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  1. #1
    Join Date
    Sep 2010
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    Freeport, Texas
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    Default Really bad compression #'s on one of my 225's.

    As some of you may know, I bought these used with approx 850 hrs. I've been going through everything to bring them back up to spec. The final thing to do was to get a compression baseline. The port motor was:

    1-185
    2-185
    3-185
    4-184
    5-184
    6-175

    The starting batteries are mid-life 500 CCA, so not the strongest. Cranking has always been "lazy" with them. With that in mind, I'm ok with these numbers.

    The Stb motor was all over the place:

    1-130
    2-170
    3-205
    4-182
    5-155
    6-105

    My mechanic went through the stb motor twice to verify. He is very experienced, and even he was scratching his head.

    At first I thought, "Darn, I adjusted the valves wrong". But, the "shimmy" in that motor at idle has been there from day 1, long before I did the valves. It had been my hope that adjusting the valves would clean up the idle. Nothing that I have done.......from injectors, to Ringfree, to H/L filters, VST, plugs, the works.....has ever changed the "shimmy" at idle. I had begun to suspect bad compression numbers, and I was correct.

    This motor runs out at 6000 rpm and is smooth through acceleration.

    My mechanic said the rule of thumb is.....if compression is above 100, it'll run, so go run it with more Ringfree in the tank (not super-concentrated) for 50-60 miles. It could just be really gunked up. But, I have my doubts about that, because I've already run a fair amount of RF through it.

    It would be one thing if all the cylinders were low, in the 110 range, give or take. That's a tired, nearly worn out motor. But this.....?!

    So my initial question for you experts out there is.......what, in your experience could cause such wild swings? And supposing I wanted to fix it instead of run it, should the next step be a leak-down test?

  2. #2
    Join Date
    Apr 2016
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    barnegat NJ
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    2,707

    Default Re: Really bad compression #'s on one of my 225's.

    yes to the leakdown test My guess motor running too lean before you got it. See if you can bore scope it before teardown

  3. #3
    Join Date
    Sep 2008
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    Hague, Virginia, USA
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    Default Re: Really bad compression #'s on one of my 225's.

    WOW! Not good. I don't have experience with this on an outboard. But it it were an old car engine I would strongly suspect burnt exhaust valves. Yes, do the leak down test for sure. Running more RF through it won't hurt. If that doesn't do it, I don't think you're going to have any choice but to pull the heads and find out what's going on.
    CHawk 25 DLX

  4. #4
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    Default Re: Really bad compression #'s on one of my 225's.

    I'll do the leakdown test. If it appears the valves are at fault, and further inspection shows the rings and cylinder walls to be good, then I don't feel too bad doing the heads. I'll be able to do the manual part to save on labor costs.

    In the meantime, my mechanic says to go have fun with the boat for awhile. It's not something that has to be done right away. He says it's not likely that any further internal damage could be done to the motor. It just won't idle smoothly.

  5. #5
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    Default Re: Really bad compression #'s on one of my 225's.

    Sounds like a plan. Keep us all posted on this.
    CHawk 25 DLX

  6. #6
    Join Date
    Aug 2011
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    South Texas
    Posts
    562

    Default Re: Really bad compression #'s on one of my 225's.

    I had really low numbers on mine 170s 180s, not 105...but I ran a sea foam strong mix and I also saturated each cylinder with sea foam straight. it brought numbers up over the 200 mark.

  7. #7
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    Default Re: Really bad compression #'s on one of my 225's.

    Quote Originally Posted by Skooter View Post
    I had really low numbers on mine 170s 180s, not 105...but I ran a sea foam strong mix and I also saturated each cylinder with sea foam straight. it brought numbers up over the 200 mark.
    At this point, why not? I'll try it. Too bad I just put in brand new Mobil 1 after the Ringfree treatment.

  8. #8
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    Default Re: Really bad compression #'s on one of my 225's.

    Quote Originally Posted by Skooter View Post
    I had really low numbers on mine 170s 180s, not 105...but I ran a sea foam strong mix and I also saturated each cylinder with sea foam straight. it brought numbers up over the 200 mark.
    I want to try the Seafoam shock treatment like you did Skooter, but on an earlier thread, Chris @ Dockside Marine Services said not to use it on injected engines. He said the screen is ruined. Have you noticed any problems with your injectors?

    Does anyone else have experience with Seafoam and injectors?

    I'd like to do it today, but I think I'll wait for feedback. Thanks......

  9. #9
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    barnegat NJ
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    Default Re: Really bad compression #'s on one of my 225's.

