Engine builders take a look

[whitehot84]

Had the engine out to do some detailing and decided to pull the heads and have them messaged a little more. What to my dismay do I find in number 1 hole . . . . . . . . . . . .



These are diamond pistons. My engine builder says no sense in replacing one piston. It will more than likely do it again. The top ring groove is cut to close to the top. There is only about 1/16th inch of material between the ring groove and the cup.
What do you guys think about this???
He also says this cylinder was running lean. Why only one cylinder???

 

[Dabigguy]

If it was running lean, that could cause the bad piston. It can be caused by a bad injector, low fuel pressure, too much boost, improper air/fuel ratio.....

 

[TurboDave]

I've had a set or two in my hands (diamond). To be honest, those valve reliefs look to be "modidfied". That is to say, enlarged from their original cuts.

 

[pdzz]

Next question, where's that chunk of piston?? Any turbo damage??

 

[TurboBuRick]

That would be the first piston to lean out. It's the last injector in the rail to get fuel.

How was it running? Any signs of knock.

Seeing more and more pistons broke like this. Something is not right with them.

 

[naste87t]

What was the second ring gap, if it was too close it could cause Pressure to build up and contribute to failure, you have to have some sort of release between the 2 rings. normally top ring is set between .19 to .22 end gap and bottom to .21 to .26 depending on HP application.

 

[DCVING 6]

That would be the first piston to lean out. It's the last injector in the rail to get fuel.

How was it running? Any signs of knock.

Seeing more and more pistons broke like this. Something is not right with them.

Yep, seems popular with the Diamond pistons. I'll try to find the thread, but either Chris Lyons or Lonnie Diers had cut one in half and there really wasn't much meat in that area.

Seems detonation plays a huge role in this.

 

[DCVING 6]

http://www.turbobuick.com/forums/engine-tech/308688-broken-diamond-piston-pics-why.html

 

[WSLN 6]

Yep, I went to a set of forged CP's after that.

 

[87GNSteve]

What fuel pump(s) are you running? Alky?

 

[bison]

Wrong design for these engines. This is not the fist time weve seen this

 

[jasjamz]

How many miles on the engine?
How much is it raced?
How much power does it make?
What is the tune?
What fuel?
Did you buy them new?
Was the HG blown?

I have Diamonds also. Two years and no damage. This will be the third year for them.

 

[Pronto]

From the pictures in the other thread it's clear that the valve recesses cut close to the ring land. I'm by no means an expert but from everything I have read on pre ignition and detonation, sharp points and close to the cylinder wall have been mentioned at the areas where the ignition starts. So from a laymans view the shape of the piston in that area with it also being the thinest there looks like a fail waiting to happen.

Here's what looks to be a well designed piston:
http://www.youtube.com/watch?v=WbPJROAZbNc

 

[turbofabricator]

Tune up is everything. I've had the same problem with JE pistons, too. I have not had a problem with Diamond pistons, though. I hand blend all the piston edges to help reduce hot spots. (you have to do this BEFORE balancing) The placement of the top ring land is important for a few reasons. One being having enough material between the dish and the back side of the ring land, and then the highth of the land to reduce trapped end gasses. The higher the ring land the better at reducing trapped end gasses. But too high (even with adaquate material) and the ring tends to over heat. Hot rings lead to reduced tension, and possibly pre-ignition. What is the best piston ut there that will hold up to detonation and excessively lean tune up??? The answer is simple..........NO piston will live in this environment.

Although I did see an add on the 'net for "Unobtainium" pistons that are SURE to last in a ultra lean, detonating, pre-ignited enviornment. I think it was on "ewetube" with the reicarnated Billy Maze pitching them. I'll have to try them and let everyone know how good they are.

 

[whitehot84]

This engine had maybe 3 or 400 miles on it. Street driven. No track time. No other cylinders were affected. Cylinder walls were just like new. Car never was run over 25 lb of boost. I have an XFI system. The car never showed signs of detonating. The car ran super. Dyno'd 562 at the rear wheels. I still feel like the diamond design is faulty. To little material between the top ring and the bowl. I am going to have the injector tested. None of the other cylinders showed any sign of cracking.
From the looks of the other thread, I'm not the only one to experience this. If I was pounding the hell out of it I could understand but . .. . . . . . . .?

 

[Nick Micale]

These are diamond pistons. My engine builder says no sense in replacing one piston. It will more than likely do it again. The top ring groove is cut to close to the top. There is only about 1/16th inch of material between the ring groove and the cup.
What do you guys think about this???
He also says this cylinder was running lean. Why only one cylinder???

Since opinions are free, I will toss mine out concerning this situation.

Years ago when we were first pushing into the 10's, this exact problem was seen a few times, taking out no. 1 piston, which many were stock, not forged.

We even had extensive damage done to alum heads when the gasket would blow on no. 1 cylinder.

Our solution was to first modify the fuel rail for a dual feed, and improve fuel supply. The other significant item was to up the octane of the fuel used.

From these early problems, and other over the years, it appears damage like shown is not just detonation, but pre-ignition. It may start as detonation which then develops a hot spot in the combustion chamber, then pre-ignition does the real damage.

It takes high heat to melt pistons and heads which does not come from the detonation, but will develop from pre-ignition.

That style Diamond piston has thin edges which can easily heat up and become a hot spot. They also make a turbo piston that has a conventional dish similar to stock.

To help eliminate piston hot spots, we have been working with JE on a spherical dish piston that they have used on some competition applications. The first set has been installed in a Buick engine we built, but no results yet.

 

[challengermike]

what up with the 2 circles in the middle of the piston?looks like # 3 doesnt have them.Also the piston looks really clean,carbon build up differs from the others,coolant leak?

 

[LOT]

That would be the first piston to lean out. It's the last injector in the rail to get fuel.

Have to disagree with this logic. The fuel rail is pressurized with the same pressure from #2 to #1. The pressure is controlled by the reg. which is after #1. The fuel rail will have 40-50-60 or whatever psi @ all injectors @ all times. I've seen the same argument with air flow being more to the 2 back cyl.--have yet to agree with that one also.

 

[TurboBuRick]

That would be the first piston to lean out. It's the last injector in the rail to get fuel.

Have to disagree with this logic. The fuel rail is pressurized with the same pressure from #2 to #1. The pressure is controlled by the reg. which is after #1. The fuel rail will have 40-50-60 or whatever psi @ all injectors @ all times. I've seen the same argument with air flow being more to the 2 back cyl.--have yet to agree with that one also.

Yes you are right until the fuel pump starts to fail or demand becomes grater than it was designd for.. You have to take that into consideration. There becomes a point with all fuel pumps where demand surpasses supply. At that point the last fire hydrant in line will starve.

 

[87GNSteve]

Have to disagree with this logic. The fuel rail is pressurized with the same pressure from #2 to #1. The pressure is controlled by the reg. which is after #1. The fuel rail will have 40-50-60 or whatever psi @ all injectors @ all times. I've seen the same argument with air flow being more to the 2 back cyl.--have yet to agree with that one also.

Your thinking about a system that is working properly or up to demand.
If you think about it carefully, it is logical that number #1 would be the first cyl to see the effect of fuel starvation when fuel pumps start to die or fueling needs are not met.