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Old 05-27-2013, 09:29 PM
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Educate me on hydraulic lifter preload

The literature that came with my CompCamps XE274H flat tappet cam says to use 1 turn (or .045"*) of preload. Everything I am reading online says to use 1/4-1/2 of a turn. This cam says it makes power until 6,000 RPM and I would like to run the engine that high every now an then for short bursts. What are the pro's and con's of altering the preload?

* I checked the rocker studs and they are 24 threads per inch, so 1 turn = .042"

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Old 05-27-2013, 09:42 PM
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I'll add to the confusion, I run about 1/8th turn preload. Run thicker oil if you want to rev it. 10w-40 or better.
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Old 05-27-2013, 10:54 PM
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Quote:
Originally Posted by ap72 View Post
I'll add to the confusion, I run about 1/8th turn preload. Run thicker oil if you want to rev it. 10w-40 or better.
OK what kind of cam and lifters are you running and what RPM's does your engine see? Is it street? Strip?

Probably worth mentioning that I am using the Comp lifters as well.
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Old 05-28-2013, 01:46 AM
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Quote:
Originally Posted by Silver Surfer View Post
OK what kind of cam and lifters are you running and what RPM's does your engine see? Is it street? Strip?

Probably worth mentioning that I am using the Comp lifters as well.
hi all . hope its ok ap72 . i also have the same question . i have hydrauiolc lifters. which i have a sneeky suspicion wernt set up 100% . whats the correct way to set up ? crane supercharger mild street cam , car use for street. edelbrock victor jnr heads. crowler stainless steel roller rockers. people over here saying not to use hydrauilc and go for solid lifters ??
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Old 05-28-2013, 04:48 AM
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The purpose of pre-load is to keep the lifter automatic adjustment for wear and keep plunger away from the upper snap ring. The more pre-load is just more adjustment/wear/lash that the lifter can compensate for.

High performance use is usually minimal pre-load to keep the lifters from pumping up when over revved or over using weak springs. If no pre load. The lifter just acts as a solid lifter. No automatic lash take up. Also plunger rides against snap ring and can push snap ring out at high rpm.
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Old 05-28-2013, 06:55 AM
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relatively mild stuff meant for hot street use. With heavier spring pressure some people run them near bottomed out, hydraulic lifters can be finicky depending on how aggressive your cam is and how thick your oil is.
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Old 05-28-2013, 08:51 AM
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Quote:
Originally Posted by Silver Surfer View Post
The literature that came with my CompCamps XE274H flat tappet cam says to use 1 turn (or .045"*) of preload. Everything I am reading online says to use 1/4-1/2 of a turn. This cam says it makes power until 6,000 RPM and I would like to run the engine that high every now an then for short bursts. What are the pro's and con's of altering the preload?

* I checked the rocker studs and they are 24 threads per inch, so 1 turn = .042"
The lifter is looking for a preload from the valve spring which causes its internal valving to meter oil into the gap between the lifter body and the internal plunger. This is going to depend on the lifters bleed down rate and depending upon the manufacturers quality control may vary quite a bit between individual lifters or hardly at all. I'd go with the cam manufacturer's recommendation rather than an average value suitable for OEM production.

If the lifter doesn't object changing the preload is usually inconsequential to lifter operation, it is basically setting the running position of the plunger within the body.

Bogie
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Old 05-28-2013, 10:15 AM
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Originally Posted by BOBCRMAN@aol.com View Post
The purpose of pre-load is to keep the lifter automatic adjustment for wear and keep plunger away from the upper snap ring. The more pre-load is just more adjustment/wear/lash that the lifter can compensate for.

High performance use is usually minimal pre-load to keep the lifters from pumping up when over revved or over using weak springs. If no pre load. The lifter just acts as a solid lifter. No automatic lash take up. Also plunger rides against snap ring and can push snap ring out at high rpm.
Quote:
Originally Posted by oldbogie View Post
The lifter is looking for a preload from the valve spring which causes its internal valving to meter oil into the gap between the lifter body and the internal plunger. This is going to depend on the lifters bleed down rate and depending upon the manufacturers quality control may vary quite a bit between individual lifters or hardly at all. I'd go with the cam manufacturer's recommendation rather than an average value suitable for OEM production.

If the lifter doesn't object changing the preload is usually inconsequential to lifter operation, it is basically setting the running position of the plunger within the body.

Bogie

Thanks all for the info! Let me see if I have this correct...

Less preload
pro: less the lifter can pump up since there is less distance between the plunger and the snap ring retainer. This means during lifter pump up, the valves are not held open as much and less pressure is exerted on the base circle of the cam shaft.
con: more pressure exerted on plunger snap ring which can break it during instances where the lifter is pumped up.

