Evinrude 5520 5.5 hp pistons

[Buccaneer]

I pulled the pistons out of the Fisherman I’m working on, and
the top piston has a gouge on the skirt. It looks like it sucked
something in an intake port. It appears it did no damage to
the rings or cylinder. The gouged area is about 3/32 wide,
and definitely can be felt with your fingernail.

Q. What’s the general rule of thumb when to toss a piston
with this kind of injury?

My pistons have three rings, some replacements appear to
have two rings. Is it okay to run one of each if I decide to
look for a different piston?

http://www.marineengine.com/parts/johns … +Fuel+Pump

Marine Engine.com shows two different pistons for this engine…..
with two rings, and three rings, part #’s 0376427 & 0386692
Q. What’s up with that?

Thanks, Buccaneer

Prepare to be boarded!

[dan-in-tn]

Your old motor had three ring pistons in it. That was the style then. Later 6hp motors picked up the two ring piston and still later 6hp motors had pressure back rings. The top ring was a wedge shaped ring. All three motors had the same bore and could use each type pistons. I preferred to use two of the same type in any one engine, others may disagree on this site. It should be easy enough to find a three ring piston for your original engine. I may have an extra somewhere in all my stuff.

Dan in TN

[fleetwin]

I agree with Dan, use two of the same style pistons.
Where is the damage on the piston skirt? If it is on the intake side, you are less likely to lose primary compression through the exhaust ports. Toss the piston if the skirt is damaged on the exhaust side of the skirt. I guess it all comes down to the extent of skirt damage, and how much time and money you want to put into this project.
Post some pictures of the damaged piston for more opinions.
Like Dan says, you should be able to find a decent usable piston for this engine easily.

[lotec]

Personally, I’d want to know what caused the damage. Not likely it sucked in a bumble bee and did that – more likely a bad reed, reed fastener, rod cap or some other part that is broken or worked loose. The rods and crank you’ll be able to evaluate when you get it apart – if it’s the reed or something like a carb butterfly screw, that’s easy to fix.

[Buccaneer]

Thanks for the replies. I was wondering as well as to what gouged the piston
on the intake side. The carb and intake manifold were so corroded from
mice piss that I had to find different ones, but I’ll see if they’re missing
any parts that might have been sucked up. I’ll try tomorrow to take a photo
of said gouge and see what you experts think. This motor isn’t worth
putting too much more money into it…… I’m already wishing I would
have left it as a mouse hotel.

Prepare to be boarded!

[Buccaneer]

Worked on the Fisherman some more today, and changed my
mind on the piston gouge / score being on the intake side….
it’s now on the exhaust side! I found no missing parts, i.e.,
throttle plate screws, reeds, etc., that might have got sucked
into the cylinder. How does a person know if a scored piston
is heat related, lean condition, or debris sucked in?
Half the rings were stuck from carbon, so I don’t think it was
lack of oil!
Photo of the scored piston…….
Scored piston
http://grayhitandmiss.com/Outboards/piston2
Toss or use?

Wondering why there looks like there should be a core plug here,
but there’s no holes drilled that I can see.
Core Plug Missing?
http://grayhitandmiss.com/Outboards/core_plugs.jpg
Should there be a core plug here?

I’m thinking when I removed the intake manifold, that I might have drove
the dowel pins the wrong way. Are they tapered?
They seem stuck now….. may have to heat the block to loosen?
http://grayhitandmiss.com/Outboards/dowels

Trying to determine if I have all the bleeder holes unplugged.
It appears that excess fuel drains from tiny holes A1 and B1,
and go out A2 and B2, then exits into the lower unit.
Is there any other circuits I’m missing?
http://grayhitandmiss.com/Outboards/bleeder_valve

Thanks for the help, Bucanneer

Prepare to be boarded!

[dan-in-tn]

Well let’s see here. The dowel pins are definitely driven the wrong way. You may be able to just quick punch them out, but you need to support the crankcase so as not to bend the edges. It takes a solid hit to dislodge them. A little heat may not hurt, but be careful about how much. How did you get the front half over the tapered cowls? That is usually the hard part! The block has thrown a rod at some point (JB Weld) or whatever glued up. A piece of something could have been left in the block from before and that’s where your score Mark could have come from? Hard to say. Looks like it might be heat also, but you will usually see more than one place on the Pistons if heat related. Cylinders should be out of round if over heated badly. I can barely make out the holes you refer to, but they are in the area of the drains of these blocks. That core plug that is missing is not a big deal. The other one would be.

Dan in TN

[frankr]

It is my guess that the blank core plug cavity is where the identification core plug would have been on older models. When they added the fuel pump mount, they also created a new cavity for the relocated ID plug. No reason to spend the money to remove the old cavity from the mold. Making changes to those casting molds is a very expensive thing to do.

That’s my story and I’m sticking to it–until somebody points out my error.

[Buccaneer]

Thanks for the insight!
Dan, I just put the JB weld on the block…….. no rod thrown!
Mice piss corroded two pin holes through the block.
I don’t remember much trouble getting the dowel pins drove thru the intake
manifold, but they’re sure tight now. The other dowel pin that I didn’t show
is going to be a bugger to drive back, as you can’t get a punch on it straight on.
Frank…….. money always wins, so I bet your correct on the core plug holes!

Prepare to be boarded!

[Mumbles]

If you have the exhaust cover removed from the motor, it will make it a bit easier to get a punch on the end of the other pin. On these motors ever little bit helps to get that port side pin out! I don’t know why but scoring on the exhaust side of the 5.5 pistons seems to be fairly common. I have a bunch of used pistons and most of them are scored in the same area.

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