zddp oil additive

[d.j. moordigian]

MrTube,
If your 2 Yamaha's are 2 strokes then yes, they are pined to keep the rings from
rotating. You don't want the end gap rotating into the ports.

[Tom Wesenberg]

As d.j. said I've seen 2 stokes with pins to keep the rings in place, but don't recall seeing any 4 stroke engines that way. My chainsaw has both pins in line with each other. You'd think they would want to stagger the end gaps.

In the 60's I overhauled a car engine that had all the ring gaps in a straight line on one piston and it left a high line of metal, where no cylinder wear took place.

[37ford4dr]

[QUOTE=Bassman/NZ;
Incidentally, Valvoline 20-50 racing oil does indeed contain over 1200ppm of ZDDP, but it is missing several scavenging and cleaning additives required for a street engine. I would not want to do more than 300-400 miles between oil changes if using that product. A good street oil with ZDDP should go 1000+ miles, or more if an oil filter system is used.[/QUOTE]


there are several valvoline racing oils the VR1 sold in the states has the scavenging and cleaning additives and is a good street oil. they do have a strictly racing oil like you mention that is not a good street application.

[ABento]

I checked with my Union Oil rep not too ago and the 30wt still has zinc in it.

[MrTube]

Ah,
Maybe it wasn't my two Yamahas as they are 4 strokes. HOWEVER I have worked on many 2 strokes in the past. I probably just made the assumption all pistons had it and thought it was fact. I have rebuilt 2 stroke engines and obviously had to install the rings on the pistons. I have never had to rebuild a 4 stroke so never had a very close look at the pistons in hand.

You would think a 4 stroke would need it almost as bad. If and when the two notches in the rings line up this would certainly reduce compression no?

[40 Deluxe]

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Doesn't matter where the gaps are. Any compression pressure getting through the top ring gap will travel unimpeded around the piston to where ever the 2nd ring gap is and then through the gap. There's a lot of space between the rings for compression pressure and/or oil to travel through. Consider: Take a typical ring gap of say .020" and a space of .030" between cylinder wall and the ring land area of the piston. That means about .030" of the ring gap is exposed to compression pressure (or oil coming the other way)-the rest of the ring gap is tucked away inside the ring groove. So multiply .020" times .030", resulting in exposed ring gap area of .0006 sq. in. Say there is 1/4" space between the top ring groove and the 2nd ring groove. This gives an area of .0075 sq. in. for compression or oil to travel in as it goes around the piston looking for a ring gap to crawl through. That space between the rings is about 12 times as large as the ring gap area. So why does it matter where the gaps are at?

[Tom Wesenberg]

I believe the placement of the ring gaps matter, or the instruction sheet that comes with new rings wouldn't specify a location for each of the gaps to be placed.

[okieford]

I have an airplane with a Continental engine. It developed a dead miss while in flight and blew out all but 2 qts from an 8 qt sump. The problem was that the ring gaps were aligned. The piston has 3 rings above the pin and one oil ring around the skirt. The hot gases blowing through the gaps eroded the piston and finally blew a hole in the piston between the first and second ring. Then a triangular shaped piece broke out from the hole all the way to the bottom. The third and oil ring broke and pieces made their way into the screen, but not into the pump. The oil ring saved us since it held the broken piece in place. If the gaps had been aligned with the end of the pin it would have been a catastrophic failure. I replaced the cylinder and piston, cleaned the aluminum out of the sump and got about 600 more hours out of the engine. Of course I kept my fingers crossed that non of the other 5 pistons were improperly installed.

[Mike V. Florida]

Originally Posted by okieford

I have an airplane with a Continental engine. It developed a dead miss while in flight and blew out all but 2 qts from an 8 qt sump. The problem was that the ring gaps were aligned. The piston has 3 rings above the pin and one oil ring around the skirt. The hot gases blowing through the gaps eroded the piston and finally blew a hole in the piston between the first and second ring. Then a triangular shaped piece broke out from the hole all the way to the bottom. The third and oil ring broke and pieces made their way into the screen, but not into the pump. The oil ring saved us since it held the broken piece in place. If the gaps had been aligned with the end of the pin it would have been a catastrophic failure. I replaced the cylinder and piston, cleaned the aluminum out of the sump and got about 600 more hours out of the engine. Of course I kept my fingers crossed that non of the other 5 pistons were improperly installed.

