Lost some compression. Update. Pictures now on.

[steviecops]

Hi<br />I think I almost known the answer to this one, but I want make sure. Also, I suppose I'm hoping for some reassurance! Motor is a Johnson 55, two cylinder. Model number is J55EL80C.<br /><br />Last time out on my boat, I was cruising along at about 5200 rpm when the engine started to die. It slowed right down and the revs settled at around 2000 rpm. This lasted for about 20 seconds, then the revs increased back to around the 5000 rpm mark and all seemed to be normal for the rest of the day.<br /><br />Anyway, I was puzzled as to why this should have happened, so today I did a few checks. The compression came out at 150 psi on the top cylinder and 130 on the bottom. Previously they read 151 psi top, 148 psi bottom. I started and ran the engine in a water tank, and all seemed well, then I checked the compression again and there was no change.<br /><br />Do you think I have damaged the bottom cylinder? Possibly that cylinder became briefly starved of fuel for some reason when I was out last time?<br /><br />Or could it be a stuck ring? The plugs were both pretty carboned up when I took them out today. Can a ring get stuck even when the boat and engine are in pretty regular use? Or is that something that happens when the engine has sat for a period of time?<br /><br />I know I've got to try the decarb first, but won't be able to do that on the water until next week. I can do it sooner in the water tank, but obviously won't be able to run the engine at anything like WOT. Would I be better off waiting until I can get the boat on the water?<br /><br />Any advice will be appreciated.<br /><br />Thanks in advance<br />Steve

 

[Walker]

Re: Lost some compression. Update. Pictures now on.

130 is still pretty high. I think you're on the right track with the de-carb. Let us know if it helps.

 

[steviecops]

Re: Lost some compression. Update. Pictures now on.

If they were both 130 I'd be happy enough. It's just that I've lost 20 psi on the bottom since the beginning of the season.<br /><br />I certainly will let you know the outcome of the decarb. Is it O.K to do this in the water tank at just over idle speed? Or do I need to run the engine at WOT on the water for it to be effective?<br /><br />Thanks<br />Steve

 

[Dhadley]

Re: Lost some compression. Update. Pictures now on.

The decarb is done at idle. Just follow the instructions on the can of which ever product you use.<br /><br />20 lbs is a sign. The max OMC gave was 15. and if you lost it that quick, something happened. Hopefully it may be a head gasket. Personally I wouldnt run it anymore until the condition of the bottom cyl can be verified by taking the head off to look. If it is indeed OK then were good. If it is (hopefully) a gasket starting to leak then it needs to be changed anyway.

 

[steviecops]

Re: Lost some compression. Update. Pictures now on.

Thanks Dhadley, you just answered my next question! <br /><br />I was going to ask if I could run it for the rest of the season? About 2 months and 8 more trips.<br />Are you saying don't do the decarb until I've had the head off?<br /><br />Also, I don't know how suddenly I lost the compression, or whether it was anything to do with my motor dying momentarily last time out. I last checked the compression in April.<br /><br />Thanks<br />Steve

 

[Solittle]

Re: Lost some compression. Update. Pictures now on.

Steve - Follow DH's advice. It should not take more than an hour.

 

[steviecops]

Re: Lost some compression. Update. Pictures now on.

I will do. I hope to get at it on Monday.<br /><br />Thanks<br />Steve

 

[steviecops]

Re: Lost some compression. Update. Pictures now on.

Hi<br />Well, good advice from Dhadley as usual. Something certainly did happen!<br /><br />It looks like I broke a ring or something because the top of the lower piston has been beaten up quite badly around the edge. The same with the cylinder head. There were no bits of piston ring loose when I took the head off, but it looks as though some bits have embedded themselves in the top of the piston.<br /><br />There is some scoring to the cylinder, although it isn't as bad as I thought it might be when I saw the state of the piston. As soon as I figure out how to post pictures, I'll post the ones I've taken to give you a good idea of what might have happened. (Does anyone know of a free picture hosting site?)<br /><br />It looks like I will have to do a rebuild, which is worrying because I haven't ever done anything as involved as that before. Or maybe it isn't worth it? <br /><br />I do have a newly rebuilt 50hp powerhead that I bought last year when I saw it going cheap. (It actually looks brand new to me as it hasn't been painted yet, but I was told it was professionally rebuilt). It looks as if it will fit. Would I be better off putting the 50 hp powerhead on and getting the 55 rebuilt at my leaisure? (I really don't want to be without a boat for too long during what is the peak of our Bass season). Will there be much of a loss in performance between the 55 and the 50?<br /><br />Any ideas what caused the damage to my motor? There wasn't much carbon build up on the pistons at all, and I've really looked after the motor since I've had it. That is one horrible feeling when you take the head off and see the damage for the first time!<br /><br />Any more advice will be very much appreciated as I feel a bit nervous with the prospect of having to either swap powerheads or rebuilding the motor. I'll post pictures as soon as I find out how.<br /><br />Thanks<br />Steve

 

[Goodoleboy]

Re: Lost some compression. Update. Pictures now on.

