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06-16-2011, 09:40 AM | #21 |
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Re: zddp oil additive
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. |
06-16-2011, 09:54 AM | #22 |
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Re: zddp oil additive
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. |
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06-16-2011, 10:19 AM | #23 |
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Re: zddp oil additive
[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. |
06-16-2011, 11:32 AM | #24 |
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Re: zddp oil additive
I checked with my Union Oil rep not too ago and the 30wt still has zinc in it.
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06-16-2011, 12:12 PM | #25 |
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Re: zddp oil additive
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? |
06-17-2011, 03:24 AM | #26 |
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Re: zddp oil additive
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06-17-2011, 03:38 AM | #27 |
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Re: zddp oil additive
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.
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06-17-2011, 12:11 PM | #28 |
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Re: zddp oil additive
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.
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06-17-2011, 03:54 PM | #29 | |
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Re: zddp oil additive
Quote:
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06-18-2011, 03:17 AM | #30 |
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Re: zddp oil additive
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.
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06-18-2011, 02:56 PM | #31 |
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Re: zddp oil additive
Hot gas traveling 1/3 of the way along the ring gap would cool down considerably.
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06-19-2011, 02:11 AM | #32 |
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Re: zddp oil additive
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.
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06-19-2011, 09:36 AM | #33 |
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Re: zddp oil additive
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.
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06-19-2011, 10:46 AM | #34 |
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Re: zddp oil additive
Using rotella on the engine Tom rebuilt for me AND MARVEL MYSTERY OIL!!
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06-19-2011, 06:34 PM | #35 | |
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Re: zddp oil additive
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06-20-2011, 12:57 AM | #36 |
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Re: zddp oil additive
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.
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