Ive had a few posts for those of you that have seen them, but today I finally took the time and pulled out my pistons. The scratches run the entire length of every bore but cannot be caught with a fingernail. The sides od every piston also have scratches, obviously most of the scratches were caused by piston-to-wall contact. There was audible piston slap on start-up so I dont think the clearance is too tight, but maybe it ran lean a bit? The scratches on the sides of the pistons are not deep. I assume the pistons are reusable? What could have caused this? TIA and I will have pics up as soon as possible.

 

Like I promised, here are pics. Some are better than others, sorry its not a very good camera.

 

So Earl or anyone knowledgeable, what does this damage appear to be? Pic 5 shows very wide scratches on the side in just one cylinder, rings? The rest all have VERY slight scratches on the sides, with the obvious scratches on front and back from where the piston rubbed. All the scratches are not deep at all and definitely cannot feel them with my fingernail. Some if not most of them run all the way from top to bottom. Is this just damage from maybe running it too hard at initial start-up before piston expands, i.e. piston slap? Lean? Incorrect ring installation? Any and all info and input would be appreciated. I am hoping I will be good with a nice hone and new rings.

 

poor tuning, pistons expanded from to much heat, those pistons are garbage, not reusable, have your bores checked, they may be out of round. You may be able to get away with a light hone and a new set of pistons/rings

 

Wait, wait, that is not the case because this engine has never seen boost. It must be something else.

 

Also I dont see why the pistons would be garbage, the skirt is just a little scuffed, the piston expanded a lot at one time (or maybe not, when I know the cause Ill know more) and should be fine now I would think. Ive seen similar cases of ptw contact and these scratches are far less worse. Anyone have any more input?

 

TTT

 

to me it looks like incorrect piston to wall clearance due to cylinder walls being out of round, you probably just slapped the new pistons without reboring and/or honing. I would not install new pistons on an engine without going over size and not having that nice round cylinder wall finish to break in the rings.

you will have to get new slugs and rebore the cylinders to the next size over. you can still use the slugs for pen/pencil holders they look nice.

 

Thanks for the input! It was bored .020 over and I even called Arias to order rings and when I did I confirmed the pistons. The block was only build in February and has a total of around 600 miles on it. I think the pistons may be reusable though because theyre not THAT scuffed, and why would it matter because its just the skirt? Is it possible it couldve been caused by running it too hard before the piston heats up therefore slamming it with piston slap to cause damage?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xxxmikenicexxx &raquo;</TD></TR><TR><TD CLASS="quote">Wait, wait, that is not the case because this engine has never seen boost. It must be something else.</TD></TR></TABLE>

You ask for peoples help, then you tell them its not it, boost or na it dosent matter, poor tuning destroys motors. Read this if you care to learn more, or stick you head in the sand and say "it must be something else" http://www.importbuilders.com/breakinarticle.htm

 

Im not trying to be an ***, but I REALLY do not understand why the hell people keep saying poor tuning to me when I have the motor running on a completely stock p72??? The motor is running stock. Period.

 

I was reading your thread and I'm a little confused. You say your engine is stock, but if I'm reading right, the block is bored .020 over?

If it is bored out and you were running the stock ECU, it looks like the car was running lean and the pistions heated too fast and expanded to the point the skirts made contact with the cylinder walls.

 

Sorry its a low compression .020 over block. But .020 over = 1.81375L which is barely larger than stock bore. I was told the stock computer is perfectly fine for breaking in a low comp 81.5mm block, and ive seen tons of people on here do it also?

 

I don't know what caused it, but it looks exactly like my pistons and cylinders when I blew my ringlands. I wouldn't use the pistons again, but the block is probably salvagable with machine work.

 

Are the correct size injectors in? The builders possibly install smaller CC ones on accident? Throwing out ideas at this point.

Either wrong injectors, too low fuel pressure, something along those lines. Something that the computer couldn't compensate.

Good luck in finding the problem as I am no help.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xxxmikenicexxx &raquo;</TD></TR><TR><TD CLASS="quote"> It was bored .020 over and I even called Arias to order rings and when I did I confirmed the pistons. </TD></TR></TABLE>
What was the piston to cylinder wall clearance when you put the motor together?

 

Appreciate the input all...It was supposedly to Arias's specs (the piston to wall clearance). I assume the right injectors are in. The pistons + exhaust ports were black and sooty, indicating a rich mixture I would think if anything? But it looks like it obviously ran lean. Could this be because its a low-comp .020 over block running on a stock ECU and I took it to redline tons of times? I thought the stock ECU would be fine for this, and even if it isnt I assume it wouldnt run incorrectly enough to cause this damage?

 

Anyone? Id really like to know if this could be a or THE cause...especially so it doesnt happen again.

Also an apology to all for my 'it must be something else'-es before, it just really sucks to hear the worst and i know some of you have probably been down this road and know what its like, sorry again though

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xxxmikenicexxx &raquo;</TD></TR><TR><TD CLASS="quote">...It was supposedly to Arias's specs (the piston to wall clearance).</TD></TR></TABLE>
Supposedly huh? Why do I not find that an odd answer to a possible clearance problem?

 

Who assembled the motor? How did you measure the piston to wall clearance? What was the measurements?

John

 

A shop in Maine did it (I bought it from a kid who lived in Maine). They built the motor to his specs. The piston-to-wall and ring gaps, etc will be what they are supposed to be because the kid used Earl's advice on most specs.

 

So you are defending that the piston to wall clearances are correct, but you never saw them for yourself? Sounds like the motor was not assembled well.

John


Modified by 1fastVX at 12:28 PM 9/8/2005

 

Maybe so, but if it were too tight the WHOLE skirt would be scuffed not just the small portion that is, correct? Im not trying to say youre not right you may be but I dont think its PTW because you could also defintiely hear piston slap on cold starts and if it were too tight you really wouldnt.

Does anyone have any input on the ECU question I posed as a possible culprit?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xxxmikenicexxx &raquo;</TD></TR><TR><TD CLASS="quote">Does anyone have any input on the ECU question I posed as a possible culprit?</TD></TR></TABLE>

Yes, I do. The ecu has enough flexibility in it to compensate for a 0.5mm overbore. There is no "0.5mm overbore computer" or anything. If the ecu can compensate for coolant and air temperatures ranging from -50 to 250, the extra 3cfm isn't going to faze it.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 1fastVX &raquo;</TD></TR><TR><TD CLASS="quote">So you are defending that the piston to wall clearances are correct, but you never saw them for yourself? Sounds like the motor was not assemble well.</TD></TR></TABLE>

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xxxmikenicexxx &raquo;</TD></TR><TR><TD CLASS="quote">Maybe so, but if it were too tight the WHOLE skirt would be scuffed not just the small portion that is, correct? Im not trying to say youre not right you may be but I dont think its PTW because you could also defintiely hear piston slap on cold starts and if it were too tight you really wouldnt.</TD></TR></TABLE>

Denial ain't just a river...

 

Maybe you had too much clearance and experienced pistonslap, which being excessive would most likely destroy the pistonskirts and bores.