De-carbon an engine

[Old Skool]

Ok I know you guys talk about cleaning the carbon from the top of piston and the head after 500 hours, but why do it to these Kohlers and not a car engine? I'm not trying to start a debate or anything, I just don't understand why. Does it have something to do with being an air cooled engine versus a water cooled? Inquiring minds want to know.

[cubby102]

My guess would be the higher Temps and lower revs of the air cooled governed engines

[J-Mech]

Temp is a factor yes. But not necessarily in the way you think. Air cooled engines run hotter than water cooled yes.... but not many people work these engines hard enough to keep the carbon burnt off. If you work them... I mean REALLY work them.... Like for 5 or 6 hours at a time under full load.... They don't carbon up near as bad. It's the ones that "put" around and don't get worked hard, (or only work hard for short times) that carbon up so fast.


Truth be told... car engines need it too. Anyone who has ever had the intake plenum off of a "newer" automotive engine has seen the horrible carbon build up that occurs in them. There is good reason why products like Sea Foam were created. (That's a plug for Sea Foam, I am not affiliated in any way, but it's really good stuff.)

More explanation:

Carbon on top of a piston gets hot when under load. If you work the engine hard enough, that carbon will get red hot. Red hot is hot enough to cause pre-ignition. (Pre-ignition: gas is ignited by another source besides the spark plug at the wrong time.) Pre-ignition can cause cylinder damage, hot spots, "pinging" and a other damaging things. The reason that Kohler recommends you to pull the head and clean it is for longevity. The reason car makers don't recommend it is for a couple reasons: It doesn't happen as quickly, or as often as it does on this smaller engine (for reasons already discussed). Secondly: It's just too costly. Seriously... who would pay a shop to pull the heads off a 350 Chevy just to clean it and reassemble it? NO ONE. But as someone whose taken apart a lot of those motors... they need it.

[Mike McKown]

Since leaded gasoline went away, I haven't seen the need to de-carbon ANY engine that was in good mechanical condition.

Chevrolet used to recommend heavy misting water into the carburetor in the mid '60's to clean carbon off piston tops. I've done it on large and small engines both.

If the engine needed it, you'll see small pieces of carbon fly out of the muffler. The carbon gets blown out of the combustion chamber by the steam the water creates.

[ol'George]

I feel the improvement in lubricating oils has helped also.
As a young boy in the early 50's a lot of cars/trucks were seen with a blue clouds coming from the exhaust if they were a bit older.
As oils improved, that disappeared, also ring design/materials have improved.
As a teenager I spent some time in a friends junk yard, not only getting parts but working on saturdays doing what ever was needed and a lot of cars were junked with less than 100,000 miles on them.
Today normally 200,000 or more is expected before a engine major is needed.
Improved oils, material design, and overdrive transmissions all contribute.
Also we run them a little hotter @ 195* rather than *160-180 as well as positive crankcase ventilation to reduce sludge/moisture buildup.
Just my take.

[J-Mech]

Originally Posted by Mike McKown

Since leaded gasoline went away, I haven't seen the need to de-carbon ANY engine that was in good mechanical condition.

You've not been into many engines then.....

Originally Posted by ol'George

I feel the improvement in lubricating oils has helped also.

Yeah, I would agree with this... to a point. But it really has more to do with the latter of your statement. Better and much tighter tolerances. (Ring design) And also different building materials, coatings and the like. Older motors had wide ring gaps and skirt clearances. Not out of the ordinary for an older motor to have a .005" - .007" skirt clearance. Now anything over .004" is rare. Has more to do with materials they are made of expanding less under heat. Better metallurgy in how blocks are constructed.... and so on. Sure, the oil helped, in that better oil also let them run tighter tolerances.... but you can also put that to better filters and filtration systems. The old Hercules motors in Jeeps only filtered some oil on a 1/4" line bypassed off the lube circuit. Not much oil actually went through the circuit to the filter. The better oils really show up in these little Kohlers in that with NO filtration system I think we are seeing longer life on overhauls than we ever have. How many machines do we buy that had engines put in them when they were with the first owner? Several. But we overhaul them and they run for years and years. My family bought a brand new model 71 Cub Cadet. I have it now, and I took out the 3rd motor that it had in it. The one I install will be engine 4, and I bet the last. No doubt, we have come a long way in a lot of things... but it doesn't seem that one of our advancements was in fuel. The fuel we have now truly sucks.

[64fleetside]

Even in automotive engines carbon buildup depends on usage, those run hard and for long periods of time carbon much much less than the ones that putt putt around or are short trippers. Cheaper fuel also carbons more as do flathead engines verses OHV, fuel injection carbons less than carburetion-a sticky choke can carbon up one quickly.

[Mike McKown]

Originally Posted by J-Mech

You've not been into many engines then.....

You are taking a giant leap of faith to make a statement like that about someone you know nothing about.

I suspect it may be you that is lacking in experience. Your statement about today's fuel is an indicator of this. With today's fuels you can run an engine for hours and hours or years and years and the spark plugs stay clean. Usually only have to be replaced when they just wear out. Compared to yesterday's spark plugs that used to get deposits all over them in a very short space of time to the point they'd short out and that is mostly a direct result of the fuel being used. I think small engine manufacturers used to recommend changing spark plugs annually? I have engines that have run 15 years on the same plugs and are still clean and seem to fire good. We've had ethanol in the gasoline around here for close to 30 years so nothing new here for me.

I'm old enough to remember when you opened up an engine it was expected to be full of crud, both in the combustion chamber and in the crankcase. In the event of overhead valves, yeah, it was full up there too. Bearings eaten up with corrosion. Stuck rings..........................................

You just don't see problems like that anymore.

[dvogtvpe]

its the fuel injection systems that are responsible for less carbon, better ring life , less oil consumption ect. each cylinder gets exactly what it needs and not just a steady spray down its throat like a carb does. often times some cylinders ran lean while others ran rich. in these very crude flat heads with crude carbs you still get carbon deposits.

[Mike McKown]

Originally Posted by Old Skool

Ok I know you guys talk about cleaning the carbon from the top of piston and the head after 500 hours, but why do it to these Kohlers and not a car engine?

Originally Posted by dvogtvpe

its the fuel injection systems that are responsible for less carbon, better ring life , less oil consumption ect. each cylinder gets exactly what it needs and not just a steady spray down its throat like a carb does. often times some cylinders ran lean while others ran rich. in these very crude flat heads with crude carbs you still get carbon deposits.

dvogtvpe: I agree that the flathead engine design does tend to have a dirtier combustion chamber than overhead valves. I also agree some of the things you mention will make ANY engine run cleaner in addition to the other things that have been mentioned.

But let's not lose sight of what the OP's question was. And because someone offered his opinion based on what he's seen over the decades is not an indication that he "hasn't taken too many engines apart".

PS. I guess everyone knows that some of these direct fuel injection engines are having a problem with carbon packing/coking on the back side of the intake valve due to oil misting from the PVC system being sprayed directly on the hot valve.