If it were me I would put the new 50 horse on for the rest of this season.<br /><br />And rebuild the 55 this winter. I wouldnt think you are going to see all that much of a diffirence between the two engines. Mabey 2 or 3 MPH diff.<br /><br />Good luck!

 

[steviecops]

Re: Lost some compression. Update. Pictures now on.

Thanks Goodoleboy, 2-3 mph won't make much difference to me. I only use the boat for fishing.<br /><br />Steve

 

[steviecops]

Re: Lost some compression. Update. Pictures now on.

pictures

 

[steviecops]

Re: Lost some compression. Update. Pictures now on.

I'm making good progress ;o) I have the powerhead off and I'm ready to start undressing it and dressing the new one.<br /><br />Could someone please tell me if I need to re-jet the carbs? If so, does anyone know what jets I need to get? My carbs have fixed idle, off idle and high speed jets. My OEM manual shows that the jets vary slightly on the top and bottom carbs. I don't want to ruin this new powerhead, so I want to get it right.<br /><br />Thanks<br />Steve

 

[steviecops]

Re: Lost some compression. Update. Pictures now on.

Just bumping this up in the hope of getting some advice.<br /><br />Anybody?<br /><br />Thanks<br />Steve

 

[Dhadley]

Re: Lost some compression. Update. Pictures now on.

Just run your carbs as they were produced. They are calibrated for the air that goes thru them. They have no idea what powerhead they're on. <br /><br />Truthfully, it'll be interesting to see what the speed difference is. I'd bet you'll not be able to tell -- providing the new powerhead is performing as it should. This will be very interesting to everyone who wants to bump up horsepower. I know youre going down in power rather than up but the results should be the same. We're just looking at the difference.

 

[steviecops]

Re: Lost some compression. Update. Pictures now on.

Thanks Dhadley.<br /><br />I'll let you know what the difference is, if any.<br /><br />Do you think it was carbon that broke the ring on my old powerhead?<br /><br />Thanks again<br />Steve

 

[Solittle]

Re: Lost some compression. Update. Pictures now on.

Yep.<br /><br />When was the last time you decarbed the 55?

 

[G DANE]

Re: Lost some compression. Update. Pictures now on.

I know a guy who has 2 55's in boxes, they both threw a rod. OMC replaced a bunch of the twin 55 powerheads way beyond normal warranty. I dont think this was their best model, due to the big flush ports ( intake ). They are VERY sensitive to incorrect prop choise.

 

[steviecops]

Re: Lost some compression. Update. Pictures now on.

Hi SoLittle<br />I was glad to read earlier that your motors are running fine ;o) <br /><br />I decarbed the motor about a year and a half ago. There is some history to this motor that may tie in with what happened. I bought it on a boat two years ago. One of the first things I had to do was fit a thermostat because the previous owner had been running it without one. Later, I had to change prop because it wouldn't do the recommended rpm. After I changed from a 17 to a 15, all was well. I thought that making those changes, and the decarb I did 18 months ago would have prevented this from happening. In hindsight, I should have decarbed it again at the start of the season. We live and learn!<br /><br />Hi G DANE<br />I had heard before that the 55 twins were not the best motor OMC ever produced, but it is a great motor when it's running! As you've read above, the motor wasn't doing the recommended rpm on my boat with the stock 17 pitch prop that the motor comes with. I had to go down to a 15 to get the correct rpm. Maybe I was too late, maybe the damage was done already? How often would you recommend doing a decarb? I'm tempted to do it a couple of times a year now, just to prevent more damage. Were the 50 twins any better than the 55's? Maybe I'll stick with the 50 powerhead if they are a bit more reliable.<br /><br />Thanks again<br />Steve

 

[G DANE]

Re: Lost some compression. Update. Pictures now on.

I once helped my brotherinlaw repairing a twin 60 that ate a rod bearing, it scratched sided of casing and chewed up cranck journal pretty bad, but he got it stopped before it started slinging parts. The 60's are fairly reliable, though. 40's and 50's are both known as very fine runners, i dont think it is the 5 HP but an early design of the flush ports or so that does the damage. I always liked those twin loopers too, they really got the grunt, and the 60 has amazing top end.

 

[G DANE]

Re: Lost some compression. Update. Pictures now on.

Hey - if you need a head, maybe the guy with the two in boxes still has them ?? He might even have a used piston. Want me to ask ?