Kohler cv490 running problem

ResidentRogue · Jul 14, 2011

I have a lawn tractor with a kohler cv490 single cylinder engine with hydraulic lifts and no adjusters for rockers... ok, what happened is that it just got loud one day when fired up for first time that day and has no power. I checked it over and found both valves leaking... pulled head, lapped valves and reassembled engine. Test ran, same problem. replaced lifters, same problem. Anyone feel they can help me out with this? Am a pretty good mechanic and work on lots of different equipment but this one takes the cake for stumping me!

Any help would be appreciated.

Restrorob · Jul 15, 2011

Sounds like you could have a issue with the compression release;

Automatic Compression Release (ACR)
This engine is equipped with an Automatic
Compression Release (ACR) mechanism. The ACR
lowers compression at cranking speeds to make
starting easier.
Operation
The ACR mechanism consist of a flyweight, spring and
pivoting control pin assembly attached to the gear on
the camshaft. At cranking speeds (700 RPM or lower),
the control pin protrudes above the exhaust cam lobe.
This pushes the exhaust valve off its seat during the
first part of the compression stroke. The reduced
compression results in an effective compression ratio
of about 2:1 during cranking.
After starting, engine speed increases to over 700
RPM, and centrifugal force overcomes the force of the
flyweight spring. The flyweight moves outward, pulling
the arm of the control pin, so it pivots into the run
position. The control pin no longer has any effect on
the exhaust valve and the engine operates at full
power.

piston slapper · Jul 15, 2011

Ditto...Rob

ACR is probably acting up
However it wouldn't cause the intake valve to leak.
BC is a cold climate,,,,wrong oil could make the lifters jack up, although I've never seen it happen on a single cylinder Command.

ResidentRogue · Jul 16, 2011

well, it turned out to be a flywheel key failure... was sheared and spun flywheel 3/4 way around so was 90 degrees ******ed timing. So thats why it looked like valves were leaking... cuz was firing when ther are open. I still don't understand how it could run like that but whatever. New flywheel key and it runs like a top. lol Is first time have ever seen sheared key on lawn tractor. On push mowers its first thing I check for. Thanks for the input guys.

Restrorob · Jul 16, 2011

ResidentRogue said:
Is first time have ever seen sheared key on lawn tractor.

Yeah, Not very common on a belt drive application..... Glad you got it up and running !

Kohler cv490 running problem

ResidentRogue

Restrorob

piston slapper

ResidentRogue

Restrorob

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