Evinrude 175 '98 - need help with cylinder compression review pls.

gam101

Petty Officer 3rd Class
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Jun 3, 2012
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79
Hello again fellow water trotters. I apologize for the extended hiatus. I blame it on eBay, the first compression kit I ordered got lost, and the 2nd one took too long...

Anyhow, attached are the compression results I was advised to execute in a previous thread (
link). I've labelled the images. Could someone please review them & let me know what I am looking it?

My amateur mind tells me that 4 cylinders are not operating optimum, unlike the top two on either side.

I'm also attaching a picture of a plug, which had some oil on it, is that normal?

Appreciate it tremendously.

-gam101
 

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Chris1956

Supreme Mariner
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Mar 25, 2004
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27,036
Gee, I am hoping your compression gauge reads low. 75PSi stinks......

If she will start, it is likely the true compression is more like 90PSI, and the motor is likely fine.
 

gam101

Petty Officer 3rd Class
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Jun 3, 2012
Messages
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Gee, I am hoping your compression gauge reads low. 75PSi stinks......

If she will start, it is likely the true compression is more like 90PSI, and the motor is likely fine.

Appreciate the reply. Well, she starts, no problem, and runs. However, a little history (previous post link);

1) There was an overheat issue a few months back & the power pack + wirings had to be replaced. And that is why folks here recommended a compression test.

2) I have had all gaskets rebuilt too.

So, since then I've used the motor quite a few times with no issues, except the last time (a month back) I felt there was very little power. Then the urgency to get the compression test done just compounded. And here we are with this post.

My follow up question is, the approx 60psi on the other 4 cylinders (also in the pictures) is fine?

Just a reminder, the 75psi is on the top two cylinder of either side.

Thank you, again.
 

Bosunsmate

Admiral
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Apr 7, 2012
Messages
6,129
Those sparks plugs need replacing.
75 is low, 60 is low but your gauge may be wrong and reading 20psi less than it should. So if it runs ok then its most likely just a bad compression gauge. The main thing is that they are all relatively similar, if you had one like 40psi or 110psi then you would know something was up.
Hopefully you know what caused the overheat.
Its always easiest to just carry on with your prior thread btw
 

Bosunsmate

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Apr 7, 2012
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6,129
Very little power may be compression or it may be that you arent getting spark or fuel to every cylinder. Do a drop test on each cylinder and that way you can see if its something localised to one or two cylinders or if its an overall lose of compression in both banks. If you look into the sparkplug holes and see how the piston domes look then that can tell you a few things too, check there are no signs of indentations from rings breaking and hitting the piston heads
 

gam101

Petty Officer 3rd Class
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Jun 3, 2012
Messages
79
Those sparks plugs need replacing.
75 is low, 60 is low but your gauge may be wrong and reading 20psi less than it should. So if it runs ok then its most likely just a bad compression gauge. The main thing is that they are all relatively similar, if you had one like 40psi or 110psi then you would know something was up.
Hopefully you know what caused the overheat.
Its always easiest to just carry on with your prior thread btw

Appreciate the reply Bosunsmate.

Those plugs are less than a year old & only been out on the boat for no more than 10 hours since they were replaced. Still need replacement?

Yes, your observation is correct; top two cylinders on either size are identical & then the lower 2 on either side are identical in pressure. I was just concerned when I read that the pressure was really low.

Will keep in mind the prior thread advice. Thank you, again.
 
Last edited:

Bosunsmate

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Apr 7, 2012
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6,129
The plugs definitely need cleaning at the very least. Any oil, grime will affect spark and can also cause a short.
Im tight fisted so id clean them as best i can instead of replacing. Looking at that one it looks like its running rich so id do a spark test to check its firing a decent blue spark on each cylinder.
Yes pressures are low but since they are all the same id err on it being the tester more than the engine at this point but that's no certainty unfortunately
 

gam101

Petty Officer 3rd Class
Joined
Jun 3, 2012
Messages
79
The plugs definitely need cleaning at the very least. Any oil, grime will affect spark and can also cause a short.
Im tight fisted so id clean them as best i can instead of replacing. Looking at that one it looks like its running rich so id do a spark test to check its firing a decent blue spark on each cylinder.
Yes pressures are low but since they are all the same id err on it being the tester more than the engine at this point but that's no certainty unfortunately

Sure thing! I'll remove plugs & clean them all. Appreciate all the help again.
 
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