Piston Rings Worn Out, Time for a Rebuild

[Wildchild467]

What are the chances the rings could be broken in my engine? If they were in wrong from the beginning, would they be now ruined where I could not simply just flip them around? The thing is, the truck ran good when I first put it together, and then slowly went down hill loosing power and getting blowby. So what could have gone wrong if the problem is with the piston/cylinder assemblies?

Broken rings?
Rings installed wrong by the supplier? If so, can I orient them correctly or are the rings trashed?

Its getting late tonight but I am going to try cleaning one head up, throwing a new gasket on and torquing it down to perform a leak down test. From this I will be able to determine if I am getting leaks past the valves or cylinders. Since the manifolds are off, I will be able to see/hear the ports if they are leaking air. If I hear air hissing from deep in the engine then I know its a problem with the piston rings.

Well here goes to a long night, wish me luck and lots of patience.

 

[74M35A2]

Not looking good. We cleaned one head and block decks, and installed a new head gasket torqued to spec. Filled head intake and exhaust ports with water just prior and zero leaks. We only installed one head and took leak down data. #1 was 35%, #2 was 95%, and #3 was 15%. All air was escaping to crankcase, none out the adapter or ports. Looks like cracked rings or ring lands.

 

[rustystud]

I mentioned before that maybe the rings had not been sized to the bore. If they had not been sized then when the engine got hot and the rings expanded they would touch and have to expand against the cylinder walls. Since the cylinder walls aren't going anywhere the rings themselves would be crushed. We'll know when you remove the piston.

 

[gringeltaube]

... Looks like cracked rings or ring lands.

... or cracked cylinders? (unless you had checked them already?)

 

[74M35A2]

The cylinder kits were brand new. Not saying that means they were good. The sleeves installed fine, no excessive pressure needed and not loose. Didn't measure bore. This is now twice that broken rings have come out of the engine (if these rings are broken, but 95% leak and no visible holes in pistons tell me no rings are left in that hole). Even when removed from a tired engine, the rings should have just been worn out or relaxed tension, not broken. His most recent change was installing an LDS pump or hydraulic head and a repair to the IP flyweights. Could his IP timing be too advanced? He is also running WMO from an unknown source (city recycle center) and boosting to an unknown level (pegs 15psi gauge). My money would be on too much injection timing, too much boost pressure/fuel, or unauthorized fuel. I don't know what others are running for boost and such on WMO, and what happens if you run a hybrid LDT/S engine. At this point, I would say put the engine back to original pump, spec fuel screw/boost setting, and run authorized diesel fuel, and it would likely be fine. It was designed to originally develop just a pinch over 20hp per cylinder. If you want more, get a bigger and/or more modern engine. I'm scared if he simply re-rings it and doesn't make any changes, we'll be here again a month later. Some engines can easily handle more, I'm thinking this is one that can not. A Cummins ISB (later model 6.7L Dodge Ram or commercial F-750 truck engine) can be had in triple the power, and the same physical size, or maybe even partially smaller. Faster warm up, way more efficiency (mileage), higher top RPM (speed), and starts ice cold. Profit sharing is coming....

 

[Wildchild467]

My timing is at the stock setting.

Boost pressure is that I develop 15 PSI at 1900 RPM if the accelerator is to the floor... it would develop more at higher RPM but I only spin it up to about 2250rpm.

 

[74M35A2]

Not really bud. How have I seen your Issy boost needle repeatedly swing to the stop pin then on your 15psi gauge? You have tripled the boost (on an engine that was initially designed for none, but then allowed 3-7psi for exhaust clean up). If you want to keep it fueled that much, ok, then take some benchmark data of the boost levels others here are running when fueled with WMO, and what their corresponding blow-by (leak down) is. If you want others involved in helping you solve it, you have to bring all the facts into view. It's not fair to just say "my new rings broke". It is a little better to say, "my new rings broke, here is my setup......LDT engine w/LDS pump, +15psi of boost, WMO fueled, injectors set to 2100psi or whatever, etc....". I've turned up engines, and went through exactly this, put them back to stock, and never had to open the hood again. I'm ready to help with whatever you need. If you go back to 5psi of boost on diesel fuel, and they break again, then something is really wrong....

 

[74M35A2]

Re-ring your stock pistons, use the new liners, flush your fuel system back to pure diesel, and turn fueling/boost down to 5psi. Let it break in and run happy for a while, take leak down data once a month till mid summer. Then, start your changes, while continuing to measure leak down once a month. You'll find what is causing it.

