On a mild hydraulic cam, what is the optimum preload? How much is too much?

Assuming you have adjustable rocker arms or adjustable pushrods.
Tighten until there is zero slack in the rocker to pushrod and then turn another 1/4 to half turn.
IF you are using the stock rockers and stock pushrods, then you are stuck with what you have unless you can get rocker shaft shims. This would move the rockers away from the valve tip and pushrod giving you less preload. OR order custom length push rods to give you the preload you want.
I assume you know about leaving the lifters sitting in oil over night to get all the air out of the lifter plungers. IF not, you will never get the prelaod right.

More than 1/2 turn is too much imo. 1/4-1/3 turn has always worked best for me.

Recomended is .020"-.040" preload. Fine thread 3/8-24 threads per inch. 1÷24=.0417" So 1/2-1 turn gets you there.
Doug

I set them that way on the engine stand and again with the motor warmed up or hot after breaking in the cam

Does anyone know who's lifters and what part number he is using? It could possibly make a difference.

.020 to .040 is what I was taught, Should be fine for stock replacement but it probably depends on the exact parts used.

What is the OP working on, and what is the parts/machine work combination?

Yep .020 to .040 is good. If you are going to race it then I like to set mine closer to almost no preload but they can be a little noisier. I had my old 383 at about .010 because I raced it some and it was less chance of lifter pump up if over reved. Years ago my buddy used to race me in my 273 Dart and he was not good with his 4-speed Chevelle and he missed gears a lot. One day when we raced my little 273 was right with his 350 Chevelle and right after I yanked third and jumped a 1/2 a car on him with my Hurst Super Shifter he droped way back and disappeared. I went back to his house and about a 1/2 hr later he showed up. He missed third and over reved his eng and his lifters pumped up and held the valves open and shut the eng down. He said he could not get it started for almost the 1/2 hr as the lifters had to bleed back down below 0 preload to get comp back. Ron

Sorry guys, should have been more specific. My good machine shop built the short block and the heads, so I know they were correct. The problem was the shop that installed the heads and installed the motor was terrible. It is a 70 383 with stock non adjustable rockers and very mild cam. I took on the job and found the carb was very rich, the the total advance was 80 degrees and the button was missing in the rear end and the brake drums were rubbing on the backing plates. Therefor, the test drive was limited but the motor ran terrible with very little power. The car is going back together now so when I pulled the valley pan to fix the leaks, I noticed the lifters had way too much preload. .110 to be exact. I think it was holding the valves open slightly above 2500 rpm. I use adjustable rockers on all my builds and I do the 1/4 to 1/2 turn and never actually measure preload. She does not want to spring for the adjustable rockers, so I’ll have to shim the stands or get new pushrods. I called Hughes Engines and they said they liked .080 to .090 preload. That seams high as well. My bud said .060 is fine for a street engine. This motor has less than 100 miles, if that, on this rebuild.

I should add that the lifters are not performance lifters. They have the small wire retainer for the plunger and I have seen them break if not enough preload is used.

there is a school of thought that haveing the cup a few tho up from the BOTTOM is the way to go. I do not think your preload is an issue. On the snap rings there is a snap ring HO-68 from www.huyette.com (iirc) that is cheap/works well & it was suggested to install em with the squared edge on the bottom which I thought was backward but the guy (on here but I forget who) sounded sharp. I previewed this & huyette ain't right but I have the receipt if needed. MORE EDIT it is www.huyett.com HO-68 housing ring internal 11/16 CS PH

Ok then. This raises an interesting question. What will happen at .110 preload? Will it slightly hold the valve open at high rpm or seat the valve anyway. The only motor I built that had trouble was a 318 in a truck. It ran terrible at idle. I installed adjustable rockers with 1/2 turn preload and it ran fine.

stock preload with a stock valvetrain is .110"+. Chrysler tappets have .200"+ plunger travel. I like the plunger somewhere between 25%-50% of the travel distance. I use .060"-.090" preload with an adjustable valve train. never had an issue. some performance tappets have short plunger travel; maybe .100" or less. best thing to do is measure the travel and then decide on a preload distance.

