That looks right fugly !
Where to start ?
I would do a cyl. leak down test . May have a blown head gasket or cracked/worn rings / cyl. or mayhaps a worn/ missing valve stem seal.
Checked fer spark /coil ?
Have you tried a new plug, maybe one step hotter ? Might get ya through fer a bit.

 

Wow, that ain't right! Weak coil and spark maybe?

 

I'll look at doing a leak down test. I tested compression. I was right at 170psi. I used my spark tester and it visually looks the same as the other good cylinder. This plug had less than 1 hour of use on it.

 

Head gasket, rings, valve stem not sealing up right. It's definitely oil getting into the cylinder from one of those. Start with the easiest.....

 

Checked with a friend on another site. He said he's seen that before due to a failed oil scraper ring, but not in an hour of run time.

 

Look, if ya don't have cyl. leakdown tester ( i have a good test kit, but usually just do this instead : ) just pump the cyl with air and check fer leaks, lemme xplain :
- Remove plug, remove dipstick ( not you, I meant the oil dipstick ), remove valve cover.
- Bring piston up on TDC comp.
- Lock crank in that position : I use a prybar in the ring gear teeth. Whatever works fer you..
- Using yer air blowgun, pump some low pressure air in the cyl and listen fer escaping air. I use a small regulator and a rubber tipped blowgun..
- Lotta air from dipstick tube = bad ring seal
-Lotta air from the pushrod galley = blown head gasket
I usually use that quick setup, and then go from there, right ?

 

I tried your method BigFish. I didn't notice any significant amount of air from the dipstick tube, or pushrods. Just a light hiss, same on both cylinders. I'm leaning towards the oil scraper ring. Any other suggestions before tearing this engine back down?

 

Well I did more digging in to this. I read through the manual. From what I found possible issues could be:
● Loose or improperly torqued fasteners.
● Blown head gasket/overheated.
● Breather reed broken.
● Clogged, broken, or inoperative crankcase breather.
● Crankcase overfilled.
● Incorrect oil viscosity/type.
● Worn cylinder bore.
● Worn or broken piston rings.
● Worn valve stems/valve guides.

So I was confident it was either the head gasket or valves. However after tearing it down I found head gaskets were good. Heads were flat. Valve seal looked good. I replaced the head gaskets and valve seals anyway. Valves had a lot of burnt on oil deposits (in both cylinders).

I replaced the breather filter and gasket. Replaced intake and exhaust gaskets. Changed oil again with 10w-30 and checked for proper level (was good).

I checked crankcase vacuum with a manometer and it’s averaging 6in. Manual says at least 4in. The number bounces around a bit, but it's usually always above 4in

Compression is at even 170psi. I did a leak down test and found about 10% leak down in each cylinder.

Hopefully the head gasket/seals solves it. At this point I’m running out of things to try. I’m really hoping it’s not an oil scraper ring as it’s about a 10 hour job just to pull the engine out of this dingo.

 

Well, looks like I'm going to be pulling the engine. It still smokes like crazy. Must be a bad scraper ring. I also get some bad backfires if killed at full throttle, but I assume thats carb related.

 

Hmmm...
What about the breather tube, the Positive crankcase ventilation one, if that leaks it can cause all sorts of havoc...

On another note I never kill mine at WOT, always throttle down first, then turn it off.
The backfire happens because your engine doesn't stop on a dime, all the kill switch does is turn off ignition but your engine continues to spin for several revolutions... In those revs it continues to suck in gas and air, compress, then sends it all out through the muffler where... If it's been running and it's hot the muffler will combust that mixture causing an explosion (the backfire)...
It's not a good thing, you can split a muffler that way, best to always throttle down first.

 

I've commented on this earlier but since then I had a similar issue with a Kawasaki FH engine last year. One of the intake manifold bolts had worked its way out causing it to suck in crud. Sadly I caught it too late. I ended up just buying a new mower.

 

All I can tell you is this...

