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Compression Test on 225 #11159098 10/12/15 03:59 PM
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bFROG5 Offline OP
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What should the compression range be for a 225 merc?
Is 160 on all cylinders too high? 160 is what came back on a boat I've been looking at.


Matthew 4:19
Re: Compression Test on 225 [Re: bFROG5] #11159150 10/12/15 04:21 PM
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T Bird Offline
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Year and model of Merc.?


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Re: Compression Test on 225 [Re: T Bird] #11159278 10/12/15 05:29 PM
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bFROG5 Offline OP
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2003 pro xs


Matthew 4:19
Re: Compression Test on 225 [Re: bFROG5] #11159286 10/12/15 05:34 PM
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steve@S2Marine Offline
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160 seems high.

warm the engine up and take another reading.

if it still comes up high... try a different gauge.

160 psi , puts ya race fuel specs.

i think it should be closer to 110 to 120

Tommy at Rockwall Marine will know for sure


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Re: Compression Test on 225 [Re: bFROG5] #11159397 10/12/15 06:41 PM
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gary purdy Offline
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160 is high. Carbon build up, modified cylinder heads? I would recheck it. Ones I have tested I think are about 120 - 130.


The world will not be destroyed by those who do evil, but by those who watch them without doing anything. Remember what He has done and remember that He is not done yet!-- GOD IS GOOD
Re: Compression Test on 225 [Re: steve@S2Marine] #11159515 10/12/15 07:51 PM
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Originally Posted By: steve@scp
160 seems high.

warm the engine up and take another reading.

if it still comes up high... try a different gauge.

160 psi , puts ya race fuel specs.

i think it should be closer to 110 to 120

Tommy at Rockwall Marine will know for sure


And use a different compression gage.


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Re: Compression Test on 225 [Re: bFROG5] #11159608 10/12/15 08:24 PM
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bFROG5 Offline OP
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Thanks for the input guys, I thought it seemed high as well


Matthew 4:19
Re: Compression Test on 225 [Re: bFROG5] #11159691 10/12/15 08:58 PM
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that would make it an "opti pop" grin

Re: Compression Test on 225 [Re: bFROG5] #11159704 10/12/15 09:04 PM
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Waco Crappie Offline
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I would have thought that if you had carbon buildup the compression would be lower due to sticky valves not closes as they should.

I have a 90 hp Mercury and my compression is supposed to be at 220 psi which I think is super high but that is how they designed the motor.


Re: Compression Test on 225 [Re: bFROG5] #11159819 10/12/15 10:01 PM
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machinist Offline
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Waco if your compression was that high you wouldn't need sparkplugs. It would detonate
like a diesel. I might agree with it being 120 but hell my sons 565 cubic inch Chevy
with 14 to 1 comp. isn't but 170. and it makes 1300 horsepower.

Johnny

Last edited by machinist; 10/12/15 10:21 PM.

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Re: Compression Test on 225 [Re: bFROG5] #11159945 10/12/15 11:21 PM
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Mine was 119 PSI the last time I checked it.

Re: Compression Test on 225 [Re: bFROG5] #11160819 10/13/15 01:12 PM
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Tommy Yetts Offline
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These later model engines are looper motors. The comp. on these engines are anywhere from 95 - 120. Like it was suggested try another comp. gauge.


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Re: Compression Test on 225 [Re: Waco Crappie] #11160830 10/13/15 01:17 PM
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steve@S2Marine Offline
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Originally Posted By: Waco28 Crappie
I would have thought that if you had carbon buildup the compression would be lower due to sticky valves not closes as they should.

I have a 90 hp Mercury and my compression is supposed to be at 220 psi which I think is super high but that is how they designed the motor.


no "valves" on an outboard motor.

my 300 drag with o-ringed 17CC heads made 260 lbs compression.. had to run 112 octane fuel or higher.
that motor hit hard at 11k rpms.

a 90hp engine runs about same compression as the bigger ones. around 110- 120 is it.

imho. compression over 140-150 needs race gas.


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Re: Compression Test on 225 [Re: bFROG5] #11160864 10/13/15 01:32 PM
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gary purdy Offline
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The compression can be altered a lot with the camshaft on 4 strokes. Surprising Steve but those encapsulated cylinder head motors do have more compression but not over 135-140lbs. I laughed when I saw the sticky valve post too.


The world will not be destroyed by those who do evil, but by those who watch them without doing anything. Remember what He has done and remember that He is not done yet!-- GOD IS GOOD
Re: Compression Test on 225 [Re: bFROG5] #11160966 10/13/15 02:18 PM
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i didn't realize he was referring to a 4 stroke.


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