115 6c TOP piston cylinder issue

[Chris1956]

Yes, the two ring pistons use a keystone-shaped ring. It is not compatible with the older 3 ring pistons.

Most of the 1/4" bolts on the head of my engine could be drilled thru the block casting and a new bolt and nut installed externally. I probably broke 3/4 of them, since my motor was used in salt water. Ironically the one or two bolts that could not be drilled thru, came out without an issue.

 

[ianmoore]

Yes, the two ring pistons use a keystone-shaped ring. It is not compatible with the older 3 ring pistons.

Most of the 1/4" bolts on the head of my engine could be drilled thru the block casting and a new bolt and nut installed externally. I probably broke 3/4 of them, since my motor was used in salt water. Ironically the one or two bolts that could not be drilled thru, came out without an issue.

Mine is a salt water motor too. I was honestly amazed to only have one stuck bolt in whole motor. I went really slow, used heat and lots of pb. I did break off 2-3 bolt heads on that section, but was able to get them off and out.

Honestly, being in the salt is my biggest concern. I’d like to keep this motor for a while. I really like it, but there were some decent salt deposits and I have flushed the motor every time I’ve taken it out.

Anything preventative you did in that regard after rebuild?

 

[Chris1956]

Unfortunately, what I found was that the aluminum alloy of the block was getting softer due to the saltwater exposure. Bolts would strip easier and some of the castings would get some powdered corrosion.

I never flushed my engine because I kept it tied to the dock in saltwater, and there was no good way to flush it.

It was a '77 which was the last Merc 1500 model year. I had it from just about new in 1980, until it thru a rod in 2008, and it was kept in saltwater from 1993 onward. It also sunk at the dock twice, causing me to tear it down and wash it out.

If you can flush it after every use and use corrosion guard on the block, it should last. Fresh fuel and good cooling are essential or they cook pistons.

Also, the motor has no thermostat, so they depend on the engine spinning fast enough to cool the heat it generates. Don't overprop or overload the boat, as the cooling margin is good but there is not a lot of extra cooling.

 

[jimmbo]

What about those rod cap screws? Those are really expensive. I’ve heard that people tend to replace them when they get in crankcase

Those are a Onetime Use Only Screw/Bolt

 

[ianmoore]

Those are a Onetime Use Only Screw/Bolt

Yes. Ive been reading up on them. I read someone working on a rebuild that actually had an issue with new OEM mercury bolts. Does anyone have experience with the WSM road bolts?

 

[ianmoore]

I just got a call from machinist, and he did not have to bore at all. He was surprised, but the 2 cylinders with the missing rings cleaned up at .015. He did suggest replacing all the rings. The issue I'm having is that all of the existing pistons are the 3 ring pistons. I think this is the original powerhead but don't have a way to confirm. I think the 3 ring pistons were replaced with these 2 rings.
-This pic is from the manual and shows both types of pistons for this engine.
-Where can i get the older style 3 ring assemblies for those pistons?

 

[jimmbo]

So you are saying only 2 Pistons need replacing? You can use the 2 Ring Piston as a Replacement
Finding Rings for the 3 Ring Pistons might a Challenge, there are 1 set of 3 Rings here
You might try calling Dealers in your area, as they may have a few NOS collecting Dust

 

[Chris1956]

Gee, doesn't a .015 bore require a new OS piston? Did he bore it or just measure it? The cylinders get out of round. Did he see that?

 

[ianmoore]

Gee, doesn't a .015 bore require a new OS piston? Did he bore it or just measure it? The cylinders get out of round. Did he see that?

I have no experience with machinest, though the shop i intitially took it to that is an awesome mom and pop shop recommended him highly. He didn't rebore. He ended up only re-honing it. if there are questions i should ask him, let me know. i am a bit in over my head, or at least the first time in this deep

 

[jimmbo]

I doubt any Machinist would Hone a Cylinder out to 0.015 Oversize. It would take forever. 0.015 is the first Overbore Size.
2 Stroke Engines tend to have a unique Wear Pattern

 

[racerone]

If rings were broken / missing on these O/S bores it needs a new piston.-----I am not sure 0.015" pistons are available at this time.