More problems on the 425 Kohler CH25

[Modrob]

If…the engine isn’t running and I’m just bumping it over, would the electronic system have anything to do with stopping the physical action of the piston pushing up air out of the spark plug port? I would think at that point it’s just a mechanical action/process and if rings were good it would have to push the air up, yes? (See? I have a weird/warped way of mechanic-ing )

 

[etpm]

The latest has been: no compression at all—zero—on both cylinders

If the pistons are moving up and down and there is truly zero measured compression then either your gauge is broken or the valves aren't closing. Or there are holes in both pistons.
Eric

 

[MTGreen]

Your crank and your cam are not coordinated like they should be. Suspect your timing chain/belt/gear either skipped multiple teeth or sheared a woodruff key

The other option is you have a valve bent on both cylinders or as mentioned a hole in both pistons.

I would definitely eval your crank/cam link and maybe check for air going the wrong way when cranking i.e. out the carb instead of in.

If I had to guess I'm betting on crank/cam gear woodruff key

 

[MTGreen]

A quick and dirty test to see if your valves are closing and your pistons are intact is to use a compressed air blowgun with a rubber tip for sealing on your spark plug holes when your valves are at their highest points (springs extended). If you're building pressure then everything is closing/intact and you likely have a crank/cam timing issue. If you're not building pressure it's going to be blowing out the carb or exhaust or into the crankcase all of which are easily verified and you've got a bigger problem requiring engine disassembly

Blowgun rubber tips:

Amazon.com

 

[2manyrocks]

There is no shame in taking the engine to a good small engine shop for their assessment.

 

[Modrob]

There is no shame in taking the engine to a good small engine shop for their assessment.

You know, I’m slowly starting to change my outlook on some things—especially the “I’ll eventually figure this out…” meanwhile, other things just keep popping up and my age is slowing me down. IF…it didn’t appear to be so much hassle getting all the hydraulics away from the motor, I’d probably already have it figured out. I’m wimping out more and more each year—and I ain’t liking it!
But you’re right. It would be the smartest thing to do.

 

[Modrob]

A quick and dirty test to see if your valves are closing and your pistons are intact is to use a compressed air blowgun with a rubber tip for sealing on your spark plug holes when your valves are at their highest points (springs extended). If you're building pressure then everything is closing/intact and you likely have a crank/cam timing issue. If you're not building pressure it's going to be blowing out the carb or exhaust or into the crankcase all of which are easily verified and you've got a bigger problem requiring engine disassembly

Blowgun rubber tips:

Amazon.com

Thanks for this straight-ahead, more simplistic approach. That’ll be my very next move. (IF this danged cold and wind would let up! )

 

[MossRoad]

You know, I’m slowly starting to change my outlook on some things—especially the “I’ll eventually figure this out…” meanwhile, other things just keep popping up and my age is slowing me down. IF…it didn’t appear to be so much hassle getting all the hydraulics away from the motor, I’d probably already have it figured out. I’m wimping out more and more each year—and I ain’t liking it!
But you’re right. It would be the smartest thing to do.

As we get older, and more financially secure, I had to tell my wife it was OK to get the appetizer if she wanted it.

 

[MTGreen]

Hmm. Well looking further into the ch25 specifically looks like the mating gears on both the crank and cam are manufactured and sold as one piece integral crank/gear and cam/gear assemblies. Makes it less likely but certainly not impossible that the gears have spun on their respective shafts

 

[Modrob]

Hmm. Well looking further into the ch25 specifically looks like the mating gears on both the crank and cam are manufactured and sold as one piece integral crank/gear and cam/gear assemblies. Makes it less likely but certainly not impossible that the gears have spun on their respective shafts
View attachment 846795

Thanks very much for that!

 

[oldnslo]

Hmm. Well looking further into the ch25 specifically looks like the mating gears on both the crank and cam are manufactured and sold as one piece integral crank/gear and cam/gear assemblies. Makes it less likely but certainly not impossible that the gears have spun on their respective shafts
View attachment 846795

And there are timing marks on both gears so pretty straight forward to verify the timing.

 

[Modrob]

Finally…got a break in weather and other tasks to spend a few minutes back here…
Somehow I now have compression on cylinder 1, but still nothing on the original problem cylinder 2. I injected air into this cylinder and had some leakage through the exhaust pipe. Oddly, while cranking the motor to check compression earlier another push rod bent on this cylinder on the intake. Remembering the lifter being stuck on the exhaust valve earlier, I pulled the intake side and sure enough, it was near impossible to move. I bled it and got it to moving again and installed another new rod. All seem to be fine now, but at this point the injected air into the cylinder 2 plug port seems to be leaking through exhaust or carb…I’m guessing I need to look into the head gasket now…

 

[Tchamp]

Is it possible that you have a stuck exhaust valve?

 

[Modrob]

Is it possible that you have a stuck exhaust valve?

I don’t think so, because I see them all moving when I bump it over (both valve covers are off.) And I can push all valves down with my thumbs and they seem to operate freely with good spring pressure. But, I could be wrong…

 

[MTGreen]

You have a valve problem and need to remove that head

 

[Modrob]

You have a valve problem and need to remove that head

Yes sir…hopefully tomorrow I’ll get a look.

 

[Modrob]

Is it possible that you have a stuck exhaust valve?

I believe you and some others are right—further examination yesterday I found exhaust valve not fully closing, and the head gasket has break just about the area where the exhaust bolts to the head.

 

[Modrob]

You have a valve problem and need to remove that head

Sure ‘nuff! Yesterday found exhaust valve not fully sealing and a broken head gasket…

 

[Modrob]

Here’s the first look…

 

[Modrob]

Here are more…