Not that usual I guess. I went to FIT's School of Aviation years ago and remember being told a simular story about ring gaps lining up.

[40 Deluxe]

You mean that anyone flying a piston engine aircraft is at the mercy of random ring gap alignment?! And that hot combustion gasses cannot travel 1/3 of the way (or even half way) around the piston to the next lower ring gap? What's to keep these hot gasses/flame from finding their way to that next gap?--Nothing! Any piston/ring failure as mentioned above would have another cause such as detonation breaking a ring land or a broken top ring eating into the ring groove, making a pathway for combustion flame to blow down the side of the piston and start melting it, or a lean mixture overheating the cylinder or the engine inhaling something big enough to start the damage. I think we stagger the gaps because "it's always been done that way", or "Pappy said to do it this way" and ring companies don't want to be badmouthed by self-taught mechanics who assume these tiny openings can do such great harm. Just one of many old wive's tales (Oops!--urban legends) that we find in the engine repair business/hobby.

[Richard Lorenz]

Hot gas traveling 1/3 of the way along the ring gap would cool down considerably.

[40 Deluxe]

But it's still hot (at combustion temperature) as it's coming through the upper ring gap and nothing gets melted or burned because there is enough mass in the ring, piston and cylinder wall to absorb that heat. Remember, the ring gap itself is very, very small and does not let much hot gas to pass through. It then has to pressurize the space between the rings before it can be forced through the equally tiny 2nd ring gap. Whether that 2nd gap is directly under the 1st or halfway around the piston makes no difference. Unless, of course, we have a broken ring, a soft ring (lost tension), a stuck ring, a worn or broken ring land, etc. Then there'll be flame going down the side of the piston. An engine running lean has some oxygen left in tne exhaust gas. If it's under a heavy load (as in an airplane) engine temperatures go up. If it gets hot enough for long enough, the exhaust valve and top ring will get red hot and voila!- we have a cutting torch (metal is red hot and we blow high pressure oxygen at it-what is the result?). It's just a coincidence that the rings happened to rotate such that the gaps all lined up at the time of failure.

[MrTube]

I'm kinda thinking Deluxe is right. If it were that big of an issue there would be something to keep the rings from rotating like in a 2 stroke.

[msmaron]

Using rotella on the engine Tom rebuilt for me AND MARVEL MYSTERY OIL!!

[okieford]

Originally Posted by 40 Deluxe

You mean that anyone flying a piston engine aircraft is at the mercy of random ring gap alignment?! And that hot combustion gasses cannot travel 1/3 of the way (or even half way) around the piston to the next lower ring gap? What's to keep these hot gasses/flame from finding their way to that next gap?--Nothing! Any piston/ring failure as mentioned above would have another cause such as detonation breaking a ring land or a broken top ring eating into the ring groove, making a pathway for combustion flame to blow down the side of the piston and start melting it, or a lean mixture overheating the cylinder or the engine inhaling something big enough to start the damage. I think we stagger the gaps because "it's always been done that way", or "Pappy said to do it this way" and ring companies don't want to be badmouthed by self-taught mechanics who assume these tiny openings can do such great harm. Just one of many old wive's tales (Oops!--urban legends) that we find in the engine repair business/hobby.

The Continental engine that I described was a C145, the predecessor of the O300. This is a low compression engine with a fixed pitch propeller. The failure occured in the late 1970s when we routinely ran our engines full rich and it was running on avgas approved for that category of engine. Gas was a lot cheaper then. The probability of detonation was zero. The guy that repaired it had over 40 years in the aircraft mechanic business and he had seen that happen before. I still fly behind a Continental engine, more horsepower, 210, and I don't worry about ring alignment. But if you don't believe me, get your own plane, align the rings in one cylinder and go flying.

[40 Deluxe]

No doubt the mechanic had seen that kind of damage before, but was it caused by the ring gaps being in line? I'll bet he'd seen the same damage many other times where the gaps were not in line, thought nothing of it and found some other cause. Kind of the 'which came first, the chicken or the egg?' Obviously it was the chicken as the egg had to be incubated, but with mechanical failure, it's sometimes a lot harder to identify the real cause from looking at the charred remains.