Piston Rings Worn Out, Time for a Rebuild

[doghead]

Bring the Pistons with you to Findlay for the bowling tournament!

 

[74M35A2]

Hows this, If your motor blows up while dyno testing, I will donate a motor to you. Publicly stated, plenty of witnesses.Some LDS IPs were governed at 2900rpm.

I was unable to thank this post twice, even though I tried. Mostly in part that it will run 2800r's just fine, and probably run the best it ever has after that. Then, when we finally drive down to the Findlay show, he'll go more than 49mph, maybe we can actually tool along at 55mph. I'm smiling just thinking about it!

 

[74M35A2]

Does anybody have any information on what order the piston rings go on the 4 groove LDT pistons? Here is what I think so far:-Top ring #1 and second ring down #2: Bevel on the inside of the ring faces up. These two rings appear to be the same.-Third Ring down: This ring is a little thinner ring than all the others, so I know it goes here. It has a small circle stamped on the top of the ring, so I assume that circle faces to the top of the piston?-Forth Ring down: This is the oil ring. This ring is not completely smooth on the bottom (like a castle nut to exaggerate it) and I don't know what way is up. I wish I had a picture of it, but I forgot to get one this morning. So if anybody has put these in their engine, let me know... i'm confused on how to orientate the bottom ring.

The bevel info was posted earlier in this thread for you.

 

[74M35A2]

Since this is a real Dyno it will be applying a proper load to the engine. This is very important to the engines ability to stay together. If you just revved up the engine to 2800 RPM's with no load then yes it could come apart. Like Tracy (the tractor racer) told me these engines can rev pretty good with just a minimum amount of modification . So I wouldn't worry.

Thanks for the support. A rod typically comes apart at TDC of piston travel, while attempting to reverse and pull the piston weight back down from the upstroke. I can't see how engine being loaded vs not would make a difference. I have always heard people scared to rev an engine on no load vs loaded, but I think it is just a wives tale. These engines have a top end governor, and the purpose of the governor in that function is so that a safe engine speed is not exceeded and the engine does not fly apart. I really can't see a rod flying out of the engine if the oil level, oil pressure, and oil/coolant temps are correct, and the governor is working and calibrated correctly. You said you like the way my 925A2 drives with pedal to the floor and governor pulls fuel back at 2150rpm (67mph), you could basically just put a toolbox on the pedal and steer it, which I do. Yours does it too.

 

[Wildchild467]

Then, when we finally drive down to the Findlay show, he'll go more than 49mph, maybe we can actually tool along at 55mph. I'm smiling just thinking about it!

Don't get your hopes up. 5 Mph is only about 12 minutes with that trip. I don't like being in a rush all the time. I wish you kept your deuce longer so you got more experience with them. You could beat yours and I could drive mine like I always did and we could see whos lasts longer. I know diesels like to be worked but over revved is another thing I think. I know the 250 cummins dont like to be cranked up to crazy RPMs and they still do fine. After I get new rings in, then we will be able to see what it runs like for the long haul. Before we dont know if private pyle broke the rings by using too much starting fluid to get it running when uncle sam owned it... hard to say. I'm excited to get the pistons in and get it back together.

 

[Wildchild467]

The bevel info was posted earlier in this thread for you.

OK, That was post #280. Thank you.

So I know how all the rings go with the exception of the oil ring. I will have to get pictures of that and post them. It is unlike any other oil ring I have seen before.

 

[Wildchild467]

Here is the oil ring. One side is raised as shown in the pictures below. The other side is completely smooth, like a regular ring would be. So what side is up and what side is down?

 

[Wildchild467]

Bring the Pistons with you to Findlay for the bowling tournament!

Yup! We could also drop them out of the Huey in simulated bombing runs.

 

[74M35A2]

Don't get your hopes up. 5 Mph is only about 12 minutes with that trip. I don't like being in a rush all the time. I wish you kept your deuce longer so you got more experience with them. You could beat yours and I could drive mine like I always did and we could see whos lasts longer. I know diesels like to be worked but over revved is another thing I think. I know the 250 cummins dont like to be cranked up to crazy RPMs and they still do fine. After I get new rings in, then we will be able to see what it runs like for the long haul. Before we dont know if private pyle broke the rings by using too much starting fluid to get it running when uncle sam owned it... hard to say. I'm excited to get the pistons in and get it back together.

Who has a 39 page thread of their engine not running right, and being fully apart....twice?

 

[Wildchild467]

Who has a 39 page thread of their engine not running right, and being fully apart....twice?

How many times have you ran your truck out of fuel and not been able to steer it on the highway? How many times have you parked your truck and not put on the parking brake? How did that work out for you?

