late last summer, I bought a JD212 with a kohler K301AQS that has automatic compression release. A brief internet search shows that it runs off the cam. Can I check compression on this thing?
kohler K301 compression release
- Thread starter bucktail
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I think this makes sense. The cam has springs that hold the exhaust valve open until the rpms get high enough for the weights to overcome the springs
Technically you're right but I'm not interested in what the compression is when the compression is released.
If you want to defeat the compression release you could increase the exhaust valve clearance, it is adjustable.
Correct, but you also lose some valve lift which may affect power-among other things.
You check compression on these like any other engine. Screw the gauge into the hole, crank engine until needle stops rising. Should be, IIRC, 70 psi or more. There is a reason it's got a compression release. It eases the load on the starter. The ignition timing is not really adjustable and it's always advanced, to the point where if it didn't have a compression release, it'd be nearly impossible to reliably start it. Seen a few Mule 610's with failed compression releases, and the starter WILL NOT spin it over, and it's a big starter with a lot of torque turning a relatively small 400cc engine. Actually "most" single cylinder engines, and even a lot of twins, have been using acr's for years for this very reason-so that they're able to be started without destroying themselves or the operator trying to yank start it. Even my little outboard's got an auto compression release and I'm glad it does! The old B&S dump valve motor's had them too...used to be called "easy spin"...was a small lobe on the cam that popped the valve open before TDC to bleed off some pressure so that you could pull the rope. I raced B&S powered karts for years and one of the things we were able to do was put aftermarket cams in them, which did away with the easy-spin feature, but in order to use a manual starter, you had to be like hercules. The motors were only about 6.5:1 compression. We used electric starters (divorced) because sometimes even if you was big enough to spin it over with a rope starter, the ratchet would sometimes shatter, or the recoil starter would break, and if that was the case and you couldn't change it in 2 minutes, you were out of the race.