Some engines, especially small engines, have compression release valves so that it's easier to turn the engine when you first start it because there is less compression in the cylinder. Examples would include the Ducati 1199, or more in my field, the Kohler CV460S.

How do they work? Diagrams and complete answers would be appreciated!

1 Answer 1



First time I have heard of this but cool.


cam with compression release

cam with compression release

The weight is pulled to the center of the cam using that small spring around its pivot point. This makes the lever on the end of the weight spin that pin around creating a bump in the cam profile. This bump opens the exhaust valve allowing some of the pressure to escape during the compression stroke.

When the RPMs are high enough the centrifugal force pulls the weight away lifting the lever and spinning the pin so the flat side is in line with the back of the cam lobe.

  • 4
    Could you include the essential parts of this video instead of just sharing the link, please?
    – anonymous2
    Nov 4, 2016 at 10:14
  • 1
    Also, you may want to include the important part of "how does this all work" ... What does the weight, lever, cam lobe actually do? Nov 6, 2016 at 14:10
  • @ Paulster is there something I missed? should I change something? The how it works is at the bottom of my answer under the images. I did add a little but cant find anything else I am missing.
    – Cc Dd
    Nov 6, 2016 at 23:19
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    Thanks for the add. You'll discover with complete answers, voting will go up on those answers. Please don't you forget to vote on posts others have placed as well. Votes don't cost you anything and they are replenished daily. Nov 7, 2016 at 14:15
  • 1
    @CcDd, there's even a top voters page
    – anonymous2
    Nov 7, 2016 at 21:19

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