FishOn Posted September 25, 2011 Report Share Posted September 25, 2011 I would like to know what is a good compression numbers on a 2005 Mercury 90 hp 2 stroke. I am about to buy one and the numbers presented to me were as follow; 110, 110, 110 in all three cylinders. I spoke with the service advisor and was told these are good numbers for a 2 stroke engine. Usually 4 stroke engines will have higher numbers I was told?? Is this true?? What about the reading of this engine. THANKS ALL Link to comment Share on other sites More sharing options...
GYPSY400 Posted September 25, 2011 Report Share Posted September 25, 2011 Those numbers seem ok, ideal compression is 120+ , but anything over 90 is good.. If the compression is low, the motor won't troll very good. Link to comment Share on other sites More sharing options...
Terry Posted September 25, 2011 Report Share Posted September 25, 2011 they are all the same and that is important I had my 1990 2 stroke 90 hp tested this summer and it was 125 across all three Link to comment Share on other sites More sharing options...
Oryx Posted September 25, 2011 Report Share Posted September 25, 2011 Mines sitting between 125-130 on all three Link to comment Share on other sites More sharing options...
Garnet Posted September 25, 2011 Report Share Posted September 25, 2011 The general rule is no more than 10% difference. So that motor looks good. Check all the head bolts for signs of wrenches. Check lower unit oil. Link to comment Share on other sites More sharing options...
FishOn Posted September 25, 2011 Author Report Share Posted September 25, 2011 To mee they seem low for a 2005 Engine. I was told by the tech the engine can't have more than 50 hours of run time. He was the one that inspected the motor in and out. Who knows?? Link to comment Share on other sites More sharing options...
esoxansteel Posted September 25, 2011 Report Share Posted September 25, 2011 I would want to see the actual compression test been done instead of taking someone word, it only takes 10 minutes, if those numbers are right, they are the same or within 10% and that is what matters, other than that follow Garnets advice, if the head bolts have been touched the paint will be missing of the face of the bolt Link to comment Share on other sites More sharing options...
Dutch Posted September 25, 2011 Report Share Posted September 25, 2011 Shouldn't really matter what the numbers are - some compression testers are more accurate than others. The main thing is that all the numbers are within 10% of each other. Sounds like you are good to go. If there are wrenches on the head bolts, you may have a rebuild. You would need to ask how many hours on the motor since it was rebuilt. As long as there are at least 20 since the rebuild, you are probably fine as the rebuild was most likely done professionally. Link to comment Share on other sites More sharing options...
linweir Posted September 26, 2011 Report Share Posted September 26, 2011 110 is OK. The more importantly, compression # of 3 cylinders are even. I think the motor should be running good. Link to comment Share on other sites More sharing options...
scugpg Posted September 26, 2011 Report Share Posted September 26, 2011 In my experience the 4 strokes do have higher compression at least when trying to pull them over. Link to comment Share on other sites More sharing options...
Tybo Posted September 30, 2011 Report Share Posted September 30, 2011 10% is for the defection of the guage.110 is a little weak. With it being the same all across 3.I say bad guage or a poor rebuild. Link to comment Share on other sites More sharing options...
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