 

[Wildchild467]

The cylinder heads are the same for LDT and LDS, the pistons are LDS pistons, the injection pump is LDS. The LDS engines are the same as an LDT with the exception of the pistons, injectors and injection pump timing. That is how they get the extra power out of the engines.

This weekend we can pull pistons and see what they look like and go from there. If the rings are broke or worn, I don't know. We can also check to make sure the rings were installed correctly because we never checked assuming they would be correct from the factory. Time will tell. My old pistons are still good, so at least we can go back to that route if all else fails. All I need to do is buy a hone to hone the cylinders and buy new rings.

 

[o1951]

Hi, some comments, worth what you are paying for them:

Dye penetrant, which is what you are doing, is NOT magnaflux. Dye just seeps into cracks that are clean and large enough for it to get into. I have checked parts with dye and seem ok, still had trouble, had them magnafluxed - find a crack not visible to eye.

Magnaflux detects cracks too small for dye penetrant. Simply put, the part is magnetized. Where there is a break in metal, poles change, so applied magnetic particles separate.

That crack sound you BOTH heard has me thinking. I would check the top of the block with straightedge. Could be a bit warped, and when head was pulled down, it cracked. When you take it off, crack closes up, and will only show with magnaflux.

Since you have it right there, I would also check top of block with dye penetrant. Highly unlikely you will find anything, but very little work.

Just checked, My formatting is holding, so I will continue.

That might explain your coolant leak, but not poor compression.

I have not seen 3 ring pistons on a diesel, but what do I know - only been working on engines for a bit over 60 years, and very few diesels. The short skirts surprised me - I like them on women, but not so much on high compression engines. Skirt reduces piston cocking in bore. Wrist pin location, conn rod design and crank have a lot to do with that.

The deposits on your new pistons were more than I expected for the little time you ran it, but what do I know - I only worked on engines that ran diesel. Your unknown WMO source could be contaminated with antifreeze or who knows what. People dump all kinds of stuff in our town recycling center WMO tank - paint thinner, liquid insecticides, acid etch - anything they want to get rid of, and have no legal place to dispose of.

How are you cleaning the WMO- you have a centrifuge, like some of the WMO experts on this site, or just settling and filtering?

I think you are running on the edge with over 15 pounds of boost and unknown fuel. I think you may find blowby is caused by ring or land damage. Kinda fits with it running good at first, and poorly later.

Best of luck, hope my post helps you.

 

[JasonS]

My timing is at the stock setting.

Boost pressure is that I develop 15 PSI at 1900 RPM if the accelerator is to the floor... it would develop more at higher RPM but I only spin it up to about 2250rpm.

I don't see any reason why an LDT couldn't do LDS power levels. However, based on your boost pressure, you are WAY WAY beyond stock LDS power levels: stock LDS boost is 4.9psi at 1600 rpm and 9.9psi at 2400.

Your rings may simply be stuck due to the excessive piston temperature forming ring carbon deposits (the original reason why Continental designed the LDS piston cooling channels).

 

[Wildchild467]

I wonder what the original piston rings are made out of vs what the rings are made out of with the new style pistons? If I pull the pistons out for inspection and find some issue, I will probably end up putting my original pistons back in.

I will need to buy a ball hone and from my research, 240 grit seems to be the one to go with for most types of rings.

 

[74M35A2]

I wonder what the original piston rings are made out of vs what the rings are made out of with the new style pistons? If I pull the pistons out for inspection and find some issue, I will probably end up putting my original pistons back in.I will need to buy a ball hone and from my research, 240 grit seems to be the one to go with for most types of rings.

Mass production piston compression rings are typically made out of iron. That is why they snap when over-expanded. Piston oil control rings are made out of steel, which is why they don't break, they just bend. You are on unauthorized fuel from an unknown source and double the factory boost pressure. I wonder if that has anything to do with it....? The WMO could have something unknown in it which is out of the cetane (ignition delay) range of the engine as configured, and therefore the combustion timing is way too far advanced, and the combustion is detonating rather than burning fast. This alone would be like me running my 6CTA8.3 @ 50psi, and wondering why it won't stay together. I would venture to guess injection timing vs RPM would need to be altered according to the cetane of the fuel you intend to use. Re-ring original pistons, reduce fueling/boost to factory spec, run 100% diesel, and report back. Should be happy as a clam for years like that. Leak down should be at < 10% on all cylinders. Then double your boost, run 100% mystery WMO, and take another leak down reading 6 months after. I'd go dollars to donuts that your issue shows its head again. Pull your pistons out, and let's see what those new rings look like. If broken, that will be two sets in a row that have been removed broken from that engine. If the aluminum ring lands are melted over the rings, then your EGT is way too high/aggressive. I really wish my paragraph formatting worked like it used to.

