Export thread

I recently replaced the head gaskets on the engine and put it back on my mower. I’ve connected all necessary wiring, I’ve got spark, I’ve got fuel and I’ve got compression. I cannot figure out why I’ve got no start. The motor turns and has shot fireballs out of the muffler and the carb. Where am I going wrong? Could it be a timing issue? If so, can the flywheel go on wrong on these mowers?

Any help is appreciated. I’ve gotta get this mower out of my shed.

Double and triple check your valve clearance. That’s where I would start. If that doesn’t work we will need to have all engine numbers so we know you’re not working Dodge Hemi or Chevy big block.

Being a kohler Command with the hydraulic lifters, there is a chance that the lifters have over pumped preventing the valves from closing completely.. Letting it set for a day or so may just allow the lifters to bleed down and then have it work properly

ILENGINE said:

Being a kohler Command with the hydraulic lifters, there is a chance that the lifters have over pumped preventing the valves from closing completely.. Letting it set for a day or so may just allow the lifters to bleed down and then have it work properly

Click to expand...

So I’ve been dealing with this issue for a couple months now. I’ll leave it sitting for several days and then try to tackle it again with new information. It started one time when I first put it back on the mower but didn’t run for very long before it died and wouldn’t restart. The lifters have good contact with the valve stems and I’ve watched them actuate up and down so so don’t think they're stuck.

Rivets said:

Double and triple check your valve clearance. That’s where I would start. If that doesn’t work we will need to have all engine numbers so we know you’re not working Dodge Hemi or Chevy big block.

Click to expand...

Do you have any information in regards to valve clearance? It has hydraulic lifters so it’s not adjustable in any way. Are you asking about valve clearance on the cylinder side or at the lifters?

Sorry I made a mistake thinking it had solid tappets. Since you had the heads off I would start by checking to make sure you have no leaks around the intake manifold. If no leaks I would pull the valve covers and plugs and check to see if the valves are opening and closing properly when turning the flywheel by hand. I would only check for a sheared flywheel key if I had the flywheel off. Here is a service manual for your engine. https://www.mymowerparts.com/pdf/Ko...ual-Command-CH18-CH20-CH22-CH23-CH25-CH26.pdf

Rivets said:

Sorry I made a mistake thinking it had solid tappets. Since you had the heads off I would start by checking to make sure you have no leaks around the intake manifold. If no leaks I would pull the valve covers and plugs and check to see if the valves are opening and closing properly when turning the flywheel by hand. I would only check for a sheared flywheel key if I had the flywheel off. Here is a service manual for your engine. https://www.mymowerparts.com/pdf/Ko...ual-Command-CH18-CH20-CH22-CH23-CH25-CH26.pdf

Click to expand...

So when I turn the flywheel by hand the lifters move and everything seems to function as it should mechanically. I can see an intake stroke, a power stroke and an exhaust stroke. I don’t see or hear any leaks around the intake manifold as both have fresh gaskets. I’ve got about 110PSI of compression on both cylinders and no leak after 5 minutes with the oil cap off so I wouldn’t think it’s a piston rings issue. Add to that there isn’t a surplus of oil in the pistons.

Thank you for the manual. I’ve got a digital copy of one, I’ll have to make sure this is the same.

one thing my manual says is that there is supposed to be 160psi of compression in the cylinders, but I’m not sure what would cause a 50psi drop in compression?

Air, fuel, spark and compression.

Could be a safety switch, sheared flywheel key, clogged fuel delivery, leaking head gasket, cam out of time and many more. Will it fire off with a flammable starting fluid sprayed directly into the engine? Pull the kill wire and check for operation.

slomo said:

Air, fuel, spark and compression.

Could be a safety switch, sheared flywheel key, clogged fuel delivery, leaking head gasket, cam out of time and many more. Will it fire off with a flammable starting fluid sprayed directly into the engine? Pull the kill wire and check for operation.

Click to expand...

I checked the SAM for voltage and my manual said I should at least 7 volts. I had 12 so I can’t imagine that being the issue. The safety switches, in my experience, won’t even allow the motor to turn over if they’re tripped. My head gaskets are holding as far as I’m aware (no leak after several minutes of setting compression). It’s definitely getting fuel. It will fire off every now and then but it’s never a running fire, it’s always a backfire or prefire (muffler or carb).

I’ve had a feeling it’s an issue with timing but with this motor being the way it is (keyed shaft, sensor ignition) I haven’t been able to pinpoint exactly where it would be. My pistons and flywheel move in unison so that leads me towards the key being slightly sheared (if that’s even possible) and getting my timing slightly off so it doesn’t start. I’ll pull it and remove the flywheel to take a look and get back. I really don’t want to do an entire tear down this close to season.

Ahflippin said:

it’s always a backfire or prefire (muffler or carb).

Click to expand...

There's your sign......