And any influence by the amount of oil pressure? As in might to much pressure makes hydraulic lifters act like solids?

2 schools of thought. #1;Very little preload so if it loses valve train control it cant pump up much. #2; With the lifter almost bottomed, valve train load can't collapse the lifter much losing lift/duration.
Doug

I see this preload topic brought up and battered to death with opinions and such.

Question for those that may have checked.
How much plunger travel exists on a production Chrysler lifter?
How much plunger travel exists on a late model aftermarket lifter?

Reason I ask.

The service manual calls out .060” - .210” dry lash.
That equates to .040” - .140” plunger preload.

If you have production level plunger travel - your engine should not run poorly, idle poorly, perform poorly with this preload.

I ran production juice lifters in Stock Eliminator in the 70’s with a GK cam, production pushrods and rockers and never floated a valve, broke parts, etc. I kept my preload at .060”. No issues for 5 years using the same parts without replacement. Of course I only spun it 6K back then but it never failed me.

Take a 1/8 of a turn out of all of them and see
if it acts better.. if not I would look at the
cam timing.. if its retarted it will be a mutt..
and dont take the word of your shop.. we are
all human and make mistakes

“Too much” preload is when the plunger is down far enough to plug off the feed hole in the side of the lifter.
Other than that........ any preload that doesn’t result in that happening should work fine in a daily driver type application.

In the OP’s situation, if he’s not comfortable with .110 preload, a set of .050 shorter pushrods would certainly put him well within the preferred range.

In a similar scenario as Rons Chevelle story....... I was out wailing on a car with a tired old 361 that did the exact same thing.
I wound it out hard in 1st...... it sputtered a bit, then just shut off.
I had no clue what it was.
I was under the hood looking at wiring and such. When I cranked it over it was like the plugs were out of it.

Then, after a period of time, I tried it again.......just because.........and I could tell some compression was back, at least on a couple cylinders........ and it started.
Running really rough at first, then started smoothing out, and then it was fine.

Any thoughts are appreciated on this subject. I’m trying to learn. I never had the car running long enough to get to the lack of power problems. I was afraid the rear end would loose an axle! I’ve always used adjustable rockers on all builds save my last 440 and it was all original untouched oem parts. So basically, any amount of preload short of a mechanical lockup if the lifter should never hold open a valve, correct? It would just loose lots of lift and duration.

Fastmark - how did you determine how much preload you have ? What method did you use ?

A question for fast - in theory, wouldn’t weaker valve springs allow quicker and more violent lifter separation/pump up?

Wouldn’t weaker valve springs take longer to “pump down” the plunger versus a stronger spring?

all the tappets I've measured had .200+ plunger travel. this does not include any of the race tappets, just factory or OEM replacement.

heavier springs do allow the tappet to resist pump up. like anything else there's pros and cons to heavier springs.

I think the .020"-.040" thing came out of the mid to late '60's. I remember the chevy guys reducing their tappet pre-load by backing off the rocker. I don't think any of us back then truly understood pre-load; we were just trying to get more rpm by eliminating pump-up. a lot of the hobby is monkey see-monkey do so the ford and mopar guys thought they had to do the same thing; me included. I can't say that I gained much, if anything, by doing this. if I remember correctly valve spring changes meant more than tappet adjustments. now I just put the plunger somewhere around mid travel and just let the juice lifter be what it is.

I used a dial indicator on the tip of the rocker by the pushrod and tightened the rocker stands until the pushrod had zero preload. The cam was on the base circle, of coarse. I tightened the bolts till the shaft was tight to the stands and then read the indicator. Comp had a different way in some instruction I had once. They said to mark the pushrod at zero preload and and then tighten the shafts and mark again. Measure the difference and you have your preload. Both methods came out the same, .110.

I would think so.
In my case, the tired old 361 had the 100,000 mile stock single-without-damper springs...... so not much pressure.

