1998 Johnson 90hp

[ciscodlr]

Re: 1998 Johnson 90hp

supposedly a certified mechanic, he claims he had already ran the engine before giving me a call that it was ready. He never did mention anything about any difference in oil. What a nightmare!

 

[ondarvr]

Re: 1998 Johnson 90hp

If all the cylinders had similar comp #s then its most likely OK and different gauges can give different #s, so another one could read 10 PSI or more higher on the same engine. Like DH said, If 5,000 RPM is all you got at WOT then the setup is wrong, you should be turning 600 or more higher than that for long engine life.

You said it was rebuilt, what was the original problem? I ask this because I have the exact same motor (same year) and there is no sign of it being even close to tired or worn out. If you didn't address the original problem then you will soon need another rebuild.

Put in a new set of the correct factory recommended plugs, use some fresh 87 gas and start it up to see if it runs smooth, if it does then start looking at how to raise the RPMs at WOT.

 

[ciscodlr]

Re: 1998 Johnson 90hp

The original issue was that one day coming in from a trip on baffin bay, the engine began to backfire. A mechanic checked the compression and the #1 cylinder was dead, after removing the head he realized that a piston ring had broken off and had apparently (according to him had exited the exhaust port) since there was no sign of it anywhere. The top of the piston looked like someone had put a chisel to it and so did the head. Thats what led to replacing the 4 pistons and rings, as recommended. That is all this mechanic was to do. I have had this boat and motor for about 8 years now, and it has always topped at 5000 rpm. When this problem first started, i noticed that the linkage rod from the timer base to the (carbs i think) had come undone from the timer base, since it was worn, I replaced the ball and socket type connection. And here I am now.

 

[bktheking]

Re: 1998 Johnson 90hp

Just replacing 4 pistons and rings wouldn't have fixed the problem. The one cylinder with the broken ring had to have been bored out by a machine shop and and oversized piston/ring set installed, the 3 others honed if they were in good shape. That's why I asked , if the true fact is that the piston's were replaced and rings and nothing was done to the block, there a problem. Judging from the even compression it was fixed properly. All of this is speculation on my part, just offering up advice and my father's advice. Your mechanic may indeed have ran it to break it in properly and didn't bother telling you cause it was already taken care of. The whole running fine to the fishing hole and 3K rpm on the way back, bad idle, hard to start just sounds too strange to me.

 

[ondarvr]

Re: 1998 Johnson 90hp

The broken ring was most likely caused by the 5,000 RPM at WOT, The lugging will create carbon build up which can cause the rings to stick, or be forced out and possibly catch in a port.

Now its time to look at the current setup and make improvements so you can get up it to at least 5,500.