Kohler CH640 rocker backing out and bending pushrods...

[BrownCoat]

Hello all. My first post here. I ran a search and didn't come up with any results so I apologize if this has been asked before.

I think my dads old Grasshopper 720k has a Kohler CH640. I can't tell exactly since the tag is trashed and I can't find any other markings on it so I went off of pics on google images.

The issue is that the rocker bolts are backing out and dropping the pushrods out. At a quick visual inspection it doesn't look like there was any other damage other than one rod getting bent. The springs and rockers look good and no other damage to the parts other than the bend. The rod ball ends are good too.

Can I put some loctite on the bolt or will that not hold? I need to find some torque specs too, but is there any solutions to keep this from happening again? One of the valve cover bolts already broke off so I'm not thrilled at the prospect of pulling the head off an old machine like this and checking it out, although I may have to.

This is probably going to catch some fire, but I'm going to bend the rod back into shape and see what happens until I can find some replacements. It's just bent with no kinks or other damage and I have some tools to get it pretty straight.

Thoughts on how to fix the backing out issue?
Thanks in advance.

 

[bertsmobile1]

:welcome:

Go to Kohlers web site, support/ manuals and type in CH640
That should bring you the service manual.
At some time a screen will pop up making it look like you have to be adealer or something but down the bottom will be a button that says guest.
Click on it then agree to the terms & conditions.
You will then have the service manual.
From memory there is one for the courage & another for the Command but both cover vertical & horizontal shaft engines.

So you are not dissapointed, :thumbdown: on fitting the old rod, it will most likely jump right off, remember it is moving 1800 times a minute and has to do a minute move to decompress the engine.
They are not expensive and if you have a real repair shop around you can usually get a used on for free I think they are only about $ 10 in any case.
Locktite is not likely to do much good as the head gets real hot so you will have to use the high temp ( red) loktite

 

[BrownCoat]

:welcome:

Go to Kohlers web site, support/ manuals and type in CH640
That should bring you the service manual.
At some time a screen will pop up making it look like you have to be adealer or something but down the bottom will be a button that says guest.
Click on it then agree to the terms & conditions.
You will then have the service manual.
From memory there is one for the courage & another for the Command but both cover vertical & horizontal shaft engines.

So you are not dissapointed, :thumbdown: on fitting the old rod, it will most likely jump right off, remember it is moving 1800 times a minute and has to do a minute move to decompress the engine.
They are not expensive and if you have a real repair shop around you can usually get a used on for free I think they are only about $ 10 in any case.
Locktite is not likely to do much good as the head gets real hot so you will have to use the high temp ( red) loktite

Thanks for that info. I was hoping I could stick it in my lathe and indicate off of the straight part of the rod and use a press to squish it back to shape. Not the best solution but it would let me know a little better what kind of shape the valves are in. Probably best to buy new ones. I do have red loktite. I just don't understand what would make it back out. And by back out, I mean a whole lot. I'll grab that service manual that you said and see what the torque specs are for that bolt. I appreciate your help. Thanks. The nearest repair shop is a little over an hour away from me

 

[bertsmobile1]

Usually it would be because it was not properly tightened in the first place.
Other cause is excessive heat caused by blocked cooling fins and bad timming.

 

[reynoldston]

Usually it would be because it was not properly tightened in the first place.
Other cause is excessive heat caused by blocked cooling fins and bad timming.

Just replaced one of them heads a couple of days ago myself. 160 in lbs. They bottom out onto the head and shouldn't back out. Look what bertsmobile is telling you about overheating. That engine tens to over heat with grass clippings between the heat shield and head which block the cooling fins. When it overheats the valve guides will move out of place and bend the push rods. The only fix is a head replacement. One more thing make sure you bleed the lifters before you put it together or you will just bend the push rods again.

 

[BrownCoat]

Usually it would be because it was not properly tightened in the first place.
Other cause is excessive heat caused by blocked cooling fins and bad timming.