So in my mind ( and you seem to agree a bit ) a weaker spring would take longer to pump the plunger down - and that may be why some engines like Ron’s buddy and your 361 too so long to regain compression.

Of course other factors may play in to this - condition of the lifter itself and maybe actual cranking oil pressure, would be a neat experiment.

Thanks for all the replies to my questions -

Pretty simple. If the spring pressure overcomes internal tappet leakage, it collapses the plunger in the tappet. Then the valve train loses lift. Valve train is noisy due to lash in the system until the lifter recovers and fills with oil. If the valve train loses contacts between components the lifter fills with oil trying to take up the extra clearance. Now the valve doesn't seat as the lifter is too long. Engine runs rough until the lifter bleeds the excess oil fill. Providing the the lifters don't leak down or pump up any preload will work.
Doug

.010" worked best for my combo - SB with Morel Hyd. Roller lifter, PSI 1.290" dual spring 175 lbs. seat, 8300 RPM

Well from what I am seeing here, it appears it does not really matter on a non performance application. As long as the lifter does not bottom out and go solid, it can’t hold open the valve, right? On a performance app, too much preload, robs you of lift. I guess it gets to a certain preload and stays at relatively the same position because it can’t bleed off
the oil pressure fast enough to matter. Am I thinking correctly here?

Most stock lifters will pump up and hold the valves open at the upper RPM if they have to much preload, setting the preload from .010 to .030 hot will help stop that

I keep going over this I’m my brain and I think this is has got to be the case. The higher the rpm, the more they will pump up. The more room they have to pump up, the more like they are to hold open the valves.

the valve spring controls pump-up, not pre-load. reducing pre-load just reduces pump-up distance.

Yes but the point here I believe is if you run the lifters with almost no preload even if you over rev the eng the lifters cant pump up enough to hold the valve off its seat. I have seen that a few times over the years on stock type engines. When I worked at a used car dealer I ran a 351 Mustang real hard on a road test and the lifters pumped up enough to hold the valves off the seats and stall the eng. I had to wait a bit before it got comp back. That's why I ran only about .010 preload in my old 383 since I raced it sometimes and used basically the stock valvetrain with Comp single springs. Course to close to no preload and it has more valve train noise. But I understand what you mean also about the spring tension making a difference if you run the normal preload. Ron

Basically your right but the stronger valve springs will fight against the lifters pumping up and holding the valves off the seats. Ron

What I do is: with it mocked up, put a swath of dykem on the pushrod, then slide a thin flat razor blade over sideways from the valve cover flange on the head & make a slight mark in the ink then undo the rocker to let everything raise up till the cup "just" reaches the snap ring then make another razor mark then measure the distance between the (2) "marks" on the pushrod.

I’ve done it this way before. I got the same measurements both ways. I fixed the problem yesterday without buying adjustable rockers at he customers request. I settled on .035 to .045 using Shim’s under the stands. It was a royal pain. Way too time consuming just to save the customer money and be a one time fix. I had to use more shims at one end of the drivers side head. Better than .110 to .145 preload though.

I had to use more shims at one end of the drivers side head. Better than .110 to .145 preload though.

That just doesn't sound like a good solution to me Wouldn't that stress the shaft? I wouldn't sign off on that repair

Gus

Aaaaahhh yes........ the old “stand splitters”, er...... I mean shims.

I dont have the last word on this but it recollected something about custom shims that someone offered that are thinner on the "sides" to counteract this.

I gave her the options and she chose the cheapest ones. I don’t like them but that is what she would go for. I used the tapered shims from Hughes.

As Dwayne pointed out, those shims are pedestal breakers. Also, they only half fix the issue. If the shaft needs to go up, it also needs to move away from the valve. Those shims don't do that.


The only good thing was if the heads had a bunch of money in them and it broke a pedestal, the customer was more inclined to fix them the only way I had back then which was to mill the stands off and use offset stands and shafts like should have been done in the first place.