What has happened to my Kohler ?

[Scraperman]

I have a ride-on Scag that is quite old and I think I may have a very serious problem with the engine, a 20hp Kohler (details below).

Basically, although the engine will fire and run for a few seconds it then slows right down and stops. I then discover that there is engine oil in the carburettor and air cleaner, also dripping out of the exhaust, and when I first noticed all of this it had also leaked out of the engine oil filter which was slightly loose, I wonder if this may have been because the rubber sealing ring of the filter may have been fractured because of back pressure.

My first reaction was that some or all inlet and exhaust valves must be permanently closed or open for some reason. Or has one or more of the piston rings broken and thus allowing oil to get on top of one of the pistons which in turn is throwing it out through the inlet and exhaust valves ? The only other thing that I can think of is that the engine breather is totally blocked.

I would appreciate it very much if anyone on this Forum could suggest what the problem could actually be or shed more light on the problem in any way. I have very limited knowledge of this type of engine. Thank you for reading this.

 

[Bertrrr]

Need a little history on the machine like how has it been running , did this happen all at once , has it been smoking for a while , is there motor oil in the fuel ? If it runs for a minute then dies , the valves are not stuck
You will need to run a compression test to see the condition first , this will point you in the right direction for trouble shooting the problem . Post your compression test so these guys can give you a better idea of things

 

[Scraperman]

Firstly, thank you for your informative reply. That was much appreciated. I actually bought the machine in 2002 and I discovered that it was the one Scag that you shouldn't buy - a Turf Runner. But I have kept it going because I have my own workshop and I only mow 1.5 - 2 acres each week around the farm. But to answer your questions. Yes, this did happen all at once. I was riding the mower along the track to the farm drive and my 'phone went off and so I stopped the engine to answer it. But then it wouldn't start again. As far as I know there is no motor oil in the fuel. Certainly none was put in there.

 

[Rivets]

Two things I would be checking. First pull the dipstick and check to see if it is above the full mark and is if it smells like fuel, if it is overfilled or smells like gas, I suspect that the carb needle valve is not sealing, allowing fuel to freely run though the carb straight into the crankcase. Solution is to clean and rebuild the carb with a new needle.
Second, if oil level is good I would both plugs and see iff either is carbon or oil fouled. If either is bad I suspect the head gasket on that cylinder is blown and needs to be replaced. I’ve attached the service manual for your engine which also be of some help. https://mymowerparts.com/pdf/Kohler...ual-Command-CH18-CH20-CH22-CH23-CH25-CH26.pdf

 

[Mark H_NO]

If gas got into the oil, change the oil after fixing/replacing carb, and change again after a little run time.

 

[Scraperman]

Two things I would be checking. First pull the dipstick and check to see if it is above the full mark and is if it smells like fuel, if it is overfilled or smells like gas, I suspect that the carb needle valve is not sealing, allowing fuel to freely run though the carb straight into the crankcase. Solution is to clean and rebuild the carb with a new needle.
Second, if oil level is good I would both plugs and see iff either is carbon or oil fouled. If either is bad I suspect the head gasket on that cylinder is blown and needs to be replaced. I’ve attached the service manual for your engine which also be of some help. https://mymowerparts.com/pdf/Kohler...ual-Command-CH18-CH20-CH22-CH23-CH25-CH26.pdf

Thank you very much for your reply and help. I don't think that fuel is getting into the crank case and diluting the oil but I have had to top up the oil because too much was sent through the exhaust and also the carburettor and air cleaner but I will drain the oil and see if I can detact fuel in it. With regard to the plugs I am having a difficult job removing them. I know have changed them before and although I have many plug and box spanners I seem to have difficulty in keeping the spanners on the plugs when I try to undo them.
And thank you so much for that service manual. It is much better than the one that I already have. I have already discovered what the CH20S translates into.

 

[Scraperman]

If gas got into the oil, change the oil after fixing/replacing carb, and change again after a little run time.

Thank you very much for your reply, it is very much appreciated. I don't think fuel has got into the oil but I will investigate that more. Wouldn't it have ignited if mixed with the oil when going through the exhaust ?

 

[Scraperman]

Need a little history on the machine like how has it been running , did this happen all at once , has it been smoking for a while , is there motor oil in the fuel ? If it runs for a minute then dies , the valves are not stuck
You will need to run a compression test to see the condition first , this will point you in the right direction for trouble shooting the problem . Post your compression test so these guys can give you a better idea of things

I do apologise for not replying properly earlier, I do have a bit of a problem sometimes when logging in to this site and it won't let me quote when I reply to a post. Regrettably I don't have access to a compression tester. Are they expensive ?

 

[Bertrrr]

They are not expensive , look at Amazon , I think the last one I bought was under 20 bux
While you're at it get a 6 point socket to fit your plug , it will not slip off and you'll be able to pull and inspect them,
there is no better way to see what condition your engine is in by using a compression gage in my opinion

 

[Scraperman]

They are not expensive , look at Amazon , I think the last one I bought was under 20 bux
While you're at it get a 6 point socket to fit your plug , it will not slip off and you'll be able to pull and inspect them,
there is no better way to see what condition your engine is in by using a compression gage in my opinion

Very much appreciated there - thank you. With regard to plugs I have changed plenty of those in my time but the ones on this engine seem to be tucked away behind tinwork with a small hole which obviously must be large enough to get a plug spanner in. I've changed them before on this engine but I am struggling with things nowadays