I think maybe excess heat sounds about right. My dad isn't the best with maintaining his stuff. I was out of state for a long time or I would have done it. I'm sure the fins are packed or were. I didn't have a chance to work on it today but I'll get on it tomorrow.

 

[BrownCoat]

Just replaced one of them heads a couple of days ago myself. 160 in lbs. They bottom out onto the head and shouldn't back out. Look what bertsmobile is telling you about overheating. That engine tens to over heat with grass clippings between the heat shield and head which block the cooling fins. When it overheats the valve guides will move out of place and bend the push rods. The only fix is a head replacement. One more thing make sure you bleed the lifters before you put it together or you will just bend the push rods again.

Gotcha. I'll definitely look at the guides tomorrow and see. The heat could have been a factor but I haven't looked it over super close yet. Thanks for the torque specs. When I looked at the head the valves and springs looked perfect. Just like you'd expect them to look. From what I could see is that the rocker bolt just backed way out and dumped the rods. There might be more than just that but it was dark and raining so I'll have a look tomorrow when it's nice out and inspect everything more closely.

I got that manual. I still don't know exactly what engine it is but it looks like the one manual covers just about any engine that would be in his mower. Here's a shot of the rods

 

[motoman]

Reynoldson has touched the topic of the lifter. When you look at the manual see if there is a very specific procedure in first setting the valve train up. Sounds like it has hydraulic lifters which means there are very tiny oil feed holes in the lifters which allow the lifter to hold and collapse during firing cycles. They are notorious for failing due to oil contaminants. Also I would check the rocker threads and lock nut threads with a thread gauge to see if they are just worn out (too loose). Forgive any errors here. Do not know your machine, just sayin'...BTW online I have seen a great little Kohler video of a working lifter. It is good for refresh or general introduction to that device.

 

[BrownCoat]

Thanks for the info I'm a car guy so I'm familiar with a lot of aspects of engines but some of these little ones kinda throw me sometimes.

Well I massaged the rod back into shape and checked it on my lathe. The axis is on the money and it's pretty straight. I'm gonna see where I can order new ones from. I think it's a CH620, 20 horse but still can't tell for sure. I reassembled it, tightened to 160 in lbs with a little blue loctite for good measure and she seems to run ok. I ran it with the valve cover off and the rod seems to be running true.

The battery is dead so I have to jump it and if I engage the mower it dies. I guess it needs the battery when under load? I'll check for rods tonight unless y'all have a spot you like to shop that I should buy from.

 

[BrownCoat]

Reynoldson has touched the topic of the lifter. When you look at the manual see if there is a very specific procedure in first setting the valve train up. Sounds like it has hydraulic lifters which means there are very tiny oil feed holes in the lifters which allow the lifter to hold and collapse during firing cycles. They are notorious for failing due to oil contaminants. Also I would check the rocker threads and lock nut threads with a thread gauge to see if they are just worn out (too loose). Forgive any errors here. Do not know your machine, just sayin'...BTW online I have seen a great little Kohler video of a working lifter. It is good for refresh or general introduction to that device.

I checked the bolts with my thread gauge and they checked out. They looked brand new with a nice pitch. I cleaned all the bolts on my wire wheel just to be doubly sure then clean out each hole with brake cleaner then air so I wouldn't hydraulic the bolt hole when I reinstalled the bolt. To be honest, I don't really know this machine either. It's my dads and I'm just trying to help him out the best I can. The service center near here (over an hour away) really sucks. They don't keep any records of the services they perform or the machine we have (I called today to see what engine it has). The last time he had it in for service was to install a new muffler and they totally burnt his choke cable to cinders and then lied that it was like that, and screwed something up with the throttle linkage that I'm still trying to figure out. It wont return and gains speed. I have to manually control the throttle. Now that I'm back in the same state as them and can help, I'm going to learn how to service this thing myself. At least I'll know that it's being serviced by someone who cares instead of someone waiting to get off work. Frustrating.