i doubt seriously the blades being upside down caused an engine problem, most likely coincedence.

 

When the problem recurs, use a pair of insulated pliers to remove one plug wire at a time. If removing one wire stops the engine, the other cylinder wasn't firing. It could be a defective coil (you should hear the snap of the spark as you remove the wire), or an intermittent mechanical problem, such as a stuck valve. While you're playing with it, be sure the cooling system is clean. Overheated heads will lead to valve problems.

 

Follow this advice. It sounds to me like your engine is only running on one cylinder. Crank it up and detach one spark plug wire at a time. If you remove one wire and the engine's running pattern doesn't change, that cylinder is not firing. You can also take an infared thermometer and measure the temperature of both exhaust header pipes, right where the pipes come off the heads. If one pipe is much cooler than the other, the cylinder with the cooler pipe is dead.

90 psi is a tad weak, but that is enough compression for it to fire. Pop the valve cover on the left cylinder with the weak compression and have a look at the rocker arms. The studs holding the rocker arms to the head can back out, or strip, especially on the exhaust side. This will cause running problems, as the valve lash will increase until the rocker arm twists to the side and the pushrod eventually pops off. Don't pull a head unless you absolutely need to. Those head gaskets CANNOT be re-used. Install a new one anytime the seal has been broken.

 

A little new information from my tinkering today:

First thing I did was clean air filter and checked spark plugs, then I replaced the fuel filter because i've heard of similar problems happening because of that.

Then I ran it again and it didn't seem to make a difference.

I rented a compression tester from autozone, the right cylinder reads 120psi max. the left is 90. This seems to me to not be correct. I've heard that compression between cylinders should be withing 10% of each other.

So what should I do now? It seems that compression problems can be caused by a number of different things, blown head gasket, loose seal between cylinder bore/piston rings,exhaust valve, stuck intake valve. How can I diagnose which of these is causing the problem? The only way I know how to isolate one of them is to put some motor oil in the chamber and repeat the compression test. Will this method even work with a horizontal piston?

 

yes ,this is called a wet compression test! this will determine ring sealing ability! the other test done to narrow down problems is a "Leakdown" ,where you put compressed air to the cylinder and measure the percentage of air loss!while doing this you can sometimes hear the air escaping from the crankcase,carb, or muffler which can help locate the problem! you need to use caution when doing this test as the cylinder needs to be held at or near top dead center and the compressed air has a lot of power which can launch a tool that's holding the flywheel!

 

But will the wet compression test work with a vertical crank shaft? If the piston is on its side, won't the oil want to sit only on one side?

Also, is 90 really that low? From some google searches i've heard that other people get around 100 or so. But what do you think, considering the other cylinder is at 120?

I'm also pursuing the possibility that this is a fuel system problem.

 

Another question,

Can you reinstall a head gasket after you check it? I am tempted to just pull the head off and take a look at the gasket but I don't want to waste the gasket if that isn't the problem.

 

Maybe, but not a good idea. Kohlers like to blow head gaskets, especially on the right side.

 

Which is the right side? If i'm looking from above, standing at the base of the V, this would be the right side cylinder

 

I'm definitely going with valve or head gasket issue. As Jeff stated the Kohlers are notorious for head gasket leaks. 90psi is definitely low. I have one in the shop now that will run (not well) with 120/135 on the respective cylinders....however I can visibly witness compression gases exiting the chamber via the head gasket on the RH cylinder. Even at 120 it can cause a severe loss of power under a load.

It seems logical to trace your steps back to the last affected component, but in this case I think it is just coincidence that the engine concern popped up at the same time as the blade reversal.

 

I'm beginning to side with you that this was not caused by the blade reversal, which is a big relief. (I was envisioning a totally blown engine, or engine block, costing hundreds of dollars).

My main reason is that while the blades were inverted (unknown to me at the time) I did not notice the engine struggling at all. I have run it successfully cutting 12" grass at times when I HAVE heard the engine bogging down and have not experienced any issues from those events.

