Results of compression test on 1988 merc150 black max...good?

[saltfisher]

Well I went to autozone and rented a compression tester. Went to the boat im thinking of buying, and took all the sprak plug wires off the plugs. Took out 1 plug at a time, started from left side of motor at the top. then right side at the top. Here are my compression numbers. 105-105-105-105-110-105

We cranked it about 6 times each cylinder untill the guage stopped. I think someone told me that it should be between 110-120? My g/f called the boat mechanic at her work, and told him, and he said not to buy it, as it should be around 125-130? So how do those numbers sound? Motor is a 1988 150 mercury black max. 2.5 V6 and i used a OEM brand compression tester.

Thanks

 

[hkeiner]

Re: Results of compression test on 1988 merc150 black max...good?

All six plugs should be removed at the same time when you check compression, otherwise the starter will not spin the motor fast enough to get a good reading. Also, the battery should be fully charged or else the motor may not be spinning fast enough to get a good reading. Some say that the carb throttles should be held open and the motor warmed up during a compression test, although I have not seen these two steps as making much of a difference myself. Decarbing the motor can also improve compression if the piston rings are carbed up. The readings between cylinders (say within 10 psi) is much more important than the actual reading value you see on the gauge. Gauges are not always that accurate and compression taking techniques are not always optimal, although the gauges can be used effectively to compare PSI readings between cylinders. You might try doing the compression test again following the above guidelines.

Having said all that, the readings you got seem OK to me, especially if you had five plugs in the motor each time you tested. This is based upon my experiences. Others may have additional or better advice than me.

 

[saltfisher]

Re: Results of compression test on 1988 merc150 black max...good?

Yes we left all plugs in, and just did one at a time, and put the plug back in. The motor hasnt been run since last year and was still fogged. We ran the motor for about 15 minutes or so to get some of the fogging out, then checked compression. So it was a semi-warm motor we were checking. It started right up, everything looked like you could eat off of it inside and out. The guy only used the boat/motor 1 week per year in canada. He said in the past 14-16 years he may have put 50 hours on the motor. Also no matter what he fogged the motor every season before winter.

 

[JB]

Re: Results of compression test on 1988 merc150 black max...good?

Since you left 5 plugs in when you took the readings on a cold engine your results are good to excellent.

Using the correct procedure you would probably have gotten them all in the 120-125psi range.

The important thing is that they are all very close to each other.

 

[saltfisher]

Re: Results of compression test on 1988 merc150 black max...good?

Awesome!! I was hoping you guys would say that. Plus the guage could be off a little also. A long time ago, My buddy had a compression tester, and my other buddy wanted to see how close his guage was compared to his. The one guage was off by about 15psi on the same engine cranking the same amount of times.

So im guessing this is a good engine?

 

[Barnacle_Bill]

Re: Results of compression test on 1988 merc150 black max...good?

I would buy it if the price was right.

 

[saltfisher]

Re: Results of compression test on 1988 merc150 black max...good?

$2500 for boat/motor/trailer 1988 basstracker fiberglass

Extras include newer ft controll trolling motor
Predator SS prop
Spare aluminum prop
Jackplate
2 fish finders, one flasher and one newer base model for front of boat
Boat just needs fiberglass buffed, and some spots iof rust on trailer. i tested bilge, fish finders, ect. and everything works. Even trailer lights. carpet is in great condition. Just needs minor TLC/cleaning.

 

[hkeiner]

Re: Results of compression test on 1988 merc150 black max...good?

Boat just needs fiberglass buffed

If you plan to buff the gel coat on the boat, for about $150 in equipment/supplies (buffer, pads, and polish) and some minimal effort, you can probably make that gel coat shine like (almost) new. I bought a 10 year old boat last fall whose gel coat surface was faded. After a good polish, the finish was shiny like almost new.

I suggest the following equipment/supplies:

- Porter Cable 7424 buffer
http://www.autogeek.net/dual-action-polishers.html

- Meguires Color Restorer
http://www.autogeek.net/boat-color-restorer.html


- 4" yellow polishing pad (just the right amount of polishing effect with the Meguires)

 

[saltfisher]

Re: Results of compression test on 1988 merc150 black max...good?

Nice!! Thats what i like to hear. I know it will polish up good, because it you lick your finger and touch where its oxidized it takes it away and you can see the nice shiny silver sparkles. Of cource it comes right back, but buffing it out will keep it away, at least for a long time. I have a professional buffer at work i can barrow so i have that covered. I think its a 8" or maybe even a 10" dewalt maybe? Not sure, but my buddy did his car with it and it lookes like brand new.

 

[hkeiner]

Re: Results of compression test on 1988 merc150 black max...good?

Perhaps you already know this, but I thought I should warn you to be careful if you are not experienced using a professional circular buffer on gel coat. The pads spin pretty fast and you can damage the gel coat finish if you let the circular pads sit too long in one spot and get hot. A random orbital buffer is much more forgiving to the less experienced user. One drawback with random orbital buffers, however, is that they don't have as much bite when it comes to removing heavy oxidation and scratches. They do pretty well with medium to light oxidation and it is impossible to overheat the pads and cause damage to the gel coat finish.

 

[saltfisher]

Re: Results of compression test on 1988 merc150 black max...good?

Yeah, I never used a professional buffer, but i know all about "burning" through paint/gel-coats/clear coats. I worked at a lubeshop/carwash and heard all about it from the guys down at the carwash. That was there biggest thing they stressed when doing a job like that. Nothing like a $60k BMW comming in and burning through the paint/clear with a buffer. LOL. I worked at the lube shop so never got to try anything 1st hand. I did have a polisher i got at walmart, and worked with that quite a bit. My g/f works at a boat/rv dealership as parts person, so I get hook-ups on all my boating needs. Thanks for your info. My 1st job will be replacing that water pump impeller.