More preload
pro: removes the possibility of plunger/snap ring contact, so it helps prevent lifter destruction at high RPM use.
con: if lifter pumps up, the plunger can really move the pushrod a lot which keeps the valve open (when it should be closed) and also causes the lifter to exert more pressure on the base circle of the cam.

So perhaps we should investigate pump up. I hear this term thrown around a lot, but I am not sure on what it means. Based on my reading, this is what I understand it to be...

At high RPM the lifter cannot follow the profile of the cam on the closing ramp. This is due to lack of spring pressure or pushrod flex. This allows oil pressure to force its way into the lifter which causes the lifter to go down and plunger to go up.

Solutions to pump up:
  • Buy expensive lifters rated for higher RPM use.
  • Use heavier valve springs (wiped cam lobes for us flat tappet guys).
  • Keep total drive train weight as low as possible.
  • Keep your foot off the gas pedal.
  • Use less lifter preload.
  • AP72's solution of higher viscosity oil (is this to slow the rate at which oil can fill the lifter) coupled with less preload?

If you do experience pump up, are you causing bad things to happen to the engine? Or do you enter a time of lowered performance since the valves are not on the seat? Is this the same thing as "valve float"?

Last edited by Silver Surfer; 05-28-2013 at 10:30 AM.
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Old 05-28-2013, 11:02 AM
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Originally Posted by Silver Surfer View Post
  • Buy expensive lifters rated for higher RPM use.
  • Use heavier valve springs (wiped cam lobes for us flat tappet guys).
  • Keep total drive train weight as low as possible.
  • Keep your foot off the gas pedal.
  • Use less lifter preload.
  • AP72's solution of higher viscosity oil (is this to slow the rate at which oil can fill the lifter) coupled with less preload?
valve train, not drive train

and higher viscosity prevents collapse, not pump up

using a milder lobe will help stabilize the valvetrain

As will switching to solid lifters

For a cheap cam setup I like a solid lifter cam with grooved lifter bores or face oiling lifters, beehive springs, and lift around .525". Its mild enough to last but aggressive enough to provide good power.
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Old 05-28-2013, 11:09 AM
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valve train, not drive train


LOL you know what I meant!
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Old 05-28-2013, 01:04 PM
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Originally Posted by Silver Surfer View Post
Thanks all for the info! Let me see if I have this correct...

Less preload
pro: less the lifter can pump up since there is less distance between the plunger and the snap ring retainer. This means during lifter pump up, the valves are not held open as much and less pressure is exerted on the base circle of the cam shaft.
con: more pressure exerted on plunger snap ring which can break it during instances where the lifter is pumped up.

More preload
pro: removes the possibility of plunger/snap ring contact, so it helps prevent lifter destruction at high RPM use.
con: if lifter pumps up, the plunger can really move the pushrod a lot which keeps the valve open (when it should be closed) and also causes the lifter to exert more pressure on the base circle of the cam.

So perhaps we should investigate pump up. I hear this term thrown around a lot, but I am not sure on what it means. Based on my reading, this is what I understand it to be...

At high RPM the lifter cannot follow the profile of the cam on the closing ramp. This is due to lack of spring pressure or pushrod flex. This allows oil pressure to force its way into the lifter which causes the lifter to go down and plunger to go up.

Solutions to pump up:
  • Buy expensive lifters rated for higher RPM use.
  • Use heavier valve springs (wiped cam lobes for us flat tappet guys).
  • Keep total drive train weight as low as possible.
  • Keep your foot off the gas pedal.
  • Use less lifter preload.
  • AP72's solution of higher viscosity oil (is this to slow the rate at which oil can fill the lifter) coupled with less preload?

If you do experience pump up, are you causing bad things to happen to the engine? Or do you enter a time of lowered performance since the valves are not on the seat? Is this the same thing as "valve float"?
There are two schools of thought on pump up one says to sink the plunger to the bottom. Mine of course is different which is to run the plunger against its retainer. This requires using a Circlip in place of the wire bale if the lifter is so equipped, this will ensure the guts don't come out. This you run at zero to maybe a couple thou lase with the engine hot, so it will not pump up (as it is pumped up) to hold the valve proud of the seat.

Bogie
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Old 05-28-2013, 01:10 PM
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OE and aftermarket GM hydraulic lifter preload is designed to be set at 1/2 lifter travel.