 

Well I repeated the compression test today (same as before, warm engine) and got a reading of 120 on both cylinders!!! I'm thinking when I did it yesteday I may not have had the fitting tight enough.

According to what you were saying about your engine, would this mean that BOTH cylinders have low compression? (BTW, I checked with the service manual, and it says proper compression should be at least 160 and no more than 15% difference.

So I guess I answered my own question and it seems that both cylinders have low compression.

 

Next questions, While i've got it apart, is there a way I can check to see if it is properly delivering fuel? The local small engine people here said that it could be a fuel problem, so I already replaced the fuel filter, but could it be the fuel pump? How can I make sure that the carb is getting fuel properly?

 

I went and got a cylinder leak tester. The leakage % gauge doesnt seem to be working properly, it shoots past "low" into the unmarked range of the dial.

HOWEVER, I was able to hear air escaping into the valve cover area on both cylinders THe funny thing is, like I said, this is on BOTH cylinders. I've attached a picture which shows where the air comes out: The air comes out of the little hole in the bottom left of the valve cover (bottom right on the other cylinder)


What I don't understand is how the air comes out this hole on both cylinders regardless of which I put the air into? It will come out this hole on both sides as long as the cylinder i'm putting air into is at TDC

 

Worn rings...that hole is the oil return hole, and allows collected oil to drain back into the case.

What you are hearing is air leaking past the rings, into the crankcase, and escaping out the smal openings.

If you plugged them, you would hear air escaping out the oil dipstick, or breather hose...

On a used engine, some air escaping past the rings is to be expected..if its not smoking and using oil, I wouldnt worry about that part of it.

If you unhook the plugs wires 1 at a time, does it continue ot run on 1 cylinder?

 

Its remotely possible that your spark advance could malfunction at higher engine speeds, but that's very rare and probably not your problem. As long as spark is present at both cylinders and both sides are firing, rule that possibility out for the moment.

I bet you have a blown head gasket. Possibly on both cylinders. RED is right....worn rings will let air escape past the rings and come back up through the oil return hole (circled in your pic) and pushrod chamber. HOWEVER, you have a lot of air hissing out right at the hole, and that's exactly where Kohler head gaskets tend to blow. They will burn right through where the gasket is supposed to seal off the oil return passage, if only because the gasket is at its thinnest here. Trust me....Ive changed many.

Time to pull the head and have a look inside. If you find a blown gasket, order and install a replacement 24-841-04S kit. This head gasket kit comes with a redesigned head gasket (much stronger than the original....the new gasket has a fire ring made into it and will probably never blow again), as well as new intake and exhaust gaskets. Best $$ you will ever spend on a repair.

But before you go through all this hassle, can you get ahold of a working leakdown tester?

 

\
I bet you have a blown head gasket. Possibly on both cylinders. RED is right....worn rings will let air escape past the rings and come back up through the oil return hole (circled in your pic) and pushrod chamber. HOWEVER, you have a lot of air hissing out right at the hole, and that's exactly where Kohler head gaskets tend to blow. They will burn right through where the gasket is supposed to seal off the oil return passage, if only because the gasket is at its thinnest here. Trust me....Ive changed many.

So you mean that air getting into the crankcase can sometimes be caused by a blown head gasket and is not always caused by worn rings?

\
Time to pull the head and have a look inside. If you find a blown gasket, order and install a replacement 24-841-04S kit. This head gasket kit comes with a redesigned head gasket (much stronger than the original....the new gasket has a fire ring made into it and will probably never blow again), as well as new intake and exhaust gaskets. Best $$ you will ever spend on a repair.

That P/N isn't listed as working for my engine, mine is a CV20S, Is there a similar kit for my engine?

My complete engine number: CV20S-65610

Also, I'm picking up a complete engine rebuild kit tomorrow for about $80! It includes pretty much every seal and gasket on the whole engine.

