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

Registered: 05/24/15
Posts: 518
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 Offline
TFF Celebrity

Registered: 03/07/10
Posts: 6064
Loc: Temple, Texas "Rail Town 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
Pro Angler

Registered: 05/24/15
Posts: 518
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: 6826
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: 11423
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 Offline
TFF Celebrity

Registered: 03/07/10
Posts: 6064
Loc: Temple, Texas "Rail Town 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
Pro Angler

Registered: 05/24/15
Posts: 518
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: 2315
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]
Waco Crappie Offline
Outdoorsman

Registered: 06/06/13
Posts: 238
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: 1842
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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#11159945 - 10/12/15 06:21 PM Re: Compression Test on 225 [Re: bFROG5]
Fast Lane Offline
TFF Celebrity

Registered: 07/24/06
Posts: 5867
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: 3578
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

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

Registered: 08/25/06
Posts: 6826
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: 11423
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.
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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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#11160966 - 10/13/15 09:18 AM Re: Compression Test on 225 [Re: bFROG5]
steve@hydrodynamics Offline
TFF Celebrity

Registered: 08/25/06
Posts: 6826
Loc: Quitman,Tx
i didn't realize he was referring to a 4 stroke.
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