Piston Rings

[ngentile]

I have a 1987 Mercury Mariner 25hp 2 stroke 2 cylinder serial#0B211923. Runs good, clean carb everything is "OK" HOWEVER - I don't want an "OK" motor. I want a POWERFUL MOTOR!.

I think the guy that had this motor before me ran it into oblivion and it could probably use some new rings right about now. The compression is pretty much equal in both cylinders. It's about 95psi on both.

I said all that to say this: I want to change the piston rings and here are my questions:

1: Do I need to take off the whole power head off along with every accessory to do this? Or is there a way to take only the head off the powerhead and somehow detach pistons without pulling everything apart to change the rings?? (am I dreaming?)

2: On Mercury Parts Express it lists piston rings for $200 for 12 rings.. Now in my experience it's 2 rings per piston I need to change for a "ring job". I found sites that were selling my rings (quicksilver) for like $4 per ring. This brings me to believe I really only need to be spending about $16 for this job. (I already have gaskets for everything)

3:Given excessive hours of runtime on this model and it's age, would it be recommended to even do a ring job? (BTW I already de-carbed the pistions and cylinders soaking the chamber with seafoam etc...)

Any other advice would be very welcomed. If there are any threads that you think could be helpful please send them my way. Many Thanks for any help I can get on this one.

Nick

 

[latin monkey]

Re: Piston Rings

with compression that low you should take the block to a machine shop for a bore job and buy new oversize pistons, especially if you want a powerful motor. yes you have to take the powerhead off to change rings. get a factory merc manual for your motor and read it thoroughly, there is alot more to it than just putting new rings on the pistons

 

[ngentile]

Re: Piston Rings

I thought you only bore if cylinders are damaged? Assuming they are not...

BTW - I get my 14ft aluminum vhull with 6 gallons of gas, a huge marine battery and me (180lbs) up to 30mph with this 25hp. I think some minor "overhauling" is what's needed. It seems to be going within normal speed range. However I could be wrong.

Maybe there's some tweaking I can do to improve my top end speed?

NOS?


Nick

 

[saumon]

Re: Piston Rings

It's about 95psi on both.

Could only be a gauge thing. Get the engine warm then shut it off. Remove all spark plugs and flip the kill switch. Open the throttle and screw in the gauge to take the reading. Also try with another gauge.

1: Do I need to take off the whole power head off along with every accessory to do this? Or is there a way to take only the head off the powerhead and somehow detach pistons without pulling everything apart to change the rings?? (am I dreaming?)

Yes, you are dreaming. As said, get an OEM service manual.

2: On Mercury Parts Express it lists piston rings for $200 for 12 rings.. Now in my experience it's 2 rings per piston I need to change for a "ring job". I found sites that were selling my rings (quicksilver) for like $4 per ring. This brings me to believe I really only need to be spending about $16 for this job. (I already have gaskets for everything)

Quicksilver parts are considered OEM and not aftermarket like Sierra or Mallory. Something's wrong with your Marc Parts Express search.

3:Given excessive hours of runtime on this model and it's age, would it be recommended to even do a ring job? (BTW I already de-carbed the pistions and cylinders soaking the chamber with seafoam etc...)

Sometimes, if cylinder were not scored or scuffed (if you're lucky), a ring job will bring it to life. Take note that you'll have to hone it first to remove the glazed finish on the cylinder walls so the ring can seat properly.
Nick

Hope it help.

 

[latin monkey]

Re: Piston Rings

i can understand if you dont want to spend the money on what i suggested because it can get expensive but you were saying you wanted more power out of that motor. you might be able to get away with honing out each cylinder and installing new rings but thats assuming the pistons and cylinder walls have no damage. you should have better compression after and the motor should last a while

 

[Chinewalker]

Re: Piston Rings

I'm not sure you can hone those cylinders. I might have my years crossed, but I think that block had NicaSil bores. It's an aluminum block with plated bores. Not honeable. I believe some outfits offer boring with a sleeve insert - pricey!!

 

[Faztbullet]

Re: Piston Rings

Your motor is on the border line of being a chrome bore or a Mercosil block. If it has the words Mercosil cast into top of cylinder block it can be bored and repaired if needed and it uses a special ring also for piston. If it does not have Mercosil its a chrome bore and you can only resleeve the block as its not boreable or honeable(I usually toss em and replace block). If chrome is in good shape mic the cylinders as they can be out of round and still have good surface. If its a chrome bore 95psi is pretty good and doubt you will gain more than a couple of psi with new rings.....

 

[ngentile]

Re: Piston Rings

Well thanks everyone for your input. Other than trimming, decarbing and cleaning the carb I don't think there's much else I can do. I'm going to try a deep decarb and see what happens. Other than that I think a new motor altogether would be my next move. At this point I'm probably going to be running this thing into the ground.

Nick