When I pull the head and replace the gaskets, do I have to have the heads or block re-milled? Also, to disassemble/reassemble the heads, will I need any special tools? (Valve spring compression tool?)

When I pull the head, will that allow me to check for certain whether it is the head gasket or the piston rings? Is there a way to tell visually tell if the piston rings are worn? If the piston rings need to be replaced? Do I have to get anything done to the block to fit the rings properly?

 

Some things i do not see, are burnt oil film on the top of the heads, just clean aluminum..meaning the engine has been maintained. Also, I do not see dirt and grime built up on the air filter housing. Generally with a blown head gasket, or oil return, the air filter are becomes oily from all the vapor blowing into the intake.

the last Kohler gasket I diagnosed and fixed was a CH730S on a GT5000 sears. It cranked right up, but smoked some, and felt down on power in the cut. compression on 1 side was 125, the other was 75, and that side had a plug loaded with carbon. The area inside the air filter housing was loaded with oil and some fine dirt, it was a real mess, had been used maybe 25 hours like this.

The gasket was slightly blown near the pushrod galley.

ule of thumb...if its loading up a plug or plugs..its either head gasket or rings...and both require pulling the head.

 

I'm doing head gaskets on a CH22 in a 3225 right now and the difference in head gasket construction between new and old styles is night and day!

I also found half of the head bolts were barely 100in/lbs on both heads.

 

Yea, I always wondered how they torque a new engine.

When you rebuild, they recommend running for X hours, then re-torquing.

That never happens on a new engine. :dunno: Does it?

 

Thanks for all the input guys, I think we're getting closer.

I've ruled out:
Ignition-because it runs beautifully with no load, did the spark plug test and will run on each cylinder individually.
Fuel system/carb-because i've replaced the fuel filter, the fuel pump sprays gas all over when you disconnect it from the carb, carb visually looks clean and like I said, it runs beautifully with no load.

I bought a leak tester from harbor freight yesterday, i don't think its working right because the % leak gauge is at 60psi with no pressure! the pressure gauge works fine which is how I was able to get this far. I will see if they will take it back and exchange for another.

Hopefully one I get a new gauge.... I will do the test again and see what the percentage is, I will report back later today. From what I understand, if the air leakage shows as minimal on the gauge (not sure the figure), then its ok because used engines always leak a little bit past the rings.

Things I should have mentioned earlier:
-The engine has less 700hrs
-It has intermittently burned oil on startup for the past 3 years. (just a little bit, only for the first 10 seconds)

This probably doesn't change anything, just felt like I should mention it.

 

Sounds like you're getting there! In what sort of shape is the air filter and the intake behind it? Is it wet or soaked with oil? Or still dry?

 

Everything is clean: filter and intake totally dry. Also, the spark plugs show no signs of burn't oil, they look used, but otherwise healthy.

 

If the piston rings are worn, would we expect it to burn oil? I mentioned earlier that it occasionally burns a tiny bit on startup but with air leaking into the oil pan wouldn't it smoke like crazy?

 

I think we've finally got it nailed:

I repeated the compression test today for peace of mind, running a regular compression test I got 102psi right 110left (with engine at 200F)

Then I ran a wet compression test by squirting a bunch of oil in there and repeating. I've heard this won't yield a conclusive result on vertical shaft engines, but I gave it a go anyway!
Then I got 150psi right, 144 left!!!
So based on my frantic internet searches and help from guys like you over the past 2 days, can I conclude that it is most definitely the piston rings?

If so, what do I need to do to replace them? I understand this is bit of an operation (much more intensive than changing the oil )

I'm guessing I'll need to set an afternoon or day aside, pick up all the usual gaskets(head gasket, oil pan gasket, etc), get a torque wrench, valve spring compressor.
Will I need anything else special to install the rings/remove the crankshaft? Do I need to have anything specially machined or re-bored?

