CV740 27hp bogs severely under average load

[Turbodriven]

Once it's back together running again, if it's possible, post a video of it acting up. Maybe even one of it sitting running with no load at idle and also full throttle. Who knows. Maybe someone will hear something.

Ok here you are with the videos.

First video, cold starting and running.

Second video could use some narration as it's loud and bumpy (my yard isn't as smooth as I'd like) and I'm trying to drive a 2 stick zero turn with one hand in most of it.
1. First part is me running with blades engaged. You'll notice she falls on her face at about the 0:50 second mark a few seconds after moving. Make sure you full screen and have it the highest resolution so you can "pause" the video and maybe see the RPMs better at any given moment (youtube didn't upload at the full resolution for some reason). RPMs seem to hang mostly around 1500-1600 though and it dips down to 1200 when going up hills which is barely running.
2. Second part is driving with the blades disengaged. It hangs about 2500 and dips to about 1400 or so once after an uphill.
3. RPM's always come back up when I pull the sticks back though. And as you can see, the problem is at about 40% intensity with just the hydro drives engaged, and 100% with the drive and blades combined.

I'll take this moment to bring up two ideas.
#1 - a collapsed or locked hydraulic lifter? Would this manifest itself under load and cause the condition we have here? Or would this be apparent event while manually rotating the crank by hand (or running but sitting still).
#2 - heavily gummed up valves? On the back side of the valves. I've had the heads off previously and looked in the ports. I remember them being dirty, naturally, but not to the extreme. But this was just a cursory glance at best and my eyes haven't been calibrated in years. I didn't have the right valve removal tool so I never took the valves out.

 

[Turbodriven]

After you get it back together, try running it on one cylinder at a time and see if it runs the same on both sides.

I did this and just grounded the unplugged boot with a alligator clip test lead. (note, I think these new MDI coils have built in protection though. As they have a lead running back from the boot and grounding out under a bolt of your choosing).

Neither side runs great by itself and neither would hold idle. The only noticeable difference between both sides is that when #1 was running, I was getting black sooty exhaust (noticeable). Whereas the #2 did not. I suppose this is to be expected. Edit: I realize though, that with black soot coming out of #1 under a no-load situation, it confirms that this is indeed a motor problem and not a loaded hydro (or other external) issue.

 

[VegetiveSteam]

I would agree. It's an engine issue but all the tests so far aren't revealing anything. A collapsed lifter should cause less rocker arm movement and be noticeable. They all move the same, so to me, that rules that out.

I'm going to bore you with a couple more questions. This is exactly how the engine ran when you got it correct? And after everything you've done it is unchanged? No better and no worse?

 

[Turbodriven]

I would agree. It's an engine issue but all the tests so far aren't revealing anything. A collapsed lifter should cause less rocker arm movement and be noticeable. They all move the same, so to me, that rules that out.

I'm going to bore you with a couple more questions. This is exactly how the engine ran when you got it correct? And after everything you've done it is unchanged? No better and no worse?

Essentially yes. I would say that I feel like when I first got it I could still mow my lawn with a bit of a struggle. But now I feel like I'm a bit worse. Seat of my pants meter only. I could just be frustrated. None of the data has changed though. Still bogging about the same. Still getting carbon fouled on #1 only. Everything is the same except once in the beginning I ran compression with my crap Amazon tester and got like 170 instead of 160. Cylinders may have been wet though. I can't say. Which would have explained it.

 

[VegetiveSteam]

Essentially yes. I would say that I feel like when I first got it I could still mow my lawn with a bit of a struggle. But now I feel like I'm a bit worse. Seat of my pants meter only. I could just be frustrated. None of the data has changed though. Still bogging about the same. Still getting carbon fouled on #1 only. Everything is the same except once in the beginning I ran compression with my crap Amazon tester and got like 170 instead of 160. Cylinders may have been wet though. I can't say. Which would have explained it.

Anything above 150 psi is good and your leak down test was good so the rings and cylinders seem good. I know there is the issue with some smoking on #1 cylinder but whatever is wrong seems to be affecting both cylinders.

It sounded really good when you started it cold even at idle. I know the flywheel key was checked and you had correct overlap with all valves open at TDC exhaust but to me it still acts like it's slightly out of time.

You did say that the valves were moving slightly less than spec so pulling the engine and inspecting the cam might be the next step. This may sound like an odd question but have you noticed anyplace on the equipment that looks like it's been welded on with an arc welder?

 

[Turbodriven]

This may sound like an odd question but have you noticed anyplace on the equipment that looks like it's been welded on with an arc welder?

Nope. I haven't done a full inspection but I got a pretty good look at the heads when they were off and a decent look at the cylinder sections.

That said, it wouldn't surprise me if this thing got a bit hot in it's 1200hr life. I'm in Florida so we're in a pretty warm climate and the fins were a bit caked up when I got in there. Heads were flat though (not perfect but well under 'max out of spec' ).

If something was cracked or out of shape in some way I have to assume it's going to be a pretty obvious defect given such a severe lack of power it'd be causing.

I'm going to start pulling the motor out of the mower and tearing it down. I think we're at that point unfortunately.

Thank you for your help. I'll keep you posted.

