Kohler CV25 problems

[Mr Mower Man]

There is a CV25-69513 in my shop that seems to be running rich on cylinder #2.

At first, I just agreed with the customer that it was a fuel system issue, and I ordered both the carb rebuild kit and the accelerator pump kit.

But then I had second thoughts about it and tested it further. I ran each cylinder by itself. #1 is pretty smooth, but $2 is where there seems to be a lot of blubbering/missing/popping going on. So I hooked up my spark tester and ran the engine with the tester in-line. It sparked consistently, and there was no correlation between spark and engine performance problems.

Then I tested the compression. Cylinder #1 (the smooth one that seems fine) had 130 lbs, and cylinder #2 (the bad sounding one) had 165 lbs. A pretty significant difference, so I loosened the rocker arms and did a leakdown check. As you could imagine, there was more leakdown on cylinder #1 (80% actually) than on cylinder #2 (50%). I watched the gauge as I rotated the crankshaft against the pressure. Cylinder #1 was noticeably easier to turn against than #2. The leakage was from the intake valve on both sides, as I could easily hear air escaping through the carburetor (crankcase breather was not mounted, so no air was coming through the breather tube).

The funny thing about all this is that when the engine runs, cylinder #2 sounds like it's the problem. However, it's clearly the stronger of the 2 cylinders. Which leads me to think I really do have a carburetion problem. Because if compression were the problem, it would run better on #2 than on #1, which is backwards from what it is really doing. It has been running rich, with the spark plugs looking pretty black and sooty.

I'm thinking we really do have a carburetor problem, which was causing the customer to complain. But I'm thinking there's an unrelated compression issue as well that the customer didn't notice.

What do you think?

[bgsengine]

Is leakdown test being done correctly? 80% and 50% is an awful lot given the compression readings (You want 20% or less leakdown) unless you are reading it backwards (then the "80%" cylinder actually being 20%) leakdown should be done at exactly TDC on compression (with flywheel/crankshaft locked in place) and if you still have air leaking through intake then (and maybe pop intake manifold off and check at ports to be 100% sure, probably pop manifold off anyway for carb service) you got valve clearance or bad valve issue obviously. (maybe seats popped loose , some engines notorious for that after an overheat) but 165 seems a little high compression, could be a camshaft issue (might re-do leak down yet again after the first double-check, with rockers rotated off the valves - if no leakdown through intake then, you may have a camshaft problem) But your numbers don't seem to make a lot of sense at this point, I'd suggest re-checking that things (testing) are being done correctly.. 50% or 80% leakdown either case, should be burning oil like a bug fogger..

[KE4AVB]

When you say black sooty is dry or wet?

I agree that is off about the leak down numbers as the engine shouldn't even be running @ 80% leakage. As for the compression being 165 the SM the CV should have 160 or better with both cylinders with 15% of each other. With readings given they are with 21.3% of each other. But considering the leak down results it can explain why there is this difference.

Also you got remember even though you have good compression readings nearly all of it can loss right before TDC if top the cylinder wear is the problem. I have a Stihl 55 chainsaw here that has 145 psi compression yet will not start because all the compression is loss right at TDC. Verified the cylinder is damage in this area. Customer not repairing it. I also had a Tecumseh that had only 12% leakage at TDC and then when checked midway it had 50% leakage.

Even if I had only 50% leakage I would be pulling the heads and checking those indicated leaky intake valves and seats. BTW loose seats can be good at hand turning but be bouncing in and out while running causing problems. I even had Briggs last that was running until the valve seat pieces jammed the cylinder over a 1/4 of the seat was missing. It shouldn't even been running but it was. Got lucky only had to replace the head and piston. You could it ran a while considering the amount of piston damage.

[Mr Mower Man]

Is leakdown test being done correctly? 80% and 50% is an awful lot given the compression readings (You want 20% or less leakdown) unless you are reading it backwards (then the "80%" cylinder actually being 20%) leakdown should be done at exactly TDC on compression (with flywheel/crankshaft locked in place) and if you still have air leaking through intake then (and maybe pop intake manifold off and check at ports to be 100% sure, probably pop manifold off anyway for carb service) you got valve clearance or bad valve issue obviously. (maybe seats popped loose , some engines notorious for that after an overheat) but 165 seems a little high compression, could be a camshaft issue (might re-do leak down yet again after the first double-check, with rockers rotated off the valves - if no leakdown through intake then, you may have a camshaft problem) But your numbers don't seem to make a lot of sense at this point, I'd suggest re-checking that things (testing) are being done correctly.. 50% or 80% leakdown either case, should be burning oil like a bug fogger..

