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2020/04/15 15:29:51
LDC5

Briggs 15hp Compression

Hi, have a 18yr old Briggs 15hp (28Q777-0645-E1) on my Ariens Sierra, and has been well maintained. Compression measures ~117psi (wet&dry). When asking Briggs Tech Help what is compression spec, they say no comp spec, but this engine has 8.5:1 compression ratio.....Question: assuming atmosphere is 14.7psi x 8.5 = 125psi, therefore, does this engine still have 94% (117/125) of max compression?
1 comment Leave a comment
AVB
If you are getting 117 psi either your valves are out of adjustment or the camshaft's ACR has failed. Normal compression with the ACR working is around 65-80 psi.
 
And Briggs Tech support is correct that is no publish compression numbers for these engines. You are to do a leak down test or modified leak down test. What looking for leak down rates under 40% preferably around 10-20%. The modified test involves disabling the valve train.
2020/04/15 17:19:17

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