115 6c TOP piston cylinder issue

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

racerone said:

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

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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

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.

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?

jimmbo said:

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?

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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.

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

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

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!

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

jimmbo said:

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

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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!

No

jimmbo said:

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

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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

I finally heard from machinist. I'll know more about what he's doing, but i know he can do it, so I am going to start planning out my process.
Here is my plan so far.
- rebuild water pump. I think its in ok shape, but if i did it, was a while ago.
-clean carbs, check floats and needles, replace gaskets. Not gonna rebuild unless i see something unexpected
-redo fuel pump. I did it a few years ago, but its so easy
-new fuel line. Cheap, and easy to do while motor is apart
-replace all gaskets on head.
-replace out of spec reeds. They aren't bad, but I'm hoping to not have to take the head apart again
-replace at least 2 pistons..Possibly all 6, depending on what machinist tells me

Does anyone have an affordable source for bolts. iboats, where i order a lot of stuff, gets really expensive for individual bolts. My head bolts are toast. Most of the rest seem pretty good. A little bit of rust, but nothing that can't be cleaned up.

Anything obvious Im missing?

Find bolts at your local hardware store.-----Replace the 5 bleed inserts if equipped with them.

racerone said:

Find bolts at your local hardware store.-----Replace the 5 bleed inserts if equipped with them.

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Do you use zinc plated grade 5? Is it a bad idea to use stainless with anti seize?

Gee, the water jacket cover bolts are grade 5 or 7 steel in 1/4-20 or 5/16-18. Pretty common stuff at any HW store. Most of the trouble comes when the 1/4-20 water jacket screws break, when you try to remove them. I would skip replacing the cylinder heat water jacket gasket, unless you really need to. Sometimes the machinist needs the bare block. Ditto on the exhaust cover, baffle and inner exhaust cover. If they do not leak now, leave 'em alone.

Gaskets for your carbs are real cheap. Replace them.

If your floats are the old foam type, replace with the white hard plastic. The foam tends to dissolve in gasohol. Make sure the little springs are intact on the floats.

The inlet needles and seats should be stainless with neoprene tips, and the seats are all brass. If you have the old rubber and brass seats and nylon needles, replace 'em.

Unless your reeds are cracked or bent, they are likely fine. The originals hold up real well.

Replace end cap seals and crankcase seals. Reuse the shims under the upper end cap. Check the bearings in the endcaps for wear and replace as necessary.

Do a link and synch. 21* BTDC is max spark advance. ADI ignition calls for 0-9* ATDC for idle pickup. At idle pickup, the carbs must be closed, but ready to open.

Check the copper water tube for damage. Sometimes they get crushed by salt or silt. Replace the rubber seal that holds the water tube in the exhaust extension.

If you reuse pistons, make sure you get original style rings. Replacement pistons usually have 2 keystone rings, vs the 3 rectangular rings on the orig pistons.