[kyle_blake]

Hi

These are some pics of inside my 400 engine with domed pistons.


trw-l2279f30

I actually think parts of the piston are disintegrating?

Just curious if anyone has seen this type of appearance before?

They are flaking pic 1 and flaking2 pic. Other pics are just other pistons in engine.

leak down is perfect, compression perfect, perhaps just detonation or pre-ignition at some point .

[steve25]

Please post up some good close up pictures of your plugs looking up into there nose.

[kyle_blake]

these were the plugs at the time.

[Lee]

The usually-sharp edges of the valve reliefs appear to have been smoothed over. I bet those pistons were coated at one time, and the coating is coming off. Coatings don't adhere well to sharp edges, and rounding them over helps.

[kyle_blake]

Wow, what are coatings? I have not learned about assessing a piston's "ability" and then choosing to coat it? can you tell me more about it? thanks for offering a reason.

kyle

[Lee]

https://swaintech.com/race-coatings/.../piston-domes/

https://www.cerakote.com/shop/cerako...coat-oven-cure

https://www.enginebuildermag.com/201...s-even-better/

https://www.polydyn.com/pistons

I've personally have used Techline coatings, applied myself, for about 20 years. Available to the public since, at least, the 90's.

https://techlinecoatings.com/

[Brian Baker]

What CC heads are you running and what octane fuel are you running?

[P@blo]

Those L2279 are the same old school pistons I have in my 400. My heads are 6X though putting me around 9.5:1 compression.

You run the #64 heads if memory serves me correctly Kyle? If the dome is 10cc and your heads are ~87cc your compression may be too high. I get over 10:1 with a zero deck but check my numbers either way.

[Shiny]

I don't have any direct experience with this but it's interesting so fun to speculate.

It doesn't look like any particles are sluffing off as the surface remains flat but could still be something happening at grain boundaries. I agree it could also be a coating failure but I would expect adhesion loss and flaking if that was the issue. I don't see this.

I am only guessing but could be "decoration" (selective deposition or build-up of deposits) or selective chemical attack at grain boundaries (ie a corrosion mechanism). I think it's inconsistent with mechanical stress (ie fatigue) as the damage appears uniform and boundaries are "sharp" (no deformation) but maybe thermal cycling could cause this??

Intergranular attack of aluminum alloys is a "known" thing and would be my first guess. Here's an example:

https://www.nace.org/resources/gener...ular-corrosion

"Many aluminum base alloys are susceptible to intergranular corrosion on account of either phases anodic to aluminum being present along grain boundaries or due to depleted zones of copper adjacent to grain boundaries in copper-containing alloys."

Here's another blurb:

https://www.totalmateria.com/page.as...ite=ktn&NM=187

"Intergranular Corrosion

Intergranular (intercrystalline) corrosion is selective attack of grain boundaries or closely adjacent regions without appreciable attack of the grains themselves. Intergranular corrosion is a generic term that includes several variations associated with different metallic structures and thermomechanical treatments. Intergranular corrosion is caused by potential differences between the grain-boundary region and the adjacent grain bodies.

The location of the anodic path varies with the different alloy systems. In 2xxx series alloys, it is a narrow band on either side of the boundary that is depleted in copper; in 5xxx series alloys, it is the anodic constituent Mg2AI3 when that constituent forms a continuous path along a grain boundary; in copper-free 7xxx series alloys, it is generally considered to be the anodic zinc- and magnesium-bearing constituents on the grain boundary. The 6xxx series alloys generally resist this type of corrosion, although slight intergranular attack has been observed in aggressive environments."

[Skip Fix]

The last flat top 455 TRW I bought as a single for mock up was flaky looking in one of the valve reliefs. Almost like some peeling off.

[JLMounce]

To me, these really look like oily film deposits. Some of your plugs look to have some oil deposits on them and in the threads. Do those plugs correspond to the pistons you're seeing this on?

[kyle_blake]

Thanks everyone.

1 - Yes #64 heads, 87cc but probably milled a bit over it's years
2 - 94 Octane
3 - Yes the plugs seen were removed from engine as the main running plugs since rebuild
4 - I do not know if pistons crown reaches top of deck or if it's in down in the hole a bit, I suspect it's flush with the crown top. Based on those pics.

I have since, put new plugs in. o2 sensor and set A/F so it is fine although jetting was never that far off from a holley's out of box settings.

Actually some of the piston pics, if one looks along the cylinder wall they do look like detonation has pitted them. Not sure if anyone else sees that. I think that these pistons are at end of life it appears, pitting and parts of the crown edge are chipping off. Hmmm

I was going to ask TRW or whoever owns them what they think but can not locate a email address for their rep.

Added some more pics.

[Mike Davis]

I'd throw 2 cans of seafoam in the tank and drive it a bit then see what it looks like. Just my .02

[dataway]

Now and then during the course of my metal working I've come across aluminum alloys that react very strangely to surface work hardening, developing that scaly hammered look. Has happened on different pieces of the same alloy (but different batches).

No idea what the cause is, but in my case I suspect it's something to do with the tempering or hardening process. Doesn't seem to effect strength in any way but does effect how it welds ... kind of like anodizing. Could also be due to something I've done to it but didn't remember ... heating etc.

[kyle_blake]

Yah, true $80 bucks in seafoam might clear out all the deposits and give a true 100% accurate look which could be giving us false alarms on cylinder crown edge being detonated. Compressions is 178-190 across the board. I suppose the pistons have been around since 1988 with one removal during rebuild. There was no coating on the side like you see on new pistons, on the skirt I'm talking.
At least when I saw them in the varsol tank at the shop in 2000 with my video camera. would if be standard practice to then recoat them? That is to be expected as the coat material should come off during break-in from the skirts but didn't know from factory they had coating on the top? I certainly don't hear any detonation and never really have except for the odd odd time going up a hill and always run 94. It runs 34 or 36 degrees total all the time with no audible. Sometimes though you don't hear it as I've learned.

I just assume she's lived a long life although not many miles. Yah could just be standard piston break down scaly hammered look.

thanks everyone. i'll report back on seafoam in the coming months. if any one else has any other ideas to clean out maybe one piston. I'm all ears.

In the old days we'd run transmission fluid down carb and run it out that way.

[steve25]

Piston top cleaning = rubber gloves, Kerosene soaked rags and lots-o- elbow grease!