I opened up my motor today and this is what I found....







Cylinder #1 with the 18% compression leakdown has a large mark on the bottom of the piston where it is contacting the cylinder head. Almost all the cylinders show evidence of the pistons hitting the head to some degree.

Either the motor was built incorectly or the ARIAS ED pistons which have a large taper are rocking in the bore allowing uneven ring wear and the piston to strike the head parallel to the wrist pin. As the ring wear worsens the degree of rocking gets larger and larger.

There is no sign of detonation, high or low AFR or any tuning issue.

This situation is similar to the one joedirtpharmd had in this thread... https://my350z.com/forum/forced-indu...ltzmotors.html He was using Arias ED pistons as well. But he states the motor was built incorrectly. The taper on the pistons could be a factor overlooked.

My machinist said this motor proboably wouldn't have lasted another day at the track.

History of the motor.... This motor has 4500mi on it. 4 track days at Sebring. The last 2 track days saw little track time due to the engine issue. The motor used conventional oil for the first 1000mi and Motul 300V for the remainder changed after every track day. This motor was rebuilt from the last failed motor I had which didn't last as long as this one. The last motor also exhibited visible rocking back and forth of the pistons in their bores. The last motor had one piston strike the side of the cylinder ending that motor. ARIAS ED pistons were also used on that motor.

The motor will be torn down next week and measurments taken to determine if it was built correctly.

 

damn man. if you don't mind, where did the motor come from?


Edit: NVM

 

Good luck Jet, hope you get it all sorted out.

 

damn man, hope everything gets worked out.

 

+1

 

wow that sucks, hope you get this worked out, and get that bad boy going again.

 

Sorry to see this Jet...stating the obvious but, can't be a coincidence that those 3 motors all used ED pistons.

Would expect JoeDirt's motor to show the same signs.

 

sucks to hear man. I know you have had a hell of a time w/ this car.

I will say though that i will sleep better tonight knowing i didnt use arias ED pistons.

 

I'm not saying it's the pistons yet but they are something we are looking into. Sam and Sharif have built plenty of motors with these pistons. I would like to see what they have to say about the pistons and the amount of play they have.

 

I checked out my GTM short block before the installation and I also noticed a minor piston rock. I have Wiseco/GTM ED pistons.

 

I don't know normal from abnormal. But when a guy who is a respected engine builder known throughout every existing sanctioned racing organisation says it doesn't look right I listen. Pistons obviously shouldn't be hitting the cylinder heads either.

 

hmm good luck with all this Larry

 

piston rock is normal,thats why you have a wristpin.sloppy bore that allows excessive rock will effect ring sealing......hmmmm

it will also push your piston to valve clearance to the limit.

 

what were the symptoms? did you hear any funny sounds when the engine was running

im curious because i have the arias ed pistons and i have strange noises sometimes

 

The syptoms were the leakdown test. High leakdown on 2 cylinders. The motor was a noisy motor from the begining. I went to Jeremy to tune the car after the motor was installed and he didn't want to tune it because he said it sounded weird. I believe "piston slap" was the term he used. He was weary of touching it for fear he would be blamed if somethign went wrong. I had a hard time convincing him to tune it. So this situation may go back to the time the motor was new leading me to believe it's the piston taper.

Quadcam had spec'd up an ARIAS ED piston I had given him that was taken out of my last motor and said it had a dramatic taper. I thought it was becasue of the low silicon alloy which has a tendency to expand more than other alloys, but Quad said it's an alloy used by many piston manufacturers and none of the other manufactuers Z applications had such a dramatic taper.

Quadcam has a degree in internal combustion engines and impresses me every day with his knowledge. So he knows more about IC engines than most people.

 

Bummer...unfortunately this is an experiance that will help everyone else in the community. I have Arias pistons myself, but they are not the ED one's and my builder also told me that "piston slap" is normal. Does anyone know if the "taper" is the same for all their pistons? Do you know yet what your putting in the new block?

 

Damn good luck with everything.

 

No, just statistically probable given they are one of the most commonly used. The fact that FP builds almost exclusively with Arias ED and has not had a built motor failure to date says something.

Sorry to hear about all the troubles Jet - but thanks for sharing and look forward to the complete teardown details. I for one won't be jumping to any conclusions until your expert has examined everything and put together a complete picture of what possibly went wrong...

 

i stongly believe this is NOT due to the pistons. That would be an easy excuse by a builder IMO, if they did their homework checking the measurements they should have no clearance issues. . PLus this arent any arias, i believe its gtm spec and have beeen used by lots of builders. IS tunning totally ruled out?

go-fast's got it right.

 

Your not referring to the non carboned area of the pistons near the intake valves right? Because thats normal fuel wash from the intake stroke.

Although I do think I see some touching on the bottom #4? piston. Thats terrible that something like this could happen. I have always wondered why the VQ community loves the arias line so much? they are hated in so many other circles, I personally would never ever run arias unless they were given to me and even then I would feel weird about it, I grew up around forged pistons and have seen more arias issues than any other brand. I would only run wiseco, or Cp..in that order of availability, anything else is just a waste of time/money.


I must say if I ever encounter half the issues you have sir, I will toss the Z sooo fast and get into something alittle more proven. Good luck with the rebuild, I sincerely hope things get better for you, this is the worst bad streak I have ever heard of...