Rod shortens after a rebuild

[miksebik]

Hi guys, this is weird. My friend had his engine rebuilt 3 times. Every time the engine started knocking in 2000km max.. the culprit being not bearings but one/two rods shortened by 0,4 mm.
This happened everytime, the guy did flash MHD stage 2/3, did not break down the engine. He rides hard his cars, doing full throttle on highways (300kmh) etc.
But still.. have not heard of rods being shortened, in his case 3 times in a row. New parts were always used.
Do you know why would this happen? Thanks

 

[martymil]

Did he run i beam or h beam rods ?

I beam rods are cheaper and weaker but lighter and most likely the reason why they shortened due to constant abuse.

If H beam then it most likely cheap Chinese built units and you get what you pay for as no reputable built rod will ever do that.

 

[miksebik]

Well, he used oem rods. Not sure whether new or like-new.
it is weird that I have many N54 around me but have never heard of this damage due to abuse. Plus with so few km on.

 

[martymil]

Many don't check the rods prior to install, I know early rods where slightly different to later ones.

Maybe they mixed them up during install thinking they where the same.

Also different casting batch maybe.

Hard to tell after the fact.

I had my engine blueprinted and everything was checked for this very reason, even the pistons where weighed.

 

[martymil]

I find very hard to believe the rods shortened unless he was running nitrous or mega boost, if they were oem rods they would bend first.

Most likely the builder stuffed up during install, to late now after the fact to prove anything but take it on the chin and build a new engine.

Happen to me years ago with a so called reputable builder on a v8 build I was doing, these days I check everything myself and get my current
engine guy to do it again just in case I missed something.

 

[SlowE93]

Well, he used oem rods. Not sure whether new or like-new.
it is weird that I have many N54 around me but have never heard of this damage due to abuse. Plus with so few km on.

A bent rod will be shorter than a straight one.
Slightly bent rod would be my guess and can definitely be attributed to tuning and/or driving habits.