355 Pistons

After recently rebuilding the engine in my 355 it was discovered that the pistons removed were 18 grams lighter than the replacement pistons obtained. Both pistons came from Ferrari and were manufactured by Mahle.

Any of the guru's out there heard of a change in piston weight from early 95 to late 95?

This is rather alarming to say the least...Curious to know when and where the change occured...


*I know someone will ask....---Engine was rebuilt as a result of finding a valve stem seal in the pan during a routine oil change, after discovering the seal, I disassembled further and found more seals floating around. Keep in mind no seals were missing from the heads I understand the guides were replaced prior to my ownership and this was verified correct. Turns out that not only did the car have at one time bad guides, it also had a cracked header and a bad cylinder liner. I decided to go all the way through it, glad I did, all is well now and I know what I have.....
Thanks to Dan/David(Ricambi), Dave (Scuderia Rampante), Gary (Sharpe Racing)

 

Very interesting, thanks for posting your whole experience. As for the heavier pistons, that can't help con rod stresses and bearing loads at 8500 rpm...

 

Wow..... so when the guides were redone, no one bothered to locate the missing guide seal pieces ????

As for the extra piston weight.... were the crank,rods and pistons rebalanced before reassembly???

 

Scary stuff huh?

 

I guess when I was building my engines, I was going the extra mile !!!

 

how the heck can the pieces find their way to the pan? pistons boke?

 

It happens... here's some of what was found in my oil pan:

 

Daniel is right........... I believe they go through the passages that allow the valve train oil back into the sump (dry sump that is ).

 

You are exactly correct.... They went through the oil return tubes all the way to the pan.
We estimated about 5-6 of these were found. The tiny springs and rubber pieces had travelled through the entire engine and I was about to spin a bearing as a result. It was such a mess that a full rebuild was the only logical solution! I do not understand how it happened, I guess they may have previously failed, or were left over from a previous repair....I'd like to know, I guess it doesn't matter much now....

 

Gothspeed,

To answer your earlier question, yes all pistons from Ferrari although heavier were within a gram or so and were sent away for an accurate balance.

They were matched up perfectly...

 

great to hear!!! At the RPMs the 355 spins, balancing is a great thing !!

 

Last year I had to have a rebuild on my 355 as it suffered a couple of oil ring/liner wear and failure issues. Nothing broke exactly but it was burning oil heavily and degraded very quickly.

On taking it all apart, the skirt of the piston which was in the liner that showed the most wear showed some wear on the oil hatching on it i.e. there wasn't hardly any hatching left at points. So a new piston and ring set was purchased, other one just had a new ring set as piston was as new.

At the time we were told that the only difference was red or green dot, for both liners and pistons. Mechanic thought he'd ordered the wrong one's at first as what came thru was significantly different to what was already in there. Mine was a 2.7 1996 spider, dealers ordered two more pistons in and they both came in like the first they supplied, i.e. different to current engine items. They did however have an old piston that was originally new but they had messed with it, drilling etc, murphy's law this was exactly as per the one we needed and matched the one's in the car. At this point they then appreciated we weren't mad and finally got off their backsides and had one last look in the parts bins, as luck would have it they had misfiled one piston and it was indeed the one we needed, phew!!

The worrying thing is what happens if the story repeats for that car or anyone else, that will be 8 new piston sets sir....!!!!! Or maybe as you guys found, you simply get the pistons rebalanced and be done with it. The piston crowns were quite different though so I'm guessing there could be slight volumetric differences as well in the chamber even if you did get weights balanced?? Obviously this is based on what we were experiencing, I'd be curious to hear from jimfxr on his thoughts and experience, i.e. was the crown etc different??

We found all part numbers etc were unchanged, merely red dot or green dot, no-one could explain but there was indeed as you guys found clear differences between the current supply and what was in the engine.

ps jimfxr, as above, like yourself we had header failures and I'm reasonably confident imho this could be a large factor in the oil rings/petrol wash/liner failure. Ferrari should have replaced the headers as recall items long long ago, worse though is to still be making them with the same insufficient grade of material as i think they still do!!!