115 6c TOP piston cylinder issue

[racerone]

Milling machine and boring bar is the way to do them.-----Not that hard.

 

[ianmoore]

Milling machine and boring bar is the way to do them.-----Not that hard.

It seems so. The trick is finding someone who knows how to do it and will take it on. I followed every lead I could find and they were all dead ends. And I live in the seattle/tacoma area, so I thought it would be easier.
Waiting to hear if the machinest’s buddy can do it

 

[ianmoore]

Waiting to hear from the machinest. Ive been going through pieces of the engine I have here. The reedvalves facing cylinder 3 were a little out of spec. There were a couple of petals that were probably .009 or .01.
Im trying to understand things that could have contributed to losing the cylinder. It is interesting that the only reeds out of spec are facing that cylinder.
I'm waiting to get some info before i put any more money into the engine, but i want to be using the time wisely.

 

[jimmbo]

Myself, I wouldn't even give those Reeds any concern.
Lean ness, Overheating, lack of Lubrication, and Detonation are some of the primary causes of Cylinder/Piston Problems.
How long have you had this Motor, and do you have the Service/Repair History of it?

 

[ianmoore]

Myself, I wouldn't even give those Reeds any concern.
Lean ness, Overheating, lack of Lubrication, and Detonation are some of the primary causes of Cylinder/Piston Problems.
How long have you had this Motor, and do you have the Service/Repair History of it?

Thanks. I’m trying to set up a path to not just fix it(assuming I can get someone to rebore) but also to be aware of possible issues.
I bought the motor about 7 years ago, but it did not have a repair history. I am thinking that 1,3, and 6 have been rebored because they are all .015s.
I completely rebuilt all the carbs. The boat was never heavily used, always non ethanol gas.

It is possible that those two cylinders were lean. I did all the work, including tune up work, and though I was as thorough as I could be, I am relatively novice with boat engines.

This is a motor in the salt. I did find some decent salt residue on the head side. Wondering the last time this was all cleaned up.

 

[ianmoore]

Good news! sound someone who can do it. I'm assuming he is gonna try for .03 on 3 and 6, but will wait to talk to him when he has block in hand. Will update as i know

 

[jimmbo]

Cylinders 1&2 share a Carb, 3&4 share another, and 5&6 share the last one.
A leaky upper Crankshaft Seal can result in #1 running Lean
Hmm. You say it is an 80s motor? If so, it has what Mercury called the Back Drag Feature on the Carb, a way to improve Fuel Economy at Part Throttle. Works well, unfortunately, once Refineries started adding Alcohol to the Fuel, chemically leaning it, the mixture these Carbs deliver is actually too lean at Part Throttle. There is an easy Fix. There is a small black Hose running from the Carb Body, to the Fuel Bowl Cover. Remove the Hose from the Bowl Cover and push a small Ball Bearing into it to Plug it. You can leave the Barb on the Fuel Bowl Cover open as it just becomes another Bowl Vent

 

[ianmoore]

That is interesting! i never knew what those little hoses were for. I figured it was part of some deep black art I wasn't meant to know.
Ive only been using non ethanol gas, so I would imagine that makes the particular effect at least a little less pronounced. I was also thinking you could put a hose on the non bowl side with a cap on it for the same effect.

The interesting thing to me is that of the cylinders, 2 of the bad ones come from ones that seem to have been bored out. I can't totally confirm this, but the only pistons that have markings are .015 on 1, 3, and 6. And my rough measurments show these to be a little bigger. This makes me wonder if there were issues with the cylinders before that were related to whatever happened recently, and I would assume the gaskets had all been redone since the piston fix.

Im reading everything i can about this, and what I'm reading says when a cylinder that is lean melts down, there is often aluminum on the wall, lots of scoring, and seizure marks, but my walls are relatively clean, bar a small scrtach on #6.
I also read that if a cylinder runs lean for a long time, it will typically have a more clean piston crown, and these all look like the other ones.

Im really curious to hear what the machinest says!

 

[jimmbo]

The Hose provided a Vacuum Draw on the Fuel Bowl during part throttle operation, resulting in Less than Atmospheric Pressure on the Fuel in the Bowl, reducing how much Fuel was pushed into the Venturi. A Metered Orifice for the Bowl Vent prevented the Pressure in the Bowl from dropping too Low. Under further Throttle Opening, the Vacuum dropped off and Normal Atmospheric Pressure was restored in the Fuel Bowl.
Alcohol is not the only means of Chemically Leaning Gasoline, so Non-Ethanol Gas isn't being clear of the Issue. There was a Service Bulletin from Mercury instructing Shops to do what I had described

 

[MNhunter1]

Cylinders 1&2 share a Carb, 3&4 share another, and 5&6 share the last one.
A leaky upper Crankshaft Seal can result in #1 running Lean
Hmm. You say it is an 80s motor? If so, it has what Mercury called the Back Drag Feature on the Carb, a way to improve Fuel Economy at Part Throttle. Works well, unfortunately, once Refineries started adding Alcohol to the Fuel, chemically leaning it, the mixture these Carbs deliver is actually too lean at Part Throttle. There is an easy Fix. There is a small black Hose running from the Carb Body, to the Fuel Bowl Cover. Remove the Hose from the Bowl Cover and push a small Ball Bearing into it to Plug it. You can leave the Barb on the Fuel Bowl Cover open as it just becomes another Bowl Vent
View attachment 416681

Not to highjack the thread, but genuinely interested and the information may be helpful to others as well. I plugged my hoses with a BB, but still have both ends connected. Is there any harm in not leaving the barb on the fuel bowl cover open?

Great information here, thanks!

 

[jimmbo]

No

 

[ianmoore]

The Hose provided a Vacuum Draw on the Fuel Bowl during part throttle operation, resulting in Less than Atmospheric Pressure on the Fuel in the Bowl, reducing how much Fuel was pushed into the Venturi. A Metered Orifice for the Bowl Vent prevented the Pressure in the Bowl from dropping too Low. Under further Throttle Opening, the Vacuum dropped off and Normal Atmospheric Pressure was restored in the Fuel Bowl.
Alcohol is not the only means of Chemically Leaning Gasoline, so Non-Ethanol Gas isn't being clear of the Issue. There was a Service Bulletin from Mercury instructing Shops to do what I had described

Thanks for the additional details on what it does. Ive got a lot of work to do, but will do this after i go through the carbs