Small Engines (Lawn Mowers, etc.): Compression test on 10 HP Tecumseh, auto mechanic, ohv engine

Question
Question
I have a snow blower with a 10 hp tecumseh engine. How do I do a compression test on this engine given that it has a mechanical decompressor. Is there a way to disengage the decompressor.

Answer
Hello Rick:

 The OEM Says to Turn the Engine in Reverse Rotation and if you Get Good Kick Back the Compression is Good. However, I haven't had Much Luck with that Test. Depending on the Model, If this is the OHV Engine, then Remove the Rocker Arms and Remove the Exhaust Valve Push Rod. Check the Compression. If Not the OHV Engine, it More Complicated. If you need the Instructions, then Let me know. Hope this Helps. I am here if you Require more Assistance. Let me know what Happens, Please. Thanks.

 Good Luck

 Respectfully

 John

This is not an OHV engine. It is a 10 HP Tecumseh snow  King serial HMS100 159280T D
LH358sa. Please send me the in depth instructions for doing a compression test on this engine. You can email me directly at rrobertson1256@yahoo.co.uk. I have been told that this engine does not have the decompressor however, this info does not appear to be correct for this engine. Tried the reverse rotation and I get good kickback however, compression shows only 40 psi. Cleaned carb engine seems to be running good now but no snow at this time to test it in. My background 25 years as an auto mechanic in that time I have worked on most small engines as well with the exception of diesel.  

Answer
 Hello Rick:

 From your Description it Sounds like this Engine Does have the Compression Release. That is why you Only Get 40psi when Doing this Compression Check with the Gauge. You have to have an Extra Intake Valve for this Engine that the Stem has been Ground Down so the Stem Doesn't Touch the Tappet. Remove the Intake Valve and Replace it with the Shortened Valve. Check the Compression. You know as Well as I that an Engine Will Not Run with Less Than 70psi. This Means the Compression is Good on your Engine as you have Stated it is Running. Start the Engine and Go to Full Throttle. Carefully Use your Hand and Increase the Engine RPM's. Override the Governor by Pushing the Governor Arm. If the Engine Will Over Rev and Not Stall or Lose Power then it should be Fine. If the Engine has a Power Loss when Over Revving, then Turn the High Air Mixture Screw IN Until the Engine Over Revs with No Power Loss. You can View a Breakdown/IPL at this Addy http://www.outdoordistributors.com/ and Select the T. Then Select Tecumseh. Then Select Don't have Part Numbers. Then Enter the Model Numbers LH358SA. The Select the First File and Download the Breakdown for Online Viewing. Hope this Helps. I am here if you Require more Assistance. Let me know what Happens, Please. Thanks.

 Good Luck

 Respectfully

 John