jimxms

I think I'll just start with the pushrods. If that fixes my knocking noise then I may get adventurous and replace the springs and trunnions using a combination of compressed air and jumping the engine to get the pistons up high (as a backup).

If the pushrods don't fix the knocking, then it needs to go to a professional engine builder and I'll just buy a big box of forged/reinforced parts and tell them to fit it all.

Internets_Ninja

well poop

B-17/B-25 CC

Didn't use compressed air when we changed the valve springs on my '78 Trans Am years ago. What we did was stuff a small rope into the cylinder and then brought the piston up-rope kept valve from dropping when spring keeper and springs removed. Worked for all 16 valve springs.

JHEBERT

I just heard the vid, that’s a DOD lifter failure. Sometimes they will destroy the lobe on the cam. Pay attention to the lifter and it’s roller when you remove it. Half the lobes on a dod cam suck for power production anyway, just keep telling yourself “I need a cam, I NEED a cam”

It can be done without pulling the engine, but you’re going to need a very competent technician.

jimxms

You say that with such conviction...and that worries me

If the lifter has failed, wouldn't you expect to see play in the pushrods or rockers though? I couldn't get any movement out of them at all.

JHEBERT

I’m sorry, my intent was not to worry you further...but surely you must know that noise was not caused by a SLIGHTLY bent pushrod. The noise occurs at 1/2 the rate of crank speed. You can replace the pushrod, but the noise will still be there.

Sad part is that it did not have to happen, if only GM where not forced into the dod setup on vettes. It’s stupid, charge the guzzler tax and get on with life GM. Engines don’t often fail in c7s, but when they do, it’s this or a thrust bearing. Not counting the lt1 piston failures because of boosted c7s running too much timing.

I wish we could make it easier for you, but you’re on the other side of the pond.

raylo

What is it about these DOD lifters that makes them susceptible to failure? While I like the great highway mileage it just isn't worth this complexity for a couple MPG.

Higgs Boson

I always disable AFM/DoD in all my GM cars and trucks since 2011 and have never noticed a change in MPG.

That's the sad part. Something about it helps with the EPA tests but in real world use it doesn't do anything.

robert miller

Op do what Ant is telling you

sjhanc

That shiny area on the edge of the #5 could be where carbon deposits came loose and got hammered onto the cylinder head where they stuck, causing a carbon knock that is heard, or not, depending on engine temp. There are additives in Chevron gas here in the US to prevent carbon buildup on valves and cylinder parts (Techron). I was a GM engine tech for many years, carbon knocks were common when an engine always got light use, or low grade gas, additives sprayed through the intake MIGHT help, but I always removed the heads for cleaning at a machine shop. Enough carbon buildup can beat the rod bearings out and possibly collapse piston skirts.

I had one pickup truck 454 engine with so much carbon damage that replacing the engine was the only fix. The owner came to see for himself, he told me that his farm hands had been driving it only on his farm for 10,000 miles. I got him a warranty engine to make him happy after advising the dealership owner that good will was more important than blaming him for his problem.

If you can, turn your borescope to see the head above the shiny spot on the piston, the carbon might still be there.

raylo

My parents had DoD on a 2006 Impala SS and it ran perfect its whole life. That car was a bit of a beast... too much motor in a sorry FWD chassis.

It'd be hard to test 100% in the real world but if you could do a long flat highway drive in Eco and then repeat the same course in Tour (M7 car) I suspect you would see a little better MPG with DoD on in Eco. But I agree it isn't worth it.

DomLS3

If you're replacing the springs, you might as well go ahead and stick a cam in there too.

jimxms

I've said f**k it and am going on a spending spree at Vengeance Racing today. I'm gonna build the snot out of this c7.

jimxms

Just rinsed the credit card on this lot:

Vengeance Racing Forged Drop-In LT1 Pistons
Vengeance Racing Stage 3 Camshaft
BTR .660" Lift Dual Valve Spring Kit w/ Ti Retainers
Vengeance Racing 3/8" Hardened Pushrods
C5R Timing Chain
Smith Brothers Bronze Bushing Trunion upgrade
CompCams Phaser Limiter (5450)
GM VVT Cam Bolt
GM LS7 Lifter Set
GM Lifter Trays
GM MLS 6.2L Head Gaskets
GM LT Exhaust Gaskets
DOD Delete Plug Kit
ARP Cylinder Head Bolt/Stud Kit

New NGK LTR7IX-11 6510 plugs
Amsoil 5w30 Signature Series



My wife is SOOOO happy with me right now...

raylo

Holy cow, Batman. Are you pulling the motor? I did a cam swap on my 1994 Camaro with the motor in the car and it was a PITA, even though it came out well. Had to move the a/c condenser out of the way and lower the oil pan to remove the front cover. Not sure if this gen LT1 has the same front cover/oil pan interface. Are you doing it yourself? T'would be quite a project.

eboggs_jkvl

Those can be used with the heads off to get the lifters in/out but not the valves.

Elmer

jimxms

I've found a couple of local racing engine builders, so I'm going to check them out later this week and get a feel for who is the most competent.

Sadly I just couldn't pull off a job like this myself. I don't even have a proper garage on my house

Bill Curlee

If you want to check for a collapsed lifter, you have to put EACH CYLINDER PISTON at TDC so the lifters for that cylinder are on the base circle of the cam. Then you can check for excessive valve train clearances on that cylinder, & see if the lifter will collapse when you press down on the back of the rocker. You have to do that for Each cylinder. Just start with #1 at TDC and follow the firing order for every 90 degrees of crank rotation.

A good lifter will remain FIRM and not collapse. If you are replacing the pushrods, why are you going with 3/8 dia. If you can use a 5/16 dia push rod, up-grade to the larger diameter. If you change cams, you will most likely need a different length push rod. You will need to check with the cam manufacture and or use a push rod length checking tool to be absolutely positive of the correct length.

IF,,, you change cams, you WILL NEED to re-tune the ECU. SO, add in another thing to spend money on..

I have done several valve spring and valve seal replacements on C5 LS1/6 and LS2 engines. Ive used the compressed air method and the close line (COTTON ROPE) in the cylinder method of holding the valves in place. The compressed air method does work but you need to use a rubber mallet to hit the valve retainer (it breaks the valve retainer loose from the retainer locks) to make it easier to dislodge the retainer from the retainer locks. Then it is real easy to press the retainer down with the valve tool and not unseat the valve. The compressed air form a compressor holds the valves in place well.

The rope trick works very well and will not harm anything. I use a STRAP WRENCH to turn the harmonic balancer and that works very well and is very easy to turn the engine crank very precisely. When all of the spark plugs are out, the engine turns over by hand fairly easy.

I have to agree with "JHEBERT" That very SLIGHT BEND in the push rod is NOT causing that noise. You have other valve related issues (collapsed lifter or something else)

If you use a Mechanics Stethoscope you can place the metal rod on a non moving area above each valve rocker and be able to PIN POINT exactly where that noise is emanating from. Pin pointing the exact cylinder and or valve can save you a LOT of time and maybe money.

I also would eliminate ALL other easily to eliminate sources of noise (like removing the drive belts... )

Let me know what you think..

Bill