 

[Turbodriven]

Ok, so I really don't know what I should do at this point. To be honest, I don't see anything glaringly wrong anywhere inside this motor. No cracks or case defects. Cam lobes all measure the same, governor gear assembly looks good. Crank seals are tired but they weren't leaking (I'm going to replace anyways). Oil passages look clear. And the valves don't look overly gummed up (just a small amount of carbon buildup which is normal I think).

So, I know that my rings aren't perfect (acceptable but not perfect). But I'm feeling like I should do a ring job while I'm in here. I haven't pulled the pistons yet but I do want to check the current rings too in order to see how they look. Make sure none are seized or anything. Cylinders look glazed but 100% smooth. I can still see cross hatching in the metal walls. A quick hone and fresh rings wouldn't hurt if I plan to put more years on her. And rings are fairly cheap.

The bigger question is the cam. We know my valves were opening 7mm instead of the manual recommended 8mm. But all my cams lobes measure the same (34.5mm). A new cam is $170 plus I've read scare tactic posts that you have to replace your hydraulic lifters too. And then break them in with 20 minutes at 2000rpms or the cams will be toast within an hour. Putting new cams in is another $80+. Probably a realistic $300 total parts list after tax. Unless I just throw a good used cam in for significantly cheaper. But I've heard that's just throwing money down the drain as you'll likely only get 30min in before the lobes wear down to round using old (mismatched) lifters. Scare tactics?

I know you have some experience with these engines. I'd love to hear your opinions on this. In the bigger picture too, and to the point of this thread, I've got this gut feeling that these cams aren't my problem. *shrug

 

[slomo]

What I hear with headphones on, from your video OP, is normal RPM's in the first video. Low idle is lower than you will ever use and high sounded fine to me.

Your next video, sounded like, you have one or several bad bearings in the deck. Sounded awful mechanical when you engaged the blades. Heard a lack of engine rpm with the blades on. Like you have some aftermarket blades or some high lift wonder blades of the week on her. Are you running OEM blades?

Summation the engine sounded fine until you loaded her up. I would be looking into the deck then the engine if it was me. Or your Chinese tachometer is not reading proper rpm's.

 

[VegetiveSteam]

Ok, so I really don't know what I should do at this point. To be honest, I don't see anything glaringly wrong anywhere inside this motor. No cracks or case defects. Cam lobes all measure the same, governor gear assembly looks good. Crank seals are tired but they weren't leaking (I'm going to replace anyways). Oil passages look clear. And the valves don't look overly gummed up (just a small amount of carbon buildup which is normal I think).

So, I know that my rings aren't perfect (acceptable but not perfect). But I'm feeling like I should do a ring job while I'm in here. I haven't pulled the pistons yet but I do want to check the current rings too in order to see how they look. Make sure none are seized or anything. Cylinders look glazed but 100% smooth. I can still see cross hatching in the metal walls. A quick hone and fresh rings wouldn't hurt if I plan to put more years on her. And rings are fairly cheap.

The bigger question is the cam. We know my valves were opening 7mm instead of the manual recommended 8mm. But all my cams lobes measure the same (34.5mm). A new cam is $170 plus I've read scare tactic posts that you have to replace your hydraulic lifters too. And then break them in with 20 minutes at 2000rpms or the cams will be toast within an hour. Putting new cams in is another $80+. Probably a realistic $300 total parts list after tax. Unless I just throw a good used cam in for significantly cheaper. But I've heard that's just throwing money down the drain as you'll likely only get 30min in before the lobes wear down to round using old (mismatched) lifters. Scare tactics?

I know you have some experience with these engines. I'd love to hear your opinions on this. In the bigger picture too, and to the point of this thread, I've got this gut feeling that these cams aren't my problem. *shrug

How do the lifters look? Can you post a pic of the side that runs on the cam? And you don't want to change the cam if it's not needed obviously, but for a different reason than you may think.

Kohler says to replace the camshaft and crankshaft together. Never just replace one. So you'd be looking at a cam, crank and new lifters. The reason is, the teeth on the crank gear and the cam gear create a wear pattern on each other over hours of running. If you were to replace just the cam and lifters, and not the crankshaft, at best the engine will probably have a knock. It sounds very similar to a rod knock. I've hear it several times. At worst, the uneven pressure being put on the crank gear now with new cam teeth running against worn crank teeth can cause the crank gear to crack letting the crankshaft turn inside of it causing valve timing to be off. I've also seen that a number of times. The same result we discussed previously with an overheated engine and valve overlap.

The good thing is you probably don't need a new camshaft so none of what I just typed will probably matter.

If everything inside looks good, and there is no odd wear on the cam side of the lifters, I would take them apart and clean them. Then reassemble them with just a drop or two of oil. With the lifter sitting if front of you, you should be able to take a push rod and push in the lifter plunger. The plunger should spring back when you release the push rod pressure. Then put them back in the engine coated with oil on the outside but just the drop or two inside. You want them pretty much empty. They will clatter when you start the engine but will quiet down in just a few seconds.

I'm going to read back over some of what you posted to see what other ideas might come to mind.

 

[VegetiveSteam]

While you have it apart, look at the crankshaft gear very closely for anything resembling a crack.