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Old 02-16-11, 07:38 PM   #1
bassfisher
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Default My 03 Mercury compression test

Went and had the compression checked on my 03 Mer and here is what they found:

#1 130psi
#2 125psi
#3 135 psi
#4 135psi
#5 130psi
#6 130psi

How does that look to you folks?
I wish #2 was better, but the rest are fine I think, plus I did not know what normal is either. (Should had asked, and will tomorrow)
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Old 02-16-11, 07:47 PM   #2
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Harold, is it an Optimax or an EFI?
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Old 02-16-11, 08:15 PM   #3
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It has 6 carburetors.
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Old 02-16-11, 08:18 PM   #4
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It has 6 carburetors.
Last year of xr-6's made i think.
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Old 02-16-11, 08:23 PM   #5
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Last year of xr-6's made i think.
That's it the XR-6.
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Old 02-16-11, 08:55 PM   #6
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Harold, your numbers are just fine....pretty great for an 8 year old outboard. Don't worry about the 125. Everything is within 10%.
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Old 02-16-11, 10:39 PM   #7
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ready to roll
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Old 02-17-11, 01:58 PM   #8
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Looks good to me.
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Old 02-17-11, 02:53 PM   #9
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For future reference, what does the compression need to be in motors? I have a 1997 200hp evinrude? How do you check it? I am not meaning to hi-jack the thread, if I need to move it then I will.
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Old 02-17-11, 03:15 PM   #10
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Look at it this way. Normal atmospheric pressure is 14.7 psi. I'm sure most of you have dealt with compression ratios on cars, especially if you do any hot-rodding.

For an automobile engine, the minimum CR you will find on a daily driver is about 8:1.

If you do the math, 8 x 14.7 = 117.6 psi.

Hot rods can be much higher, 10:1 and up. 147 psi +.

However, compression checks are usually done with the engine cold, and the piston rings do not seal quite as well, so a compression check will often yield lower values. So while an outboard engine would probably fall somewhere between daily driver and hot rod as far as engine output, I think 110-135 psi is pretty healthy for any outboard.

The reason compression checks are done cold is to find out if any cylinders are bad, not for a real compression ratio. If one is drastically lower than the others, then you have some mechanical troubles, most likely a bad ring, valve seat, or blown head gasket.

Without knowing the particular
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Old 02-17-11, 05:22 PM   #11
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Originally Posted by nofearengineer View Post
Without knowing the particular
Did you fall asleep in the middle of your sentence? My grandfather used to do that sometimes...
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Old 02-17-11, 05:32 PM   #12
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Did you fall asleep in the middle of your sentence? My grandfather used to do that sometimes...
Ahhh.....I was trying to organize my post at the end, by moving paragraphs around. The window must have been too big, and that got scrolled to the bottom, off of the screen where I couldn't see it to delete it before I posted it....

Though I am not above falling asleep while talking....
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Old 02-17-11, 07:12 PM   #13
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I know exactly what you're talking ab........zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz....... .............zzzzzzzzzzzzzzz........zzzzzzzzzzzzzz zzz
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Old 02-19-11, 05:57 PM   #14
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For future reference, what does the compression need to be in motors? I have a 1997 200hp evinrude? How do you check it? I am not meaning to hi-jack the thread, if I need to move it then I will.
Go right ahead and jump right in my friend. It's all good!!!
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