 

[o1951]

Mass production piston compression rings are typically made out of iron. That is why they snap when over-expanded. Piston oil control rings are made out of steel, which is why they don't break, they just bend. You are on unauthorized fuel from an unknown source and double the factory boost pressure. I wonder if that has anything to do with it....? The WMO could have something unknown in it which is out of the cetane (ignition delay) range of the engine as configured, and therefore the combustion timing is way too far advanced, and the combustion is detonating rather than burning fast. This alone would be like me running my 6CTA8.3 @ 50psi, and wondering why it won't stay together. I would venture to guess injection timing vs RPM would need to be altered according to the cetane of the fuel you intend to use. Re-ring original pistons, reduce fueling/boost to factory spec, run 100% diesel, and report back. Should be happy as a clam for years like that. Leak down should be at < 10% on all cylinders. Then double your boost, run 100% mystery WMO, and take another leak down reading 6 months after. I'd go dollars to donuts that your issue shows its head again. Pull your pistons out, and let's see what those new rings look like. If broken, that will be two sets in a row that have been removed broken from that engine. If the aluminum ring lands are melted over the rings, then your EGT is way too high/aggressive. I really wish my paragraph formatting worked like it used to.

74M35A2 is telling you the same thing I said.

Re WMO - you have to know what is in it. A town about 10 miles from me is running diesel drain oil in their dump trucks and garbage trucks. They heat, settle, centrifuge and use fine filters. Started with 50% WMO, I heard they had problems, cut to 30%. Their trucks are otherwise stock. I think you want a cetane rating of at least 40

 

[Wildchild467]

I pulled #2 cylinder... the one that had 95% leakdown. No Broken Rings.



Picture 1: The piston ring on the top is real shiny while the second ring is not as shiny.
Picture 2: The relaxed state of the piston rings as shown. the top ring measured a gap of about 5/8" while the second ring measured 3/8"
Picture 3: Just shows the rings all one one piece.
Picture 4: This is what I am most curious about. The top ring has (2) dots, while the second ring only has (1) dot. Are these backwards of what they should be? I need to research this to be sure but it seems like the (1) dot should be on the top and the (2) dots should be on the second groove. I need to pull the #1 piston out which shows only 15% leak down and see what the piston ring dots are on that one. As I said before, I never checked the rings before I put them in. They were already assembled on the piston, so they should be in order.

I also noticed that the gap where the ring goes in was looser than what I would have expected. I am talking about the height distance of the gap. Usually they should be about .0015"-.003" or so, but this one seemed a little more than that. Maybe these are not the correct rings for the pistons?

Well it is getting late and I'm confused as what could be wrong. My only thought now is these pistons are not as good as the earlier ones or the rings were installed wrong at the factory. They were not clocked correctly, that was for sure... but I fixed that before I put them in. I clocked the compression rings 180 degrees apart. When I pulled them out, I discovered the compression rings were at about 10:00 and 1:00 maybe.

 

[Wildchild467]

Oh, I took the top ring off and put it inside the cylinder to measure the ring gap. It measured about .010"

 

[rustystud]

That top ring is almost polished ! You don't have many miles on this engine correct ? That ring should have a dull finish on it if it had broken in correctly. Also, what is going on with all the carbon on the piston ? I'm beginning to think this engine was wet staking. Way too much fuel. It washed down the cylinders and actually polished the rings making them totally ineffective.
We'll see what the next piston looks like and go from there.

 

[Wildchild467]

That top ring is almost polished ! You don't have many miles on this engine correct ? That ring should have a dull finish on it if it had broken in correctly. Also, what is going on with all the carbon on the piston ? I'm beginning to think this engine was wet staking. Way too much fuel. It washed down the cylinders and actually polished the rings making them totally ineffective.
We'll see what the next piston looks like and go from there.

Why isn't the second ring polished then?

What explains the difference in ring gap in the relaxed position?

What about the ring dots on the pistons? I am thinking the rings are not in the correct order from the factory and that messed everything up. Other pistons will tell if they are in the same order.

 

[daytonatrbo]

The second ring is going to see more oil even with wash down.

 

[V8srfun]

Top rings are supposed to have more gap than the second ring because they get more heat and will expand more. The gap only matters while in the cylinder. Out of the cylinder the gap means nothing. The second ring that was not contacting the cylinder wall is most likely the culprit for so much leak down. It is obvious that the second ring was not completely contacting the cylinder wall reducing compression I would guess it was just a faulty part that wore out prematurely. Even if the rings were put in the wrong position it should not have lost so much material to where it would not contact the cylinder wall.