In the past I have purchased more than a few machines, all of which were deemed something along the lines of "catastrophic failure" because somehow, somewhere, something wasn't acting like it should at all... By catastrophic failure I mean anything under the categories "blown engine, rod thrown, jacked up the crankshaft, main seal" and so on... They all said replace the engine because it was done, yuuup!
Mind you some of these assesments came from dealerships.

I have purchased quite a few such machines, usually dirt cheap.
Out of all the ones I purchased, one or two were in fact something bad...
The rest were all something simple that had been overlooked, I suspect in some cases the repair person didn't even bother looking into it.

It happens to the best, it's happened to me too.
I've had to chase problems down for years before I finally nailed the culprit, and sure enough it was something simple. The hardest part in these cases is always getting to the bottom of things. So I have learned always start with the easiest and cheapest repairs, start with those and work your way down the list.

The first problem I see here, is we don't know the make and model of the engine.
So we're all guessing based on our own Briggs or Kohler or Kawasaki or Honda...
But maybe if we had the make and model we could narrow things down a little?
Just a thought of course.

Obviously if you need the machine to work like yesterday, then the easiest is to pull the engine and drop in a new one.
Keep the old one for when you have time to tinker with it.
That's the 2,000-dollar 4-6 hour solution.
For a fouled spark plug?

I also wouldn't necessarily go tearing into it, especially if it has never been taken down before.
What they say, don't fix it if it ain't broke. There are a lot of parts to an engine, never assume the worst starting out...

One thing you might do, is replace that spark plug and torque it down according to spec.
Could be a simple thing like a rich fuel mixture, for example, can cause this condition.
You think possibly someone ran it with the choke ON?

The most common reasons why a lawn mower spark plug fouls are listed below:

• Air Intake blockage (this could be caused by the choke being left ON?)
• Clogged fuel injector (I assume yours is carbureted so no)
• Problems with the crankcase breather (PCV)
• Oil fouling from piston rings (I doubt it?)

So I don't know, but always the first step for me is to replace the "bad" part (especially if it's cheap), snug it all up correctly and see if the problem comes back... If it does we then have a "confirmed" condition.
If the problem persists, then we can proceed with the next step.

You might also check all the throttle linkages and springs, see if something there is amiss, because an improper throttle assembly can cause havoc too (such as by supplying incorrect amounts of fuel or not letting the throttle valve open enough)... On that note you might check the butterfly valve on the carburetor, pull off the air filter and make sure that's working and opening and closing correctly.

 

It's oil right? You have a bad head gasket. The way those leak you can still show good compression and leak down. Are you going through a lot of oil? Usually a failed head gasket will cause the engine to go through almost a quart of oil in about 8 to 16 hours of run time.

 

I'm going to pull the engine again on this today. I've already inspected the breather, head gasket, valves etc. As stated in the title this is a Kohler Command CH20. I'll be doing a full teardown and inspection of this engine, so hopefully I'll spot something. My bet is on the scraper ring.

 

Just my opinion but my bet is on the head gasket. I've seen hundreds of those failed and never seen a failed scraper ring. Not saying it couldn't be. Just saying I've never seen it and Kohler is pretty much the only engine I've dealt with in the last 27 years.

Now that being said, the majority of those I've seen fail have been on larger bore Commands but it's definitely not unheard of on CH20s. It's not the easiest thing to detect but the gasket would fail in that little area, circled in yellow below, that seals the combustion chamber from the little triangular oil drain back hole. There are two of these areas and one will probably be just fine and if you look close at the other it may be slightly darker and softer. If you find that then you have found where the oil is getting through and fouling the plug. It's pretty subtle sometimes but other times it's a very noticeable difference from side to side. If that area is good then you may not have any choice but to tear into it.

 

In post #8 I mentioned I replaced the head gaskets even though they looked good. I'm half way through pulling the engine. On these dingos it's a good 6 hour job just to get it out.

