[GREEKFLEET]

Hello Guys,
I come from Greece and as you know we have nice sea and islands that you should visit.
Anyway, i would be gratefull if you aswer me the question about the exact compression in a brand new Yamaha 90hp, 2-stroke of 1992.The other question is what compression will be adequate and what variation between the 3 cylinders.I am about to buy the respective engine used and i will have to make a compression test.
Thank you in advance and i am happy to be in this forum....from the other side of the ocean

[cr2k]

I would think the compression would be in the 125 range. Depending on the model it could be from 115 to 150 new.

More important is the variance between cyls. all should be within 10% of your highest.

Even More important is getting a leak down test. This will tell you if there are any gouges or scratches in the cyl. walls. Done right it can "map" the sealing of the cyl. between port close and port open. 5% or less here is good.

[GREEKFLEET]

Originally Posted by cr2k

I would think the compression would be in the 125 range. Depending on the model it could be from 115 to 150 new.

More important is the variance between cyls. all should be within 10% of your highest.

Even More important is getting a leak down test. This will tell you if there are any gouges or scratches in the cyl. walls. Done right it can "map" the sealing of the cyl. between port close and port open. 5% or less here is good.

Thank you very much , but can you please give some details about leak down test?i will try also to find about it in internet. Thanks a lot

[GREEKFLEET]

Finally i did the compression test and hopefully the pressure is equal in the 3 cylinders.Moreover is between 120-125 psi , that i think is pretty good. I am going to buy the engine although is actually an 1992 engine. I have heard that is very reliable ! The other question is how many hours do you think that an outboard engine can run without overhaul. Any suggestion/opinion is valuable.

[rodbolt]

most the US market inline 3cyl motors actually have about a 10-15 PSI difference built into the motor.
its the way its designed.
leak down test on a two stroke 10% is allowable.
never saw one actually wear out, usually the cooling system maint isnt done and they overheat and die.
be wary of differences in US market motors and international market motors as sometimes the designs are different and some replys may not be correct for the market motor in question.
but the leak down test covers all market motors.