Replacing piston without taking engine apart

[crem1]

Hi!

I have a MERC 500 1973 outboard engine with a low compression piston. Is it possible to replace the piston with a minimum amount of engine work?
Thanks

Alex

 

[Moody Blue]

Re: Replacing piston without taking engine apart

Sorry to tell you there is no easy way. Powerhead comes off and you pretty much have to strip the whole block then split it in two. There is not a traditional "head" on those motors, only a waterjacket cover.
Before going to all that trouble you can remove the intake and/or the exhaust covers and have a look at the pistons and cylinder walls to see if its worth anymore time or effort.

 

[crem1]

Re: Replacing piston without taking engine apart

Thanks. Somebody made mention that if you take the carbs, reeds, and manifold out, by turning the flywheel you can access the end of the rod of the piston.

Alex

 

[Droll]

Re: Replacing piston without taking engine apart

It could be a relatively quick job but....

• Powerhead needs to be removed
• Powerhead needs splitting, crankshaft and ALL pistons will have to come out
• ( are put in as ONE assembly ).
• Now the cylinder can be checked out and hopefully a new piston can be inserted.

Would advice you to hone ALL cylinders and put in new rings ( new oversized piston if the cylinder needs boring ).
+ new rodbearings
+ new top/bottom crankshaft bearings ( would not hurt to replace the center crank bearings too )
And of coarse new top/bottom crankshaft seals
+ New gaskets.
+ New impeller
Would NOT hurt to clean the carbs and give them some new carb kits too ( gaskets + jets + inlet valve )...

And before trying to start the engine.... figure out WHY it failed the last time, it could be the the carbs or impeller ( but they should be good as new now ? ) .


Arne Kjetil

 

[crem1]

Re: Replacing piston without taking engine apart

Aside from the previous obvious solutions nobody has tried the piston rod side, if it's possible then that route would save considerable labor. Assuming the cylinder walls are not affected.

 

[arsenalpsu]

Re: Replacing piston without taking engine apart

Aside from the previous obvious solutions nobody has tried the piston rod side, if it's possible then that route would save considerable labor. Assuming the cylinder walls are not affected.

I don't think you know quite what you're talking about, there is no way to remove a piston from it's rod w/o removing the crankshaft from the block. You have to remove 2 snap rings from each side of the piston that holds the piston pin in place. This metal rod goes through the piston and holds the bearings in place with the connecting rod. You can't get to them from the exhaust or intake ports.

AND what do you mean by "piston rod side?" There is no such thing, the rods rotate to both port and starboard sides of the block?

 

[coolguy147]

Re: Replacing piston without taking engine apart

how low is it? you might be able to do a decarb on it if you really dont want to do a rebuild

 

[Moody Blue]

Re: Replacing piston without taking engine apart

Aside from the previous obvious solutions nobody has tried the piston rod side, if it's possible then that route would save considerable labor. Assuming the cylinder walls are not affected.

Not only the obvious way to do it, but the ONLY way to do it . Not sure where you got the information that it could be done any other way. A proper manual will be your best investment.

How about some compression numbers?

 

[Faztbullet]

Re: Replacing piston without taking engine apart

You need to follow and reread previous posts as your earlier adviser(s) must not know a Merc inline engine..

 

[crem1]

Re: Replacing piston without taking engine apart

Thanks to all the people that put their knowledge on the line. Just checking whether anybody has heard about this possibility, by the responses it looks like a no go
Thanks