Push rod length / LS7 lifter preload sanity check
Discussion
There seems to be a lot of misinformation out there concerning LS7 lifters, especially since they now get used in LT1 engines...so indulge a quick sanity check please! I've changed my heads and the 7.400" pushrods I've taken out appear too long. The pushrod length checker gets zero lash at about 9+2/3 turns, so ~7.2835". There seems to be disagreement about LS7 lifter preload, but my options seem to be:
7.375" --> ~.092" preload
7.350" --> ~.067" preload
I'd convinced myself the larger preload figure was better given the LS7 lifter apparently has a large travel (4.22mm = .166") and GM spec preload as 2.09mm (.082"). I guess that's the gospel...there's lots of s
tty numbers floating about though (I think from people counting turns of the rocker bolt and using the wrong multiplier), and my existing pushrods are only .025" longer than what I've ordered but seem awfully tight (to the point of no lateral play in the rocker and the valve stem looks to start move from closed).
7.375" --> ~.092" preload
7.350" --> ~.067" preload
I'd convinced myself the larger preload figure was better given the LS7 lifter apparently has a large travel (4.22mm = .166") and GM spec preload as 2.09mm (.082"). I guess that's the gospel...there's lots of s
tty numbers floating about though (I think from people counting turns of the rocker bolt and using the wrong multiplier), and my existing pushrods are only .025" longer than what I've ordered but seem awfully tight (to the point of no lateral play in the rocker and the valve stem looks to start move from closed). Have you run the engine at all ?
IMO measuring zero is fine with engine off and working from there. But anything else would really need done after the engine had run for a bit, as the lifters can bleed down, pump up, do all sorts of things that may affect how it looks or feels after the engine has been off for some time and when you've allowed the lifters to come back to rest by removing the pushrods.
IMO measuring zero is fine with engine off and working from there. But anything else would really need done after the engine had run for a bit, as the lifters can bleed down, pump up, do all sorts of things that may affect how it looks or feels after the engine has been off for some time and when you've allowed the lifters to come back to rest by removing the pushrods.
I can depress the springs in some lifters by pushing on the pushrod with my hand, but not others. Is this normal, or is it time for heads off again and new lifters?
E: I guess that's where the strangeness was coming in when I was torquing down the rockers - the valve spring was squashing instead of the lifter spring. I'll try turning over the engine a few times to see of the lifters loosen up, but failing that I guess I'll consider changing the lifters. If the lifters are just stuck pumped up then I suppose they'll feel less horrible with the incoming shorter pushrods, though the ones I tried are only a smudge long (about .117 preload using the 7.400s).
E2: turned over the engine a few times and the lifters softened up, so I'll just run the things...I think the 7.375" ones I've ordered should be ok (and the 7.400" ones I have feel borderline ok once the lifters have evacuated). What noone seems to say about measuring pushrods is to make sure they aren't pumped up when you take your measurement.
E: I guess that's where the strangeness was coming in when I was torquing down the rockers - the valve spring was squashing instead of the lifter spring. I'll try turning over the engine a few times to see of the lifters loosen up, but failing that I guess I'll consider changing the lifters. If the lifters are just stuck pumped up then I suppose they'll feel less horrible with the incoming shorter pushrods, though the ones I tried are only a smudge long (about .117 preload using the 7.400s).
E2: turned over the engine a few times and the lifters softened up, so I'll just run the things...I think the 7.375" ones I've ordered should be ok (and the 7.400" ones I have feel borderline ok once the lifters have evacuated). What noone seems to say about measuring pushrods is to make sure they aren't pumped up when you take your measurement.
Edited by Mud_ on Monday 11th July 18:00
Mud_ said:
I can depress the springs in some lifters by pushing on the pushrod with my hand, but not others. Is this normal, or is it time for heads off again and new lifters?
E: I guess that's where the strangeness was coming in when I was torquing down the rockers - the valve spring was squashing instead of the lifter spring. I'll try turning over the engine a few times to see of the lifters loosen up, but failing that I guess I'll consider changing the lifters. If the lifters are just stuck pumped up then I suppose they'll feel less horrible with the incoming shorter pushrods, though the ones I tried are only a smudge long (about .117 preload using the 7.400s).
