Time to pull the head?
with as much travel as there is in the stock lifters, i don't think a difference on the measure of a few thousanths would bend a pushrod if his preload was set correctly to begin with. there's more variance than that between each lifter/pushrod/rocker combo, and there's more expansion than that when the engine reaches operating temp vs cold.
if his lifters were almost bottomed out, or he was running solid lifters, maybe i could see how it could.
if his lifters were almost bottomed out, or he was running solid lifters, maybe i could see how it could.
with as much travel as there is in the stock lifters, i don't think a difference on the measure of a few thousanths would bend a pushrod if his preload was set correctly to begin with. there's more variance than that between each lifter/pushrod/rocker combo, and there's more expansion than that when the engine reaches operating temp vs cold.
if his lifters were almost bottomed out, or he was running solid lifters, maybe i could see how it could.
if his lifters were almost bottomed out, or he was running solid lifters, maybe i could see how it could.
I’m not ignoring anything guys. I simply SUGGESTED to START with measuring pushrod length, to ENSURE that the rocker geometry, and cup location is kosher.
I never said that’s absolutely the problem, I simply said that’s where I’d start. You know as well as me that it’s virtually Impossible to diagnose issues like this over the net. It’s probably not the issue...but it could be...it’s a free easy simple step, and that’s where I’d start. AND THEN I’d look at at other issues once I ruled this out.
I never said that’s absolutely the problem, I simply said that’s where I’d start. You know as well as me that it’s virtually Impossible to diagnose issues like this over the net. It’s probably not the issue...but it could be...it’s a free easy simple step, and that’s where I’d start. AND THEN I’d look at at other issues once I ruled this out.
The window inside the ls7 lifter at least for preload is pretty wide and is usually the safety net that people do not realize they are relying on when they put pushrods in.
Some people like to use .080-.100 on them. Seriously thats been put here on tech many many times.
But i do agree it is a simple test, can be done without pulling heads etc, and would be a good check anyway.
Joined: Aug 2007
Posts: 24,241
Likes: 89
From: Turnin' Wrenches Infractions: 005
Why would a post like this, make you want to punch your computer screen? Chill bro...stop punching stuff.
Op changes his rockers, and now has backfiring out of the exhaust.
FIRST inclination is that the valves aren’t closing. Remember that we are working with a non-adjustable valve train. I like the guys at WS6Store, and I buy from them, but maybe something is a little off? I understand variances from hydraulic lifter preload, I really do. Install too long a pushrod in your engine, go out and run it hard and you’ll likely have the same issues.
And your suggestion is to run a diagnostic, when this is clearly a mechanical issue?
Maybe my SUGGESTION to have the op check his pushrod length is out of line?
Call me crazy, but that’s where I’d start...
Op changes his rockers, and now has backfiring out of the exhaust.
FIRST inclination is that the valves aren’t closing. Remember that we are working with a non-adjustable valve train. I like the guys at WS6Store, and I buy from them, but maybe something is a little off? I understand variances from hydraulic lifter preload, I really do. Install too long a pushrod in your engine, go out and run it hard and you’ll likely have the same issues.
And your suggestion is to run a diagnostic, when this is clearly a mechanical issue?
Maybe my SUGGESTION to have the op check his pushrod length is out of line?
Call me crazy, but that’s where I’d start...
Didnt mean to sound like a dick. If i did, i apologize. The way you said this is clearly mechanical though rules out alot of electrical issues that could be the problem also.
The window inside the ls7 lifter at least for preload is pretty wide and is usually the safety net that people do not realize they are relying on when they put pushrods in.
Some people like to use .080-.100 on them. Seriously thats been put here on tech many many times.
But i do agree it is a simple test, can be done without pulling heads etc, and would be a good check anyway.
The window inside the ls7 lifter at least for preload is pretty wide and is usually the safety net that people do not realize they are relying on when they put pushrods in.
Some people like to use .080-.100 on them. Seriously thats been put here on tech many many times.
But i do agree it is a simple test, can be done without pulling heads etc, and would be a good check anyway.
I would check compression on that cylinder at a minimum as others have suggested. With that many bearings missing the valve train really couldn't control that one valve and it may have tagged the piston. I assume you looked down the pushrod hole for needle bearings, but a pushrod sitting on a bearing wouldn't be good either. If the compression is good then at least the mechanicals should be good and I would tend to look more at fueling and spark if compression is OK.
Not sure I saw it, was the bad rocker on the intake or exhaust valve?
Not sure I saw it, was the bad rocker on the intake or exhaust valve?
Thread Starter
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
It was the frontmost rocker on the passenger side - #2 cylinder - exhaust. We put a magnet down that pushrod hole and pulled out one needle bearing.
Last edited by RevGTO; Dec 29, 2017 at 06:50 PM.
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If I read this right it was doing it before the rocker swap and after. I'd look elsewhere than the rockers, especially considering they are stock units and locations should remain the same. The hydraulic lifters will make up for small variances in push rod length needed, if any was needed, and I'd say there isn't any in this case.
The bent push rod is a bit more telling, the pop out the exhaust and the bent pushrod (assuming it was on the exh valve?) would make me think the exhaust valve or spring is suspect and the mixture is lighting off with an exh valve that isn't sealing or is open. That or maybe you're loosing valve control at upper RPM (weak springs).
