1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

[gungalunge]

I took my ebay baught blocks apart and found it had Two 3 ring pistons and four 2 ring pistons in it. My question is can I use either one when i buy new pistons? I am trying to make one good engine out of 3 that I have apart. So should I use all 2 ring or all 3 ring ? THe block I am using has the serial # starting With #4 and some odd numbers . my blown one Is #365 and some odd numbers .I cleaned all the gasket surfaces honed the cylinders.Just getting started on the rest.I halted on this piston thing.so far i baught the gasket set,crankseals, and top and bottom crank bearings.I am still evaluating the rest as i go .

 

[Texasmark]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

Gonna reach out here. My first experience with 2 rings was when OMC built the first (that I know of) looper way back in 1967 or 8. Was 3 cyl at 55 hp; tuned exhaust included to help the fuel scavenging. <br /><br />Additionally the piston was flat topped (didn't need the diverter crescent we have always seen) and of course the 2 rings and ported (one or more holes drilled in to get the fuel/air mixture to loop). And by the way, that process turned out to be revolutionary. Gone were the days of gas guzzlers when it came to outboards....and today I know of no high hp (2 cycle)engine mfg'd in the world that isn't looped.<br /><br />The rings were wedge shaped and were built to seal as the piston goes thru the compression stroke....had to move to function (hence part of the reason for decarbing today as most engines are loopers if 2 cycle). Hence if the rings were wedge shaped, so were the piston grooves one would thing......however I never saw one disassembled.<br /><br />Merc did a thing called "Direct Charge" to compete with it and it had ported pistons and tuned exhausts as were the loopers. It was surely fuel efficient; at least mine was. <br /><br />As I recall my '89 115 6 cyl (still) had the domed "cam turned" square ring pistons and there were 3. I think '89 was the last year this "tower of power" (and it surely was) was mfgr'd. Then they went to the loopers with big bore and fewer cylinders. When they did this they also went to the wedge shaped 2 ring arrangement.<br /><br />More guesssing. This redesign should have been in '90 and the OMC patent should have expired by then allowing anyone to loop their engines. My current reference goes back to a '94 Mariner catalog and most (80%) of the lineup was looped, with all in the high hp (over 40 hp) having it.<br /><br />So, to answer your question, if the 2 ring pistons are flattopped, they were made to run in loopers. If your engine is not looped you may (probably will) not get proper combustion. Your Merc dealer should be able to supply you with the correct pistons/rings.<br /><br />I would not personally use the 2 in non-looped engines.<br /><br />My 2c,<br />Mark

 

[Texasmark]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

Forgot something. You didn't mention it, but if your block was direct charged, as I mentioned, it has ports in the pistons also which means there are strategically located holes in the block to feed these holes in the (side of the) pistons. Your ports have to line up with the holes in the block to work.<br /><br />Not sure the holes in loop pistons are in the same place, same number, and size as the direct charge. <br /><br />Mark

 

[AMD Rules]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

You can mix 'n match 2-ring and 3-ring pistons. Be aware that the piston geometry must be the otherwise identical as Mark already mentioned. Also, watch that you position the rings properly, keeping in mind that the 3-ring and 2-ring ring thicknesses and shape are different.<br /><br />Here's a 3-cylinder picture for reference. I had the same question when my new pistons arrived.<br /><br />

 

[Clams Canino]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

Either one is OK. And yes you can mix / match. I try to keep cylinder pairs the same because I can. <br /><br />-W

 

[WillyBWright]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

When they are mixed, if you do a compression test the acceptable range is within 15%. 10% is the usual tolerance. That's the only difference worthy of note I can think of. The 2-ring piston will probably perform slightly better than the 3s, but give a lower compression reading.

 

[Chris1956]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

Gung, The two-ring pistons are an improvement (by Mercury)and have keystone-shaped rings. The rings have a definite topside to them. The three-ring pistons have a rectangular shape and may be installed either side up, in any groove. You will easily get replacement rings for the 3 ring pistons, since they are standard. There was a time when I was unable to get replacement keystone rings. Luckily, my sister-in-law's father works for Mercury Marine in Fon-du-lac, and was able to run down the stock number.

 

[Clams Canino]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

BUT... beware the 2 ring Wisco pistons. Not advisable for use in the inlines!<br /><br />-Wayne

 

[Texasmark]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

Ok Clams,<br /><br />Just for my personal curiousity, if you will. Tell me about the 2 ring pistons for the towers. Were they specially mfgr'd by Merc to backfit the Direct Charged inline 6?<br /><br />If so, then I can understand that the ports would match the ports in the block for inlet fuel scavaging.<br /><br />But what about the change in pre and post combustion circulation caused by a flat topped piston vs a domed one?<br /><br />The other curiousity, I have is what was said about compression. If cranking compression is different, then surely operational combustion is also which would make for unbalanced combustion which would be analagous to an unbalanced engine (like weight differences in the moving parts) resulting in vibration and possibly engine damage when operated at high rpm's......like snapping a crank or throwing a rod.<br /><br />Thanks,<br /><br />Mark

