1999 90 hp 2 stroke compression numbers,

[chrome dome]

considering a 90 hp mercury/ mariner 2 stroke, but the listed comp figures seem low to me at 100 lbs, supposedly all even though,
are these numbers too low for this year motor, or is it in the "normal" range for a used '99?
cheers

 

[JB]

Re: 1999 90 hp 2 stroke compression numbers,

Readings differ from gauge to gauge but it is impossible for 3 cylinders to go bad the same amount at the same time. I would declare that engine healthy.

 

[jbjennings]

Re: 1999 90 hp 2 stroke compression numbers,

I'd agree with JB, but also suggest you get the comp. #'s yourself--as I'm sure you intend on doing. If they're not nice and even, I wouldn't consider it. I've seen motors lately with a piston with one broken ring, and 2 out of 3 rings on a piston totally stuck and still made 150psi of compression on that cylinder.
Nice and even is USUALLY a good sign.
JBJ

 

[Faztbullet]

Re: 1999 90 hp 2 stroke compression numbers,

Its good numbers

 

[wired247]

Re: 1999 90 hp 2 stroke compression numbers,

A lot of the modern 2 cycles are 100 psi motors.

 

[chrome dome]

Re: 1999 90 hp 2 stroke compression numbers,

thanks gents, much appreciated,
cheers

 

[Texasmark]

Re: 1999 90 hp 2 stroke compression numbers,

My service manual, OEM Merc/Mariner PN 90-830234R3 publication date Dec. 1997 states in section 1C-6 "Important Information", Compression Check:

REMOVE SPARK PLUGS
Install gauge
Hold throttle plate (carb butterflies) at WOT (fully open)
Crank engine till gauge peaks
Record the reading
Check all cylinders.
15% difference between cyls. or less OK.
A reading below 120 (PSIG) MIGHT indicate a total engine wear problem.

There sir you have it from the "hosses mouth".

In all her wisdom, mother Merc. didn't mention it, but a fully charged battery and some lube on the cylinder walls surely helps; not 30 wt oil, mind you but enough light lube to allow the rpms to come up to par. You save the 30 wt for a CYA final check: Is it rings or not. Test, oil and test. If a big difference then you have to go the long haul.

HTH,
Mark