    That was a reply to a thread that i typed, that was on a runaway engine i believe, Chris what do you have?

  10. #10
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    South Texas
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    Default Re: Really bad compression #'s on one of my 225's.

    I haven't had injector or fuel screen issues related to seafoam. Check their website, they recommend it for fuel injected engines.

  11. #11
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    Sep 2008
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    Hague, Virginia, USA
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    Default Re: Really bad compression #'s on one of my 225's.

    I've not hear of any problems with injectors from SeaFoam either. I guess it's possible for any loosened fuel varnish to plug the injectors or injector screens. Just not heard of any. Given your compression numbers, what do you have to lose?
    CHawk 25 DLX

  12. #12
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    Sep 2010
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    Default Re: Really bad compression #'s on one of my 225's.

    I took my mechanics advice and went offshore fishing today, putting about 80 miles on the motors. Probably 70 of those miles were at 4200rpm. Fishing wasn't kind, but the boat runs like a scalded dog! The motors were flawless and the boat handles nicely.

    Near as I can tell, this hull with 225's, fully loaded @ 11,200lbs and propped right, should run right at 30-31mph at 4200rpm on flat water with no current or wind. We were slightly under that.......approx 29mph @ 4200rpm. At the end, inside the jetties on flat water I hit 5700/5900 WOT and 41mph. This boat with 225's, propped and running well, should top-end at 45mph and 6200rpm. So, there is room for some improvement, but I think that will come from tweaking the props.

    It's strange that a supposedly weak motor runs so well? The weak motor is the one that hit 5900rpm.

  13. #13
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    Default Re: Really bad compression #'s on one of my 225's.

    Hmmm! Maybe your compression test was off - I think you know the drill - all plugs out, fully charged batteries, throttle wide open, warm engine. Possibly your turnover was too slow. I think it's supposed to be at least 300 rpm. Anyway, just keep the RF flowing. You may not have the issue you thought you had.
    CHawk 25 DLX

  14. #14
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    Default Re: Really bad compression #'s on one of my 225's.

    Warm?......I thought compression was done cold. We did it cold.

    I forgot to say in my last post that I also did the Seafoam shock treatment 2 days ago.

  15. #15
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    Default Re: Really bad compression #'s on one of my 225's.

    OK, Sea Foam strikes again!

    I was always told to get the engine as warm as possible. I know that's a PITA, pulling hot plugs out of an engine just before a compression test. But that's the way I've always done it.

    Maybe Mike, Jimmy or Chris will straighten me out on that.
    CHawk 25 DLX

  16. #16
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    Default Re: Really bad compression #'s on one of my 225's.

    I did a brief search on the Internet. There are advocates for doing a cold compression test and a warm compression test. However, it seems that the most knowledgeable folks advocate for a warm compression test because it more closely mimics how the engine is really running. Generally, you will get higher compression numbers on a warm engine. Would still like to hear from some real experts on this issue.
    CHawk 25 DLX

  17. #17
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    Default Re: Really bad compression #'s on one of my 225's.

    I imagine there are proponents of one or the other. I seem to recall that all 3 mechanics working out of our marina say cold, but I'd have to check that.

    I will be doing a leakdown test later this week for more insight inside the motor. It's still likely that compression on that motor is imbalanced, because the motor still has the same "shimmy" at idle that it always has.

  18. #18
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    Default Re: Really bad compression #'s on one of my 225's.

    Chawk_man your more of an expert than many on this site!! warm test has my vote.

  19. #19
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    Cincinnati, OH USA
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    Default Re: Really bad compression #'s on one of my 225's.

    From what I hear, the warm test is probably more accurate.

    I do it normally only when I am doing a decarb to see how things are improving.

    Practically speaking....if the cold test indicates there is an issue with a cylinder, the automatic next step is a leak down test to see why.

    I have not found a need to go through the extra time to run the engine just to warm it up. Perhaps for a cylinder drop test and doing some other diagnostic tests.... but not to warm it for a compression test.

    Maybe I am missing something.

    Jimmy will certainly have a scientific reason that it should be done warm.

    Mike

  20. #20
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    Default Re: Really bad compression #'s on one of my 225's.

    How about warm and cold readings,that should satisfy everyone

  21. #21
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    Assens, Denmark
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    Default Re: Really bad compression #'s on one of my 225's.

    I tested mine both warm and cold a while back. The warm gave much improved results.

  22. #22
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    Default Re: Really bad compression #'s on one of my 225's.

    Should the leakdown test be done cold or hot? Same as compression.....either/or?

