compresion test

[martin47]

i tested my 115hp mercury and they tested at 145 psi to 150 psi is all ok ?

 

[scothorn]

Re: compresion test

martin,
I'm fairly new here, but, I just got off the phone with a mechanic at a well known shop here in town and they told me 105 would be a minimum, as long as they are within 10% of each other and above 105 you should be good. That was for a 225, I'm guessing that those numbers apply to most engines, if not all. But I may be wrong.
Scott

 

[Chris1956]

Re: compresion test

It would help to know what year you motor is. As long as they are close together in reading, they are OK. Those numbers you posted are a bit high, but depending on the year they are likely excellent. Also, how accurate is your gauge?

 

[martin47]

Re: compresion test

the year is 1982 and the gauge set is snap-on and was recently calibrated....(this is not mine i borrowed it from a good freind )

 

[hkeiner]

Re: compresion test

I believe that carbon build up in the cylinders can cause a higher than normal compression test result. If so, decarbing would lower your PSI readings to a "normal" level. I have not experienced this effect myself, so I am only relaying what I had learned elsewhere.

 

[Bob_VT]

Re: compresion test

That is very good compression. 2 strokes need not be at the very high end of compression.... the most important thing is if the cylinderers are within 5-8% of each other.

Since you had the plugs out take a peek inside.... I imagine you will see some carbon built up on the pistons which is normal. When that carbon builds on the rings they get stuck and will NOT seal properly which Lowers compression. This is why the De-Carb process is so important.

Were you just checking compression for something to do? or is there a problem? Decarb, water pump and rebuilding the carbs (fuel pump too on older outboards) are all maintenance items that keep the outboard alive.

 

[martin47]

Re: compresion test

i had a slight miss fire last week so i changed the plugs and checked the ht leads. as a quick check i ran the engine and removed the ht leads one at a time to see which one was down...they where all fireing but one seemed to react less than the other 5 . so on advise is have done this comprestion test..i have changed the fuel and replaced the plugs with ngk from champion as advised, cleaned and checked all the wirering from the coils..now every seems ok........going out this weekend so let hope its solved....thanks for everybodys help.