Piston destruction possible cause?

[TurboDave]

My mate has a forged GT which has covered about 10k over the past ~ 2 years, its always been a bit rattly more so than my forged engine used to but not too bad, anyway he was driving and started to hear a slight knock which got worse as he drove home, I went over to have a look and done a comp test, it was making good compression on all cylinders ~170psi. The knock was pretty heavy so I knew it had to come apart.

Got it in bits and found that a skirt (intake side) on one of the Weisco 75mm pistons has completely come away! Ringlands are not cracked and there is no evidence of excessive blow by, block still feels fine and crank/big ends are undamaged well the big end is slightly scored but thats to be expected with a skirt floating around in the sump!!

Car was only running 1.1 bar on a CT9 hybrid with all supporting mods etc and scat rods...

Anybody experienced anything like this before?

 

[spuddy]

At a guess I'd say the bore was too big for the piston, piston slap over a long period has weakened it.

But thats just at a guess.
I think I have heard of Weiscos bering prone to slap due to the short skirt, but dunno if thats of relivence in a 4E.

Looks to be alot of markings on the top edge/side of the piston, either det or rubbing, hard to tell from the pics.

 

[corofin12345]

thats mad..

 

[TurboDave]

At a guess I'd say the bore was too big for the piston, piston slap over a long period has weakened it.

But thats just at a guess.
I think I have heard of Weiscos bering prone to slap due to the short skirt, but dunno if thats of relivence in a 4E.

Looks to be alot of markings on the top edge/side of the piston, either det or rubbing, hard to tell from the pics.

I was thinking along the same lines as block.. but wanted to see if anybody said the same sort of thing, the top is slightly scored (looks worse in the pictures) but I think this was done after the skirt come away as the other pistons are pretty smooth...

I'll take some better pics as it was taken on my phone .

 

[AdamB]

If you can get hold of an internal micrometer, I would measure the size of the bore that, that particular piston came from, and then measure the rest. Also measure the piston size with a micrometer. That does look pretty mad!

Is there any damage to the cylinder walls?

 

[TurboDave]

If you can get hold of an internal micrometer, I would measure the size of the bore that, that particular piston came from, and then measure the rest. Also measure the piston size with a micrometer. That does look pretty mad!

Is there any damage to the cylinder walls?

Yeah I will defo be measuring it all up something is up....

Nope bores are fine which seems crazy with that 3/4 of a piston bashing about!!

 

[AdamB]

Does seem a bit strange, the rest of the skirt must not have been in the bore long, must have dropped straight down to the sump. Otherwise you would see score marks on the cylinder walls.

Deffo seems like a measuring jobby mate!

 

[TurboDave]

Will give it all a good measuring, got a standard motor to go in the car for now so plenty of time for that!

 

[GTti]

That's a rather catastrophic failure! What does the face of the pistol look like?

 

[billybob]

could of been the bore was too big ..as you did say it was a noisey engine ..does look like det marks on the top sides of the piston also

 

[TurboDave]

That's a rather catastrophic failure! What does the face of the pistol look like?

It looks fine! If you didnt look at the piston from the side it looks normal, no build up or marking. I think the only time the car has ever had any throttle was when I have been setting the boost etc my mate had it forged and shortly after started working away so his partner has only been driving to work and back, it should be like new inside but this failure raises some eyebrows!

could of been the bore was too big ..as you did say it was a noisey engine ..does look like det marks on the top sides of the piston also

Its going to be shitty if the block wasnt bored properly... If it was running 75mm pistons what sort of bore diameter should I be looking for?

 

[Rory]

Dave
you will get all the sizes you need from the piston maufacturer website.
certainly looks like an excessive bore size, also worth checking the ring gaps aswell.

Rory

 

[ramses974]

75 is not so standard in this block .a lot of company in my island has refused to do that for me ...the only company has done that for me as result a block failure and i loose my 4e like this.74.5 seems good if the job is well done ...perhaps 75 too if job is well done too.
That is why i prefer taking a 5efe instead of boring engine

 

[TheStarletGT]

If thats a dead set forged piston, there must have been major slapping going on "overtime" to creats stress marks on that partiqualr side of the piston. hell, maybe the conrod was installed backwards.