More problems on the 425 Kohler CH25
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Waiting on parts to arrive…in the meantime, here are more pics of the cylinder head and stuff…
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MTGreen
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Hmm -"tapped back in"? Those should need a press or some pretty firm "tapping" with a drift to seat. This could be part (or all) of your problem if the seat is coming out. Remember the coefficient of heat expansion is different for the head than the valve seat so it may stay now and fall out when the engine heats up. I would consider either replacing all 4 of them or at least removing the seats and center punch peening the ID of the valve seat bore in the head to tighten up to a firm press fit
Here's an explanation of what I'm talking about with bearings but the same principle applies:
How to Make a Loose Bearing Race Fit Snuggly into a Housing
Whenever a bearing is replaced, the race it rides in should be replaced too. Learn how to make a loose bearing race fit snuggly into a housing.
www.grainews.ca
Ahhh…good catch. I wouldn’t say it was an “easy tap-in” as I delivered short, sharp blows to a socket that fit exactly around the seat. But, I will try that peening method too.Hmm -"tapped back in"? Those should need a press or some pretty firm "tapping" with a drift to seat. This could be part (or all) of your problem if the seat is coming out. Remember the coefficient of heat expansion is different for the head than the valve seat so it may stay now and fall out when the engine heats up. I would consider either replacing all 4 of them or at least removing the seats and center punch peening the ID of the valve seat bore in the head to tighten up to a firm press fit
Here's an explanation of what I'm talking about with bearings but the same principle applies:
How to Make a Loose Bearing Race Fit Snuggly into a Housing
Whenever a bearing is replaced, the race it rides in should be replaced too. Learn how to make a loose bearing race fit snuggly into a housing.
More…in my hand is a small metal rod that was laying on top of the piston, along with a couple of small “dark colored wads of thin fibrous material”…looks like the valves show some marks where it was bouncing around in there…I don’t have a clue…
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ponytug
Super Member
Wow! That would explain a lot, like the loose valve seat. I doubt that the pin was doing anything good. Is it possible that it fell in during a spark plug service or compression test? (As in, it was in the hose for the compression tester and fell into the cylinder?)
Thanks for the posts.
All the best,
Peter
Thanks for the posts.
All the best,
Peter
Whoa!! I wouldn’t have thought to look at the compression tester setup. I think that piece is too big to be part of it, but…I’m going to check it out for sure…
Thinking more about it…I’m trying to imagine how it got there. Maybe it wasn’t there until AFTER the motor started this episode? But…it kinda looks like the valves have little marks in them, as if that piece were bouncing around on top of them…
Or, maybe it was lying on the top of the motor, somewhere around the carb and between the heads…and when I pulled this #1 cylinder head, I had to lift it about straight up to clear stuff around it, so I wouldn’t have been able to see if anything were laying in a place in which it could fall in when the head was lifted? That seems like a stretch to me, but I can’t rule it out. I’m out of ideas now LOL…
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MTGreen
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Is the rod steel or aluminum?
Was this in the cylinder with the valve seat falling out or the other one?
Assuming it did appear while the engine was buttoned up and it did bounce around in there, there're not too many places it could have come from -either through the plug hole like @ponytug mentioned or the intake/carb.
I would be inspecting your carb/intake assembly very closely. It doesn't resemble a carb part much but could be and could certainly be part of your airbox assembly. Remember also it could have had pieces break off and pass out the exhaust and what you're looking at is a partial piece
Was this in the cylinder with the valve seat falling out or the other one?
Assuming it did appear while the engine was buttoned up and it did bounce around in there, there're not too many places it could have come from -either through the plug hole like @ponytug mentioned or the intake/carb.
I would be inspecting your carb/intake assembly very closely. It doesn't resemble a carb part much but could be and could certainly be part of your airbox assembly. Remember also it could have had pieces break off and pass out the exhaust and what you're looking at is a partial piece
MossRoad
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YIKES!
2manyrocks
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Hard to even imagine what that came from.
edit: spark plug core????
edit: spark plug core????
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I believe it’s steel. I can’t feel any flats so it appears to be round but the ends I can’t tell if original or maybe lopped off…
No, this was the opposite cylinder (1) supposedly the “gooder” one
First off I thought it could be a carb butterfly rod (I had one on my lawn tractor 17hp Kohler a few years ago that loosened up, and the rod and butterfly went into the motor. I found all the pieces when I went through the motor and remarkably no real damage…did need rings though) but seeing no threaded hole or flat spots in it I don’t think so now. I’ll keep digging and see if I can come up with a believable reason.
Spark plugs were intact.
For sure! One thing I’ve realized—these motors are sure picky and appear to be subject to breakdowns more-so if best maintenance isn’t done. I think that the previous owner and then me, made things worse with wrong oils, and not enough frequent oil changes. (Heck, I had a Murray push mower for over 20 years I never changed the oil in…sat out under an open shed roof and no air cleaner! It never stopped!
)2manyrocks
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PT's website says the PT425 weighs 1,387 pounds. Add the weight of an implement and an operator. Do something like mow down 6' tall brush. That's a lot to ask of a small gas engine, especially over a long period of time.
MossRoad
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When we got married in 1985, my in-laws gave us a little Craftsman push lawn mower with a small B&S engine. I never changed the oil. I'd just top it off in the spring and tap out the air cleaner on the garage floor. Original spark plug, too. That darn thing would start 1st pull every spring. Just had to push the primer button 15-20 times. I never drained the fuel in fall. Always used E10 87 octane. It got to the point I'd call the wife and kids out to watch the annual event to see if it would start first pull. Amazing. 29 years later, the deck cracked and the wheel mounts bent out, but the little engine was still good.For sure! One thing I’ve realized—these motors are sure picky and appear to be subject to breakdowns more-so if best maintenance isn’t done. I think that the previous owner and then me, made things worse with wrong oils, and not enough frequent oil changes. (Heck, I had a Murray push mower for over 20 years I never changed the oil in…sat out under an open shed roof and no air cleaner! It never stopped!
I pulled the engine off the deck and it sits in a place of honor in the back of my garage.
MossRoad
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Change the oil and filter regularly. Keep the air cleaner clean. Keep the debris from building up on the engine cooling fins. That's about all I do to mine.