I needed help putting this engine back together and that is why I asked Zach to help. I know you are busy and cant help for more than a couple hours at a time. I didn't want to bother you and rush through it. When you rush, mistakes can be made.

 

[74M35A2]

0, once, and fine, respectively. I'm not sure what any of that has to do with engine longevity, but mine is still running great through all of that regardless. I said I can help load your pistons whenever you are ready to do so. You are not at that point yet. I don't have time to sit around and drink beers, I wish I did bud. Working full time, running 2 side businesses atop of that, and raising a family. You'll be there one day too when you are 40. Let me know when you have everything cleaned, honed, new rings installed, and I'll come over with the new calibrated digital 1/2" Snap On torque wrench, and we can install your slugs, and tighten your rod caps and head nuts to spec. Throw your manifolds and oil pan on, wait for your road salt to go away as you desire, and we'll tow it up to the dyno and load it however you please. Bring your pacifier.

 

[rustystud]

Thanks for the support. A rod typically comes apart at TDC of piston travel, while attempting to reverse and pull the piston weight back down from the upstroke. I can't see how engine being loaded vs not would make a difference. I have always heard people scared to rev an engine on no load vs loaded, but I think it is just a wives tale. These engines have a top end governor, and the purpose of the governor in that function is so that a safe engine speed is not exceeded and the engine does not fly apart. I really can't see a rod flying out of the engine if the oil level, oil pressure, and oil/coolant temps are correct, and the governor is working and calibrated correctly. You said you like the way my 925A2 drives with pedal to the floor and governor pulls fuel back at 2150rpm (67mph), you could basically just put a toolbox on the pedal and steer it, which I do. Yours does it too.

So why do manufacturers like Porsche and GM and Ford put in "neutral and park" rev limiters ? Also rods don't just come apart at Top Dead Center. Haven't you ever seen a rod through the oil pan ? Or the side of a block ? and trust me I have seen rods fly out of engines that had great oil pressure, where not overheated and in general where running great until the rods flew out !
Generally speaking I don't engage in "old wives tales". My comments come from my years of training and working as a mechanic. Yes I can be wrong and I will admit it when it happens, but in this I have the manufactures on my side.

 

[74M35A2]

They now have park and neutral rev limiters to prevent slam shift on the auto transmissions. With electronic throttle valve now, this is easy to do without giving the customer the old style rev limiter feeling of cutting out spark. I have seen rods through oil pans and blocks also. Usually the big end is still on the crank pin. The rod stays connected to the crank when it pulls apart, and spins around knocking and poking holes in things as the engine continues to run. Cams get broken, etc.... I've seen bottom ends of rods come apart also, but usually from improper fastening (too loose or tight). I've also seen rods break when the engine has no oil, and the big end seizes to the crank pin, and then snaps the rod apart as it tries to rotate the arm of it around. You're right, I should have been more clear. But regarding just excessive RPM, I believe the only way a rod comes apart is by tensile force since the force on it pulling apart is exponential or square of the rpm.

 

[Wildchild467]

Last night we found something interesting with the piston rings.

When we put the compression ring that came with the "new LDS piston kit" in one of the sleeves and then inserted a piston (that had no rings on it), it would push the ring all the way down the cylinder. When we did the same thing but used an NOS LDT piston compression ring, the piston could not push the ring down the bore. In other words, the force of the NOS ring was able to keep the piston's weight from sliding down the bore. The "New LDS Piston Kit" compression ring did not have enough friction to keep the piston from falling down the bore. The rings do not seem to be as strong as the NOS LDT piston rings at all.

We cleaned up my old pistons and found the wring grooves on them to be worn enough where they may not handle replacement rings that well. So now I'm looking for LDT pistons. I just don't have any faith in these "New LDS Piston Kits" at all from the lack of the extra compression ring with them and the lack of field tested experience.

 

[rustystud]

They now have park and neutral rev limiters to prevent slam shift on the auto transmissions.

They also come on manual transmissions, so your theory needs a little work. I know you have a degree in electronics but that doesn't automatically translate into a mechanics degree. Also I "have" seen rods collapse on themselves. That is not tensile forces at work. I've seen pistons and rods rammed right into the combustion chamber. I've seen rods "snap" off at the crank and the engines where still running pretty good. They just had a "lag" as the customer described it. In my almost 40 years in this field I've seen some really screwy stuff rods have done. So to come out and say "with" certainty that they only fail because of one thing is telling me you haven't seen near what I've seen. Now I respect your knowledge when it comes to electronics, now respect my knowledge when it comes to mechanics. Sometimes I stray into "Physics" and there are plenty of guys here who will correct me when I put my foot into my mouth. This is not one of those times.

