Scuffed piston top land

[tttype]

Ideas on cause of this ?

 

[SHADOWII]

What's the cylinder look like? Check the pin, press fit or slip(too much or out of round)? Piston cracked in the ring land? Rod straight and properly installed?

 

[TurboDave]

That's pretty ugly!! Bent rod???

 

[tttype]

Looked into this more.

#6 scuffed in 3 O clock position ( viewing piston from top passenger side ) thats toward front of engine
#4 between 2 - 3 oclock ( front)

# 3 9 oclock position , viewing from Drivers side top, ( rear )
#1 9 oclock ( rear ) just starting

only common thing I can see is that scuffing is below intake valve on each cylinder .

no cracks visible in ring lands.
pins are pressed into rods , no obvious play in pins.

wear marks on cross thatching are differest in each cylinder.

Rods would have to be removed to check straightness ?
lay on flat surface & compare ends for parralel ?

Engine only has a couple thousand miles on it when #3 exhaust lobe went flat, necesitating the current teardown.

 

[TurboDave]

Are the rods stock or aftermarket? If aftermarket, do they have the proper offset for running in an offcenter motor?

 

[tttype]

rods are stock

 

[SHADOWII]

Is the crank walking? Maybe from the converter not having enough play?

 

[Chuck Leeper]

Been a while.. rods in backwards?

 

[tttype]

Checked rod orientation & all seem to be offset towards the inside of the journals. So looks like they were installed correctly.
The 2 steel main caps have picked up a bit of iron , so maybe the caps were moving around.
Heres a diagram of scuff locations if that helps diagnose anything.

 

[Chuck Leeper]

What do the rod brgs look like? Are they showing signs of wear on 1 side? Pics?
Also, what do the plugs look like?
Injectors good?
Pins pressed to correct location?
I can't read the stamping on the piston. Is this an over bored engine?
What kind of pistons are they?
If rebuilt, what are the piston to wall clearances? All the same? [I'd measure them and see, just to eliminate that possibility]
A pic of the main caps would be good, too.

Given you are seeing signs of cap walk, and the damage is on the weak side, [pin bore], of the pistons, I'm wondering if detonation is in the mix.

 

[tttype]

Rod bearing pic, right is front of engine, top row is #5,3,1
Pistons are .030 over TRW forged

Only the front main looks unusual. Starting to think the cam was really dragging with the one bad lobe. Looks like it put alot of pressure on the front main bearing.


Plugs all looked ok.

Pins pressed to correct location? Please explain ?

Probably did see more knock than usual, as was running the version of XFI that they latter announced that the knock retard didnt work.

 

[Chuck Leeper]

"Probably did see more knock than usual, as was running the version of XFI that they latter announced that the knock retard didnt work"

Did all your data logs show no retard activity? NE knock shown?

Been a long time since I used pressed pins. AIRC, the pin is pressed with a special alignment tool, to prevent piston damage. The tool presses the pin in to a particular place. If it's not in the right place, with regards to the inside of the pin boss, when the rod is put on the crank, the small end of the rod will be forced to one side, and ride on the boss. [Someone else may remember this more accurately..]
Some heat the small end, and push the pins in that way...
Did U check crank end play B4 U took it apart??

 

[HelloBozos]

I've seen the ""exact"" same thing ,multiple piston scuff's... ,KDK in Orlando,FL did the builds,After 3 total rebuilds (motors all let go at 1/2 track),I sued him an won!! I then changed machinist, Problem solved!!



Good luck!

 

[tttype]

Chuck
We didnt notice anything unusual about KR untill the anouncment came out. Then realized no advance was being pulled.
Will upgrade to newer XFI version this spring.
Didnt measure crank end play at disassembly. Just got crank back from polishing & dont want to put it into the old bearings to test.
You think I could reuse those pistons & be more carefull tuning ?

Hello Bozos
Any idea what caused your scuffing ?
You reuse the same block, crank, rods etc on the build that lasted ?

 

[bison]

Xfi showed KR in the log but the timing didnt change which would have been very obvious in the log. If it didnt show KR then it wouldnt have mattered.

 

[turbofabricator]

One word. DETONATION. Piston rocked toward the rod offset and did that.

 

[tttype]

Location of scuffing makes sense with the rod offsets.
Is this a common result of knock ? Mechanical friction ,rather than a corner melting or pitting of top surface ?

Now, can these pistons be reused ? #6 shown in top pic is worst one.

 

[m233roller]

There are several things that could cause your problem and they have been mentioned here. Don't know about the rest of your pistons but I WOULDN'T use the one in your pic. Another reason I like full floating rods, less apt to have that much scuffing from severe detonation.

 

[turbofabricator]

Hit it with some scotchbrite and then repost the pic. Hard to tell how much material is missing. That part of the piston doesn't carry the thrust load, so it might be OK to run again. Shoot a few pics of the skirt and carefully check the top ring lands for distortion. If the cost of pistons is gonna kill ya, then you gotta do what you gottta do. Might be time for new rods, though. K1 rods are pretty cheap these days.

 

[m233roller]

ttype, if that scuffing was due to severe detonation you had better be on your game checking ALL the ring lands for distortion and or cracks. Iv'e seen this happen acouple of times in the years Iv'e been into these cars and pistons that looked about like yours. Pistons were checked and cleaned up with a scotchbrite and run again with poor results. Soon as the engine started seeing boost afew times BINGO busted ring land problem. Your engine and your money but I know what I'd do. If you end up with new pistons and rods FLOAT the rods.
PS. If and I say if those pistons are out of the engine in your signature you are making some pretty serious horse power and stock off set rods are known to tip over ever so slightly under big H/P.