Mine felt like it was hitting the rev limiter at 5k rpm whenever I adjusted them too much.
lifters again?!?!
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Melting Slicks
Joined: Mar 2004
Posts: 2,141
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From: Pittsburgh Pa
lifters again?!?!
ok so i finally got my pcmforless tuned computer in the mail today... so i put it in fire it up and give it some hell to see how it runs.. well it ran smoother till i got it out on to a major road and i flog into it.. it gets to 5k rpm and makes a weird noise backfires and starts missing.. i am like awe crap.. i limp it home to find that it bent a pushrod.. pull the intake and the lifter exploded out the top....they have over 3k miles on them. i noticed that only a few were still pumped up and holding the valves open.. so i run and get a new lifter spider retainer and throw some pushrods in it.. fires up but doesn't seem to have all it had before?!?! i need to drive it to new york friday and don't feel like having to pull a head for a bent valve... check engine light is now on? why am i having constant lifter issues with this?? free reving seems fine underload doesn't pull as hard.
Le Mans Master
Joined: Feb 1999
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From: South Carolina
St. Jude Donor '03 & '05
Originally Posted by FD2BLK
what lifters are you running? I know I have read quite a few post on the Comp "R"s blowing out the retainer clip. I am running stock GM lifters and run her up to 6500 with no problems.
I have some of the original, supposedly good, Comp Cams R's. I am useing the factory GM lifters for my engine now. Just too many bad posts of Comp Cams R lifters with the new retainer.
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
How far are you pre-loading them? I think that CC recommends a pretty minimal pre-load on most of their lifters, such as a maximum of an 1/8th turn (around .005") or less.
Le Mans Master
Joined: Feb 1999
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From: South Carolina
St. Jude Donor '03 & '05
Originally Posted by Corvette Kid NC
How far are you pre-loading them? I think that CC recommends a pretty minimal pre-load on most of their lifters, such as a maximum of an 1/8th turn (around .005") or less.
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Large Impressive Member
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Originally Posted by pr0zac
speed pro's and mine is an lt4 so i can't really adjust the preload
Le Mans Master
Joined: Feb 1999
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From: South Carolina
St. Jude Donor '03 & '05
What cam are you running? I had a friend put a Hot Cam in his factory LT4 and there were no issues. The valve springs in the LT4 are the same springs sold inthe hot cam kit.
Do a compression check and verify springs are good by physically pushing on them with your hands. I had to do this once as it wasnt visible.
Do a compression check and verify springs are good by physically pushing on them with your hands. I had to do this once as it wasnt visible.
Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
Ok,
I am thinking you may have changed something in the geometry the LT4 non adjust rockers can not handle. I installed a set of LT4 rockers on an LT1 a while back with a HC and was not sure if they would work so I observed how much preload was applied when the rockers hit the torque spec (24 pounds or something like that) It was 3/4 of a turn past zero lash, about the same as many use for preload on a std set of rockers. A quick check for you would be to loosen one of the rockers while that cyl is at TDC comp stroke and note zero lash then note how much preload before it reaches TQ, this should give you a pretty good idea if you are close.
I am thinking you may have changed something in the geometry the LT4 non adjust rockers can not handle. I installed a set of LT4 rockers on an LT1 a while back with a HC and was not sure if they would work so I observed how much preload was applied when the rockers hit the torque spec (24 pounds or something like that) It was 3/4 of a turn past zero lash, about the same as many use for preload on a std set of rockers. A quick check for you would be to loosen one of the rockers while that cyl is at TDC comp stroke and note zero lash then note how much preload before it reaches TQ, this should give you a pretty good idea if you are close.
Last edited by FD2BLK; Mar 16, 2006 at 01:08 PM.
Advanced
Joined: Feb 2006
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From: Reading Pa
If the preload is correct the plunger should never contact the clip. I believe you either have a spring bouncing or a clearance problem. I'm betting on weak springs. The other possibility is that you are running heavier oil and pumping the lifters up, this is probably less likely.
