Hi , Can you explain what that is? " top end rod " in ls engine
A friend told me he had a ls7 motor with "blown top end rod " ? What does it mean ?
Thanks for help

 

Bad

 

You can write more ? I'm not a mechanic, unfortunately
friend said that the engine block was not cracked, I thought that it would be bad

 

In a LS-7, would dare to guess that he snapped a valve, and the lower half did some damage to not only the piston and heads, but maybe the cylinder liner as well.

Hence the ls-7 comes oem with ls7 sodium filled valves that are lighter and helps to transfer heat better than a solid valve. The glitch is that the OEM guides for them in the heads is not the best in the world for a motor that will rev to 7K, so as the valve guides quickly wears, it can cause problem with the valves head snapping off instead. Gm has come out to state that is some motors, the valve guides where not machined correctly (that the motors quickly snap a vavle), while in other cases that GM has not addressed, it just the valve guides worn out to cause the problem in motors with more milage instead.

So with the LS-7 motor since when a valve head does snap off and does major damage, there is a per-empted strike to solve the problem before the motor is blown instead.
Being that the heads are pulled, the Valves are replaced with SS valves, and new valve guide installed/fitted to the new SS valves. Do the new valve guide last longer than the OEM's, not really over all on a motor that is reving to 7K, but when the guides to valve stem fit does become loose again, less likely for the SS valve to snap a head off instead.

To be blunt, the sodum filled valves are light years better for the motor than the SS valves, and any one racing the motor will use the sodium filled valves for this reason. But at the same time, heads are pulled often enough to make make sure that the valve guides channels for the valves are still in spec (fit between the two), and any sign of out of spec tolerances and the guides (and some times the valves as well) are replaced.

So what have we learned, LS-7 is a great motor since it's a 427 in a 383 block, but will not hold up to 100K of mileage if it spends all it time being played rev ranger instead. In the case of stock motors that the guide was not correctly machine and still under warranty, GM has no problems replacing the stock motor. On the other hand, if the motor or tune was mod'ed to pull the motor out of warranty, then your own your own when a valve snaps isntead.

 

I think so too , If the friend did not remove the engine from the car, he did not check the block, how does he know that the block is not cracked ...

 

I can only guess he knows the sounds it caused when it went perhaps he could explain more of what he heard when a valve drops usually destroys the sleeve in that cylinder as well as the head.
A friend with an ls7 was at a traffic light stop waiting and a valve dropped he just pulled off to the side into a parking lot instead of shutting off the engine immediately as a result the block and one head was destroyed if it happens at wide open throttle catastrophic.

I must admit I never heard the phrase "top end rod" as there really is no rod in the top end so your friend is likely not a wrench doctor you may want to ask him what that means,

 

Thank you for your interest
I also , But I thought that more experienced people in the forum will know what does it mean
I asked him again and he said again : "blown top end rod "
I do not know if it is possible to break the titanium rod in ls7 , not in stock engine.

 

I which him well he's got his hands full poor guy.

The rods have a big end and a small end holding the piston with a wrist pin perhaps is what he is referring to as is the top part of the rod take some pics and share your findings with us.

What mods does he have.

 

mods ? probably zero ( engine is sitting in z06 ) , I guess he could used nitrous oxide, but will not admit it
if i can i take pictures

 

Yep, NOS on a motor that the piston rig gaps was not increased for the added heat that the rings will receiver, ends up with a Zero ring gap as they heat up and expand, the zero gap ring still expanding for the heat bind to the cylinder liner, and it snaps the top section of the piston ring channel up and off the piston.



The other problem with NOS on a stock motor, you can spin a lower rod bearing just as quick as well.

 

The connecting rods have two ends.....the bottom end connects to the crankshaft & the top end connects to a piston. Your friend may mean that the top end of a connecting rod at a piston was "blown" but that would also cause other major damage to the motor (piston, cylinder bore; possible the block and/or the crankshaft). The block & rotating parts will need to by inspected by magnaflux or x-ray to determine full extent of damage.