Kohler losing Power

[Little Guy]

Hello, A friend told me about the site so I thought I would give it a try.

I have a Kohler 18hp. single cylinder vertical engine (model # VC493S, serial # 27523) sitting on a 2004 Snapper zero-turn. I was mowing and the engine started losing power. It acts like you need to either adjust the carburetor or advance the timing.

Things I have checked;
There is no water in fuel and the fuel is flowing to the fuel pump with no problem, the filter is not stopped up. Changed the spark plug. The fuel pump is pumping plenty of fuel to the carb. With the throttle wide open the engine is starving. Checked the flywheel key and it is good. I could not adjust the carb. so I took it apart and cleaned, really didn’t see anything wrong so I reinstalled. Still no change in power. I bought a new carb. and installed, that wasn’t the problem. When checking the compression there is only 75 psi for a few minutes then there is a click sound and the compression jumps up to 200psi. I thought maybe a valve seat or valve guide had come lose so I pulled the head to check. Took the valves out and everything looks good there. Is it possible a lifter is not pumping up all the way?
Any advice is welcome.

[bgsengine]

That "click" sound and sudden jump in compression - sounds like your compression release is stuck or broken return spring (Part number 12-089-37-S) - it'd require removing & replacing the camshaft.

But, inspect head gasket carefully between the cylinder bore and the valve pushrod galley - quite possibly a blown head gasket.

75PSI Cranking is about normal for a compression release engine, which the CV493 is, and the fact that it kicks up to 200 would tend to indicate the compression release is kicking out due to a broken spring.

[Little Guy]

The head gasket looks good. I got the lifters out and as I look down at the cam shaft there is a little pin, like a roll pin I can see on the exhaust valve cam lobe. I do not see how the lifter can ride smooth on the cam with that pin there. I assumed that the pin is spring loaded and moves out of the way after the engine is running. If the spring is broken will the pin stay out on the lobe and not allow the valve to close all the way which will cause the engine to have low compression during operation? I have worked on compression release engines before just not one like this.

[Deere2me]

You need to get ya a manual here: http://www.kohlerengines.com/manuals/landing.htm

[KE4AVB]

The head gasket looks good. I got the lifters out and as I look down at the cam shaft there is a little pin, like a roll pin I can see on the exhaust valve cam lobe. I do not see how the lifter can ride smooth on the cam with that pin there. I assumed that the pin is spring loaded and moves out of the way after the engine is running. If the spring is broken will the pin stay out on the lobe and not allow the valve to close all the way which will cause the engine to have low compression during operation? I have worked on compression release engines before just not one like this.

The decompression should operate same as others with this type of system. The spring holds pin assembly out during starting then allow the pin assembly to retract after starting as the cam reaches normal rotational speed so if spring was broken it is more likely leave the pin in the retracted position instead being out to bump the lifter.

Sounds like decompression is hanging extended either by spring jamming it movement or by a mechanical bind. The only to really know what is going on with the cam is to disassemble the engine. If it the decompression system is jammed or the spring is missing you will need a replacement camshaft. Note if the spring is missing; look for it just don't want it wandering around inside an engine as it could cause other damage.

[Little Guy]

Thanks for the advise. I do have the manual downloaded already. Since it looks like I have to tear it down I might as well go ahead and re-ring it as well. The engine has 959 hrs. on it.

I have been reading other post as well. This looks like a good site for information where I can keep up with the newer models.

What is ya'lls ( I'm from Ga.) favorite site to get parts?

[bgsengine]

when it comes to favorite sites to buy from, It varies - to each their own - Some of us are dealers and buy direct from distributors or manufacturers, then there is eBay (If you look for mine on eBay, the user ID is trukfixer1) , Amazon (We are starting to sell there, too), and of course, there's my website, plus ereplacementparts.com, partstree.com There's also ordertree (Dixie Sales Co. Some dealers really hate them for competing with us, since they are factory distributors) , jacks small engines, mowtownusa, M and D, and many others - just google search on what you need, and chances are you'll quickly find one.

Be aware, however that both ereplacementparts and partstree, among others, will jack up their prices (Sometimes considerably so) above MSRP ( we do, too, but not quite so high, plus for small packages, we (meaning my website) are probably one of a *very few* that offers low-cost first class mail shipping, (Doesn't make sense to pay $8.99 shipping for a $2 part, does it??!)

The drawbacks to shopping online - not ALL online sellers have up-to-date inventory, so it is possible to order a part and find out it is NLA, discontinued, or backordered. (On eBay and Amazon that's a common issue - so as far as I go - we only list on eBay what we actually have on the shelf, and we don't bait and switch by listing a part as OEM and then ship a cheap aftermarket version.. so if the price seems too good to be true, it PROBABLY IS! )

Do be aware that on these forums - linking to a parts website for the sake of selling parts is forbidden - only sponsors and paid advertisers can do that. (Although it is no problem to link direct to the parts view if it is directly in context to the subject at hand, and of course, some of us put a link in signature line, which is OK, too. as they only come up when you actively participate!)

[KE4AVB]

I might add does pay to shop around if you have the time especially on more expensive items. Sometimes the seller will advertise parts at different prices. I have save as much as $100 on OEM electric PTO clutches especially on the green and gold mowers where a vendor is clearing his stock for newer products.

[Little Guy]

Well it's not the spring on the cam shaft but the lobes look mighty small though. How much lobe height are the exhaust and intake lobes? From the small dia. to the height of the lobe there is only a different of .048. The manual says the min. lift on the intake valve is .353 and the exhaust is .360. With only .048 difference between the small and large dia. the cam lobe seem to be worn down considerable amount. I think there in lies the problem.

[Deere2me]

Well it's not the spring on the cam shaft but the lobes look mighty small though. How much lobe height are the exhaust and intake lobes? From the small dia. to the height of the lobe there is only a different of .048. The manual says the min. lift on the intake valve is .353 and the exhaust is .360. With only .048 difference between the small and large dia. the cam lobe seem to be worn down considerable amount. I think there in lies the problem.

Dunno what the cam lobe height is, but I do know you have to figure in the rocker arm ratio to get the valve lift. Even so, .048 seems a tad low. Are they scuffed up, etc. You can always Email Kohler tech. support, they answered a question I had pretty quickly.