Piston Rings Worn Out, Time for a Rebuild

[welldigger]

That's why I was saying I would have used the new LDT rings. More tension is better, especially since you have less rings anyway with the new pistons. I don't feel like those pistons are right for our engines. I'm thinking they are for another application, but since they fit, the dealers are selling them anyway. I doubt they care how well they work as long as they get their money.

Except numerous other people have used those lds piston kits with excellent results.

 

[o1951]

If I see something that might cause issues, then I try to go after it and fix it... hence the new turbo. The compressor wheel was shot and if its not putting out the right amount of boost maybe that will make it not run as well or something. If I didn't replace something and I knew it was bad, somebody would tell me replace it. If I didn't replace it, I would have somebody telling me that I should have. I just try to explain the best I can what I'm doing so everybody can see the process and comment on what knowledge they have. We all come from different backgrounds and I value EVERYONES input.

From what you posted, I think you did the right thing with the turbo. You had to replace or if still good, rebuild. Don't want to take a chance that turbo lets loose and dumps some debris in your rebuild. As I said before, I hate in vehicle engine rebuilds. You are a young guy, so not so bad, but I am sure twice was enough and you don't want to do it again.

 

[gimpyrobb]

Except numerous other people have used those lds piston kits with excellent results.

That, and the NSN...

 

[Jeepsinker]

I don't like them. I don't want less rings in my engine.

 

[welldigger]

I don't like them. I don't want less rings in my engine.

The problem is we are reaching a point that these may be all that is available.

 

[Jeepsinker]

If it ever comes down to it, I'll take them and get a couple more ring grooves machined into them.

 

[o1951]

If it ever comes down to it, I'll take them and get a couple more ring grooves machined into them.

Jeep, the other issue is the much shorter skirts. The people who designed the engine seem to have done a good job. It has worked well for it's intended purpose.
Successfully changing their piston design is above most people's pay grade.
Pistons on a high compression engine develop quite a bit of side force. Long skirts control the force and transmit it to the cylinder. Shortening the skirt will increase the load on the remaining skirt material, and I think, make the piston more susceptible to scuffing under extreme operating conditions. I would also expect shorter engine life, although, with good lubricants, there might be a very slight power increase. Hopefully Wildchild's dyno work will give us an indication.

Racing engines used to have a trade off - short skirts weigh less, allow for higher RPM, but at some point significant compression is lost because the rings do not seal as well when the piston cocks. Due to frequent rebuilds, durability is not a factor in race engines.

 

[rustystud]

In all heavy duty diesel engines they use long skirt pistons. This has been a industry standard for decades and is still used today. Since heavy duty diesels do not rev much past 3000 RPM there is little problem with scuffing or undue wear. These are not race engines. The ability to utilize more compression rings has helped with the high compression diesels must deal with, and the longer skirt adds more stability to the piston under heavy load. You don't want a piston "cocking" in its bore.

 

[gringeltaube]

Jeep, the other issue is the much shorter skirts...

For comparison:

• 3 comp.ring-LDT piston: 4-7/8" tall + 5-1/8" skirt => total length 5-1/2"
• 2 comp.ring-LDS piston: 5.0", no skirt => total length 5.0"

G.

 

[Wildchild467]

That's why I was saying I would have used the new LDT rings. More tension is better, especially since you have less rings anyway with the new pistons. I don't feel like those pistons are right for our engines. I'm thinking they are for another application, but since they fit, the dealers are selling them anyway. I doubt they care how well they work as long as they get their money.

I saw them in a TM somewhere and I thought it was under deuce stuff. I can't remember now. I might have posted something earlier in this thread. It all seems like a blur to me now.

 

[Wildchild467]

From what you posted, I think you did the right thing with the turbo. You had to replace or if still good, rebuild. Don't want to take a chance that turbo lets loose and dumps some debris in your rebuild. As I said before, I hate in vehicle engine rebuilds. You are a young guy, so not so bad, but I am sure twice was enough and you don't want to do it again.

