90' merc compression

[phatazbass]

I am buying my first boat and i have very little two stroke knowledge. Everyone i have asked about checking the motor says the compression needs to be 3 to 5 pounds from each other. The boat has been seting dry for a year and i cant run it with a hose because there isnt one nearby. so i checked it dry(not started) it produced these numbers...92 92 89 91 90 91 psi. The motor is a 1990 Merc. 200hp ... i need to know if these #s are exceptable.

 

[petryshyn]

Re: 90' merc compression

Compression looks OK (even). But I'd be a little concerned about cranking it over with no water. The water-pump impellar is not going to be happy......

 

[phatazbass]

Re: 90' merc compression

thanks schematic.<br />i need all the help i can get. The comp. was bothering me because everyone says there engine has 110-120 psi.

 

[petryshyn]

Re: 90' merc compression

Have you tried another gauge? Pressure is very subjective. Was the throttle wide open? Was the engine warm? All this will affect compression. The best guess is that its OK cause they're even.....but its only guessing!!

 

[phatazbass]

Re: 90' merc compression

Is there anything else that needs to be checked on the motor,that i can do,to make sure im not buying a lemon. The boat seems to be in great condition(90 astro 19foot). wich tells me the 1st and only owner took care of it.

 

[petryshyn]

Re: 90' merc compression

A boat is one of the top 3 largest investments one may make in a life time. Don't go cheap now.....it may cost you down the road. Get a first hand opinion from a marine tech. Pay him if needed, but get it checked thoroughly.<br /><br />Sad but true, many people spend more time reasearching a VCR before buying it, than they do purchasing a house.....

 

[Dennis4b]

Re: 90' merc compression

phatazbass, a few months ago we bought a 1988 Merc 150. Brought an expert, did cold compression test (was fine), checked plugs (they were not just new ones popped in for the sale but looked very good). <br /><br />Checked lower part, prop shaft should have an every so tiny bit of play inwards and outwards, used to engage the gears with the load from prop in the water. <br /><br />Engine block still covered in the paint, all wires neat and intact, controls etc everything there. It was very properly winterized and squeeky clean. <br /><br />We took it, installed it, connected it to the fuel (was even old fuel , squeezed the bulb, turned the key, and wham it fired right up and idled perfectly. (after 8 months of no use). Works perfectly! Got a nice 21" SS prop thrown in too.<br /><br />So moral of the story, if compression, plugs, wiring, lower unit, etc, all look ok, then get a price where you can't go wrong even if there is something (minor) you'd still have to fix.<br /><br />But bring someone who knows what they're doing!!