Exhaust valve opens on compression stroke

[Stuart 3]

I am giviing my Wheel Horse some long over due attention. It was stored after developing some spectacular somewhat frightening backfires. I have purchased a new carb and removed the head to clean away the heavy carbon deposites. Ground the valves and reset the the valve clearances. Prior to adding fuel , I performed a compression test which resulted in virtually no compression whatsoever, upon removing the head and inspecting the valves , I am mystified to why the exhaust valves opens a little on the compresion stroke ? Increasing the valve clearance to 0.050" prevents this occuring, raises the compression to 50 PSI, but the starter motor finds this dificult to cope (still not add fuel yet). I cannot work out why the cam should wear in this way ? So there must be another explanation but other than some sort of decompresion reason I can not think of one. Any guidence on this subject will be much appreciated, I am based in the UK and I am sure there are other owners of such machines but I do not know of any. ps. I am purchasing parts from the USA.

 

[953 nut 51,657]

     Kohler and some other engines have an Automatic Compression Release that opens the exhaust valve slightly at very low RPMs to allow the starter to gain momentum. This is covered in several posts on this site, do a search and you can see what others have found. This manual should be helpful.

Kohler_Guide_To_Engine_Rebuilding_19890900.pdf

[Digger 66 3,476]

Beat me to it ^^ 

 

[953 nut 51,657]

Here is another that you may want to read.

Kohler 4-72 SM Section 11.1-11.6 Engine reconditioning HR (1).pdf

[KC9KAS 4,741]

@Stuart 

And like others have said, it is probably the ACR (automatic Compression Release) that hold the exhaust valve slightly open up to 600 RPM's.

[Stuart 3]

Thank you to those you replied to my enquiry. I understand how it works now. I have never come across such a mechanisum like this before. I appreciate the downloads you have suggested and have already printed one off. Thanks again Stuart the Newbie

[JPWH 5,308]