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Compression Test on 225
#11159098
10/12/15 03:59 PM
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Joined: May 2015
Posts: 776
bFROG5
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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
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Re: Compression Test on 225
[Re: bFROG5]
#11159150
10/12/15 04:21 PM
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Joined: Mar 2010
Posts: 25,659
T Bird
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Okie by birth, Texan by choice. USAF "Thunderbirds" Alumni 1985-1989
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Re: Compression Test on 225
[Re: T Bird]
#11159278
10/12/15 05:29 PM
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Joined: May 2015
Posts: 776
bFROG5
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Matthew 4:19
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Re: Compression Test on 225
[Re: bFROG5]
#11159286
10/12/15 05:34 PM
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Joined: Aug 2006
Posts: 7,182
steve@S2Marine
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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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Joined: May 2003
Posts: 11,586
gary purdy
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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
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Re: Compression Test on 225
[Re: steve@S2Marine]
#11159515
10/12/15 07:51 PM
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Joined: Mar 2010
Posts: 25,659
T Bird
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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 And use a different compression gage.
Okie by birth, Texan by choice. USAF "Thunderbirds" Alumni 1985-1989
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Re: Compression Test on 225
[Re: bFROG5]
#11159608
10/12/15 08:24 PM
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Joined: May 2015
Posts: 776
bFROG5
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Thanks for the input guys, I thought it seemed high as well
Matthew 4:19
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Re: Compression Test on 225
[Re: bFROG5]
#11159691
10/12/15 08:58 PM
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Joined: Nov 2006
Posts: 2,846
TLW
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that would make it an "opti pop"
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Re: Compression Test on 225
[Re: bFROG5]
#11159704
10/12/15 09:04 PM
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Joined: Jun 2013
Posts: 238
Waco Crappie
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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.
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Re: Compression Test on 225
[Re: bFROG5]
#11159819
10/12/15 10:01 PM
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Joined: Aug 2006
Posts: 3,980
machinist
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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.
I fish on the edge and stay out of the middle
99 BassCat Jag w/225 Merc Optimax Retired TXU Outage Manager
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Re: Compression Test on 225
[Re: bFROG5]
#11159945
10/12/15 11:21 PM
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Joined: Jul 2006
Posts: 6,046
Fast Lane
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Mine was 119 PSI the last time I checked it.
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Re: Compression Test on 225
[Re: bFROG5]
#11160819
10/13/15 01:12 PM
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Joined: Dec 2002
Posts: 3,826
Tommy Yetts
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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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Joined: Aug 2006
Posts: 7,182
steve@S2Marine
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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. 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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Joined: May 2003
Posts: 11,586
gary purdy
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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
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Re: Compression Test on 225
[Re: bFROG5]
#11160966
10/13/15 02:18 PM
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Joined: Aug 2006
Posts: 7,182
steve@S2Marine
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i didn't realize he was referring to a 4 stroke.
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