Large Impressive Member
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Originally Posted by FD2BLK
Ok,
I am thinking you may have changed something in the geometry the LT4 non adjust rockers can not handle. I installed a set of LT4 rockers on an LT1 a while back with a HC and was not sure if they would work so I observed how much preload was applied when the rockers hit the torque spec (24 pounds or something like that) It was 3/4 of a turn past zero lash, about the same as many use for preload on a std set of rockers. A quick check for you would be to loosen one of the rockers while that cyl is at TDC comp stroke and note zero lash then note how much preload before it reaches TQ, this should give you a pretty good idea if you are close.
I am thinking you may have changed something in the geometry the LT4 non adjust rockers can not handle. I installed a set of LT4 rockers on an LT1 a while back with a HC and was not sure if they would work so I observed how much preload was applied when the rockers hit the torque spec (24 pounds or something like that) It was 3/4 of a turn past zero lash, about the same as many use for preload on a std set of rockers. A quick check for you would be to loosen one of the rockers while that cyl is at TDC comp stroke and note zero lash then note how much preload before it reaches TQ, this should give you a pretty good idea if you are close.
Safety Car
Joined: Dec 2002
Posts: 3,655
Likes: 24
From: Charleston SC
Originally Posted by Corvette Kid NC
Don't forget though, although the LT4s are not adjustable, the LT1s are. And the stock preload setting for them is one full turn, which is approximately .041". So assuming the LT4 is preloaded somewhere close to that, we're talking about a preload that is several times what Comp Cams recommends for their lifters. I would not make any mods to an LT4's valve train w/o changing it to adjustable lifters. A set of ARP 1.75" studs and some CC Pro Mags or other quality rockers and he'll be good to go.
Chris,
I installed a set of 10mm stud LT4 rockers on my HC LT1 motor and at the proper TQ spec it was about 3/4 of a turm past zero lash. While they may not be adjustable you can stil check the amount of preload the same way using a torque wrench. Just wait for Zero lash then note how far the TQ wrench turns before proper spec, in my case 3/4 of a turn. If he barly gets to zero lash and is at TQ then he will know there is a problem.
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From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Originally Posted by FD2BLK
Chris,
I installed a set of 10mm stud LT4 rockers on my HC LT1 motor and at the proper TQ spec it was about 3/4 of a turm past zero lash. While they may not be adjustable you can stil check the amount of preload the same way using a torque wrench. Just wait for Zero lash then note how far the TQ wrench turns before proper spec, in my case 3/4 of a turn. If he barly gets to zero lash and is at TQ then he will know there is a problem.
I installed a set of 10mm stud LT4 rockers on my HC LT1 motor and at the proper TQ spec it was about 3/4 of a turm past zero lash. While they may not be adjustable you can stil check the amount of preload the same way using a torque wrench. Just wait for Zero lash then note how far the TQ wrench turns before proper spec, in my case 3/4 of a turn. If he barly gets to zero lash and is at TQ then he will know there is a problem.
Le Mans Master
Joined: Feb 1999
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From: South Carolina
St. Jude Donor '03 & '05
Originally Posted by Corvette Kid NC
I've never seen the stock LT4 set-up so I can't say that I really understand. All of the non-adjustable rocker systems I've ever dealt with were just that. Years ago I used to race a 351 Cleveland in a stock car. These had non-adjustable pedestal style rockers. Since I was a totally low buck racer back then, I couldn't afford to have the heads machined to accept adjustable big block Chevy rockers, which was the hot set-up on these. When I installed a wild cam, I'd shim the rocker mounts to reduce preload. Good God, how these things ever held together is beyond me but they did. I only ever blew one in several years of dirt track racing. And when that happened I had it geared down trying to set fast time. I had been so close but it didn't happen that night!
Safety Car
Joined: Dec 2002
Posts: 3,655
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From: Charleston SC
Here is a pic that shows the difernce from Jim Masons web site. The rocdkers preses into the 10mm taper untill it reaches the specified TQ. This may be a good refence for the original post as well
http://www.hashmarks.com/techtips/valve_springs.htm
http://www.hashmarks.com/techtips/valve_springs.htm