The Alchemist

iTrader: (19)

I agree that using the block and cylinder head as a guide plate for the pushrod isn't the best option. Having a strong enough pushrod that doesn't deflect as much is the optimum choice. So my reccomendation is to go with larger diameter pushrods, larger than what most sponsors sell as upgrades, and then install them and check to see if there is a clearance issue manually turning the motor over by hand. If you have sufficient clearance through the range of motion, there shouldn't be a need to clearance the holes any more. FYI, most sponsors sell 5/16" diameter pushrods, but I can tell you that 3/8" will fit, and are considerably less prone to flex than the hardened 5/16".

TURBO6.0L

iTrader: (1)

Would I get more flex at lower RPM's when I could here it hitting? I am using 5\16" smith brothers rods.

The Alchemist

iTrader: (19)

It might not be flexing as much, but the frequency, and sound level of thee engine might make it more perceivable at lower rpms. It's entirely possible that as the rpms go up you don't hear it as much as the harmonics change.

My reccomendation, step up to 3/8" pushrods and reduce the amount of flex, I did, and my car is quieter at idle now than when it was box stock.

TURBO6.0L

iTrader: (1)

I finally got around to getting some pictures of the push rods with the witness marks on them from hitting the cylinder head pass through holes. These are hardened push rods with a black coating so it is much easier to see. I cleaned the oil off of them before the pics.



I had one more on the passenger side that was still hitting a little. Had to open the hole up some more. I colored all of the rub marks on the rods this time so if they are still hitting I will be able to tell what is new.
The easiest fix for this clearance issue is to use a 1/2 drill bit and bore that sucker out with the heads off of the car. Do it before final assembly.

TURBO6.0L

iTrader: (1)

Here are a couple more pics from 2 other engines. First one is from a bone stock 6.0L and second one from a stock LS1 with SLP rockers only. It is a little hard to see in the pics since both rods are shinny. The 6.0L only had about half of the rods with marks on them. The LS1 had marks on every rod.

White.Lightning

iTrader: (53)

Is this the cause of the "ticking/sewing machine" noise the LSx cars are notorious for???

TURBO6.0L

iTrader: (1)

I think that a lot peoples sewing machine noise comes from this. I have 3 engines with push rod witness marks. Just trying to spread the word.

White.Lightning

iTrader: (53)

Interesting. If I ever build a motor for my car, I will take notice to this.

TURBO6.0L

iTrader: (1)

The bad thing about this is that it looks like it should clear fine during assembly. I did not get the noise until the engine was in the car. The lifters must pump up a little more and change the clearance when running. Unless you can throw a hand full of cats through the hole next to the push rod in the head it is most likely going to hit.

TA_BUD

iTrader: (4)

im getting reading to do a cam install, thanks for being so thorough, and glad you had a few engines you checked out, i will be looking for this, thanks again

TURBO6.0L

iTrader: (1)

You bet. Good luck.

printmanjackson

iTrader: (1)

wow, this should be a sticky. great find

White.Lightning

iTrader: (53)

So just to re-cap. If you take a dremel and make the holes larger or more oval, that should take care of the problem? Is there any problems with making too much clearance?

The Alchemist

iTrader: (19)

Hey Andy, I wouldn't do that to the cylinder heads unless the pushrod is hitting during the normal rotation of the motor. If it's not hitting normally, then the reason it's hitting is because of flex. Go with a set of 3/8" pushrods like I have, and it will reduce the amount of flex dramatically, and quiet down that sound.

TURBO6.0L

iTrader: (1)

I would only clearance the holes if they are hitting. 1/2 drill bit is the easiest if off the car.

printmanjackson

iTrader: (1)

that seems like the easiest thing to do if you have the heads off.

White.Lightning

iTrader: (53)

Someone said above that the clearances looked "okay" during assembly with the 5/16" pushrods. Then I guess the pushrods flex under high RPM and it causes them to make contact with the head as shown in the pictures.

If someone gets 3/8" pushrods, will that 1/16" make that much of a difference? If you think about it the tight clearance that was there before is now smaller. I'm sure most all pushrods flex to some degree. The harmonics of the valve train isn't perfect and probably leads to some deflection. (I am by NO means an expert on this but I am thinking of the physics of the valvetrain)

So if the 3/8" pushrod is installed and appears to have tight clearances with the head during assembly, is it recommended to make more clearance? What is an acceptable clearance?

The Alchemist

iTrader: (19)

Adding 1/16 to the diameter of the pushrod adds quite a bit of strength, I forget the exact measurement. I posted that article basically stating that the cylinder head is somewhat of a guide for the pushrod, and I would want it to help control pushrod flex which creates a more stable valvetrain.

71-Camaro-98

iTrader: (17)

Where would you pick up a set of bigger rods when most sponsors mostly sell hardened stock diameter? And your sure that a 3/8 will have no clearance issues in LS based engines right?

TURBO6.0L

iTrader: (1)

All my ticking noise was all below 3000 RPM. I am not sure after that if it just gets drowned out by exhaust noise or actually went away. I don't think you would be getting much deflection at lower RPM's so a thicker push rod will likely not help in most of the cases I have seen. I would think if you are hitting with a 5/16 rod going to a 3/8 rod would make it worse. Rather than spend the extra money on another set of push rods just clearance the holes and fix the problem for good. So far I have only seen one person state that going to a 3/8 rod fixed their problem.