De-Lip or not?

[Turbo Performance]

Just bought 2 more engines. Got one torn down, seems to be good enough to run in my swap. Plan on re-ringing, fresh bearings & gaskets. That's it.

Question is, would you guys de-lip and coat the pistons while I have them out or just let it ride? I only ask after seeing all the piston talk in the other thread, with Fingers posting up that de-lipped pistons might actually be weaker than a stock untouched piston. Here's a link in case you missed it, good reading. http://www.duramaxdiesels.com/forum/showthread.php?t=28700&highlight=piston+bowls

Power level will stay less than 600-650hp with parallels since engine will retain stock rods.

Opinions?

 

[McRat]

I have found pistons from other engines that have a hairline cracks starting at the lip.

Delipping makes it harder for a crack to get a start, and at the same time decompresses the engine.

I'm always running delipped with factory pistons now.

 

[Iceman56]

At that power level you probably won't ever have a problem with stock LB7/LLY pistons... IDK though $800 seems like cheap insurance though:dontknow:

 

[emiller3]

I would at least get them deliped even if you don't get them coated.jmo

 

[S Phinney]

If I was going to go trough the trouble of de-lipping them I would definitely spend the money for some good coatings. Just remember everybody that does the machining process are not equal. You need a experienced one with a good track record.

 

[madmatt]

My build will be coated stock pistons,,,,, not de lipped.

 

[Turbo Performance]

IF I decide to de-lip, they will be coated. I can get the coating done for not a lot of money so it's cheap insurance in my eyes. It's sounds like catch 22 though, Pat has seen cracks starting at the piston lip while the model Fingers posted showed a de-lipped piston being weaker than factory. Maybe it's going to come down to doing a set of each and borescoping occasionally.

It's not so much of a concern at the power level I'm wanting to run but I have a feeling I may decide to turn the wick up. Vehicle is light enough I'm wondering if stock parts may last longer with less load.

 

[WolfLMM]

IF I decide to de-lip, they will be coated. I can get the coating done for not a lot of money so it's cheap insurance in my eyes. It's sounds like catch 22 though, Pat has seen cracks starting at the piston lip while the model Fingers posted showed a de-lipped piston being weaker than factory. Maybe it's going to come down to doing a set of each and borescoping occasionally.

It's not so much of a concern at the power level I'm wanting to run but I have a feeling I may decide to turn the wick up. Vehicle is light enough I'm wondering if stock parts may last longer with less load.

The piston is weaker, when you de lip.... If Finger's FEA is accurate, I would order blanks, and use his bowl design.

 

[Turbo Performance]

The piston is weaker, when you de lip.... If Finger's FEA is accurate, I would order blanks, and use his bowl design.

Only one problem with that....budget. I'll have less into the entire truck than most race builds have in a long block. I honestly don't like the idea of dropping the coin for pistons and not putting them on forged rods. Now the slippery slope has started and I've got 7+K in an engine after it's all done. I honestly won't need to make a ton of power, with a race weight target of 2000-2300lbs, 550hp gets it into the mid 9's.

Only thing I'm on the fence about is whether piston lips should stay. Although, after hearing Pat's take on the subject. They'll probably be leaving. I'm gonna take a shot and trust his experience and what he's seen, over the model Fingers posted and hope it pays off.

 

[Leadfoot]

The piston is weaker, when you de lip.... If Finger's FEA is accurate, I would order blanks, and use his bowl design.

I don't know how true it is, but my father (a machinist by trade) once told me that you can actually remove material and make a piece structurally weaker, but make a part more resistant to SPECIFIC failures.

The only thing that comes to mind is plastic moldings. Our old 250 Quads would crack the rear plastic fenders after use and abuse. We filed radius's on all the sharp corners and all but kept the fenders from cracking. Not sure if that applies here.

Yes delipping the piston makes it weaker "overall" (assuming forces can be exerted from any direction/plane), but since the forces in the cylinder only affect the piston in specific ways, it would seem to reason that machining off an area that is prone to START cracking could increase its life in certain application.

Much like shot peening (which while not removing nearly as much material as tradition blasting, does remove material) can actually increase the life of a rod by removing microscopic fractures in the material of the rod......

Or is that my old man blowing smoke up my butt?

