02 zo6 11k with 500 boosted miles. The car ate a comp 918 blue stripe, before I put the blower on. Now it ate a dual rev spring with only about 500 boosted miles. Old style yella terras (not the ultralites) stock cam with 7.4 hardened push rods. Why the hell does this car keep eating springs

 

What size cam???

Look for coil bind, and spring overheating.

What harmonic Balance are you using? Possible valve train harmonic can cause weird valve isues.

Bill

 

Stock cam

Stock balancer

????????

 

stock timing chain with dual springs?

 

Hmmm...stock cam, stock heads, stock size pushrods, so what does that leave that could have changed the valve train geometry?

 

yea I know, should have at LEAST locktighted the bolt:o


The only thing I can think of is:

The first set of comp 918's were from 2002. I know they had a few bad batches of blue stripes back in that day.

Also I've read that some REV springs from the same time period were bad too.

After my comp let loose, my brother had his old REV's from his old set-up and I just used them.

Maybe some bad springs and luck

Just glad I didn't drop a valve the first time.

That is why I went duals (for peace of mind)

 

The yella terra Pedestal mount rockers??

I got no more than the 1 1/2 turn preload as instructed????

 

Is this a question...or a statement? So the rockers are adjustables? If so, why are you running adjustable rockers on essentially a stock motor?

 

Statement.

They ship with shims to install under the pedestal (if needed).

They claim to use them to get the proper "preload" of no more than 1 1/2 turns past free play on the push rod.

I'm currently running no shim with the 1 1/2 turn preload.

 

Well, it certainly is an unknown variable in this case. If I was faced with this situation, I would buy a set of new stock rockers(not that expensive), and get rid of the unknown factor.

I was always curious about the adjustables, especially for a non-solid lifter application. After talking to a number of supporting tuners/vendors, and surveying forum members that use them....not one person could demonstrate any advantage on a stock platform...in rwhp, valvetrain stability, etc.

Good luck with your issue

 

Thanks
I installed them to keep the needle bearings (stockers) from spewing into the motor

 

I understand. The replacement rockers available from GM have been corrected, so that is no longer a concern.

 

The Yella Terra installation instructions are confusing. LS1howto then reinforces the confusion with wrong information. The shims are used to correct the rocker geometry. They shouldn't be used to set the lifter preload. I see several things that need to be examined.

1. How much preload are you now running on the lifters?

2. What is the wipe pattern of the rocker across the valve stem with the YT rockers (assuming you keep them) but good information to have to determine what is going on?

3. What is the installed seat force of the valve springs you are running and what is the required seat and over the nose valve spring force to control the valves for this setup (hopefully the blower manufacturer will have this).

4. If stock pushrods, they may be flexing and contributing to valve bounce or other issues.

The rockers you are running are pretty heavy, the new YT's are much easier to control due to their lower inertial properties. Because you will need to ensure that you can maintain control of the valve train with a blower these may not be the best rocker to use in your application. Since the cam and heads are stock, I would return to stock rockers as suggested by lucky. I would call PAC and speak to them about your application. They may recommend shimming to reduce the distance to coil bind when open to help keep spring surge in check and eliminate any valve bounce.

 

Is there a new part number for these rockers??

I may just cut bait and run with the new set of GM rockers and just upgrade to a new dual spring for safety.

 

Stock Rockers always!!!! unless you are running some AFR heads or something.... no reason to waste the money on roller rockers since they do nothing for adding extra power and most of the time they just cause problems

 

Do you let the engine warm up to at least 150° before revving the snot out of the motor? Valve spring stress at colder temperatures is severe, especially with HD / race springs. If you regularly get above 4500 RPM when the engine is cold, you're more than likely going to see spring failure long before the wear life of the part.

 

Though I agree with your comment that letting an engine warm before “revving the snot out”, is a good idea, but I disagree on the comment that any harm to the valve springs would occur from being cold. Things like piston to bore clearance at extreme cold temperatures can be an issue, but valve springs are designed to handle -40 degs and up without any issues for thousands of miles.

 

did you do a swipe pattern to check geometry?

Not sure why you guys like to beat someone up over rockers but the stockers are not the greatest when the needle bearings spit out. Yes its an easy fix but I dont see a reason to beat someone up over thier personal choices. Comp didnt used to have the rebuild kit and you had to send them to HS for $265 to get them done.. and if YT's were only $385-$425 then I can see why someone would upgrade vs rebuild and adjustables allow for other things. ... $120 more for a better rocker vs re-building a factory one wasnt a bad waste of money at the time, or even a waste at all.

 

I must have missed the post where people were beating someone up. Are you saying that replacing rockers with current stock rockers is not a good suggestion?