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What Should My Compression Be On S12D

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#1 york0060 OFFLINE  



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Posted October 16, 2013 - 12:39 PM

i have a Wisconsin S12D  (12 1/2HP) engine and i am needing to know what the compression on it should be. It starts and runs good until you get a load on it and it kills the motor ( ts in my Bush Hog).  It is running about 74 lbs now. thanks for your help!

#2 EricFromPa OFFLINE  



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Posted October 16, 2013 - 02:40 PM

Compression is hard to read on an engine with ACR (Automatic Compression Release) And they do not give Compression specs for they're engines because of it.


It does however kick out at 650rpm


Or you could use a Leak-Down tester to check for worn rings,valves and head gasket issues.



Here's a Very good S10d-S12d-S14d manual.Right click and save link as Pdf document.



That being said 74lbs does sound a bit on the low side.I like to see them with 90-110 psi even with the ACR.



Have you taken the head off and checked the valves,head and gasket?


I've seen several Wisconsin engines with cracked heads.Some with rather large cracks.


You might have to put a set of rings in it if all else fails.

Edited by EricFromPa, October 16, 2013 - 02:44 PM.

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#3 superaben OFFLINE  

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Posted October 16, 2013 - 04:47 PM

I would also make sure you have good fuel flow from the gas tank and on into the carburetor.  I had a machine that was getting enough of a sniff to run by sucking through the closed sediment bowl (I know, idiots live in Mt. Solon as well as Washington) but would die as soon as you put it in gear.


A weak spark will cause the same thing.  You might polish the points.


Ben W.

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#4 HDWildBill OFFLINE  


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Posted October 16, 2013 - 06:35 PM

I think Eric and Ben pretty much covered it.  Compression checks on these engines, I think, do OK a an indicator but if I had one with 74 PSI I would certainly be investigating a lot further. 

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