Mercury Guys Set me Straight please

[MURX]

I've read a couple things here that have me a little bit confused, maybe you guys can set me straight: one guy says his merc 150's have about 100#'S compression after a rebuild, another says he has a used 200 for sale that has 125 across the board, what should the compression be on a '91 175 mercury outboard, the one I'm buying has 100, 95, 110 100, 100, 100, I'm a little puzzled can one of you guys please advise me on this, thanks Don A.R.B (amatuer rookie boater)

 

[norman158]

Re: Mercury Guys Set me Straight please

compression readings change with diffrent gauges and will change if motor is warm or cold. most recomend + or - 15 lbs across all cyls. motor warm, throttle open, plugs out

 

[MURX]

Re: Mercury Guys Set me Straight please

Anyone else want to add to this? I'd really appreciate hearing from someone that owns a '91 or later 175, that knows the specifications for these later model's

 

[12Footer]

Re: Mercury Guys Set me Straight please

Poundage isn't half as important as equality.<br />I would try runnin the engine until warmed up good,and recheck. No doubt, all the numbers will go up. But be mainly concerned with the equality of readings between cylenders.<br />And Norman is right on the gauges being relative. Two different gauges are liable to give two different sets of readings.<br /><br />Welcome to Waterworld,Don. And to the forum.<br /><br />

 

[kenthrussell]

Re: Mercury Guys Set me Straight please

Hi well I have a rebuilt 200hp merc v6 with about 15 hrs on it and cold readings on all 6 are 124-125 and that is cold with throttle wide open,and this is after 15 hrs running,the rule of thumb is and anyone can correct me if i'm wrong but they should all be within 10% of each other....hope this helps

 

[12Footer]

Re: Mercury Guys Set me Straight please

I've heard 10% and 15%. My Merc book doesn't specify, but the Force manual does,and claims 15% for thier engines. Again two gauges will read differently.<br />This Clymer manual also does not specify the specify the compression anywhere in it. So, maybe someone will chime-in with the Seloc manual,if it's in IT.<br />I would try it with a different gauge before I declare the compression "good".<br />You got me wondering what the compression should be on my baby merc. I got 135PSI on both lungs. ????<br /> <br /><br />

<br /><br />USA All the way!

 

[clanton]

Re: Mercury Guys Set me Straight please

1992 to 1999 105/140Jet/135/150/XR6/MAG111/175/200/150XR1/<br />200XR1/PRO MAX/SUPER MAGNUM 150/200/225. Compression 110-135 psi not to exceed 15 psi between cylinders.

 

[grandx]

Re: Mercury Guys Set me Straight please

Question for Clanton, where did you find this information? I have never seen anything but +/- 15 psi between cylinders in my Clymer book and hear the same from the Merc dealer. Thanks in advance.

 

[clanton]

Re: Mercury Guys Set me Straight please

Merc service manual, pn 90-824052R2. A 1986 150 should be about 97 psi new, but cant find book for that engine. I like 10 psi between cylinders.

 

[grandx]

Re: Mercury Guys Set me Straight please

Mine are 1996 merc 150's, I've never checked them warm or since after break in, but your earlier thread says 110-135, is that correct?<br /><br />dg

 

[clanton]

Re: Mercury Guys Set me Straight please

Correct, that is in the service manual.

 

[jrbpit1]

Re: Mercury Guys Set me Straight please

My Seloc manual for my Chrysler says between 145 to 155. I am pretty sure about those #'s but I will check it when I go home.

 

[MURX]

Re: Mercury Guys Set me Straight please

You know its funny this is my third Merc, I've owned the 100 2+2 4 banger, the 90 3cyl, and now this 175, I quess this is a 2.5 litre engine? Well I spoke with two of the big Mercury dealers here, one wasn't much help at all the, other BTW is just a great place to do business, once I brought this guy a lower unit in a basket, the shop that resealed it had me wait about 10 days on the re-work of a repair that took 2 days initially! I was pissed so I decided to try a mercury dealer instead of an independant, this shop BTW is Modern Mariner in Anaheim California, what a decent honest guy Rod is, he put the lower back together with a couple of new bearings too, and installed for 400.00, anyway Rod tells me the later models after '91 have a lower compression ratio to help with detonation issues do to todays wonderful gasoline, he says the compression cold is normal @100 psi, he also said if you could actually check it running hot it would be around 130, he reffered to the piston rings as KEYSTONE rings, I don't really know what he meant by that, anyway I'm buying the boat and <br />I want to thank each and everyone you for taking the time to help out, you're a great bunch to know! BTW I just got the puter and I'm just learning about stereotyping (using both hands) so go easy on me for my punctuation or lack there of! LOL again thank you all

 

[clanton]

Re: Mercury Guys Set me Straight please

A Keystone ring, and L ring is a pressure backed ring, which means that the ring is pushed out against the cylinder wall with compresion pressure.