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Old 30 December 2011, 07:49   #1
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Compression psi for a Yam 50hp

Hi dose anyone know the ballpark compression a Yamaha 50hp 2 stroke should produce? I think it's a 1985 engine.

I need to re do the test because I didn't have the throttle wide open. But I can't find any figures regarding what it should be. All the readings were the same and I've noted them down but left my note book in the workshop! The engines running well I just thought I'd test it for piece of mind and I got a compression tester for Christmas so had to use it!

Cheers

Ross
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Old 30 December 2011, 08:12   #2
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As long as all the readings are the same you're ok. Compression testers aren't usually very accurate in PSI-it's just the needle position being the same that counts.
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Old 30 December 2011, 08:35   #3
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Excellent there all the same! Just wanted to see how they compared to what there supposed to be.
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Old 31 December 2011, 21:34   #4
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Originally Posted by CornishRoss View Post
Hi dose anyone know the ballpark compression a Yamaha 50hp 2 stroke should produce? I think it's a 1985 engine.

I need to re do the test because I didn't have the throttle wide open. But I can't find any figures regarding what it should be. All the readings were the same and I've noted them down but left my note book in the workshop! The engines running well I just thought I'd test it for piece of mind and I got a compression tester for Christmas so had to use it!

Cheers

Ross
Anything over 100 P.S.I and it's OK. 130 P.S.I would be good for that year.
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Old 31 December 2011, 21:49   #5
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How important is it to have the throttle WOT?
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Old 01 January 2012, 00:04   #6
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How important is it to have the throttle WOT?
Think about what the piston is doing. Compressing a static volume of air by a given ratio = 100 psi "compression".

Idle does this about 800x a minute. WOT about 5500. Its still just a static volume by a given ratio. You will get more blow-by when the rings are cold. But you wouldn't run a cold engine WOT anyway.
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Old 02 January 2012, 17:01   #7
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How important is it to have the throttle WOT?
WOT every time you test
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