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#11159098 - 10/12/15 10:59 AM Compression Test on 225
bFROG5 Offline
Angler

Registered: 05/24/15
Posts: 392
Loc: Fort Worth, TX.
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.
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#11159150 - 10/12/15 11:21 AM Re: Compression Test on 225 [Re: bFROG5]
T Bird Online   content
TFF Team Angler

Registered: 03/07/10
Posts: 4618
Loc: Temple, Texas USA
Year and model of Merc.?

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#11159278 - 10/12/15 12:29 PM Re: Compression Test on 225 [Re: T Bird]
bFROG5 Offline
Angler

Registered: 05/24/15
Posts: 392
Loc: Fort Worth, TX.
2003 pro xs
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Matthew 4:19

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#11159286 - 10/12/15 12:34 PM Re: Compression Test on 225 [Re: bFROG5]
steve@hydrodynamics Offline
TFF Celebrity

Registered: 08/25/06
Posts: 6728
Loc: Quitman,Tx
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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#11159397 - 10/12/15 01:41 PM Re: Compression Test on 225 [Re: bFROG5]
gary purdy Offline
TFF Guru

Registered: 05/24/03
Posts: 11095
Loc: Littlefield Tx & Lake A. H. US...
160 is high. Carbon build up, modified cylinder heads? I would recheck it. Ones I have tested I think are about 120 - 130.
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�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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#11159515 - 10/12/15 02:51 PM Re: Compression Test on 225 [Re: steve@hydrodynamics]
T Bird Online   content
TFF Team Angler

Registered: 03/07/10
Posts: 4618
Loc: Temple, Texas USA
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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#11159608 - 10/12/15 03:24 PM Re: Compression Test on 225 [Re: bFROG5]
bFROG5 Offline
Angler

Registered: 05/24/15
Posts: 392
Loc: Fort Worth, TX.
Thanks for the input guys, I thought it seemed high as well
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#11159691 - 10/12/15 03:58 PM Re: Compression Test on 225 [Re: bFROG5]
TLW Online   content
Extreme Angler

Registered: 11/16/06
Posts: 2197
Loc: ft worth
that would make it an "opti pop" grin

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#11159704 - 10/12/15 04:04 PM Re: Compression Test on 225 [Re: bFROG5]
Waco28 Crappie Offline
Outdoorsman

Registered: 06/06/13
Posts: 228
Loc: Waco TX
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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#11159819 - 10/12/15 05:01 PM Re: Compression Test on 225 [Re: bFROG5]
machinist Offline
Extreme Angler

Registered: 08/22/06
Posts: 1752
Loc: Lake Graham, Lot 30
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


Edited by machinist (10/12/15 05:21 PM)
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99 BassCat Jag w/225 Merc Optimax

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#11159945 - 10/12/15 06:21 PM Re: Compression Test on 225 [Re: bFROG5]
Fast Lane Offline
TFF Celebrity

Registered: 07/24/06
Posts: 5746
Loc: Tyler, texas
Mine was 119 PSI the last time I checked it.

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#11160819 - 10/13/15 08:12 AM Re: Compression Test on 225 [Re: bFROG5]
Tommy Yetts Offline
TFF Team Angler

Registered: 12/14/02
Posts: 3468
Loc: Rockwall, TX USA
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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Tommy Yetts

www.rockwallmarine.com

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#11160830 - 10/13/15 08:17 AM Re: Compression Test on 225 [Re: Waco28 Crappie]
steve@hydrodynamics Offline
TFF Celebrity

Registered: 08/25/06
Posts: 6728
Loc: Quitman,Tx
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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#11160864 - 10/13/15 08:32 AM Re: Compression Test on 225 [Re: bFROG5]
gary purdy Offline
TFF Guru

Registered: 05/24/03
Posts: 11095
Loc: Littlefield Tx & Lake A. H. US...
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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#11160966 - 10/13/15 09:18 AM Re: Compression Test on 225 [Re: bFROG5]
steve@hydrodynamics Offline
TFF Celebrity

Registered: 08/25/06
Posts: 6728
Loc: Quitman,Tx
i didn't realize he was referring to a 4 stroke.
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