View Full Version : OMC 57L 260hp running rough

ryan corbett
04-04-2004, 09:25 AM
" I have a 1993 5.7L 260hp Merc and when the engine starts it sounds and rides rough. There is also a clicking noise coming from some part of the engine(possible valve?). When out on the water it takes more time for the boat to get on a plane. I did a compression check and found all at 155 execpt one (when looking at the engine from the front of the boat, its on the right side 2nd from the back) which was at 95. I have replaced the starter,dist. cap, plugs,manifolds,risers. What could possibly cause the engine to sound rough. Could it possibly be miss firing? The marina said that one cylinder at 95 shouldn't cause the boat to be that sluggish. I have noticed my gas milage as been terriable since replacing the risers and manifold. Could this be cause by the valve problem? Thanks Ryan C. "

CJ Inglis
04-08-2004, 11:18 AM
" Ryan,
Does the "clicking" sound get worse when you give it throttle? Or does it sound like BBs in a can? If its' the latter, I would say to retard the timing a bit or get some higher octane gas. If its' the formar, could be a lot of things. Checking the tention on the rocker arms will give you an idea of the culprit. If you have a lot of play in one of the lifter rods and you've done no work on the engine, you may have a stuck lifter. Marvel Mystery oil is pretty good for a quick fix there. I would have to say that because you also have a compression loss in one cylinder that the problem is more serious though. If its' as simple as carbon deposits on the valve, same product could clean it up or even some carb/choke cleaner sprayed directly into the spark plug hole. Careful there though because too much can seap by your rings and contaminate your oil. I would try those things first though because its' cheap and effective if the problem is simple.
Let me know if it works. If not I might have more ideas.
CJ "