Geneqco

Hi Patrick,
I remember a comment that the JE spec sheet seemed very tight. I guess this was the issue you were referring to when you said piston squirters would be a good idea if using a windage tray?

333pg333

Well indirectly yes Scott, or at least we thought that the windage tray was a contributor to the oiling issue. Now not so sure as I wasn't running with a tray. The next issue we're faced with is if we go to another brand of piston, what gap to set? I SO don't feel like going through this again! May have to start talking to Darton themselves and see what they recommend? I am thinking the squirters may be a good idea anyway.

Rob

Man Patrick, that's really a bummer. Your car looks amazing by the way. Hopefully you'll get this figured out and back up and running in no time.

evil 944t

Patrick, .008 to .012 is going to slap around. I would try a different brand but be careful picking brands. Another mixed matched set and you'll be testing gap sizes again. Thats just how it is.

badmofofosho

I would think at .012 it would sound like Ike and Tina Turner in there.

I've heard waaaaay too many JE horror stories to use them.

I went with Venoilia for my 931 build, and they are set at .004

Hope it gets sorted without too much pain.

fast951

Patrick, Sorry to hear about this, terrible news. I have no doubt you will be up and running soon. Just a a PITA speed bump.

I have used JE pistons on my 3L car, It had old style sleeves, non-MID. As I recall the clearance was .006. When cold the pistons were noisy, but fine once heated up.

Before taking it apart, did you check the sleeves? Did they move? At this time, the piston to wall clearance, ring gaps, sleeve integrity all must be examined.

Good luck, let me know if I can assist.

333pg333

Thanks guys for all the comments. The strange thing is that even with mine set at .006 there was no slap, and the wear on the sleeves is in the middle not at the ends so that suggests that the gap is too close. If there is wear at either end of the piston then it is moving or slapping around due to too much gap, or at least that is what we understand to be the case. John I didn't disassemble it to know if there was any movement with the sleeves but my understanding was that they were in pretty tight.

Chris White

The .006" will slap during warm up at ‘normal’ temps - but you guys are still pretty hot down there!
.0045" is the point where you will start hearing slap on a dead cold engine at an ambient temp 60 degrees or below.
You are not really seeing wear on the sleeves - it looks more like metal transfer from the aluminum piston to the sleeve.
There are several possible causes and I am trying to get in touch with my rep at JE to verify the engineering info on these particular pistons.
I will post an update when more is known!

evil 944t

Sometimes the radial depth of the ring is bigger than the piston groove is deep. Its important when using different brands, to check all these specs. Sometimes suppliers change them with telling. I have these problems with MPR ring kits.

333pg333

Upon checking with the machinists my piston to wall clearance was closer to 0.007" so that should have provided plenty of room.

Chris White

I have been trying to remain positive about this…but that is just plain impossible.
At .006” it should have sounded like a cheap diesel. At .007” it should sound like a cheap diesel with 250,000 miles on it. The empirical evidence (as view from half a globe away!) points to insufficient clearance – less that .004” in reality. I have checked the spec on the pistons and rings and they are fine. (Sean’s machinist said the pistons and rings were fine also). That leaves only two possibilities – either severe overheating (I doubt that) or insufficient clearance. The lack of piston slap at cold start says that you need to look at the clearance issue again – it’s not right.
We are talking about thousands on an inch – you need to measure this at a temperature controlled environment (allowing at least a couple of hours of time for parts to go through thermal equalization) and calibrated mics.
One other note – any measuring work or machine work/finishing done without the sleeves installed in the block is not recommended. I do all that work with the sleeves installed and a torque plate installed. The sleeves are rigid enough that it ‘may’ be OK to make measurements and hone the sleeves outside of the block but I don’t do it that way and don’t recommend it.
BTW – the pistons and rings were both sourced from JE. The dimensions have been double checked, part numbers verified and engineering drawings reviewed.

Chris White

dand86951

Just to add a bit of personal experience, my engine didn't rattle or sound like a diesel even in cold starts around freezing. On first starting there was a slight mechanical noise then no different from normal.

I think the skirt coatings help knock the noise down and like I said above I think the .006 was sufficient clearance. Keep in mind most American V8s running JE pistons are running in cast iron cylinders with clearances in the .003 to .006 range and they don't scuff like this.

So if the clearances really are .007 I don't see how that could be the problem. Was the bore checked for roundness and taper after boring. Can only be done with the right equipment. I would check the other bores very carefully.

Any clearance past approximately .008 is in my opinion is going to cause other problems such as leak by and possible egging out of the bore over time due to the piston slapping around when not fully expanded.

333pg333

We will go back and do some more checking. I think that there is something obvious probably staring at us so we will continue to investigate.

333pg333

Hey Chris,

I have to agree with you here in that what has happened must point to clearance issues. I'm getting more info everyday of which I'm sure you're aware of anyway, but to be honest I don't think we'll ever know exactly why this happened. All I can say is that from everything I've gathered it is possible that the JE's expand a bit more than some other pistons (not a judgement by the way) so the next question is that if using a different brand just how much do we allow for expansion? From the manufacturers of the pistons, the generic spec's would be to cater for the lowest common denominator meaning n/a street car, not driven too hard. Then to road / track, boosted cars, followed by track only then drag cars. This is a summary, but for each step up I understand that you allow for a bit more clearance each time. So if I follow this pattern and the stock JE specs ask for 0.004 then wouldn't we look to at least 0.006 for our race oriented road turbocharged cars? Also as you alluded to, our weather down here is on average a fair bit warmer which may account for something as well?

Chris White

We do know what happened – we just what to know why!!
The pistons started to seize in the bores, as this happens the aluminum gets too hot and starts to transfer material to the cylinder walls. That’s what happened.
Now the question is why. We can rule out the pistons being the wrong size – the bores were finished to match the pistons (or at least that is the way I do it, I won’t bore the sleeves without the pistons in hand.)
The expansion is a known issue – some folks have mentioned that different pistons expand at different rates, the truth is that different alloys expand at different rates. There are 2 primary alloys used -4032 and 2618
2618 is a stronger alloy that is more resistant to detonation – but it expands more than 4032.
So you have to set up the 2618 alloy pistons with a little more clearance than the 4032 alloy, not a big difference but it is worth it for the high output engines (100-150 hp per cylinder is very high output).
One other note on your failure – you never got a serious load (heat) in to this before the failure, so I really think the actually clearance was very small. If I saw this damage after a long track session I might think that there could be other issues at play such as very high coolant temps. The fact that this has happened twice now really indicates that here is something flawed in the clearance measurement process – it ain’t adden up!

I have run quite a few engiens in the .004 to .005 rnage with no problems.