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Engine Compression on Broadmoor


pops_n_scratches

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pops_n_scratches
I have a Simplicity 728 Broadmoor with the 8hp Briggs engine. Its running about 75 psi compression. If this were a car engine, I would be concerned. What would a good compression range be for an old small engine like this? If its low, I'm thinking of rebuilding.
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Briggs doesn't provide a compression recommendation for their engines, due to the "Easy Spin" compression release system. They recommend spinning the flywheel backwards, by hand, against the compression stroke. If the flywheel "rebounds". The compression is sufficient. Pat
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Pat is right, it is difficult to get a accurate reading. 75Psi is not bad, try to get a cold compression check and one after running it a while, or hot reading the see the difference. On my cast iron Briggs 12hp i get 85 cold and 65 hot psi. I feel I need rings. This is a general shop test, but the best test for a engine is to put it to work. If it blows blue smoke and or looses power after its under a heavy load for a hour or so, and you see the oil level going down (like me) that is my best test. I have a problems here for now, i have never mowed with a 12ph ci Simplicity under a load so i dont if it is pulling ok or not. And the better designed tractor like AC and Simpicily it will most likely be very difficult to notice a drop in power unless you have had some seat time. If it starts good and stay running, restarts after it's hot you sould be ok. But i and loosing oil after just a small time under little or no load. I feel a oil ring has given out on my Landlord. But not knowing the history of the engine the rings my have been change and never seated properly. Any way plans are to replace the rings befor spring. I think (85 cold) and (65 hot)psi difference is a lille to much and feel my rings have lost there spring if you know what i mean.
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I checked the compression on a couple of mine and got varying results. All of mine are cast iron Briggs with horizontal cranks. My 12hp has 40psi, my 13hp has 90psi and my 10hp has 110 psi. With such results I'm inclined to believe that the 12hp has a problem somewhere. But when I do the test the Briggs suggest, spinning engine backwards against power stroke it kicks back. Is there anyway to confirm weither or not may 12hp needs some work, or do I just put it to work and see what happens.
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just at thought , wouldnt a leakdown be a more accurate test than a compression test anyway....just a thought badcars
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HI, The leak down test is the way to go. 75 lbs is normal for that engine due to the compression relief. Also on these small engine use a compression guage that has a short tube with the valve in the tip. One with an extension hose will read significantly lower. The reason is that the air in the hose is added to the air in the combustion chamber and effectively reduces the compression ratio. My 2 cents worth and its free value accordingly. Al Eden
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pops_n_scratches
Wow! Lots of great information here. Thanks to all. Now I'm out to the garage to put it to use. I'll pass along what I learn.
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Thats what makes this club so worth while. Lot of experience, some good some bad, and people not afraid to pass it on. I love it.
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