First thing I would do is pop the rockers off and stick air pressure in that hole and listen for air to come out the tail pipe. If you're capable of viewing data check your basics, fuel trim etc, but I doubt that'll be the culprit. I have cars come in all the time with whacked out fuel trims and they don't backfire or sneeze. Backfiring or sneezing is always a timing issue, or a valve open during the light off of the mixture (timing off or valve not sealing same thing)
The bent push rod is a bit more telling, the pop out the exhaust and the bent pushrod (assuming it was on the exh valve?) would make me think the exhaust valve or spring is suspect and the mixture is lighting off with an exh valve that isn't sealing or is open. That or maybe you're loosing valve control at upper RPM (weak springs).
First thing I would do is pop the rockers off and stick air pressure in that hole and listen for air to come out the tail pipe. If you're capable of viewing data check your basics, fuel trim etc, but I doubt that'll be the culprit. I have cars come in all the time with whacked out fuel trims and they don't backfire or sneeze. Backfiring or sneezing is always a timing issue, or a valve open during the light off of the mixture (timing off or valve not sealing same thing)
If I read this right it was doing it before the rocker swap and after. I'd look elsewhere than the rockers, especially considering they are stock units and locations should remain the same. The hydraulic lifters will make up for small variances in push rod length needed, if any was needed, and I'd say there isn't any in this case.
The bent push rod is a bit more telling, the pop out the exhaust and the bent pushrod (assuming it was on the exh valve?) would make me think the exhaust valve or spring is suspect and the mixture is lighting off with an exh valve that isn't sealing or is open. That or maybe you're loosing valve control at upper RPM (weak springs).
First thing I would do is pop the rockers off and stick air pressure in that hole and listen for air to come out the tail pipe. If you're capable of viewing data check your basics, fuel trim etc, but I doubt that'll be the culprit. I have cars come in all the time with whacked out fuel trims and they don't backfire or sneeze. Backfiring or sneezing is always a timing issue, or a valve open during the light off of the mixture (timing off or valve not sealing same thing)
The bent push rod is a bit more telling, the pop out the exhaust and the bent pushrod (assuming it was on the exh valve?) would make me think the exhaust valve or spring is suspect and the mixture is lighting off with an exh valve that isn't sealing or is open. That or maybe you're loosing valve control at upper RPM (weak springs).
First thing I would do is pop the rockers off and stick air pressure in that hole and listen for air to come out the tail pipe. If you're capable of viewing data check your basics, fuel trim etc, but I doubt that'll be the culprit. I have cars come in all the time with whacked out fuel trims and they don't backfire or sneeze. Backfiring or sneezing is always a timing issue, or a valve open during the light off of the mixture (timing off or valve not sealing same thing)
or, perhaps the valve stem is slightly bent and the exh valve isn't seating all the way.
Sounds like what has possibly happened here. OP you may need to pull that head a slap a valve in it. Lap the new valve in and run it. After a compression and or leak down check of course to verify there is a valve issue.
01ssreda4 posted a lap in vid recently if I recall correctly if you wanna search his posts and check it out, in case you're unfamiliar with lapping valves.
Thread Starter
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
Yep, I'm familiar with valve lapping in old school applications. Not so much in the LS context, though I think I did see the thread about it.
Leakdown test was done on the affected hole this morning. Came in at 13%.
Tomorrow I have some time to mess with it, so I'm thinking to do two more procedures:
1. Scan individual cylinders for misfire at speed.
2. Check other pushrods.
The key thing to remember here is that there were no driveability issues (backfiring, rough idle) while the bad rocker was in there. It was only after the replacement that all these issues arose.
Leakdown test was done on the affected hole this morning. Came in at 13%.
Tomorrow I have some time to mess with it, so I'm thinking to do two more procedures:
1. Scan individual cylinders for misfire at speed.
2. Check other pushrods.
The key thing to remember here is that there were no driveability issues (backfiring, rough idle) while the bad rocker was in there. It was only after the replacement that all these issues arose.
Joined: Aug 2007
Posts: 24,241
Likes: 89
From: Turnin' Wrenches Infractions: 005
I hate when your mind does that, forces you to accept something as 100% truth. It makes finding the real truth so much more difficult because you chase shadows. My single best piece of advice is stop focusing on that rocker arm. You have a misfire, find it. No more, no less. Prime example is you did 1/8th of a leakdown test. If you had the rocker out of your mind you would have done it complete and have much more valuable info to work with. My .02.
Thread Starter
Joined: Nov 2003
Posts: 6,216
Likes: 236
From: Wichita KS / Rancho San Diego
Scanned for misfires yesterday and found random misfires on multiple cylinders. The counts went up as the car got progressively warmer, which you can notice just by driving it. We also redid the torque sequence on all the rockers to make sure we got it right. Still having rough idle and backfiring at higher rpms.
Next stop is to inspect for bent pushrods and needle bearings in all the holes on bank 2, and if we find the former, then on all 8.
Next stop is to inspect for bent pushrods and needle bearings in all the holes on bank 2, and if we find the former, then on all 8.
When looking for misfires you cannot just say we have some and go on. There is so much info there. You need to look at history and current misfires. Target them and see if you can single out what is causing the issue there. Then look at the cyls with the worst misfires. Adding a cam will cause some "misfires" but normally a tuner will soften them up. If you show misfires but no service engine soon light, then the tuner turned them off...which is never good.
If you are having issues at wide open, then stay away from it during testing and until youve figured it out. All of your testing can be done at idle and mild throttle.
If you are having issues at wide open, then stay away from it during testing and until youve figured it out. All of your testing can be done at idle and mild throttle.