'85 Johnson 15 low compression in 1 cyl - looks scored

[wineyarders]

Hi,

I'm relatively new to the site but have done a lot of reading. I've seen plenty of discussion regarding compression but still have a couple unanswered questions. Hopefully someone has a little time to help me on my way.

Short story: low compression on one cyl; I think because it's lightly scored (see pics). What should I do? New gasket, new rings, rebore + new pistons, other?

I guess I'm too new to post photos. Here's a quick link to the photos that show what I'm talking about: http://www1.snapfish.com/snapfish/t...otsc=SHR/otsi=SALBlink/COBRAND_NAME=snapfish/

Long story: I have an '85 Johnson 15hp that I used probably once a week this summer in the ocean. It always needs a squirt of fuel in the carb to get things going, and after that it runs ok, although it will not idle for more than a minute or so at best, and if the engine is off for more than 5-10 minutes I'll need to shoot more fuel into the carb to get things going. Picked up a compression tester and the top cyl was about 70-75 and the bottom was 55-60. The lower plug has a little carbon/oil buildup while the upper was without but had a little chalky residue buildup. Anyway, hoping it's just a bad gasket I pulled the head. The gasket looks pretty good (pic 1) but there's a distinct scoring in the lower cylinder (pic #2). I can barely feel the scoring with my finger, it feels like very fine scratches. Now I'm trying the figure out my next steps. It seems like my options are to just replace the gasket, replace the rings, or rebore the cylinders and pick up oversize pistons. The last 2 options are a bit daunting as I've never completely opened up any engine, and I would need to pick up a few tools to remove the flywheel and deal with the rings and pistons. Looking at the manual and all of the steps doesn't help. On the other hand, I'm pretty much stuck with this motor and want to be able to rely on it to start when I need it to.

Also, not sure why, but the lower cylinder was very dark and moist with carbon buildup while the upper was very dry with a thin layer of chalky substance built up on the front of the piston (pic 3). I scraped most of it off but you can still see some in the 3rd picture. Anything to be concerned with for the upper cyl?

Any advice much appreciated,

Ryan

 

[Haffiman]

Re: '85 Johnson 15 low compression in 1 cyl - looks scored

Pull the power head and dismantle. If lucky, some honing, new pistons and rings may get you up and running again. Do water pump and water tube grommets at the same time.

 

[raczekp1]

Re: '85 Johnson 15 low compression in 1 cyl - looks scored

pull apart powerhead.
do the honing job
if after honing cylinders will be ok, then order on ebay new standard pistons and rings(ofcourse if pistons are ok, only 2x rings set)
1 head gasket, 2 water jacket gaskets and exhouse siede panel gasket, upper seal and lower one
1 powerhead base gasket and 1 water pipe gromet(inlet to powerhead)

after puting back all staf you will get new strong motor
here is alink http://forums.iboats.com/showthread.php?t=493516

http://www.youtube.com/watch?v=jd8WC98JGCI

 

[Silvertip]

Re: '85 Johnson 15 low compression in 1 cyl - looks scored

Even with those compression numbers the engine should start properly without squirting fuel into the carbs. You need to determine why it is apparently running lean. Chances are that's what caused the scratches in the first place. I suspect the carbs have not been cleaned and or they simply need adjustment to allow the engine to idle properly. Unless you fix this issue, you may be doing a rebuild again (as is often the case when little to zero diagnosis is done). Rebuilding an engine is due to the "result" of a problem and rebuilding does not fix the "cause".

 

[sutor623]

Re: '85 Johnson 15 low compression in 1 cyl - looks scored

Hey bud. I started out with a Johnson 9.5, and fiddled with a few of those, then I got into the Johnson 9.9's. They are great motors. Just so you know it is basically the same motor as the 15 that you speak of, except for the carburetor. They added bigger shims and eventually a different exhaust housing, but basically, the motor is VERY similar to the motors that I have worked with.

My experiences have led me here with these motors. I have had two 9.9s. One of them the compression was 65 in one cylinder and 72 in the other. The compression kept gettin worse and worse, until one cylinder was just over 45, and the other was around 60. Performance didnt change THAT much. It took me 5 years, about 150 motor hours, and lots of hard use until the motor finally wouldnt run because the compression was just too low.

I thought hard about a rebuild. With all of the parts that Id need, as far as tools, rings bearings etc. were well over the $300 mark. And a whole ton of time........

Sooooo instead of jumping into the motor and getting attached to the project I started looking around on CL. I found a GEM. It was a 1981 Johnson 9.9. It had 110lbs. compression in both cylinders. I picked it up for $350.00 Then I bought a water pump, thermostat, and changed the lower unit oil, and she runs PERFECTLY!! I have the older 9.9 for parts if I should ever need them. Point is this, with these smaller motors, a lot of the time it is way cheaper to just retire one motor to a 'parts' motor and buy another one.

(Of course if you had a 150hp motor, it may be worth it to do a rebuild and have a very reliable motor, because with bigger motors it seems to be harder to find something reliable, unless you want to go 4stroke and spend a fortune)

P.S. Just my opinion on the matter. Here is a link to my 9.9 on lake anna this summer. http://www.youtube.com/watch?v=JYQLR740JEY

 

[wineyarders]

Re: '85 Johnson 15 low compression in 1 cyl - looks scored

Thanks for the feedback everyone. I've been trying to squeeze in time to take a closer look, and finally was able to pull things apart to look at the cylinders and crankshaft. There were a few things that seemed like they could be the rooy of the problem. Foremost, there was a decent amount of salt buildup that would have been restricting water flow and probably causing the engine to run hot. Also, a few years ago when I first used it overheated due to a bad water pump, that could also have caused some problems that are just now becoming apparent. Another odd thing was there was some very fine shredded rubber debris on a small screen at the top of the leaf plate. But most concerning is what looks like the lip of the cylinder liner (the part on the outside edge of the cylinder, crankcase side) is wearing away, and losing material which is in all likelihood ending up in the cylinder and causing the problem. There was even a small sharp nick that was protruding off the edge that I rubbed off. There was also some very fine metal shavings on the part of the crankcase where the head of the crankshaft would rest. They looked like aluminum, very shiny and seemed somewhat soft/pliable. The wearing is happening on both cylinders but strangely only the bottom piston and cylinder have any damage. The bottom piston needs to be replaced, and I will probably try to hone the cylinder because the scoring there is very light and appears superficial. I'll try and attach a picture of what I'm talking about, had a hard time with attachments last time. BUt along the lip of the cylinder you can see some black, which is worn aluminum. Anybody have thoughts on what to do about this? Could it be the result of the overheating? I have my eyes open for a replacement, but it seems there's more ads looking for these engines than ones selling them around here. Thanks again for the advice.

 

[sutor623]

Re: '85 Johnson 15 low compression in 1 cyl - looks scored

If you keep your eyes open you will find one. But hey there is NOTHING wrong with the rewarding experience of rebuilding your own motor and KNOWING every nook and cranny of that thing. The downside is that if you do end up blowing it for some odd reason, it hurts that much more. If something happens when you are out on the water, at least you have a good idea on what may have went wrong. Personally, I like to change the impeller, gear oil, 2-stroke gas mix, thermostat and sometimes plugs every year. Especially if I leave the motor sitting for 3-4 months. It is nice to know that the chances of having a massive failure are minimized as much as possible. Keep us posted on if you go the rebuild route or not!!! These are great motors and are always in high demand!!