Briggs & Stratton Engine Compression Nos.


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Old 04-01-24, 10:52 AM
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Briggs & Stratton Engine Compression Nos.

Who knows or where do I find the silly secret Briggs & Stratton compression nos. (psi) for a 16HP Vanguard V-twin lawn tractor engine? Model 303777 1147-E1
I want to check the condition of my engine. Starter cranking; cold compression test, warm engine compression test. What should they be, in psi? I'm sure the engine has a compression release when it is cranked. The specs indicate it is an 8.2:1 C.R. Thanks for any help you can provide! Old Handyman
 
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Old 04-02-24, 02:11 AM
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I don't think you'll find any specs for compression on an engine with a compression release.
 
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Old 04-02-24, 03:07 PM
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I don't think B&S publish compression numbers. I checked a couple of the B&S manuals I have and did not see compression numbers. The standard formula for converting compression ratio to PSI is to multiply the atmospheric pressure by the ratio. So 8.2 x 14.7 = 120.54/1 = 120.54 (14,7 is sea level)

That sounds high to me, but that is what the engine gurus say.
 
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Old 04-02-24, 05:15 PM
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130 is optimal but you won't get that unless you disable to compression release.
 
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Old 04-03-24, 09:50 AM
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Thanks Cheese & Whittsend, good information! And the formula is new to me, will help too. I guess I should do a leak down test. Are there specs for that? Is it a time thing? OldHandyman
 
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Old 04-03-24, 11:52 AM
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I prefer a leakdown test. But I do it very non-technically with no gauges. You can get a feel for the engines compression by rotating it backwards.
 
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Old 04-08-24, 05:43 PM
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Thanks folks. I did a cold starter cranking compression test and it was 125psi on both cylinders.
Then i did a low-pressure psi leak down test with just line air and it gurgles in the oil tube, so the rings etc. are wore out. Both cylinders did the same thing, so I think the engine has seen it's life expectancy. Not sure what I will do with the unit yet. Thanks again for your thoughts. OldHandyman
 
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Old 04-08-24, 09:29 PM
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You're supposed to get the air past the rings, that's normal. 125 is great, I think the engine is probably in great shape since that was with the compression release working. The twin cylinder Japanese Vanguard engines were some of the best engines made IMO.
 
 

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