1979 L48 lifter preload
Thread Starter
Pro
Joined: Aug 2007
Posts: 707
Likes: 31
From: Pitman NJ
1979 L48 lifter preload
Team,
I have a 1979 L48 bone stock. I pulled the valve covers off, and want to adjust valve lash.
My question is, after I find 0 lash (when the valve is in closed position), how much preload should I put into the lifter? I'm finding conflicting information, some places say 1/2 turn, while others say full turn, so I decided to ask directly.
Should I just compromise, and go with 3/4 of a turn?
Everything is stock, and the car is a cruiser, not a race car. It has 71k miles on the original engine.
As always, any help is appreciated.
I have a 1979 L48 bone stock. I pulled the valve covers off, and want to adjust valve lash.
My question is, after I find 0 lash (when the valve is in closed position), how much preload should I put into the lifter? I'm finding conflicting information, some places say 1/2 turn, while others say full turn, so I decided to ask directly.
Should I just compromise, and go with 3/4 of a turn?
Everything is stock, and the car is a cruiser, not a race car. It has 71k miles on the original engine.
As always, any help is appreciated.
Drifting
Joined: Aug 2010
Posts: 1,839
Likes: 45
From: nassau co. new york
i just went through this and would recommend 1/2 turn.do yourself a favor and examine each pushrod carefully for signs of roughness on the ends,make sure they are straight clean and all the same length.i had to replace all of mine as the engine would not hold the adjustment for long.one rod installed by the po was 1/4 shorter than the rest and at the oil hole there was an edge on each tip.when i rub my finger across the ends of the new rods it is real smooth compared to the originals.good luck.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
GM recommends "1 turn CW" on the final lifter adjustment. Many folks believe that 1/2 turn is best, if you want best performance from the engine. I usually use 3/4 turn when I adjust them cold.
Thread Starter
Pro
Joined: Aug 2007
Posts: 707
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From: Pitman NJ
I took the dog for a walk tonight instead, so I didn't get a chance to work on the car yet. I know my priorities are not quite right, but my dog is cool, and it was a nice night.
I'm still not 100% sure what to do, I'm leaning towards 3/4 turn ... and I will do what you suggest Bill, and check every push rod for length and straightness.
I'm still not 100% sure what to do, I'm leaning towards 3/4 turn ... and I will do what you suggest Bill, and check every push rod for length and straightness.
Drifting
Joined: Aug 2010
Posts: 1,839
Likes: 45
From: nassau co. new york
dogs and cats are great,unfortunately i am allergic to both and cannot have one.hence the vette as my pet.i believe many of gm's spec's were due to insurance restrictions and not toward performance.my objective is to get my car ,cold,at 1/2 turn lash and hold that setting.i replaced the lifters,pushrods,roller rockers with comp cams instead of the inferior proform that was there and put assembly lube on the lifter cam side and both ends of the new pushrods.i have no ticking sound and hopefully the parts will wear evenly and not require further adjustment.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
On your stock engine, it makes no difference whatsoever whether you run them at 1/2 or 3/4 turn preload. As long as you have some preload, and you're not bottoming the plunger out, it will run just fine in the stock rpm range. Running the preload "shallow" (1/4 to 1/2 turn) can gain you a slight rpm advantage before the lifters pump up and float, but your stock cam will poop out over 1000 rpm before that ever happens: a stock 79 L48 won't make power beyond 5400 rpm. A slightly "deeper" (3/4 to 1) setting will allow you to run the engine a lot longer before needing to re-set the preload: GM set them at 1 so that you would never have to reset the lifters for the normal life of the engine, and this acted as a factory "rev limiter" to keep you under 6000 rpm - not a bad idea on a stock engine. On the stock engine, you'll never notice any difference at all in performance, so just set them anywhere between 1/2 and 1 and don't worry about it.
Lars
Lars
Last edited by lars; Aug 18, 2014 at 10:22 PM.
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Thread Starter
Pro
Joined: Aug 2007
Posts: 707
Likes: 31
From: Pitman NJ
On your stock engine, it makes no difference whatsoever whether you run them at 1/2 or 3/4 turn preload. As long as you have some preload, and you're not bottoming the plunger out, it will run just fine in the stock rpm range. Running the preload "shallow" (1/4 to 1/2 turn) can gain you a slight rpm advantage before the lifters pump up and float, but your stock cam will poop out over 1000 rpm before that ever happens: a stock 79 L48 won't make power beyond 5400 rpm. A slightly "deeper" (3/4 to 1) setting will allow you to run the engine a lot longer before needing to re-set the preload: GM set them at 1 so that you would never have to reset the lifters for the normal life of the engine, and this acted as a factory "rev limiter" to keep you under 6000 rpm - not a bad idea on a stock engine. On the stock engine, you'll never notice any difference at all in performance, so just set them anywhere between 1/2 and 1 and don't worry about it.
Lars
Lars
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
1 full turn works for me now that i realize what that does for lifter bleed down that could be possible. But an L48 wont notice the difference between 1/2 or 1 full turn preload in performance. And i would not worry 'bout lifter pump up on an L48 either.
FYI the new LS7 hyd roller lifters have only 1/4 turn adjustment for preload and have a very short internal piston travel by design. Going 1 full turn on those probably will hold the vlv open. But the new lifter design reduces both the amount of lifter/piston pump up and bleed down possible.
FYI the new LS7 hyd roller lifters have only 1/4 turn adjustment for preload and have a very short internal piston travel by design. Going 1 full turn on those probably will hold the vlv open. But the new lifter design reduces both the amount of lifter/piston pump up and bleed down possible.
Last edited by cardo0; Aug 20, 2014 at 01:33 AM. Reason: add "not" correction
Intermediate
Joined: Dec 2008
Posts: 47
Likes: 0
From: cary nc
3/8-24 rocker studs equals .041 for 1 turn, .031 for 3/4 turn, and .021 for 1/2 turn. i think i did mine at 3/4 turn to get the .031 preload. being a machinist makes you think way too hard about this stuff, LOL.
Advanced
Joined: May 2009
Posts: 57
Likes: 6
I have a 1979 L48 that has had come mods; rear end upgrade, and engine upgraded. Also running headers and semi straight exhaust.. A nice sound. The problem I noticed that when driving 80 - 85 mph, the RPM's are running between 4000 and 5000. I think that this is kind of high. I think it has the 3 speed transmission. Should I change the transmission to a 4 speed auto...???, or will it be fine
Advanced
Joined: May 2009
Posts: 57
Likes: 6
Mike, thanks so much for your immediate response. I don't have any information regarding the ratio in the differential. Should I have it dynode in order to have the proper adjustments made?