head other than say .040 you begin to shroud the valves.
Even then I'd clay the head to see what the valve to head clearance is.
As far as 93 or more octane, it is a waste of money and a decrease in power on a low compression engine.
Now if you are wanting to build a competition engine, pop up pistons, relieving the cylinder, special design CNC head, larger valves/ special cam,special flywheel rated above 4000, rpm's special intake/exhaust etc. etc. to name a few things, are a start.
But a flat head engine is not an inherently power house design to start with.
They are made for work & torque.
If you are looking for factory specifications look in the service manual available from kohler free, or here on our site.

.040 in my world is quite a bit (automotive).

[cooperino]

Originally Posted by Pray-2-miss-rocks

I don't mind that answer, just thought there'd be more people on here that would understand my question. No worries.

I think everyone understood the question. Ol'George answered it quite well. Not to mention that such a slight amount of milling alone would probably not yield enough gain in compression to make the 93 work the way you intended

[cooperino]

Originally Posted by Pray-2-miss-rocks

.040 in my world is quite a bit (automotive).

.040 in automotive is quite a bit because its done to multiple cylinders. It adds up!