Opinion on my compression numbers!

[oldyeller2011]

50hp 4 cylinder.. just got it and did a compression test.. little different then what he told me. ran the test hot by the way.
dont know the year but its older im assuming because its got a distributor instead of coils.

I got 130,120,120,105.... its not really bad, but not good either.. would it be okay to take it easy on? idles good on hose and pees good. let me know what you guys think. starts first time every time.

 

[wired247]

Re: Opinion on my compression numbers!

That bottom one is a bit low. Sometimes rings get a bit stock and you get crappy numbers. Theres a number of ways to use solvents such as Seafoam or others to free the rings up. I like to use Berrymans carb dip ( in the gallon pail ) and run the piston up to an inch or so from the end of its cycle. Then I squirt a few syringes of the stuff in the cylinder and put the plug back in and continue the crank rotation ( by hand ) until the cylinder hydraulically locks. Then I let it sit for a few days and pull the plug and turn the motor over a few times to blow it out before I put the plug back in and start it up. The berrymans is safe on the aluminum pistons and really does a number on carbon deposits. Smells like *** though .


If that doesnt do the trick you may have some scoring in the cylinder. If it doesnt bother you, just run it until it does.

 

[oldyeller2011]

Re: Opinion on my compression numbers!

yah it bothers me actually. is taking the head off the same as the evinrudes? looks like you almost have to pull the powerhead off to get it off. Gettting the head off would really help getting a good look inside. I also do not understand what you mean by "run the piston up to an inch or so from the end of its cycle"? thanks for the help ill have to get onto that.

 

[GA_Boater]

Re: Opinion on my compression numbers!

Not knowing the serial number makes this a guess, but there is a good chance the motor doesn't have a removable head. Wired is saying turn the motor over until the piston covers the ports and squirt in the stuff. Almost at TDC.

 

[oldyeller2011]

Re: Opinion on my compression numbers!

Not knowing the serial number makes this a guess, but there is a good chance the motor doesn't have a removable head. Wired is saying turn the motor over until the piston covers the ports and squirt in the stuff. Almost at TDC.

sorry for stupid question.. port as in for carb or exhaust?

 

[oldyeller2011]

Re: Opinion on my compression numbers!

By the way I couldnt find the serial number.. where are they usually located? Im wondering if it was removed.. I found the one on my evinrude easy...

 

[wired247]

Re: Opinion on my compression numbers!

sorry for stupid question.. port as in for carb or exhaust?

Intake and exhaust ports are on the side of the cylinder and are located further down the cylinder.

 

[oldyeller2011]

Re: Opinion on my compression numbers!

Intake and exhaust ports are on the side of the cylinder and are located further down the cylinder.

okay thank you, i guess you just know when your at the right spot. ill have to do some more research

 

[GA_Boater]

Re: Opinion on my compression numbers!

Serial numbers are usually on the clamp bracket (holds the motor on the transom) on older motors. Also sometimes the S/N is stamped on the motor under the distributor/magneto pulley, it is not hidden.

Take a few pics, if you can.

 

[oldyeller2011]

Re: Opinion on my compression numbers!

Serial numbers are usually on the clamp bracket (holds the motor on the transom) on older motors. Also sometimes the S/N is stamped on the motor under the distributor/magneto pulley, it is not hidden.

Take a few pics, if you can.

Ill take a look right now and send some pics, its dark but lets see how it turns out. Thanks for the help.
Really hope this engine stays going for me awhile. I heard the 50 hp 4 cylinders where actually pretty good engines.

 

[oldyeller2011]

Re: Opinion on my compression numbers!

3097963 it read

 

[wired247]

Re: Opinion on my compression numbers!

Its a 1971 motor.

The head doesnt come off. There is no cylinder head. Its cast in with the block. Dis-assembly means pulling the motor apart by splitting the crankcase and pulling the crank, rods etc.. If the piston and bore are bad they can usually be bored and a new piston installed but its often difficult to find a shop to bore those blind hole blocks.

Try the chemical treatment first. If the rings are just stuck it will soften the gunk up and free the rings up in many cases. I reiterate though. If it runs good and still doesnt have perfect compression in all cylinders it would be a lot cheaper and easier to just let it run that way. If it was 80 or 90 and all the others 130, thats a different story but if you cant get much better with the solvent personally I'd just let it run itself the way it wants for a few years. Not that that is actually how I do anything.

 

[GA_Boater]

Re: Opinion on my compression numbers!

3097963 is a 1974 according to this. MERCURY OUTBOARD MODEL YEAR GUIDE 40 HP (4-CYL) - 50 HP -- Mastertech Marine

Parts breakdown: Mercury Marine 500 Outboard Motor Parts by Component

 

[wired247]

Re: Opinion on my compression numbers!

3097963 is a 1974 according to this. MERCURY OUTBOARD MODEL YEAR GUIDE 40 HP (4-CYL) - 50 HP -- Mastertech Marine

Parts breakdown: Mercury Marine 500 Outboard Motor Parts by Component

Still looks like 1971 according to their chart.

50 1971 M Short & Long 3008819 - 3235062

 

[oldyeller2011]

Re: Opinion on my compression numbers!

Still looks like 1971 according to their chart.

50 1971 M Short & Long 3008819 - 3235062

okay, I am still a bit confused on how I know if the pistons are covering the ports.. last question i promise haha..

 

[GA_Boater]

Re: Opinion on my compression numbers!

Thanks, Wired. The old eyes slipped. :facepalm:

The parts diagram is still good. Covers 285XXXX to 4140XXX,

 

[wired247]

Re: Opinion on my compression numbers!

okay, I am still a bit confused on how I know if the pistons are covering the ports.. last question i promise haha..

The ports are way past one inch down. Just bring it up to TDC and lower the piston an inch into the bore. Just stick a wooden dowel into the spark plug hole.

 

[oldyeller2011]

Re: Opinion on my compression numbers!

wont hurt the carb if it does go into that port right? thanks Wired! Ill try this tomorrow!

 

[wired247]

Re: Opinion on my compression numbers!

wont hurt the carb if it does go into that port right? thanks Wired! Ill try this tomorrow!

Its carb cleaner. I just crank them over a few times with the plug removed ( and grounded ) and blow everything out. Hose everything off. That stuff is hell on paint.

 

[oldyeller2011]

Re: Opinion on my compression numbers!

got some pics. let me know what you think. hoping this old thing will last me awhile. gunna baby it thats for sure. do a decarb like you said, and maybe change the wires they look a little old. Know a good place to get parts? Thanks wired!