Lifter travel for a OE hydraulic lifter has been standardized at .120" or .160" which means the lifter preload should be set at .060" - .080" , depending on which lifter you have. Only the GM hydraulic roller lifters used in the LS6 and LS7 engines are set at .080" preload. Aftermarket, OE hydraulic roller lifters and hydraulic flat tappets are set at .060" preload. If you "lash-out" or "bottom-out" hydraulic lifters for an additional 500 RPM on week ends, you are asking for trouble and you should be using a solid lifter camshaft instead.

Find number of turns with 24 thread per inch rocker studs with the rocker ratio factored in:
.041 = 1" / 24 tpi rocker studs
2.5 = Std. hydraulic lifters (.120" travel)
3.0 = LS6 hydraulic lifters (.166" travel)
Example:
(.041 x 2.5) / rocker ratio (1.5) = preload (.068")
.068" / .041 = number of turns
Therefore: Number of turns = 1.7 (1-1/2 to 1-3/4 turn)

Solution:
If your hydraulic roller camshaft has from .490" to .525" valve lift, you should be using Comp Cams 875 reduced travel roller lifters for the more aggressive cam lobe profile and set the preload at .005" (1/8 turn).
Reason:
The more radical cam lobe profile with high lift camshafts will loft a standard hydraulic tappet over the nose of the cam lobe and fill the lifters with oil foam (air) and hold the valve off the seats (float the valves). The reduced travel lifters cannot not fill with air and pump up because they have no where to pump up to. Similar to solid lifters with a oil cushion.

Inadequate valve spring pressure will have the same effect on valve seating as lifter pump up. Minimum valve seat pressure with camshafts having from .490" to .525" valve lift is from 125 lb. to 150 lb. and you should have hardened exhaust valve seats in good condition with that much seat pressure with no-lead pump gas or exhaust valve seat erosion will become distressingly apparent after about 20,000 miles. Evidence will be increased lifter noise, especially at cold engine start.

Last edited by MouseFink; 05-28-2013 at 01:24 PM.
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Old 05-28-2013, 01:22 PM
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Your math is wrong.

And .500" lift on a roller can is rarely aggressive, though it can be.

And I'm sort of with Bogie, by the time you figure out what an 1/8 turn cold is its almost zero lash when hot, just ever so slightly more.
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Old 05-28-2013, 01:35 PM
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If the plunger is riding against the circlip, then how often do you have to check your preload? As parts wear, pretty soon your preload is going to become lash.

Also Mousefink, I am running a flat tappet hydraulic cam, not a roller. I am using CompCam springs that came with the cam kit, so seat pressures should be good. Heads are OEM Vortec (062 casting), so I *assume* the exhaust seats have the proper hardening in place. I understand the 960 castings were for trucks and have extra beefy hardened inserts, which perhaps would be more desirable in applications you speak of.
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Old 05-28-2013, 02:05 PM
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Originally Posted by Silver Surfer View Post
If the plunger is riding against the circlip, then how often do you have to check your preload? As parts wear, pretty soon your preload is going to become lash.

Also Mousefink, I am running a flat tappet hydraulic cam, not a roller. I am using CompCam springs that came with the cam kit, so seat pressures should be good. Heads are OEM Vortec (062 casting), so I *assume* the exhaust seats have the proper hardening in place. I understand the 960 castings were for trucks and have extra beefy hardened inserts, which perhaps would be more desirable in applications you speak of.
My math is perfect...I even graduated high school.

Hydraulic flat tappet lifters adjust the same as hydraulic roller lifters.

Are your Vortec heads new? If not, how many valve jobs have they suffered? The induction hardened exhaust valve seats on the 062 castings are .007' deep. After some production valve jobs, the hardened seats may be gone. Vortec heads are thin castings and installing hardened exhaust seat inserts can cause the casting to crack when they get hot. Especially between the valves. Vortec heads are disposable, just like the cars GM places them in.

I am using Comp Cams 15850 Short travel lifters on a Comp Cam with .500" valve lift. I am using GM LS6 (GM-12499224) beehive valve springs set up at 127 lb. seat pressure at 1.700" and 315 lb. open pressure at 1.200".Random checked two valve springs at 6,000 miles at 125 lb. seat pressure and 308 lb. open pressure. I set the short travel lifters on the engine stand with just a flick of the wrist (1/8 travel), or just enough preload to clearance the push rod seat .005" from the push rod seat retainer C-clip. Valve train is silent with no valve float and responsive. I would blow the motor before the valve will float!

Most people don't use short travel lifters because they are too expensive. High performance is expensive, how fast do you want to go?

Comp Cams offers short travel lifters for high lift hydraulic flat tappet cams. I have used those on three engine build ups since 1985. GM and Comp Cams have offered short travel hydraulic flat tappet lifters since 1970.

Last edited by MouseFink; 05-28-2013 at 02:21 PM.
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