Valve to piston clearance?

[txarkitekt]

...He rattled off the order and said 7.500 length and I asked him if that was right, he said that is what the rocker arms needed...

Hmmm...

The guy I bought the rockers from said the 7.500 is what they needed, but I am just wanting to make sure he is telling me right. The cam is ground on a base circle a hair shorter than stock, is what the guy at Thunder racing told me. The heads are not being milled.

I guess the rocker arm boss where the pushord meets has a higher contact point...along with the cam having a slightly smaller base circle (think 02-04 Z06 cam), then I guess 7.500 is right. And its TR, so maybe that is a cam package that they have... Lets just hope the cam is a custom grind and its not a re-grind. But if it is a re-grind, make sure it has had it's oven time for the heat-treat on the cam lobes...

[joeoby78]

what brand rockers? 7.4" is the stock length. 7.425" for an aftermarket cam with no head work. 7.5" may compress the lifters to the point you have a solid lift cam setup and could cause you to bleed off compression and burn valves if they don't close completely.

Here are the roller rockers.
LS1- LS2 PREMIUM GOLD 1.75 RATIO ROLLER ROCKER ARMS : eBay Motors (item 290399603732 end time Mar-07-10 16:57:39 PST)

[joeoby78]

Hmmm...



I guess the rocker arm boss where the pushord meets has a higher contact point...along with the cam having a slightly smaller base circle (think 02-04 Z06 cam), then I guess 7.500 is right. And its TR, so maybe that is a cam package that they have... Lets just hope the cam is a custom grind and its not a re-grind. But if it is a re-grind, make sure it has had it's oven time for the heat-treat on the cam lobes...

No the rockers and push rods didn't come from TR, but when I was discussing the cam, which is a custom grind not a regrind, I gave him the push rod length and rocker ratio when working out the details.

[RedHeartbeat]

They don't make a mention of needing odd length pushrods in the ad. In order to require longer pushrod, the the pivot axis of the lifter would normally have to be raised if the pushrod cup location in the rocker is geometrically correct. When you get them, install one set with the stock pushrod, crank it down until the pushrod no longer spins (make sure the cam is on the low section opposite the lobe) and then tighten the bolt. You should have about 1/2 to 3/4 turn of preload until it bottoms out.

[txarkitekt]

No the rockers and push rods didn't come from TR, but when I was discussing the cam, which is a custom grind not a regrind, I gave him the push rod length and rocker ratio when working out the details.

I am really confused. All of this doesn't sound right.

First of all, the rockers should use the stock length pushrod...and those are 1.75 ratio--only .05 higher ratio than stockers--a waste of $$$ in my opinion. And a different ratio rocker shouldn't require a longer pushrod...unless blatantly specified by the manufacturer.

Second, you should have had the pushrods spec'd AFTER the cam...not before. But since the cam is ground on a slightly smaller base circle, then a slightly longer pushrod is needed.

I would run the setup, but make sure to get something in writing that shows what pushords are needed for the cam...and what pushrods are needed for the rockers--so that is something bad happens, you have documentation showing it was all spec'd out correctly.

[joeoby78]

I am really confused. All of this doesn't sound right.

First of all, the rockers should use the stock length pushrod...and those are 1.75 ratio--only .05 higher ratio than stockers--a waste of $$$ in my opinion. And a different ratio rocker shouldn't require a longer pushrod...unless blatantly specified by the manufacturer.

Second, you should have had the pushrods spec'd AFTER the cam...not before. But since the cam is ground on a slightly smaller base circle, then a slightly longer pushrod is needed.

I would run the setup, but make sure to get something in writing that shows what pushords are needed for the cam...and what pushrods are needed for the rockers--so that is something bad happens, you have documentation showing it was all spec'd out correctly.

So the rockers I got are not any better than the stock ones, regardless of the ratio?

I specifically asked the cam guy (Thunder Racing) if there would be any problem with running the those push rods/rockers with that cam and he said no. I asked the rocker/pushrod guy, Shanon's Engineering, if I would have a problem with that push rod length and the cam, and he said no, that those length push rods are what he sells to go along with those rockers.

Sorry about not going through the right procedure on push rod length, cam spec protocol. This is my first venture into heads/cam modding, that's why I'm asking the questions. Please be patient, I didn't pop out of my momma knowing all of this.

[txarkitekt]

Sorry about not going through the right procedure on push rod length, cam spec protocol. This is my first venture into heads/cam modding, that's why I'm asking the questions. Please be patient, I didn't pop out of my momma knowing all of this.

You didn't? Why not???

No worries man--sorry if I came of a little abrasive...

I'll do what I can to educate:

...First of all, the rockers should use the stock length pushrod...and those are 1.75 ratio--only .05 higher ratio than stockers--a waste of $$$ in my opinion...

Stock flat tappet rockers have a ratio of 1.7. They are actually really good. They can handle 500+ HP. For people who have high HP applications and wanna run the stockers, they just do the replacement aftermarket bushings to prevent the stock rocker's needle bearings from coming loose.

If people do switch over to aftermarket rockers, they go with a higher ratio and a roller setup, which is a stronger rocker, but the roller tip actually helps to quiet down the valvetrain. The higher ratio only really gets a slight bit more lift from the cam that is being run...

Only a few things I kinda balk at with your combo:

Larger 2.02 intake valves (1.890 stock size) + 1.75 rockers + 7.500 pushrods, and .607 intake lift on the cam (~.625 lift with 1.75 rockers)... That MIGHT come close to PTV issues. You may wanna consider the clay test to see if the intake valves are gunna be close to those pistons...

[joeoby78]

You didn't? Why not???

No worries man--sorry if I came of a little abrasive...

I'll do what I can to educate:



Stock flat tappet rockers have a ratio of 1.7. They are actually really good. They can handle 500+ HP. For people who have high HP applications and wanna run the stockers, they just do the replacement aftermarket bushings to prevent the stock rocker's needle bearings from coming loose.

If people do switch over to aftermarket rockers, they go with a higher ratio and a roller setup, which is a stronger rocker, but the roller tip actually helps to quiet down the valvetrain. The higher ratio only really gets a slight bit more lift from the cam that is being run...

Only a few things I kinda balk at with your combo:

Larger 2.02 intake valves (1.890 stock size) + 1.75 rockers + 7.500 pushrods, and .607 intake lift on the cam (~.625 lift with 1.75 rockers)... That MIGHT come close to PTV issues. You may wanna consider the clay test to see if the intake valves are gunna be close to those pistons...

Ok, I just ordered a push rod length checker so I will be taking a measurement on that part of it before I put those 7.5's in.

Did a little search on the "clay test", never heard of that before. Looks like I will be doing that as well. Have you ever done it personally? Any tips?

[RedHeartbeat]

Claying is done during engine assembly. Once the engine is assembled you should use a set of setup valve springs to check the piston to valve clearance. The setup springs are real light weight instead of strong. Put those in on the number one valve set and then roll the engine around until the pistons are near the top and the valves are opening. Put an indicator on top of the valve and push it down until it hits the valve and measure how much travel you have. .100" is recommended, .08" is marginal. Some people have run clearances less than .05" but thats really close since the length of the valve can vary as heat increases. Measure the clearance about every 1 degree of engine rotation as the piston travels to TDC. Be sure to check both the intake and exhuast valves since they have different lifts and duration and valve timing events.