Craftsman Kohler engine stuck both intake valves in the guides

[Auto Doc's]

Hello folks,

This problem is a first for me to come across. Craftsman/MTD CMXGNAM211704 zero turn with a Kohler PS-KT735-3077 engine.

The customer brought it to me after we had discussed some troubleshooting steps over the phone without resolve.

When it arrived, I check for compression and it had none on either cylinder. I pulled the valve covers to find that both intake pushrods were bent badly, and the intake valves were stuck in the closed position.

The engine is spotless under the top fan shroud/cover and has no debris is the cooling fins.

The engine had a 3-year limited warranty but is expired because the build date is 09/10/2021. It has no hour meter on the machine, but it has been well kept in a garage.

I looked up parts and found the bare heads have updated parts numbers.

Has anyone run into a similar issue on this engine design before?

 

[sgkent]

maybe bad fuel that varnished the stems and they grabbed. I did not believe in that being a possibility but have seen some videos of carbon build up on valves, guides and stems when old fuel is used that the volatiles have escaped from. Even 3 or 4 months can be enough to do it. Then there are people who add products to the fuel to stabilize it, but sometimes those products work and sometimes they turn into gels and make matters worse. This brave new world technology is hammering all of us.

 

[Auto Doc's]

Hello sgkent,

I am going to tear into it depending on how the rain holds out in my area. This has got my curiosity peaked as to what I will find out. The owner has been good about using non-ethanol fuel, but I don't know if any additives mixed in. The fuel tank is practically empty.

When I do get into this, I also need to verify the cam has not broken the compression release mechanism with this damage.

After pricing the parts and reasonable labor to replace the heads, the owner might want to consider a new direct replacement engine

 

[Tiger Small Engine]

Hello sgkent,

I am going to tear into it depending on how the rain holds out in my area. This has got my curiosity peaked as to what I will find out. The owner has been good about using non-ethanol fuel, but I don't know if any additives mixed in. The fuel tank is practically empty.

When I do get into this, I also need to verify the cam has not broken the compression release mechanism with this damage.

After pricing the parts and reasonable labor to replace the heads, the owner might want to consider a new direct replacement engine

Why not replace the push rods, adjust the valves, and send it back to customer first? I have never seen a twin cylinder engine that bent both intake push rods, but removing cylinder heads and replacing is expensive. Repowering the engine would be a last resort.

 

[Auto Doc's]

Hi Tiger,

I almost installed in a couple of good pushrods until I went to check the intake valves individually and they would not budge while being pushed down by hand with a hammer handle.

Both exhaust valves could be opened and spring right back like normal, but the intake valves stayed stuck closed.

Before pulling the heads, I'm going to start by trying to heat each of the intake valves with a heat gun and see if they will free up so I can get them moving. That will tell me pretty quickly if old fuel and additive may be the suspect cause of the sticking intake valves.

I do have various small engine valve guide hones that I can use to clean them up and then replace the intake valves, but I am concerned about a repeat failure If I cannot identify the root cause.

The customer did say he was running around pulling a trailer to pick up limbs before he parked it late in the evening, so the engine was hot when it was parked. Then the next day, he cranked it and it would not start. That is when it bent the pushrods.

New heads do show to have a newer replacement part number, so there may have been a valve guide fit issue that was identified during production or in the warranty period.

Both Kohler and B&S have had multiple valve guide issues with their engines for years.

Yes, a complete replacement of the heads or engine would an expensive solution, but only as a last resort.

 

[slomo]

Need to ask why the push rods got bent.

 

[Auto Doc's]

Hi Slomo,

That is still the mystery I have to determine. It is outside and it is raining around here currently.

I'm also going to verify the compression release has not been damaged before I dig too far into this engine. If it has, the cam will need to be replaced which just adds to the expense of repairing versus replacing the engine.