Kohler 5CKM21 no compression in both cylinders

wa8yxm wrote:
IF the cylinders built up compression with the spark plug feed, nothing coming out intake or exhause or crankcase vent or (if water cooled) radiator...

I"m stumped

You need 3 things to varroom
Fuel and air mixed in the proper portion (Explosive mix)
Compression (Appears you got that)
Spark. (Gasoline engines)
Heat (Diesel)

Missed a big item, "timing".

Everything must be done in the correct sequence one right after the other.

All it takes is timing to jump or valves to hang open slightly and it is all over.

Timing seems to be gear to gear, so no chain or belt, but there is a possibility that there could be a plastic or nylon gear in the mix..

Kohler isn't what it used to be and somewhere in the past I have read about a lot complaints of issues with many modern twin cylinder Kohler engines having valve related failures. If I remember correctly the valve guides moving out of place or valve seats causing the valves to not seal.

Basically I doubt the issue is fixable from the outside and will need some sort of teardown to assess the condition.

A bit more research, found some items for the OP to check..

https://www.lawnsite.com/threads/help-kohler-25-died-turns-over-but-no-compression.359856

Sorry, I was going to hot link but the forum doesn't like the URL above due to the formatting :M

From that website..

" Help! Kohler 25 died, turns over but no compression

Any ideas where to start looking for problem? Symptoms are like a broken timing chain would cause...just died suddenly, spins over freely with the starter, but acts like no compression (resistance). Happened late yesterday, so I haven't had a chance to investigate it yet. Any help greatly appreciated!

Here is what was wrong with mine. Engine ran fine. Shut it off and it wouldn't start again. Checked compression and there was none. Took the valve cover off and when turning the flywheel around by hand that one of the valves was returning very slowly. Sprayed some penetrating oil on the valve stem and turned the engine over and I had compression. Put the plug back in and it started right up again."

Very good chance the valve guides are gummed up and not closing quick enough..

Another which was mentioned in the link above, if you have a pressurized oil system seems Kohler in many of these engines may be using hydraulic lifters with the oil pump to create a compression release. Issues with the oil pump relief valve may not allow the lifters to release correctly to running position. Not sure how you test for that..

A broken crank gear was mentioned if the rocker arms are not moving which would mean replacement crank and cam shaft..

Need to at least pull the valve covers and see if the rockers/valves are moving correctly..

IF the cylinders built up compression with the spark plug feed, nothing coming out intake or exhause or crankcase vent or (if water cooled) radiator...

I"m stumped

You need 3 things to varroom
Fuel and air mixed in the proper portion (Explosive mix)
Compression (Appears you got that)
Spark. (Gasoline engines)
Heat (Diesel)

enblethen wrote:
If it has compression release like on Briggs, you have to turn back the crank a little to get valves to close. When engine RPM is high enough the compression release disengages.

Not sure if Kohler has a compression release.

Found a parts diagram for a Magnum M20 HERE

Don't see any thing in the valve train that looks like any form of compression release which I would not be too shocked about. Kohler often didn't use compression release at least with the 1960s cast iron engines I have played with.

Sadly, I suspect OP may need open up and dissect the engine, kind of doubt this is going to be fixable via external means.

If it has compression release like on Briggs, you have to turn back the crank a little to get valves to close. When engine RPM is high enough the compression release disengages.

Rigdon wrote:
if the intake valve had pressure coming out instead of in then you have stuck intake valves on both cylinders. the trick with pressurizing the cylinder through the sparkplug works very well. Other small engines used to get carbon fouling in the valve guides resulting in stuck valves and no compression usually from the carb running rich.

I pressurized both cylinders through the spark plug hole with 100 psi. At TDC air just rushed out of the intake, rotated fly wheel to different positions and compression built up no air coming out of the tail pipe or intake was noted . I went back to TDC and poured Chemtool into each spark plug hole and reinserted plugs and will soak the valves for a couple of days. At TDC I did not see chem tool leak out. May leak oy slowly. I still don't know how intake valves can just stick in both cylinders at the same time while the engine was running? I can see them sticking if it sat for a period of time without the engine running. Has anyone seen this happening before?

if the intake valve had pressure coming out instead of in then you have stuck intake valves on both cylinders. the trick with pressurizing the cylinder through the sparkplug works very well. Other small engines used to get carbon fouling in the valve guides resulting in stuck valves and no compression usually from the carb running rich.

YOu said no compression but you said it's sucking air in the exhaust.. This is a clue. Story or two (2nd one short)
Reading Gus Wilson's Model Garage (Series in popular Mechanics) back in High School he had a car brought in with what they thought was a blown head gasket. Well he confirmed two cylinders not working and as I recall it was the intake valves. or perhaps I'm mixing the two stories it was the intake)
He screwed a spark plug housing with the plug broke out and a air chuck brazed in into the spark plug hole and put compressed air to it and noted where it came out(I am confused it was a blown head gasket, Radiator bubbled)

My car it was the intake valves (That's how the mechanic figured it out)

Sounds like the exhaust valve on yours based on the sucking (the power stroke)

bgum wrote:
Try disconnecting the wire and start.

If you are talking about the wire to the fuel shut off(anti dieseling solenoid) I have done that. Also removed the fuel shut off solenoid to see if the plunger comes down when the starter button is pushed and it does.

Try disconnecting the wire and start.

I am not sure how this is related I thought it was just coincidence at first and it maybe, however as I stated in the OP the 12v supply wire to the fuel shut off broke and the plunger would stop the flow of fuel to the engine and the engine just shut off, no fuel to the cylinders and engine of course would not start. It just seems strange to me the problem started when this wire broke. After reconnecting the wire and verifying the solenoid was good the no compression and fuel coming out of the intake and exhaust sucking in instead of blowing out occurred. Is this just coincidence or is there something I am not seeing? Does anyone know if this genset has an electronic decompressor?