 

[Wildchild467]

They now have park and neutral rev limiters to prevent slam shift on the auto transmissions.

They also come on manual transmissions, so your theory needs a little work. I know you have a degree in electronics but that doesn't automatically translate into a mechanics degree. Also I "have" seen rods collapse on themselves. That is not tensile forces at work. I've seen pistons and rods rammed right into the combustion chamber. I've seen rods "snap" off at the crank and the engines where still running pretty good. They just had a "lag" as the customer described it. In my almost 40 years in this field I've seen some really screwy stuff rods have done. So to come out and say "with" certainty that they only fail because of one thing is telling me you haven't seen near what I've seen. Now I respect your knowledge when it comes to electronics, now respect my knowledge when it comes to mechanics. Sometimes I stray into "Physics" and there are plenty of guys here who will correct me when I put my foot into my mouth. This is not one of those times.

His degree is in Chemical Engineering although is a pretty smart whipper snapper when it comes to wiring things up, I have to give him that. I have seen a bunch of his projects and he does good, no doubt. That's why this site is great. You post one question, anything and somebody might know something... or they could be a keyboard cowboy and not know anything. Even still everything is thought provoking and its helpful to me.

I have seen some pretty weird stuff as well, although not 40 years worth. 40 years ago, I was still swimming. It's no as much fun seeing this weird stuff when its your machines.

How about pistons... my ring groove on one of my original LDT pistons seems to be pushed down a little what appears to be from wear. Imagine if the ring was installed on the piston and installed in the cylinder. Then the piston ring wore a spot on the piston groove from pushing down which also caused a small bur on the edge of the piston where the ring groove is... similar to how a chain saw bar gets when it gets worn is the best way to describe it.

After I cleaned up my LDT pistons last night, I noticed some minor pitting on the top surface of the pistons. My buddy said it was from heat cycles. I can get pictures tonight and post them. Oh, another thing, my pistons were dated 10/90. I was in kindergarten then.

 

[74M35A2]

Any pitting on the top of a piston is either too much heat or mechanical indentations from a foreign object bouncing around in the combustion chamber during running. Engines that exhibit pre-ignition/detonation will typically show this. I have never seen a ring gap close unless it is loaded with carbon or the piston was dropped and it deformed the ring land. Usually a ring gap will open up with wear over time, as the ring flutters in the gap, up and down with each stroke. Is it only the top ring that won't fit? Maybe it got to hot and started to squish. Are the rings correct for the piston? You may need to start measuring parts to see what is still in spec and not.

 

[Wildchild467]

Yes, the rings are for my piston. They just seem worn on the one ring groove area. I'm stuck on if i should try to find good take out LDT pistons or if I should put these new style LDS pistons back in and hope they break in and seal up. I don't feel like spending any more time and money on this thing.

 

[74M35A2]

They now have park and neutral rev limiters to prevent slam shift on the auto transmissions. They also come on manual transmissions, so your theory needs a little work. I know you have a degree in electronics but that doesn't automatically translate into a mechanics degree. Also I "have" seen rods collapse on themselves. That is not tensile forces at work. I've seen pistons and rods rammed right into the combustion chamber. I've seen rods "snap" off at the crank and the engines where still running pretty good. They just had a "lag" as the customer described it. In my almost 40 years in this field I've seen some really screwy stuff rods have done. So to come out and say "with" certainty that they only fail because of one thing is telling me you haven't seen near what I've seen. Now I respect your knowledge when it comes to electronics, now respect my knowledge when it comes to mechanics. Sometimes I stray into "Physics" and there are plenty of guys here who will correct me when I put my foot into my mouth. This is not one of those times.

I never said they fail only for one reason. I said they fail via only a single mode (reason) when exposed to excessive RPM, and that is tensile force pulling the rod apart via piston inertia. To better view this from the opposite end of the same story, a proper running 2 stroke engine never really experiences this because the rod is always in compression force, on both directions of its travel, up and down in the cylinder. It never has to reverse the mass of a piston at high speed and pull it down, as where a 4 stroke rod does. Ever notice a 2 stroke rod has almost no meat on the big end at the crank pin and even the beam can be nearly half the size of a 4 stroke rod? Because it doesn't require it.

 

[74M35A2]

Yes, the rings are for my piston. They just seem worn on the one ring groove area. I'm stuck on if i should try to find good take out LDT pistons or if I should put these new style LDS pistons back in and hope they break in and seal up. I don't feel like spending any more time and money on this thing.

We have a perfect running DT466E and MaxxForce 7 that we are getting ready to discard at my work. Sorry, we are not throwing away the ISX or ISB's yet...