 

[McRat]

Yes, shape and surface finish are big issues when it comes to cracking aluminum. Big radii and very smooth is the ticket.

Most FEA software is for uniform material strength, not for things like pistons. Since aluminum loses strength rapidly as temps go up over 250°F, the lip might be much weaker than the FEA model is calculating for.

Dunno though. For me, I just know what I've seen and (knock on wood) we haven't cracked a piston yet.

 

[WolfLMM]

I don't know how true it is, but my father (a machinist by trade) once told me that you can actually remove material and make a piece structurally weaker, but make a part more resistant to SPECIFIC failures.

The only thing that comes to mind is plastic moldings. Our old 250 Quads would crack the rear plastic fenders after use and abuse. We filed radius's on all the sharp corners and all but kept the fenders from cracking. Not sure if that applies here.

Yes delipping the piston makes it weaker "overall" (assuming forces can be exerted from any direction/plane), but since the forces in the cylinder only affect the piston in specific ways, it would seem to reason that machining off an area that is prone to START cracking could increase its life in certain application.

Much like shot peening (which while not removing nearly as much material as tradition blasting, does remove material) can actually increase the life of a rod by removing microscopic fractures in the material of the rod......

Or is that my old man blowing smoke up my butt?

Your father was right. Sharp edges are inherently weaker(more prone to crack formation) than edges with a radius (more material).

 

[WolfLMM]

Yes, shape and surface finish are big issues when it comes to cracking aluminum. Big radii and very smooth is the ticket.

Most FEA software is for uniform material strength, not for things like pistons. Since aluminum loses strength rapidly as temps go up over 250°F, the lip might be much weaker than the FEA model is calculating for.

Dunno though. For me, I just know what I've seen and (knock on wood) we haven't cracked a piston yet.

IMHO, the lip is prone to hot spots, which weaken the area.

I guess I am sort of retracting my earlier statement. I would de lip, for the power level TP has stated. As power goes up, compressive forces on the piston go up, there is a point at which the de lip'd piston will reach its ultimate strengh thereshold, before a stocker will.

Just know that in a pure compressive envirornment, the stock piston can take more.

 

[TheBac]

Delip if adding larger injectors, bigger turbos or above 600rwhp in general.

Dont if its going to be close to a "stock" rebuild.

Just my opinion.

 

[RENODMAX]

I think you need to be specific also as to whether you literally just want to de-lip the piston or if you are considering dropping the compression more than just a standard de-lipping.

 

[LWATSON]

When deliping pistons is cutting valve reliefs always done or only when the customer request it? I've seen an entire set of deliped pistons crack, one completely failed and the other seven had cracks starting where the valve relief and bowl meet. I would try to avoid having valve reliefs cut in the pistons if I could, I know thats not possible when using a race cam.

 

[RENODMAX]

When deliping pistons is cutting valve reliefs always done or only when the customer request it? I've seen an entire set of deliped pistons crack, one completely failed and the other seven had cracks starting where the valve relief and bowl meet. I would try to avoid having valve reliefs cut in the pistons if I could, I know thats not possible when using a race cam.

Valve reliefs have to be specified

 

[Rhall]

I say delip them. If people want to point out failures, and say something is wrong to do it that way because it failed, then they better just stay with stock engines, stock tuning, completly stock, cause you can point out failures in all stock lb7,lly, lbz, lmm, and im sure soon to be lml pistons, cut, cut and coated, forged. It does not matter, they have all failed, some sooner than others, but i would be going out on a limb here and say that stock uncut have failed MORE than any of them. Take it for what it is, not what data says it is.

 

[TheBac]

We delip pistons to remove the sharp edges of the bowl so the pistons dont start cracking.....but doesnt cutting valve reliefs adds 4 separate areas of sharp edges to the crown?
And those edges are sharper than the bowl's were, right?
And those reliefs intersect the bowl, which makes for 8 sharp corners at the bowl edge, right?
So wouldnt those reliefs make for even more spots for the piston to start cracking under stress?

 

[Turbo Performance]

For the record, I don't plan on de-lipping anymore than necessary. I'm not cutting to lower compression. The build will never make tons of boost or really have big chargers either. Just a reasonable small pair or parallel twins to get the job done.

Injectors will likely be sent to extrude hone to cut down on PW needed for the power level. Other than that, she'll be stock unless I hit the lottery.