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Engine began fluctuating rpms by itself, had little power under normal light mowing....even with the deck disengaged. Parked it for 4 days then tried to start it...doesn't fire. Is getting plenty of fuel, has spark. Fuel shut off solenoid is working. Checked compression with compression gauge, less than 20 psi. With the plug in, I can easily spin the flywheel. I pulled the valve cover and the valves appear to be fine from the outside, nothing appeared out of place. At tdc on compression stroke I can wiggle the rocker arms but I can't find my feeler gauges so I do not know what the lash is set at. So I pulled the head off and the push rods look nice and straight. Here are some pics of what everything looks like... Does anyone see anything wrong? What is my next step in troubleshooting? Does it need rings maybe? FYI, the lash caps have been removed in the photos.
Mower is Craftsman T1200 probably 2013 or 2014.
Engine is MTD 4P90HU

Checking valves for sealing without pulling them out:
Spark plug in, set the head with combustion chamber horizontal, fill with water.
If the level drops, look at where the water is coming out - in or out. That will tell you which valve is not sealing. Pull it, check face, seat.

If not that, it may be the coil. You can get a weak but visible spark outside the engine when you check, but it may die under the higher load under compression.
And checking with a multimeter doesn't help identify a shorted coil.

High oil consumption. signs of dirt ingestion from the intake side of the engine in combination with cylinder scuffing and hot spots. Minimum to fix properly would require boring oversize and fitting new piston and rings. Lower end could need work also due to wear. Best option for dealer standpoint would be either engine or complete mower replacement.

Also to properly test ring,valve, head gasket condition is to do a leakdown test. Due to compression release can't get good feel of engine condition. I have personally worked on an engine that showed less than 10% bypass on leakdown, but showed 5 psi compression.

Your in trouble if the you need to oversize as MTD offers no over sizing components for the P90 engines that I can find on their website. IL might have dealer access to look-up to see they actually can be gotten.

Now there might be a short block available if the service manual is right about short blocking but haven't any reference on ARI net about one. Looking it is one those use it until worn out Chinese engine then replace it.

Welcome to the world of Chinese throwaways.

No oversize available. Short block is $545 and complete engine is $1060 Can probably replace cheaper than that from Briggs or Kohler for that price.

Tnx, For confirming what I was seeing and thinking.

It just got to where it is just too costly to rebuild any small engine. I don't why I ever wasted the money on buying those ridge hones as I only use them 3x in 7 yrs.

LeisureSpecialist said:

View attachment 51179

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That gap for that left hand valve is HUGE !!! Can't tell for the right. Get a set of feeler gauges.

Won't help as the head is off the engine.

OP said something about lash caps on the valves. But looking at the third cylinder and piston picture that 60 thousands or so clearance at the jpiston top looks like time for a new mower.

Good news, the cylinder head is holding water and I found my feeler gauges. Bad is what Tom3 said...I can get 80 thousandths gauge between the piston and cylinder and can push gauge all the way in between the red marks shown on the photo...no hitting the rings... So looks like I inherited a lemon.
Based on the replies, it looks like I'll be sourcing a new engine or mower. Thanks all

LeisureSpecialist said:

.I can get 80 thousandths gauge between the piston and cylinder and can push gauge all the way in between the red marks shown on the photo...no hitting the rings... So looks like I inherited a lemon.

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That's an 8 thou feeler gauge, not 80.
Maybe pull the piston and check for broken rings, and put new ones in even if not broken?
The rings might just be stuck in the piston grooves.
The engine looks tired, but should still be a runner.

Wow. Maybe there are NO rings at all !!!

What I see in the cylinder picture is about .20 thousands or more on the cylinder walls from the ridge at the top of the cylinder. Signs of overheating at the bottom of the cylinder with the discoloring, and patchwork lining up with the cooling fins. Also aluminum transfer on the lower left side of the picture. So the piston rings are jumping and skipping across the cylinder walls.

Ron_AU said:

That's an 8 thou feeler gauge, not 80.
Maybe pull the piston and check for broken rings, and put new ones in even if not broken?
The rings might just be stuck in the piston grooves.
The engine looks tired, but should still be a runner.

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long day.... 80 Ten thousandths...my fault...

Quick & dirty test for a broken upper ring is to wipe a very thin layer of grease around the bore then move the piston up & down a few times at the very top f the stroke , a broke ring will leave a vertical line as will the end gap

I pulled the piston and the rings are barely extending beyond the piston. They are all intact but are hugging the piston pretty closely. I can easily replace the piston back in the cylinder with very light finger pressure on the rings. I'm going to put in a new ring set and see if it runs.

How much for a new piston ?

$40 for the piston, close to $100 for the piston, pin and snap rings.

I have had three of those so-called "MTD Engines" come through my shop with identical symptoms; Very hard or no start, very low compression, worn rings with some bore wear. All three were replaced under warranty by Craftsman without questions or hassles. They sent me a new short block and I sent back the old one for their engineers to examine and determine the cause of failure. In two of the three, dirt ingestion was the cause, and the last one, poor oil flow to the bore causing overheating and dirt ingestion. The ingestion causes premature ring wear because of poor metallurgy if the ring manufacturing process by the supplier. I do not know if it has been corrected, both the efficiency of the air filters and the ring alloy quality. I would assume so since I haven't seen any issues with them since the build dates of mid-2018.
In Summary, the failures were caused by poor air filtration and the low alloy piston rings.