Kohler Command 18HP CH620 questions

DoubleA

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Hello, I see a lot of information being shared on this forum regarding small engine repair and thought I might be able to ask a few questions.

I have a 2015 Cub Cadet UTV with an 18HP Kohler Command Pro (700hrs.) that I recently tore the engine down on. This was used by some of my guys on our construction sites. I saw them drive by one day blowing a bunch of smoke, it was running on one cylinder after that. We ordered a new Kawasaki Mule to replace it at that time. When I asked them about the Cub, it sounds like it was ran with low oil or no oil (the comment was "it wasnt on the dip stick" how much did you add "not sure"). I figured it was done for, hence the Kawasaki purchase.

I took it home to look into it a little deeper hoping to have something the kids could play around on and to use for yard work. I drove it on and off the trailer running on one cylinder. Found a puddle on the trailer, the oil filter was loose and leaking. Went to check the plugs and one plug was almost backed out all the way and the other was half backed out. I thought that may have been the reason for the issues. Did a quick compression test on cold engine without holding throttle open and had 112PSI exactly on both cylinders (wishing I would have done a hot one with throttle open) I have no idea what it would have been if I did it correctly. Anyhow, I cleaned the plugs, changed the oil, and it fired right up and ran great.

I eventually tore the engine down as one cylinder would eventually start burning oil and foul the plug. I thought it might just be a head gasket but tore it all down anyways. I'm looking for advice in an attempt to save some time and money.

The pistons skirts each have some scuffing. Nothing major and nothing around the pistons ring lands or on the top. There is a small ridge that I can feel in the top of the bore. Cylinder walls are glazed with light visible scratching and they can be felt with a finger nail is you really pay attention. I'm thinking of throwing in a rebuild kit with new rings and hoping the head gasket was the problem. Never did a leak down test so I should probably look at the valve seals but not sure what I should look for.

What would you guys do? This is a 2wd unit so there is not much value there. With what I have described in this novel what do you think needs to be checked to determine the source of the oil burning? Would a bad head gasket cause this? Would I be able to see signs on the old gasket (didnt notice anything that stood out). Warped head? Rings appear to be in good shape to the naked eye.

If you took the time to read this I thank you. I am not an engine builder. I do a lot of maintenance and some extensive upgrades on things I own and did just build the auto trans in my pickup so I am capable and understand the concept, just never actually done an engine yet. The local machine shop wont even look at it. I just happen to be in a situation where the money needs to go elsewhere and would like to make educated decision. If it was not for this I would do it right no questions asked.

Thank You
 

Coleevans321

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Running on one cylinder with identical compression on each would not make me think it would be an internal problem. Did you test spark through coil wire? Possible carb flooded cylinder, engine oil viscosity became thin enough to get past rings and when engine heated it evaporated gas from cylinder causing low oil level and oil burnt plugs. I could very possibly be wrong but I just encountered the same problem at my shop with a pro drive boat motor with a kohler cv740.

112psi of compression should have been plenty for the motor to run. The newer efi’s require a little more but I’ve seen older carbureted kohler motors still kicking with 90psi of compression. A leak down test would have been the best diagnostic tool to use in this situation.
 

StarTech

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It is to note per the service manual.

For Command Twins:
A compression test is best performed on a warm engine. Clean any dirt or debris away from base of spark plug(s) before removing them. Be sure choke is off, and throttle is wide open during test. Compression should be at least 160 psi and should not vary more than 15% between cylinders.

With this in reference the compression measured is low. If the OP can catch a finger nail in the score marks then it most needing to be hone out to .020 over provided that cleans up the cylinders ovaling and tapering; otherwise, if the OP has to go over .020 then most likely the engine is trash.
 
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