Well, I wasn't reading it backwards. The needle was in the red on the cylinder with the 80% leakage. But it wasn't smoking when running. Just ran rough. I already did it with the rockers off the push rods. Camshaft was not in play during my leakdown test. And I observed the gauge as I worked the piston up the cylinder. Leakage readings were consistent through the entire stroke.

[Mr Mower Man]

When you say black sooty is dry or wet?

I agree that is off about the leak down numbers as the engine shouldn't even be running @ 80% leakage. As for the compression being 165 the SM the CV should have 160 or better with both cylinders with 15% of each other. With readings given they are with 21.3% of each other. But considering the leak down results it can explain why there is this difference.

Also you got remember even though you have good compression readings nearly all of it can loss right before TDC if top the cylinder wear is the problem. I have a Stihl 55 chainsaw here that has 145 psi compression yet will not start because all the compression is loss right at TDC. Verified the cylinder is damage in this area. Customer not repairing it. I also had a Tecumseh that had only 12% leakage at TDC and then when checked midway it had 50% leakage.

Even if I had only 50% leakage I would be pulling the heads and checking those indicated leaky intake valves and seats. BTW loose seats can be good at hand turning but be bouncing in and out while running causing problems. I even had Briggs last that was running until the valve seat pieces jammed the cylinder over a 1/4 of the seat was missing. It shouldn't even been running but it was. Got lucky only had to replace the head and piston. You could it ran a while considering the amount of piston damage.

The spark plugs have more of a dry soot than wet. Doesn't look like it's been burning oil. Just rich fuel/air mixture is what it looks like to me. I wish I could figure out how to put pictures on here so I could show you guys.

I would like to pull the heads so I can inspect the valve seats, and the cylinder while it's exposed. I've already advised the customer that he has a compression problem, so he's OK with replacing cylinder heads if necessary. But I need to inspect and see exactly what we're working with before I decide that's what we need to do.

[KE4AVB]

To upload pictures (actually linking to them) you need to upload to a photo hosting site like Photobucket or Imgur. Either resize before upload or after to 600 x 600 or smaller. I actually changed it to 640 x 600 since my phone does 640 x 480 VGA images. Then you install the link to the image location using the Img button when posting a reply. It is very much like inserting an URL or Quote.

Well, I wasn't reading it backwards. The needle was in the red on the cylinder with the 80% leakage. But it wasn't smoking when running. Just ran rough. I already did it with the rockers off the push rods. Camshaft was not in play during my leakdown test. And I observed the gauge as I worked the piston up the cylinder. Leakage readings were consistent through the entire stroke.

That can be due to the valve or seat leaking just depends how bad they are leaking since you said you hear air escaping from the intake. You can nearly 100% when a valve is stuck open or a broken valve seat. With the reading consistent the entire stroke I say the intake leakage is probably your root cause of huge leakage in leak down tests or blown head gaskets. Anyway when you pull the heads you will need new head gaskets.

[Mr Mower Man]

Well, I took off cylinder #1 (the weaker of the two) to see what was going on. Sure enough, there is significant intake valve leakage. Looks like the valve has only been seating on roughly half of the surface of the seat. We have a nice alternating pattern of black and shiny silver! Also, the valve itself has a noticeably worn face. The face has an edge to it that I can feel. That's where the bulk of the compression has been lost. Exhaust valve doesn't look nearly as bad, though it's not in great shape either.

Problem is, I think fixing this compression problem will just expose the cylinder problems. The cylinder bore does have the crosshatch pattern in it, except for about a 3/4" wide band that starts about 1/2" from the top of the bore. Instead of crosshatch there, I see 3 faint horizontal "ring marks," I'll call them. I can even feel at least one of the marks with my finger. I don't want to spend a bunch of money on cylinder heads and the carburetor when the cylinder looks like this. I don't think the cylinder can probably handle full compression anyway. I think this engine has run its course. What do you think?

[bgsengine]

What do you think?

I think you're right.. short block or re-power if the machine is worth it, if they insist on just slapping it back together, absolutely no warranty whatever on anything after job is paid for.