Exactly. If worse came to worse, My M109A3 needs new turbo seals, so I would just swap the turbo into that truck if this engine turns out to be a flop. Not making any decisions until I see how this thing runs first. I'm trying to stay positive and still keep a sense of humor about this project! haha!

 

[o1951]

In all heavy duty diesel engines they use long skirt pistons. This has been a industry standard for decades and is still used today. Since heavy duty diesels do not rev much past 3000 RPM there is little problem with scuffing or undue wear. These are not race engines. The ability to utilize more compression rings has helped with the high compression diesels must deal with, and the longer skirt adds more stability to the piston under heavy load. You don't want a piston "cocking" in its bore.

Yes, I think we are saying the same thing with different words. Long skirt.

I have no real world experience using fewer piston rings than the engine was designed for. The engine designers felt they needed 5 rings, so I suspect using a 3 ring piston with fewer compression rings is not good.

 

[Jeepsinker]

So the newer pistons are only 1/8" shorter. Should still be plenty of meat left to cut more ring grooves.

 

[WillWagner]

I looked in the manual for the break in for an engine with new pistons and sleeves. So i was just going by that. I think the manual states the whole test was something like 5 hours. I figure time in between doing things, set up and tear down of putting the truck on the dyno... it all takes time.

I was told you were a guru with the diesels, thats why I PM'ed you. I appreciate your help!

What is your suggestion on breaking in the engine on the dyno? Plan is now to towbar it to the dyno and strap it to the down. When it is strapped down, thats when we will fire it for the first time. I hear suggestions like some guys start them up, let them warm up and check for leaks for 3 or 4 minutes at a high idle and then put it under the heaviest load you can get. Now i don't have any diesel break in experience so I was just looking to follow the manual thinking it worked back then, so it must work now. Buuuut, that was then and this is now. Oils and materials change, etc which can effect the break in. What do you think we should do for the test/break in procedure. Thanks again for your input. Sorry if I ask a lot of questions. I just like to learn from people and take in what they have to say. I like knowing how things work and I think I know about how every part of this truck works. Scary! haha!

Start it and see if you have any leaks, noises, screw ups on assembly. Idling is what kills a new engine. How far is it to the dyno?

If it were in my hands, run 1 gear down, 50-60 hp at say 18-2000 rpm til the stat opens, put a little bit more power on it, 75-80 hp and run there for 5 min, pull the rpm down to peak torque and put your foot to the wood increasing 100 RPM every 5 or so mins to rated speed. Done. Be careful when using a dyno, it is WAY different than driving and it WILL find any issue you have in the engine, cooling system or drivetrain.

Just put a load in the bed and drive it on the highway for an hour.

 

[Another Ahab]

Start it and see if you have any leaks, noises, screw ups on assembly. Idling is what kills a new engine. How far is it to the dyno?

Just put a load in the bed and drive it on the highway for an hour.

You're talking diesels here, right:

- Is that because of the wet-stacking, or is it a lot more complicated?

 

[o1951]

For comparison:

• 3 comp.ring-LDT piston: 4-7/8" tall + 5-1/8" skirt => total length 5-1/2"
• 2 comp.ring-LDS piston: 5.0", no skirt => total length 5.0" G.

• That seems about right. Look at the top right picture in post 190. Both original and new pistons are standing side by side on a flat surface. It seems like his new pistons are about 1/2 inch shorter. The top of the new one seems even with the top compression ring on the old one.

 

[WillWagner]

You're talking diesels here, right:

- Is that because of the wet-stacking, or is it a lot more complicated?

Idling a new rebuild will glaze liners resulting in non seated rings. The engine will pump oil. Wet stacking is different. That would be unburnt fuel.

 

[Jeepsinker]

So, would it be alright to idle it long enough to get the engine to at least 120 degrees before loading it for break in? I just don't feel right about putting a load on a cold multifuel.

 

[welldigger]

So, would it be alright to idle it long enough to get the engine to at least 120 degrees before loading it for break in? I just don't feel right about putting a load on a cold multifuel.

Idle it long enough to make sure you have good oil pressure. Then FLOG IT!

The idea is to heat the rings up and seat them as soon as possible.

 

[WillWagner]

Pretty much.