90psi considered good compression???

[adm1476]

I am getting ready to put a 200hp Mariner on my boat. The compression on all 6 cyl is either at or very near 90psi on all cyl. Is that good for this motor? It is a 1989 model.

 

[Dukedog]

Re: 90psi considered good compression???

If its a "known" accurate gauge or reads tha same on multiple gauges then NO................its tired! It will still run kinda decent but will be down on power. You will need to check it often if you do run it. Being a chrome bore motor it needs ta be looked now before it does some real damage.........jmo

 

[wired247]

Re: 90psi considered good compression???

Motor warm , throttle open, good gauge. Otherwise the numbers are meaningless.

 

[Dukedog]

Re: 90psi considered good compression???

Not meaningless. I always hear this n that is tha only way ta check 'em but have yet ta see tha big difference with tha "little" v6's. Hell we crank ours as soon as tha heads, (starter, flywheel temporary) only on tha rotatin' assy. sitin' on tha bench ta make sure its close before we bolted on all tha other stuff. There has never been more than 5 lbs difference, if any at all, than when its finished and runnin'. So meaningless its not.

 

[wired247]

Re: 90psi considered good compression???

Its meaningless without oil on the rings , warmed up to operating temp and the throttles open. Same goes for any internal combustion engine.

 

[adm1476]

Re: 90psi considered good compression???

These were readings from a motor that has been sitting for several years. Throttle was probably not open and it definitely was not warm from running! lol Also I think the battery he was using was going dead. lol

 

[wired247]

Re: 90psi considered good compression???

Stuff a few mice in the reeds and you might get a less significant set of readings.

Try again with a warmed up engine and a charged battery. Lock the throttle open, keep the key turned off, pull all the plugs and jump the starter solenoid to turn it over.

 

[Dukedog]

Re: 90psi considered good compression???

These were readings from a motor that has been sitting for several years. Throttle was probably not open and it definitely was not warm from running! lol Also I think the battery he was using was going dead. lol

All of that will have effect, especially tha crankin' rate. Mighta helped knowin' this at tha start. But when ya get it charged and whatever, it needs to be 115+ hot, cold, open, closed ta be healthy ta run as is period. Anything less can be ran but needs ta be checked ever so often (with tha known accurate gauge). It will be determined by tha weight of your stuff and how hard ya turn it up.....

JAN 247. I've been at these things since 1976. From bone stock ta 230+ lbs a squeeze alcohol stem winders and can't remember even a stuck piston in any of 'em for tha last 20 years or so. Instructions of tha workings on this "little" internal combustion motor aren't really needed........