low compression on 1989 Johnson 150.

[homey]

Hello, I have twin 1989 150hp Johnsons with 650 hours. The port motor has 90 or better compresion on all cylinders. The starboard motor has 90 or better on 5 cylinders, the 6th showing 60-70. These engines have been sitting for approx. 2 years. I've had the carbs cleaned, decarbonized, replaced water pumps, thermostats, plugs, 1 powerpack, fuel filters. <br /> While running the boat (25 Whaler) the motors did quite well. I kept a close eye on the temp guages and noticed while operating at slow speeds (2-6mph) the temp guage on starboard motor would rise near yellow, not red area. When speed increased temp would drop. Is this a major problem? Should I replace with new powerhead? I'm hopeing to get atleast 2 or 3 years out of these any recommendations other than operating them gently? Thank you, Homey

 

[Bobby D.]

Re: low compression on 1989 Johnson 150.

Hey Homey, Everything sounds good with your one engine but I would be concerned about the engine with the 70 pounds compression. Since you have invested some dollars into these engines keep running them until you have major problems. They can remain the way they are and give you years of pleasure. Periodically check the compression to see if it gets worse. The compression may get better from the usage because the rings may be stuck.

 

[Bobby D.]

Re: low compression on 1989 Johnson 150.

Hi again, Sorry for the double message. You wouldn't by chance have a 25" long shaft for a Johnson? Thanks

 

[homey]

Re: low compression on 1989 Johnson 150.

Dude, Sorry I don't have any old parts. I also forgot to mention there is scoring on that (70)cylinder wall. I've been told that cylinder may have been that way for years but, it still concerns me. Just looking for advice or similar experiences. Thanks.

 

[Joe Reeves]

Re: low compression on 1989 Johnson 150.

Homey..... The lowest diference in compression that you quote would be 20 lbs. That is a major difference which indicates a major problem. You go on to say that there is scoring on that cylinder wall.<br /><br />At the present time, you're looking at a major overhaul.... prices vary but for a expert rebuild job, expect a bill for approximately $1800 to $2000.<br /><br />The scoring indicates that the piston is disintergrating along with the cylinder wall. This is usually due to having a clogged carburetor or faulty ignition pertaining to that one cylinder, however it could also be due to a failing head gasket, something of that nature.<br /><br />At the present time, you may be able to get away with simply having that cylinder bored oversize. But continuing to run the engine will eventually result in the scoring being too deep, and that will necessitate having the cylinder sleeve replaced (usually a couple hundred dollars more).<br /><br />And there is always the possibility that suddenly the piston will let loose, tearing its way through the external portion of the block, destroying the crankshaft etc in the process. This scenario would have you facing the choice of purchasing a complete new powerhead or replacing the engine(s)...$$$$$$$!<br /><br />Bottom line... if you're thinking of keeping the engines you have, have that failing engine rebuilt now.

 

[homey]

Re: low compression on 1989 Johnson 150.

Joe, Thank you for your experience and advice. I do plan on keeping those engines and a rebuild does make sense.(new motors $20,000) I've checked with several local mechanics who qouted $3,500-$4,000 for a rebuild. Sound about right?<br /><br />I guess it was just wishful thinking on my part that the motor wasn't that critical. Thanks again, I'm new to this forum and think its a great source of info. Homey

 

[DJ]

Re: low compression on 1989 Johnson 150.

Homey,<br /><br />Joe Reeves is right. <br /><br />The price sounds about right. You may want to check the powerheads available on this iboats site to get cost ideas. Your price is in the range of a reman. powerhead, less installation labor. The ancellaries, carbs., electronics, etc., may cost another $5-700.00 to install on a reman. powerhead.<br /><br />If you want to rebuild yours at least you'll know where you started from. You should also find out why that cylinder went bad.

 

[NathanY]

Re: low compression on 1989 Johnson 150.

Maybe someone could tell me, in a situation like this, would it make more sense to have the whole thing rebuilt instead of just one cylinder? Does that cost more or is that included in the price? I do my rebuilds myself, and if I replace on piston, I replace all. Just wondering.

 

[Joe Reeves]

Re: low compression on 1989 Johnson 150.

NathanY..... Refering to that one cylinder is simply a figure of speech. The entire engine has to be torn down, all parts inspected, the good pistons cleaned, new rings installed through out, etc etc. The engine must be rebuilt in its entirety to restore it to new condition, otherwise it would be considered in what a reliable experienced marine mechanic would call a "Patch Job"..... and "Patch Jobs" last only a very short time!<br /><br />Bottom line.... Do it right, or do it over!

 

[Mufasa]

Re: low compression on 1989 Johnson 150.

NathanY,<br /><br /> Do not skimp on the overhaul. All six holes need to be bored and made round again. You need to restore the piston to cylinder wall tolerance to get that motor to idle proper and not stall in gear at slow speeds. On a job of that magnatude you would be short cutting it to try and reuse any pistons. It also makes a differance as to which brand of pistons the shop is using. I try to stay with OEM pistons whenever possable.

 

[Joe Reeves]

Re: low compression on 1989 Johnson 150.

Homey..... Contact me at ReevesJ32@aol.com .

 

[homey]

Re: low compression on 1989 Johnson 150.

Joe, I sent you e-mail...homeywud@aol.com