'89 Merc 60HP piston replacement..or not?

Korbs67

Seaman
Joined
Apr 19, 2012
Messages
51
Hello Forums. This is my first thread to iboats. Applause please!

I'm rebuilding a 1989 Mercury 60HP. Piston #1 burnt up. I disregarded the warning beeps because I didnt know where it was coming from, very stupid I know. First time boat owner..lesson learned! The top carb was bone dry and I believe my water pump failed.

My quesion is whether or not to reuse pistons 2 aqnd 3 they appear to be in very good condition.

I've ordered OEM rings (3ring pistons) for #2 and #3. I'm installing new needle bearings on the wrist pin for all pistons and reinstalling the same end cap bearing and cage as they appear in excellent condition.

Compression prior to disassembly measured 1-60psi, 2-80psi, 3-82psi. Now I know those seem low but I manually pulled the flywheel with a makeshift pull rope. and probably on got 2-3 cycles.

All three pistons had the same wear pattern. A picture is provided below.

I'm trying to keep the costs low on this rebuild but understand that as long as its open to replace anything suspect. The reeds appear to seat very well. Overall the crakshaft area was surpringly very clean, like new surfaces everywhere.

The wear marks are surface and you cant feel them. I have not mic'd them but assume they are true I'd like to save the $225 cost of having 2 new pistons shipped out.

Thank you!

Korbs67

..well it looks like my new account wont let me post a jpg yet. So what might I consider to be telltale sign that I should just go with a new piston??
 

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Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: '89 Merc 60HP piston replacement..or not?

It isn't just what the pistons look like. You need to check the cylinder bores as well. A proper check is to check the cylinder bores for taper, scoring, to see if they are still within tolerance and then do the same for the pistons. I can't judge by the pictures but it appears there is the beginnings of significant piston scoring going on and the cylinders probably look the same. While you may be able to hone (not bore) the cylinders, I would certainly mic the bores and pistons and then seriously consider new pistons and rings as a minimum.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: '89 Merc 60HP piston replacement..or not?

Check the block as Silvertip suggested as if the engine did get hot the other pistons and bore could be out of round. This will cause idling issues and low end performance problems...
 

Korbs67

Seaman
Joined
Apr 19, 2012
Messages
51
Re: '89 Merc 60HP piston replacement..or not?

Thank you for the repies!

As a followup, here are the specs against the manual

Manual says:
Skirt: 2.872"
Above rings: 2.863"
Cylinder Hone (They have been honed):2.874"
Oversize .015: 2.889"

Mine: using calipers (sorry best I could do)
Cyl 1: 2.866"
Cyl 2: 2.865"
Cyl 3: 2.875"

Note: Cylinders "look"great and there is absolutely no pitting, scratches or other damage whatsoever.


Pistons as measured using calipers: at 90degree measurement points to check for ovaling
P1 being replaced
P2:
Skirt: 2.867", 2.867"
Above rings: 2.850"

P3
Skirt: 2.867", 2.867"
Above rings: 2.850", 2.845

Note: oddly enough the new Sierra (Botessi??) piston I have specs the same as P3 ABove ring.

I think my tolerance are tight..thoughts??

Piston 3 has that vertical scoring below the rings. Using the fingernail you can slightly feel the scoring. Definitely replace or salvage it?

These Botessi (I'm confused why i-boats didnt just send me a Sierra product like I ordered) are real rough/unfinished looking pistons. My concern is the hard ridge and the prevelent seam as compared tot he OEM pictured as well. It would seem that this hard ridge my not seat properly and do damage at the top of the stroke. Any thoughts on this? I'm not sure if I should look elsewhere for a different piston..

Is there harm in knocking down that hard ridge with a dremel to round it a bit?

THANK YOU for any advice!!

Korbs
 

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