Kohler 5CKM21 no compression in both cylinders

Gdetrailer wrote:
Sad..

Sorry to hear this.

But, I can't blame the shops for not wanting to work on it while installed in the MH. Way to difficult to work on when you have extremely limited access. Finding a knowledgeable and good small engine tech isn't easy either and the good ones are up to their eyeballs in work and don't come cheap.

Typically many shops will want the entire gen assy to be removed form the RV, if you had to pay someone to do that plus the cost to reinstall it would get even more expensive to the point it is cheaper to replace with new or like a lot of folks have done, use a portable gen instead.

I don’t blame them either just removing the shrouds is a chore. Maybe the next owner can put a 4000 watt HF one in, they are on sale now for $ 469.

Nearest I can tell is it has 4 bolts mounted to 4 rubber isolators and has to come up and out of the rear cap. If I was going to keep it I probably would pull it out and replace it with a HF one. I rarely use it anyways only to exercise it and heat something up in the MW or power house refers during power outages.

Gary: is the genset mounted to a pan that lowers out? Mine has about a dozen bolts holding pan and genset.

Sad..

Sorry to hear this.

But, I can't blame the shops for not wanting to work on it while installed in the MH. Way to difficult to work on when you have extremely limited access. Finding a knowledgeable and good small engine tech isn't easy either and the good ones are up to their eyeballs in work and don't come cheap.

Typically many shops will want the entire gen assy to be removed form the RV, if you had to pay someone to do that plus the cost to reinstall it would get even more expensive to the point it is cheaper to replace with new or like a lot of folks have done, use a portable gen instead.

Removed the oil from pistons and checked compression. Still no compression. I guess the problem lies in either broken teeth on the cam shaft or worn lobes. At any rate I am not about to pull the genset and tear it apart to replace the cam especially when the part is obsolete. I talked to 3 techs from Kohler which had no direct knowledge of the genset and offered little help, but all thought it was a stuck valve issue. Called three generator repair shops and one mobile repair place but no one would work on a genset in an RV. Very difficult to get to. So I will just sell the MH as is like my wife has been wanting and just hotel it.

After soaking with oil a couple of day I rotated fly wheel and added Chemtool with the oil thinning the viscosity some. After several days of soaking, last night I was able to see the valves moving up and down opening about 1/4 in and closing completely. I was able to look down the sparkplug hole and see the valves moving with a small light and mirror. As a side note I did not see any carbon buildup on the valves or piston. Kohler manual recommends removing head and scraping off carbon buildup at 500 hrs. Hope to get it back together soon to see if compression has returned.

Update. I poured Chemtool into spark plug holes it did leak down somewhere. Maybe past rings because it is thin maybe down valves. The engine has opposing pistons which are horizontal. After two applications of Chemtool and soaking for 4 days I added motor oil and that seems to be holding in the cylinders. I am hoping if it is a valve being stuck this combination would free it up.

Gjac wrote:
Some good information here. My Kohler is 25 years old, only 420 hrs on it. It is a flat head engine( no over head valves) and if you look at the web site you posted the crank shaft or cam shaft with gears are obsolete, so if that is the issue I am out of luck. I am still hoping that if both valves sticking(which is confusing to me) that soaking head with Chemtool will loosen them. The oil pump relief valve is something I had not even considered, but that would make sense if oil is not getting to the hyd lifters then I guess both intake and exhaust would stay closed and if both stay closed the no air comes into cylinder so no compression takes place. I still have a call into the Kohler rep, he has not been much help but if I ask a specific question he will research it for me. So I can aske about how to check this valve.

Yeah, looked like a lot of Kohlers parts are obsolete but, there may be some parts available through aftermarket brands like Stens.

Flat head does make some difference, no rockers, more a direct drive from cam to valve which simplifies things a bit but also still has the possibility of valve/lifter issue.

Doesn't take much valve hang to stop building compression.

I think, if this were me, I'd call a Mobil RV Tech to come out and perform an analysis, and then go from there.

Gdetrailer wrote:

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..

Some good information here. My Kohler is 25 years old, only 420 hrs on it. It is a flat head engine( no over head valves) and if you look at the web site you posted the crank shaft or cam shaft with gears are obsolete, so if that is the issue I am out of luck. I am still hoping that if both valves sticking(which is confusing to me) that soaking head with Chemtool will loosen them. The oil pump relief valve is something I had not even considered, but that would make sense if oil is not getting to the hyd lifters then I guess both intake and exhaust would stay closed and if both stay closed the no air comes into cylinder so no compression takes place. I still have a call into the Kohler rep, he has not been much help but if I ask a specific question he will research it for me. So I can aske about how to check this valve.