Home › Forum › Ask A Member › Top speed with 18hp Evinrude on 14′ aluminum › Re: Top speed with 18hp Evinrude on 14′ aluminum
January 12, 2017 at 10:04 pm
#50908
quote fleetwin:
Well, you certainly did a nice paint job.
Like others have said, compression reports seem to vary, but I would think you should see 100PSI minimum. Why is it that you replaced the original powerhead? You also seem to say that the engine ran the same way with its original powerhead, do I have it right? You mention seeing score marks on pistons of both powerheads, needless to say these could be an issue, or not. Most two stroke OMCs will show some minor scratching/scoring on the pistions, usually not an issue. But, if there has been aluminum transfer, and the rings are stuck in place that is another story. You mention the engine starts easily and idles nicely, which suggests the powerhead is "OK".
You went through a lot of work cosmetically, would be a shame to mess that up over something simple. I guess I would start with something simple like having a look at the mag plate and carb linkage. Is the mag plate advancing fully, perhaps the interlock is interfering. Is the carb butterfly opening fully? Is there a chance that someone swapped out the carb from a 25hp, thinking this would make the engine run faster. Perhaps they just changed the high speed jet, thinking this would be the answer to their performance dreams. I would mention a blocked exhaust, but I’m thinking you would have seen a problem like that when you had the midsection apart.
Don’t forget to check the prop pitch, the engine will just bog down if it is over propped.
Tell us more about the history of this engine, why you changed the powerhead, and how it ran with the old powerhead. I don’t want to mislead you based on my “assumptions”.
Like others have said, compression reports seem to vary, but I would think you should see 100PSI minimum. Why is it that you replaced the original powerhead? You also seem to say that the engine ran the same way with its original powerhead, do I have it right? You mention seeing score marks on pistons of both powerheads, needless to say these could be an issue, or not. Most two stroke OMCs will show some minor scratching/scoring on the pistions, usually not an issue. But, if there has been aluminum transfer, and the rings are stuck in place that is another story. You mention the engine starts easily and idles nicely, which suggests the powerhead is "OK".
You went through a lot of work cosmetically, would be a shame to mess that up over something simple. I guess I would start with something simple like having a look at the mag plate and carb linkage. Is the mag plate advancing fully, perhaps the interlock is interfering. Is the carb butterfly opening fully? Is there a chance that someone swapped out the carb from a 25hp, thinking this would make the engine run faster. Perhaps they just changed the high speed jet, thinking this would be the answer to their performance dreams. I would mention a blocked exhaust, but I’m thinking you would have seen a problem like that when you had the midsection apart.
Don’t forget to check the prop pitch, the engine will just bog down if it is over propped.
Tell us more about the history of this engine, why you changed the powerhead, and how it ran with the old powerhead. I don’t want to mislead you based on my “assumptions”.
Honest, these engines will start and have have low end like an absolute dream but won’t make their best RPM, with lower compression. I can’t even imagine how many 18s I have pieced together over the years and have seen the results of reassembly with new rings only, vs. a TRUE rebuild. If you take it apart, check the bore or at least the ring end gap. I bet you will find the gaps too large. The bores wear out.
Long live American manufacturing!