E2: turned over the engine a few times and the lifters softened up, so I'll just run the things...I think the 7.375" ones I've ordered should be ok (and the 7.400" ones I have feel borderline ok once the lifters have evacuated). What noone seems to say about measuring pushrods is to make sure they aren't pumped up when you take your measurement.
It is not unusual. As said, no point working by feel here as the engine is not running and oil has not been pumping things up etc...although even after shutdown they can bleed back down where the valves are open and springs pushing against the lifter.E: I guess that's where the strangeness was coming in when I was torquing down the rockers - the valve spring was squashing instead of the lifter spring. I'll try turning over the engine a few times to see of the lifters loosen up, but failing that I guess I'll consider changing the lifters. If the lifters are just stuck pumped up then I suppose they'll feel less horrible with the incoming shorter pushrods, though the ones I tried are only a smudge long (about .117 preload using the 7.400s).
E2: turned over the engine a few times and the lifters softened up, so I'll just run the things...I think the 7.375" ones I've ordered should be ok (and the 7.400" ones I have feel borderline ok once the lifters have evacuated). What noone seems to say about measuring pushrods is to make sure they aren't pumped up when you take your measurement.
Edited by Mud_ on Monday 11th July 18:00
stevieturbo said:
It is not unusual. As said, no point working by feel here as the engine is not running and oil has not been pumping things up etc...although even after shutdown they can bleed back down where the valves are open and springs pushing against the lifter.
Noted...I guess it'll clatter a bit on first start as the lifters will want their oil back! If it gets torn down again it will be new (performance) lifters to go with a big cam. OP, the rockers have to be tightened down in sequence. Also, once the preloads have been set there's no point in rotating the engine and setting them again as that'll bugger it all up.
As for the amount of preload to apply, I'd consider that the hydraulic lifters are designed to compensate for wear in the valvetrain. Either preload you mentioned should be fine unless you plan to wear out your valvetrain in a hurry :-)
As for the amount of preload to apply, I'd consider that the hydraulic lifters are designed to compensate for wear in the valvetrain. Either preload you mentioned should be fine unless you plan to wear out your valvetrain in a hurry :-)
Boosted LS1 said:
OP, the rockers have to be tightened down in sequence. Also, once the preloads have been set there's no point in rotating the engine and setting them again as that'll bugger it all up.
As for the amount of preload to apply, I'd consider that the hydraulic lifters are designed to compensate for wear in the valvetrain. Either preload you mentioned should be fine unless you plan to wear out your valvetrain in a hurry :-)
I made sure the rockers being torqued were on the base circle of the cam if that's what you mean. Spinning the engine was just to soften the lifters, and seemed to work well enough. As for the amount of preload to apply, I'd consider that the hydraulic lifters are designed to compensate for wear in the valvetrain. Either preload you mentioned should be fine unless you plan to wear out your valvetrain in a hurry :-)
I keep reading that the LS7 lifter 'wants' .050-.100" preload, which seems like trying to hit the middle of the .166" range. I've not seen a range from GM, just a target of .082", so the tolerated range may be balls. People say things like bias low to prevent piston-valve contact, or bias high to ensure you get full lift, but again not sure if this is really missing the point of a hydraulic lifter.
LS7 lifters should be easy given the comparatively tiny travel on performance lifters! I realise I'm probably fretting over very little, but the 7.400" pushrods just felt a bit too tight (no lateral give in the rocker)...but that was at least in part due to the locked lifters. I'll run the 7.375" pushrods and I'm sure it will be ok.
IMO the worst thing you could do is have too little pre-load, then if the lifter does bleed down a little, it wont be able to float and bash things about.
At least with a lot or in the middle you should never be able to see a scenario where there is lash instead of pre-load.
Whether it works like that in real world, I dont know...but it makes sense to me lol
At least with a lot or in the middle you should never be able to see a scenario where there is lash instead of pre-load.
Whether it works like that in real world, I dont know...but it makes sense to me lol
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