CH18 Won''t Restart When Hot

BillyBubba · Sep 3, 2020

I have a JD317 that has a Kohler CH18 in it as part of a re-power kit I installed years ago. It will start right up and run fine for hours, but if I shut it down it will not restart until it cools down for several hours or overnight. Then it will start right up again and run fine. If I start it then shut it down right away before it warms up it will restart.

It has a new carb and fuel pump. I've tested the spark with a spark tester and spark is good when engine is hot or cold. Tried putting a little fuel down the carb when it won't restart and that did not help. Even tried the trick of unscrewing the gas cap to relieve vapor lock with no luck.

The guys at the local shop just scratch their heads and have no clue as to what it could be.

Any ideas?

T.R.K. · Sep 3, 2020

What oil are you using? It should be 10w30.

Have you checked your oil pressure? I heard of one once that would not re-start hot and the mechanic thought the oil pressure was blowing
the lifters up and holding the valves open.

Mule Meat · Sep 3, 2020

Check the valve lash clearance and timing.

Valves could be getting hot and expanding enough to not allow them to close when hot. Once cooled they could contract enough to seal properly.

Timing could be off (keyed sheared).

Oil will have nothing to do with hard starting when the engine is hot.

MtMan · Sep 3, 2020

I believe Kohler engines are a very good engine. Years ago I repaired the mowers for a landscape contractor. They were having
the same problem that you are experiencing. What I found was the valve stems were getting a carbon build up on them and they
would stick going through the valve guide. I would just remove the valves and clean them up with a fine emery cloth. You don't
want to take any of the stem valve off or they won't run well either.

joe csuti · Sep 4, 2020

A possible cause of problem is sticking,leaking or worn valve lifters,the CH18 has hyd lifters for valves,plungers may be sticking in lifter body due to varnish buildup in body not allowing valve(s)to close all the way when eng hot or leak down caused by worn/dirty check/disk valve in lifter causeing little/no lift to valve(s)when oil hot/thin.

Another possible cause is a worn oil pump,if I remember correctly eng has a full flow lube system that provides oil to lifters when cranking eng,if pump worn and lifters leaking/leaking down you not be able to supply enough oil to same and they will collapse when oil hot/thin causeing valves not to open.

BillyBubba · Sep 4, 2020

I am using 10w30 oil.

Thanks for your replies. I will give them a try and let you know. It is just so strange that it will run so well until it is shut off and then won't restart right away.

kevinstuff · Sep 7, 2020

in this hotter than normal year , it just may be
its to lean under load , or the intake/cooling fins may need a good cleaning

BillyBubba · Oct 23, 2020

Well I'm just getting a chance to back to this project. Now it won't start at all. Still getting spark and fuel. I checked the compression and it shows 90 in each cylinder - the service manual shows it should be 160, so that is a little concerning.

There was a mention of checking the oil pressure. How is that done?

Any ideas before I start tearing into it?

Here are the specs on the engine if that is helpful:

Model CH18GST
Spec 62612
Serial No 3117500641

CH18 Won''t Restart When Hot

BillyBubba

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T.R.K.

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Mule Meat

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MtMan

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joe csuti

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BillyBubba

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kevinstuff

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BillyBubba

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