Here is what I am picking up for parts:
-1x 24 755 107-S
http://www.hyperparts.com/wc.dll?ct...wc.dll?ctwp~iteminquiry~1001~1003~24 755 107-S&gclid=CJue7Nb37rcCFVQV7Aod-TkANg
-2x KH-24-108-22-S
http://www.partstree.com/parts/?lc=cub_cadet_commercial&mn=CV20S-65610+Kohler+Engine&dn=20S656100003

Can I reuse the oil pan gasket or do I need to replace that too?

 

Sorry I'm late to the party here...but it seems as though the OP is potentially doing a lot of unnecessary work.

First off, has the compression test tool been calibrated? Not all testers read the same and rental tools are notoriously wanky. Secondly, some of the CH20 engines have an Automatic Compression Release to ease starting. At 700 rpm or less you'll always get a low compression number on models equipped with an ACR. Does this model have the ACR? Did you have the throttle at WOT when performing the compression test?

Have you conducted a spark plug read to determine combustion activity? Does the engine produce a lot of blow-by, and if so, is it oil or fuel?

Finally, the compression test you have run is all but useless as a diagnostic tool. The test you want to perform is a leak-down test. This test will point to the cause of any lost compression.

Before you get too deep into an engine rebuild I'd conduct a proper analysis of the symptoms.

 

Finally, the compression test you have run is all but useless as a diagnostic tool. The test you want to perform is a leak-down test. This test will point to the cause of any lost compression.

I did perform a leakdown test, the gauge I used was a cheapo harbor freight tester so i couldn't get a % reading, however with the piston at TDC the air was coming out the oil pan/dipstick/oil relief holes.

 

THe mower ran fine for about 5 hours after that, when the engine looses power (blades engaged) and won't run faster than half of its max. RPM.

When this happened did the engine immediately speed back up when you disengaged the blades?

 

Yes, engine will run full RPM band like a champ with no blades/motion. It can even drive around fine. However I knew it was never something with the deck because if you really punch the hydros and make it accelerate quickly it will bog down in the same way.

 

Here is the final verdict:

Worn piston bore/rings.

After the results of the compression/wet compression/leakdown tests, I was confident enough that it needed serious work done so I took it to a friend of my who bores/rebuilds engines for a living. I brought him the spec sheet with tolerances for cylinder bore wear, out of round, and taper, etc. He went over the cylinder bores with a micrometer and some other tools and said for sure it needs new bores, pretty badly actually.

Kinda sucks right? The good news is he said he'd do it for $50 on his lunch break but i've still gotta drop $300 on oversize pistons.

 

Everythings on its way, unfortunately the parts order will not be here until Tuesday because the .25mm oversize pistons are of course, special order. Here's the engine as it sits now:


I have no idea why the engine failed, I've been calling my small engine dealer, talking to my engine buddy and most commonly a failure like this is cause by dirt getting to the piston rights, either through the air intake or the oil pan. This blow me away because I've always been super dedicated to changing the air filters, oil, and oil filters, along with all the usual maintenance. Beyond that, when the engine rebuild place took a look at it, they said it appeared to be a well maintained engine from the looks of the cylinder walls, just excessively worn. The small engine dealer recommended I call Kohler and see if there was anything they could do to cover the cost of parts, no luck there, its outside of their 3-year warranty so of course they're not gonna do anything about it. These engines are supposed to last 2000+ hours without needing this kind of work done and mine barely makes 700? Now I've got to drop $400 into new pistons, rings, and gaskets just to get running again. And i'm actually lucky because my friend is gonna do the re-do the bores for $50, plus i'm doing all the disassembly/rebuild work myself, if I took this to a shop it would probably be a $1200 repair when its all said and done, might as well pay an extra $300 and get a new engine if that was the case.

Sorry for the rant, i'm just upset because I only do lawn mowing part time as I am trying to make it through university, I understand how and engine works and the importance of doing the proper maintenance, I've been so careful to maintain the whole mower since I got it so that I wouldn't have problems like this.