 

[gungalunge]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

I got my gasket kit.Getting ready for those pistons soon.I got his old 115, 1974 inline all apart .Thanks for the imfo everyone. first I am going to get the 3 ring pistons. As i looked over the wear patterns with this engine the 2 ring pistons look worn more than the 3 ring ones .i had fun with the engine bearings gear pullers and stuff. but i got them out .. never saw so many neadle bearings .i had to get a 3rd crankshaft seal did not see that other one.i got 20 tupperwear boxes full of misc parts to put this engine together . i will get it soon.Any advice on what to use to keep those neadle bearings captured for installation ?

 

[Clams Canino]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

Originally posted by Texasmark:<br /> Ok Clams,<br /><br />Just for my personal curiousity, if you will. Tell me about the 2 ring pistons for the towers. Were they specially mfgr'd by Merc to backfit the Direct Charged inline 6?<br /><br />If so, then I can understand that the ports would match the ports in the block for inlet fuel scavaging.<br /><br />But what about the change in pre and post combustion circulation caused by a flat topped piston vs a domed one?<br /><br />The other curiousity, I have is what was said about compression. If cranking compression is different, then surely operational combustion is also which would make for unbalanced combustion which would be analagous to an unbalanced engine (like weight differences in the moving parts) resulting in vibration and possibly engine damage when operated at high rpm's......like snapping a crank or throwing a rod.<br /><br />Thanks,<br /><br />Mark

None of the direct charge pistons outta be purely flat topped. They all are flat topped with an eyebrow shaped deflector. They come only in low and hi dome deflectors - and you should not mix and match deflector height. Chris is correct that Mercury came out with the 2 ring semi-keystone design to combat coking around the rings. The boost port in the side of the piston outta be right where it was on the 3 ring type piston. Note that all replacement pistons have the boost port, even for blocks that don't have the finger-port. It's now a 1 size fits all kinda world.<br /><br />-W

 

[Texasmark]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

Hey AMD Rules.<br /><br />Just curious. That picture in your sign-on logo of your AMD boat hooked up isn't with a 60, like your link pictures, now is it? How about 150 or so. Beautiful wake and it's obvious "taint much hull" in da wadder....must be pushing 60.<br /><br />Mark

 

[AMD Rules]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

gungelunge,<br /><br />The way to keep the needles in place is with some assembly lube (grease). <br /><br />Texasmark,<br /><br />Yes, my avatar is a pic looking out the back of my boat, with the 60HP motor. I'd be moving around 32mph in that pic. Click my sig to see how small my boat is (14.5ft), and you'll see why it moves along so well.

 

[gungalunge]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

ok i still did not order the pistons. i am way ahead of my self .this project to get the crankshaft ready with all the bearings and measurement.My engine is tore apart.before i get to those pistons . I see the work here on this crankshaft.I ordered all my new measurment tools.<br />I pressed off all the bearings cleaned her up.i will measure the journals. they are smooth worthy of an super polish.this week i will see if i can use this crankshaft.after i measure it. <br />it was a ***** getting that top bearing un seated .i washed all the varnish off it took all day .I used denatured alcohol.it looks like new now

 

[gungalunge]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

I am still gathering all the imfo i Can on the pistons to use . I thank everyone alot. but still got alot to do until i order them ..I have time i want to do this rebuild right. Now I see tear it down first count the things you need ask Questions . I have learned things doing this tear down. I found 2 cracked stressed connecting rod collets.This goes to show dont mix those pistons .this engine ran with 3and 2 pistons.was on the ones with the 2 ring I had t cracked collets .

 

[Clams Canino]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

The aftermarket pistons I generally use, reccomend, and sell the most of, are the 3 ring type and made by Persan. I've never had a problem with them. Ever.<br /><br />-W

 

[gungalunge]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

AMd NOw that picture IS what I am talking about .. Wow .. Go mercury ..THat would be My goal ANd smile to post one like that. this summer . I LOVE IT ..

 

[gungalunge]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

i really like how those 3 ring piston wear to cylinder it looked better than the holes that the 2's were running in

 

[Texasmark]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

Ok AMD. You fessed up and I believe you. Nice wake regardless of how long your boat is...and at 32mph; I'm impressed.<br /><br />Gun....Merc used to advertise "cam turned pistons" that shaped to fit the cylinders when they heated up. Maybe that's what you are seeing.<br /><br />Mark

 

[xmen3]

Re: 1974 ,1150 , 115hp,inline 6, 3 ring pistons or 2 ring???

Just a little confused as to evolution of the 2 and 3 ringed pistons.
My '86 has 3 ring pistons but most of the pistons I have found listed are new 2 ring types.
Could someone please clarify which came first and did they switch back for some reason?