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Old 11 March 2011, 12:03   #1
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2 stroke compression question

Quick question

What should a healthy 2 stroke 4hp Mariners compression be please?

I've done a test but can't seem to find an answer, have tried the 'search' function and google, but to no avail!

Cheers,

Si.
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Old 11 March 2011, 14:53   #2
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I would say anything over 105/110 PSI is good!
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Old 11 March 2011, 16:43   #3
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And do it with the throttle at wide open, it makes a difference.
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Old 11 March 2011, 16:51   #4
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And do it with the throttle at wide open, it makes a difference.
Agree.
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Old 11 March 2011, 17:10   #5
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compression

If you canít find the manufactures figures for the compression thatís not the end of the earth, the key is to ensure all cylinders are within 10 to 20 psi or thereabouts of each other. Always crank the engine until the compression gauge reaches the maximum reading. Depending on the engine WOT improves the volumetric efficiency!

If working in Bar 1 bar =14.7psi.

Hope this is useful!
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Old 12 March 2011, 03:23   #6
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Originally Posted by DJS View Post
If you canít find the manufactures figures for the compression thatís not the end of the earth, the key is to ensure all cylinders are within 10 to 20 psi or thereabouts of each other. Always crank the engine until the compression gauge reaches the maximum reading. Depending on the engine WOT improves the volumetric efficiency!

If working in Bar 1 bar =14.7psi.

Hope this is useful!
Thanks for your answers everyone.

However it's a single cylinder, so comparing is impossible

I did as advised anyway having throttle WOT, and I'm happy enough with the result so all good cheers 
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Old 14 March 2011, 09:29   #7
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the basic way of a simple test is;

is there any compression? i.e. with thumb over spark plug hole and turning the engine very slowly i.e. one rev every 10 seconds, you should feel pressure behind your thumb, and it hisses when you remove your thumb...

Not a check I would buy a £3000 engine on, but if the compression is there at these very slow revs then the bores are in OK order at least....
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Old 14 March 2011, 12:26   #8
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Not a check I would buy a £3000 engine on, but if the compression is there at these very slow revs then the bores are in OK order at least....
Especially if the seller has just poured half a teaspoon of oil in each cylinder prior to you trying it
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Old 16 March 2011, 04:40   #9
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Yes, that trick works unless the bores are totally shot or piston melted etc..., but I did mean afer you saw it running for a while..... On small cc engines this will give you a fair idea, thats all...
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