I'm making my way through the disassembly now, Here's the next problem: I can't get the hydro-drive pulley off, it seems to be rusted on. I had a similar problem with the PTO assembly but I got a pulley-puller from autozone and that took care of it. Unfortunately this method isn't working with the drive pulley because it is made of such cheap metal; it just bends where the pulley teeth grab it. I'm soaking it in WD-40 again, but do you guys have any suggestions?

 

I am not trying to be down on you (when you are down already), but, I believe these engines are SUPER sensitive to dirt on the fins.

The pic you show above looks like what I would expect of an engine with premature failure.

The only reason I mention it is so that after the rebuild, you may want to consider annual cleaning of the fins. (Or more often, depending on conditions etc?)

This can be a pain to do, lots of times an engine will need the pans removed to clean it properly.

I am glad you are close to a solution!! :fing32:

Oh, yea, hydro pumps fall into the same sensitive to heat category.

 

I am not trying to be down on you (when you are down already), but, I believe these engines are SUPER sensitive to dirt on the fins.

The pic you show above looks like what I would expect of an engine with premature failure.

The only reason I mention it is so that after the rebuild, you may want to consider annual cleaning of the fins. (Or more often, depending on conditions etc?)

This can be a pain to do, lots of times an engine will need the pans removed to clean it properly.

Thanks for the advice. You are suggesting the fins as a means by which the engine could have overheated? Possible, but the spark plugs don't look to me to be overheated (based on the pics in the service manual).

Tell ya what, i'll post up some spark plug pics tonight and you guys let me know.

 

Just saw this thread.

I guess I'm struggling to understand how there could be intermittent power loss with bad rings and/or worn cylinder.
Wouldn't low compression mean constant power loss?

Besides these Commands seem to still run underall all kinds of maladies and very low compression that technically they shouldn't be running.

I'm sincerely seeking to understand.

For example:
1) I've run the same engine in my GT3235 with much much lower compression using the same cheapo AutoZone rental tool and didn't have the problem you are experiencing.

2) I know your photos show you didn't blow a head gasket. BUt the only experience I have with power loss was when I blew a head gasket (and even then, I was still mowing lawns for about 8-10 hours after that). My head gasket blew open about 1.5" and the orange combustion could be clearly seen. I didn't really loose THAT much power, but it sure was loud (that more than the power loss is what tipped me off to a problem).

 

I guess I'm struggling to understand how there could be intermittent power loss with bad rings and/or worn cylinder.
Wouldn't low compression mean constant power loss?

It wasn't exactly "intermittent" with a better understand of the problem now I probably shouldn't have used that word. I'll clarify now.

The engine would work nicely for the first 5 min or so, then the deck would begin to slow down and the engine would really have trouble turning both the deck and the hydro's. This is why I originally said it was "intermittent". Also, the (reduced) RPM would fluctuate a little while the deck was engaged.

2) I know your photos show you didn't blow a head gasket. BUt the only experience I have with power loss was when I blew a head gasket (and even then, I was still mowing lawns for about 8-10 hours after that). My head gasket blew open about 1.5" and the orange combustion could be clearly seen. I didn't really loose THAT much power, but it sure was loud (that more than the power loss is what tipped me off to a problem).

The head gaskets aren't "blown" but they were leaking (my engine-rebuilding friend confirmed this). If you look very closely in the earlier pictures you might be able to see a little bit of black residue on heads coming from the cylinder area.

 

You may want to verify that the engine can be bored. The cylinders are hard coated from the factory. I have re-rung these engines up to three times in the original bores and they turn out well. If it really is the rings, the engine was most likely dusted.

 

The service manual says that they can be (it said the cv25's or some other engine is hardcoated with a special process)

Beyond that, the oversize pistons were listed under my engine number so i'm sure this block is capable of a re-bore.