A buddy of mine bought a Johnson Oceanrunner 225, put it on his boat and it seemed to run fine. Although he always thought he should be getting more RPM's out of it. Max was around 4500-4600. It is pushing a heavy boat (a rendvouz 2650 deck boat) so I thought the RPM's were about right. Several different props were tested.
So, after around 20-30 hours he is having problems with it dying out when he is at idle, at first it would start right back up, now it starts up hard , if at all.
Brought it to a mechanic that has been working on Johnson's for 30 years and is pretty sure he is the guy to get it back and going.
The man says 4 cylinders are at 125 and 2 are at 100.
And he dosen't doubt him.But...........shouldn't that be enough to keep the engine running reasonably good? I see online when guys selling the same engine are bragging about the fact there engine is at between 85-95 on the compression test.
The mechanic says the 2 lower compression pistons are scored, so he is replacing them, so my buddy is going ahead and having them all redone due to the fact it isn't that much more to get them all done. ($3000.00 estimate)
He wanted me to run this past you guys and see what you can add.
I am sure there is more info you need that i have left out, so add what you can and ask me any questions that you need and and I will get back to you. Let's see if we can put his mind at ease in the direction he is going.

From what I have read in different forums, this is a strong engine, a hard runner , but THIRSTY. I guess we need to figure out if we can get it back to the hard running part.

Thanks,


John B.O.A.T.

If all 6 cylinders were 100 the motor would be worn but OK. If all were 125 it would be in great shape. But having 2 cylinders that are 100 and 4 at 125 indicates damage- like the scored pistons or other similar expensive things. The normal rule is that all cylinders must be within 10 lbs of one another for the engine to be sound. If he's lucky, with a rebuild such as he's having done all will be well. My only concern is that the motor felt weak before the problems- indicating that it may have some ignition problems too. The V-6 OMCs have an odd trait- they run very smooth on 6 cylinders, and almost as well but a bit on the slow side on 5 cylinders. It often takes a long run at full throttle with the mechanic on board checking spark to find the dead cylinder. Mercs are a lot different- if they drop a cylinder they run like crap and usually you can find the dead cylinder easily.
Doug

Thanks for the help. He went ahead and had new pistons and rings and the works. $3000.00 later and it is running good.

JohnB.O.A.T.