 

Well after about 10 hours of wrestling I finally got the engine pulled. I tore it down and found the ring end gap to be way out of specs. I have 1.6mm and the book calls for 0.77mm max. So it looks like it's just a worn engine. I still need to check my bore and pistons, but I think I have this one solved.

 

If the ring end gap is that wide, the bore is shot. Not maybe.
Book ring gap spec is for assembly, not for bore wear determination. There are specs for max wear in taper, out of round, and diameter. 3 separate measurements.

You should have been able to determine that the bore was shot with a compression test.

Toss that engine. Not worth trying to find parts and pay machine costs. Buy a new engine and be happy.

 

The CH20 (64xxx spec numbers) pistons/rings are no longer available from Kohler. These were 77mm bore, the current 20hp, called a CH640 is 80mm. You'll either have to find a dealer/distributor with some old stock or use aftermarket parts. Went through this looking for parts to rebuild a CV20 on a old Scag

 

I found that out. Luckily I found some aftermarket ones. Looks like short blocks aren't available either.

 

Deere used a CH20, (F620 ZTR) wonder if there are rings/pistons in their parts network yet, I never checked that

 

That's the ring gap of my worn rings. I don't have my new ones yet. Compression was 170 psi last I checked

 

And worn bore. I know what you measured, if you did it correctly.
If the engine is as wore out as you say, it couldn’t make 170.
“Ring jobs” are band aids. They don’t fix worn out engines. New round rings can’t seal egg shaped bores. Trust me, I’ve rebuilt a lot of engines. Do it right, or you’re just throwing money (and time) away.

 

@J. Baker How can you determine my bore is worn by knowing the end gap of my old rings?

 

Because your ring end gap is twice what it specs at new.

How many engines have you overhauled?

I don’t use metric specs, but your 1.6mm gap is .0062”, and that isn’t just horrible, but it’s a lot. It isn’t enough to cause oil consumption unless it’s been overheated and the rings lost tension, or the oil ring is broken, or the ring land on the piston is worn. I can’t see any of your parts, but I would have done a lot more checks before tearing that engine down. A ring job is always a waste of time unless something happened to cause the rings to lose tension before wearing out. In which case I would have to make a judgement call on what to do to correct it at that point. There are different options.

But not being there, not seeing any of your parts, and you only posting one picture of the coke on the spark plug of all things, (which appears to be a stock photo and was 2 years ago) and some end gap specs that I don’t know if you properly measured….. the only logical conclusion from my seat is the engine is wore out and you should overhaul it. A ring job is not an overhaul.

 

You have the decimal off 1.6mm is .062". I'll get a bore gauge and check the bore. I checked everything I could think of before tearing down the engine.

 

You are correct. I errored. If the ring end gap is .062”, then the cylinder is completely shot. It should have barely made enough compression to run, would have burned oil, and should have failed a leak down test. So, you have a lot of conflicting info.

A bore gauge is not a tool you just go borrow. They’re expensive and shops don’t loan them out.
And like Scott said, they’re only good if you know how to use one.

 

At this point you should be dropping the cylinders off at a machine shop and have them check them b4 boring them out. Or when Baker says they are egg shaped do you know what he is talking about?

 

Yes I do, and a bore gauge should show if it is egg shaped or not.

 

Well, it's taken you more then 2 years to get to this point.....Seems you are determined to fix this engine no matter what we think......

So fwiw, the way I was taught to take the measurements. I take 6 readings, two about 1/2" to 1" from the top of the bore, then half way down, then about 1/2" to 1"from the bottom. each time, going north-south, east-west, or vertical and horizontal.

And, are you 100% sure you had the ring square to the bore ? If not, put the piston back in and use it like a level, push the ring down on to the top of the piston at the point where you want to take the end gap reading, move the piston down and take your reading.

 

Only if you know how to use it. I have learned by doing everything wrong at least once to bring the cylinders into the machine shop before ordering oversized pistons.