Piston dome question?

[Captainkirk]

Ruh Roh. Might be trouble in River City, as Dad used to say...
After cleaning up the first piston dome to the luster of a somewhat dusty jewel, I moved on to the second. All was well until I got the major nasties off and saw this:

...which at first viewing, appeared to be a crack (gakk!) and then, after I calmed down some, possibly a forging flaw....but after some study by this unpracticed eye, now appears to be a line of craters probably caused by pre-ignition (detonation). A 'fault line', for all you Cali guys....if you get my drift.
Question is, is it safe to use?
Good question.
What do you experts think?

Pistons are TRW forged L-2322 STD bore (4.04)
The fault line extends from the "TRW" mark down and over the valve relief, top left.
I'm worried about a major chunk coming off in the future.

 

[jimjimjimmy]

i would not feel comfortable answering your question due to not knowing 100 % .but i do know the old trw forge pistons are heavy but darn near bullet proof and never seen one fail but im sure some have .

 

[Johnny Mac]

I probably wouldn't use it..

If this were a low compression, low RPM, street car 318, I might say hell with it... but with that dome, and the fact that you are running forged to begin with, I'd say thats probably not the case. Plus 340's aren't exactly lying around at bone yards anymore.

A chunk of piston going into a valve, then being slammed by the rest of the piston on the next stroke, is going to do more damage than a new set of pistons will cost, or at the very least, replacing that one with a weight matched piston with identical specs. do any of the others have imperfections like this??

 

[RustyRatRod]

See if it will polish out. If it will, it wasn't very deep.

 

[mderoy340]

Check the rod bearing for abnormal wear. If the bearing is good I would wet sand all the sharp edges off all the pistons. Also sand and polish the combustion chamber on the heads. You should also check the rods and see if they have stretched. Mock the heads up and clay them to check P to valve and P to head clearance, then select head gasket thickness. The tops of those pistons have a lot of meat in them.

 

[sireland67]

Hard to tell by the picture but are those domed pistons?

 

[AJ/FormS]

I havent seen many of those 340 pistons, but I have seen a lot of forged pistons. And Ive seen a lot worse come out of high mileage engines.
You know to forge pistons,they pound them into submission. That just looks like a remnant of the procedure.

 

[moper]

It doesn't look to me just like detonation... Were these in an engine? Was it running? I would take some emery cloth and polish it away. There's a lot of meat on those old pistons. I don't feel it's a crack, but I wouldn;t want to leave it there.

 

[Captainkirk]

Hard to tell by the picture but are those domed pistons?

Yes. See pics below:

 

[Captainkirk]

It doesn't look to me just like detonation... Were these in an engine?

Yes.

Was it running?

Not for quite some time. Re-using from my last build.

I would take some emery cloth and polish it away. There's a lot of meat on those old pistons. I don't feel it's a crack, but I wouldn't want to leave it there.

Pretty sure it's not a crack, as you can definitely see shiny metal on the bottom. More like a line of fissures.
Here are a few more photos:

I don't believe it's a crack...but don't want it to become one. This may have been hiding under the carbon since the last build. I never cleaned the domes last time like I am now, and quite frankly, didn't see it until after I removed the carbon.
I realize the pistons are built like a brick outhouse and can withstand a lot of punishment. The thing that worries me is the fact it's on a valve relief and close to the edge of the crown.
I may end up having the domes milled to bring down the CR anyway....
Just need to know if I should start piston-shopping.

 

[KitCarlson]

The outer perimeter edge of valve relief is a sharp protrusion. It will be a hot spot. If it is acceptable to lower compression slighty, that would be one of the first places to smooth out by rounding, and flattening the tip.

I round the ground electrode that extends beyond the center on plugs, to eliminate the two sharp corners. I also make sure the plug body is flush with head chamber, not protruding. Small details can help avoid pre-ignition on high compression engines.

 

[1970Duster]

I would get it mag checked first an foremost.

 

[moper]

Magging doesnt work on aluminum. It's a cheap piston - if it's that much of a concern then buy a new one. It seems to me like more of an affect of moisture and/or acidic build up on the dome that ate that channel. Usually you can see the white fuzzy deposits on the pistons, and when you clean them you see the pits and stains. My work PC won't show the pistures so I can't see the newer ones - but I'd still say don't sweat it, just polish it away.
Like Kit - even on brand new pistons I take the sharp edge off the valve reliefs and any surface features machined in. You can remove that whole mark and it won't hurt a thing.

 

[KitCarlson]

I think you can test for a crack using oil and a heat gun or propane torch. Wipe oil on the piston, let it sit, then wipe it off. Heat it, not real hot, but observe if oil seeps out of crack. No seep, no crack.

 

[Captainkirk]

Yesterday, I sent a long and detailed summary of what I found, including all the pictures I included on this thread. Here is the reply I received....

"I am not sure about that Kirk, doesnt look good though"

Not a vote of high confidence, but sounds like he's passing the buck on to me to make the call.
It could be he has little expertise in this area? Not sure, but I'm gonna lean on you guys pretty heavy to steer me in the right direction.
I don't want to buy new pistons if it's not essential, but I'm not a total idiot....a piston crown launching at 6000 R's can cost a whole lot more than a set of pistons.
If this was YOUR build....what would you do?

 

[moper]

If it was mine I'd be holding it - allowing for an inspection i could feel better about...lol.
If it's peace of mind - buy one piston. That design is the same as the Speed Pro. Buy one ($60?) and have them weight macthed and you're good.

 

[torkflight]

how much run time are on these pistons? are they even worth saving any of them, Have you checked the skirts? are they even round anymore?

 

[Louie70Dart]

Could that line be the result of a pour that was not continuous? I say that because if part of the aluminum cooled off even slightly, that might happen. Hopefully not talking out my blowhole. LOL

 

[69 Cuda 440]

TRW L-2322

TRW Power-Forged Piston
12.5-1 Compression
+.407" Dome

The 'old' Heavy-Slug Bastard.

That Piston can take a brutal pounding, and still keep on pushing.

Those outer line-checks are 'no big thing' to worry about. Just sand off
any high-edges for 'hot-spots' and pop them back in.

We've run many like that, without any issues.

 

[sleepyhead416]

I would not take a chance.. I'd go flat top light weight piston ... Where you find a 40 year old STD bore 340 ?

 

[Johnny Mac]

Could that line be the result of a pour that was not continuous? I say that because if part of the aluminum cooled off even slightly, that might happen. Hopefully not talking out my blowhole. LOL

considering they don't pour forged pistons...they FORGE them...you are doing exactly that. lol

 

[RustyRatRod]

Oh for God's sake. You've asked US and we've told you what to do. Then you go for outside help and want to do what they say? Like we're a bunch of frikkin idiots. I am about tire of **** like this. If you don't want to try to polish the little scratch out just throw all eight away.

 

[moper]

Now that I'm home and can see them - I'm not sure I'd run it like that. It's an old design, and HEAVY as 69 mentioned. You could probably take off the offending part on all 8... just stay away from making the margine between the pocket and the top ring land too narrow.

 

[RustyRatRod]

Either way, the "offending" area is nothing to have a heart attack over. If you don't like how it looks after polishing, mill the tops down as said. It's not rocket science. It's a very simple procedure either way. My money says if you want that compression that scratch will polish out. It does not look like a crack to me. That's what I would try first.

Now, how many other damned opinions are you lookin for?

 

[RustyRatRod]

See if this helps.