anotherone

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In the continuing saga of trying to find out about my rough idle gm flew in an engineer. Mech said he seemed really sharp and went over all the testing so far ; everything you can think of and stuff you never heard of. He called bowling green eng designers and their conclusion is "stretched rod". He also stated this was caused by abuse when I was doing an HPDE at sebring! Now this car is an 06 a6, with rev limiter and auto that wont let you downshift if it thinks your doing something stupid. Has anyone ever heard of a stretched rod.
My service mgr says car wont let you do what engineer says and agrees with me.
Im presently going through the lemon law process and the car has been at the dealer for 5 weeks. They are replacing the rods as a goodwill gesture not waranty due to his label " abuse". Should be ready thurs. If this holds up in arbitration every car thats tracked can be labled abuse and void waranty. I immediately called the liason at gm and informed her the owners manual allows for track use and she said she would research it. Please chime in with suggestions!!!!!!!!!!!!!!!!

John Shiels

how did he know you tracked it? Were you not at drivers Education? Does he know if your car went over 80 MPH or even 60 at the track? What did you mechanic tell the rep or you? Were you there? How many miles on the car? I just don't see a rod stretching before a ton of other things even if it was abused. I am far from a engine mechanic. They may also read the forums.

anotherone

my service mgr knows I track the car with safe motorsports and why should that even matter? How the hell can you stretch a rod? I wasnt there but I sure want to see when they pull the rods and get a measurement.

davidfarmer

if your car is completely stock (including tune) you will be fine. Even the owner's manual almost encourages track use these days, but if you've modified the car, you'll have a tougher sell.

They will measure everything electronically, so there really isn't much to to see. Anyway, keep us up to date on what they find. Unless you have been revving past 6900rpm, I highly doubt you stretched any rods.

Slalom4me

My vote is that the remark was about stretching the rod BOLTS.

A rev limiter can control peak engine speeds on acceleration and missed
shifts, but it can't control mechanical overruns caused by mis-matched
downshifts where the transmisson drives the crank above the redline.

Loads on rotating componants increase as the square of the increase
in RPMs. In the case of an overrev, at some point the rod bolts exceed
their elastic limit and do not return to their initial length.

Stretched rod bolts usually result in the rod bearing shell spinning in
the big end of the rod. The rod cap no longer provides adequate
'crush' and once the tang fails to hold the shell, adios amigo.

It is interesting that rough idle would be attributed to rod (bolt) stretch.
I wonder if the premise is that the rod bearing/crank journal is pooched
and causing higher loads intermittantly?

Some engineers get the most interesting jobs.

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Slalom4me

Some background info on measurement of rod bolt stretch. For engines
that live on the ragged edge, measuring RB's is an essential part of
routine maintenance in order to enjoy reasonable engine life.

Measuring rod bolt stretch

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AU N EGL

I replaced my LS1 rods with only 3 events on. When we took them out and put them on a flat surface, we could see several were slightly bent, did not roll smoothly.

Slalom4me

Idiot-proofing within the A6 programming would seem to preclude the
possibility of exceeding redline due to a downshift.

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Slalom4me

So the axes of the small end bores were misaligned from the axes of the
big end bores?

Stock LS1 or modified for more compression, power adders & ect?

What was this bending ultimately attributed to?

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AU N EGL

Cheap rods? Who knows. Needless to say we did not put them back in.

anotherone

I absolutely know it never over reved and im stock on everything but brake pads. If it was rod bolts I think a spun bearing would lead to a drop in oil pressure. Also its smooth as glass over idle. Slalom4me you said a mouthful and a half. Im planning on a new z51 but this has me worried as I think im probably a slug compaired to you guys. Could this just be a freak one time thing?

AU N EGL

I would think so. Most of the Stock LS1, LS6 and LS2 motors are almost bullet proof.

anotherone

I really appreciate your help everyone and I certainly am hooked on hpde. This has me concerned and im sure the marketing people would freak about him alluding to hpde being abuse.

Bill Dearborn

Every one of the automakers except for maybe Porsche will say the same thing. The BMW M3 is tracked quite a bit and a fair number of owners have had their warranty voided due to overreving the engine on downshifts (seems to be more common with the M3 than with Vettes). BMW openly advocates track driving with the cars but will not warranty anything that looks like abuse.

Bill

anotherone

ouch ; this could get ugly. Im still hoping the safety systems built in are a good enough nanny to proove me innocent of the abuse charge.

Slalom4me

I agree.

Keep in mind that my comments are in response to what you wrote
about the diagnosis from BG - 'their conclusion is "stretched rod".'
For a steel rod in an otherwise stock engine this seems unlikely to me.
I'm inclined to think the bolts are more prone to stretch. But with
an unmodified rev limit and with an A6 supervising downshifts, even
bolt problems seem, dare I say it, a stretch.

To my way of thinking, the LS7 has piston speeds that explore the
limits of durability and there were reports of bottom end build quality
issues that were discovered when crate LS7's were disassembled.
(Not to mention the valve spring issues.)

But the LS2 and LS1 have more conventional piston speeds. Their
bottom ends seem pretty durable even in the face of some (to me)
exceptionally hot oil operating temps.

If you can get a straight answer, it would be rewarding to hear what
they say about their findings once they've dissassembled the engine.

Since you are on good terms with the Service Manager, see if you
can be there when the bottom end comes apart. Have your digital
camera and tripod with you - the tripod will let you get photos without
a flash and there won't be the glare. Select the 'Macro' setting for
best close-up results.

You are looking for abnormal wear patterns on the bearing faces. Also
get shots of the piston tops - if there are signs of contact, then the
valve stems and guide should be inspected.

(Edit: Changed LS6 to read LS7 as originally intended)
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anotherone

Im calling the service mgr monday to advise me when its coming apart so I can be there.

Gary2KC5

Remind them about Dave Hill's interview in Autoweek where Dave was quoted saying "occasional track use will not void your warrantee"

here is the exact verbage:

"...HUD with g-meter and track mode are all standard. Speaking of track mode, Hill says occasional weekend competition use of your Z06 won’t void the warranty, unlike the case with some other manufacturers" (Autoweek Jan 10, 2005)

You also might ask them what the comp mode is for.

John Shiels

anotherone

thats great info thanks!