  23. #23
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    Default Re: Really bad compression #'s on one of my 225's.

    I think the leak down test should also be done on a warm engine for the same reasons that a compression test should be on a warm engine. But, as normal, I would defer to the experts.

    Jimmy, where are you?
    CHawk 25 DLX

  24. #24
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    Default Re: Really bad compression #'s on one of my 225's.

    MAke sure you have WOT when checking compression.

  25. #25

    Default Re: Really bad compression #'s on one of my 225's.

    My 2cents ( 1.65 cents US ) is that the cold test is the most easily repeated test standard . Like warm , really warm , a little warm etc . If you are trying to achieve a repeatable base line, cold is the answer .

  26. #26
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    Default Re: Really bad compression #'s on one of my 225's.

    Here's an interesting update. From a post up above you can see that I did a test fishing run and the motors ran great. That was right after a shock treatment with Seafoam. Now keep in mind that I had already done a shock treatment with RingFree.

    Here's the chronology:

    When I drained the new Mobil 1 after RF, it was dark. I refilled with Mobil 1 again, ran the boat briefly to check WOT, and the next day did the compression that came up bad, as stated at the top of this thread.

    With nothing to lose, I decided to do the shock Seafoam as well. I warmed up the motor, removed the plugs, tilted it all the way up, and poured 3 pints of SF in the cylinders. I let it sit for 3 hrs, tilted down and watched most, if not all, of the SF come out, and then I cranked the motor to get the rest out. I then ran the motor out of gear @ 1800rpms in water with a 5:1 SF mix for 45 mins.

    The next day we went fishing and the boat ran great, as stated.

    So, I drained the oil again, and was shocked to see more dark oil......as dark as after the RF treatment. I'm getting a ton of carbon out of that motor, apparently.

    Sometime this week I will do the leakdown test and another compression test. The results should be interesting.

  27. #27
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    Default Re: Really bad compression #'s on one of my 225's.

    Should be very interesting. Please let us all know what you find.

    If I recall correctly, when you did the Ring Free treatment you used 2 ounces per 10 gallons (which is twice the mixture of Ring Free used for maintenance.) Back when you posted that, I thought to myself that seemed pretty weak. So the question is - just what is the proper mixture of Ring Free for a shock treatment and how long should you let it sit in the engine before re-start? Does anyone really know? The bottle says to check with your engine manufacturer, but that's not very helpful.
    CHawk 25 DLX

  28. #28
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    Default Re: Really bad compression #'s on one of my 225's.

    Chawk......I did 50:1 RF. That is, 15oz RF into 6gals (768oz) of gas in the small auxiliary tank.

    768/50=15

    I put 1oz/10gal in the 200gal tank onboard. That is a 2 times normal maintenance strength.

  29. #29
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    Default Re: Really bad compression #'s on one of my 225's.

    OK. Thanks for the clarification.
    CHawk 25 DLX

  30. #30
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    Default Re: Really bad compression #'s on one of my 225's.

    I have an update after the leakdown test. To repeat from above, here are the compression numbers I got a couple weeks ago. The stb motor was not good. It still isn't. The leakdown confirmed that there are problems. Exactly what, remains to be seen. I listed the stb numbers below. I stabilized the crankshaft pulley while my mechanic put 100psi in each cylinder. As I understand it, the number recorded is what was left after the air escaped. I was unaware that the loss happens instantaneously.

    Both compression and leakdown were done cold.

    1-185
    2-185
    3-185
    4-184
    5-184
    6-175

    The starting batteries are mid-life 500 CCA, so not the strongest. Cranking has always been "lazy" with them. With that in mind, I'm ok with the port numbers.

    The Stb motor was all over the place:
    the leakdown result is in red.

    1-130/43
    2-170/66
    3-205/89
    4-182/44
    5-155/60
    6-105/25

    What we learned this time was that air was leaking out of a valve and coming out the spark plug hole of the adjacent cylinder. I believe this occurred on 3 or 4 of the lowest cylinders, perhaps all.....I'm a little foggy on that. He said he didn't think it was the head gaskets.....something about it being one-way instead of both ways. I would have to get clarification on that part.

    He said the first thing to do was to recheck the valve lash. Since I'm pretty certain I did it right, the problem is still undiagnosed. I will recheck anyway, to be sure.

    Could the valves have gotten hot and deformed? Does that happen? As in burned?

    Could it be head gaskets? My mechanic is good, but he's also scratching his head and would welcome help.

    Why the one cylinder with 205 compression?

    Any thoughts from the gurus?

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