Why are lifters adjusted different from autos.
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Road Warrior
Joined: Apr 2010
Posts: 1,648
Likes: 37
From: Monroe, Louisiana
Why are lifters adjusted different from autos.
I have been racing and building and tuning engines for many years. I do have a question about the adjusting of the hydraulic lifters. Why do you have to center the lifter piston in the middle of the travel. On automotive lifters you can take the slack to 0" and then tighten from 1/2 to 3/4 round. The engines on the bike can run the same lifter as SB chevy and they don't have to be adjusted that way in the car motor. Everyone is going to tell me the aluminum expands more that the steel is why. The heads are held in position with hardened steel bolts that don't expand at the rate of aluminum so can't understand. Most race engines have aluminum heads too. What I think is happening is the engines are idling at pretty low oil pressure and won't keep the lifters pumped up good and rely on the spring in the lifter to keep the slack out. I have run lots of anti-pump up lifters and they all adjust to 0 to .005" clearance in the cars for racing and are collapsed .005 for running on the street to keep the noise down. Lifters aren't likely to pump up too tight and hold the valve open any until higher rpms than we are running in our motors. If you run the stock lifter that way it can push the keeper out and make a mess. I may play with this sometimes. I know running loose will give a little more noise. That is why you need the exhaust and intake noise and radio to control this noise.
Generally I would say that the oil PSI may deterime the set amount of lash for the lifters. A basic HD TC hot motor will vary from 5 psi at idle & 35 psi at 3000 rpm. At idle theres barely enough pressure for the oil to get to the rockers and may not be enough to tightly seat the lifters, p-rods to rocker parts.
An auto motor generally runs between 30 & 40 psi depending on rpms. A race motor can run 60 psi or more. The added oil pressure will assure the lifter cup stays planted against the holding clip equaling basic zero lash.
Ive closely looked at the HD vs SBC lifters & did notice that the SBC lifter cup has a smaller diameter hole vs the HD lifter cup. There could be a difference in lifter spring rates too but never checked them out on a spring tester.
Just my guess anyway.
An auto motor generally runs between 30 & 40 psi depending on rpms. A race motor can run 60 psi or more. The added oil pressure will assure the lifter cup stays planted against the holding clip equaling basic zero lash.
Ive closely looked at the HD vs SBC lifters & did notice that the SBC lifter cup has a smaller diameter hole vs the HD lifter cup. There could be a difference in lifter spring rates too but never checked them out on a spring tester.
Just my guess anyway.
Elite HDF Member
Joined: Nov 2010
Posts: 3,846
Likes: 173
From: Simi Valley, CA
Great question! And one that I've never been able to get a definitive answer on. Lot's of opinions here and in similar threads but not a single definitive answer from an engineering perspective yet. Here's a link to a related thread that contains some fairly detailed discussion on the matter... https://www.hdforums.com/forum/engin...uestion-2.html
Elite HDF Member
Joined: Nov 2010
Posts: 3,846
Likes: 173
From: Simi Valley, CA
Generally I would say that the oil PSI may deterime the set amount of lash for the lifters. A basic HD TC hot motor will vary from 5 psi at idle & 35 psi at 3000 rpm. At idle theres barely enough pressure for the oil to get to the rockers and may not be enough to tightly seat the lifters, p-rods to rocker parts.
An auto motor generally runs between 30 & 40 psi depending on rpms. A race motor can run 60 psi or more. The added oil pressure will assure the lifter cup stays planted against the holding clip equaling basic zero lash.
Ive closely looked at the HD vs SBC lifters & did notice that the SBC lifter cup has a smaller diameter hole vs the HD lifter cup. There could be a difference in lifter spring rates too but never checked them out on a spring tester.
Just my guess anyway.
An auto motor generally runs between 30 & 40 psi depending on rpms. A race motor can run 60 psi or more. The added oil pressure will assure the lifter cup stays planted against the holding clip equaling basic zero lash.
Ive closely looked at the HD vs SBC lifters & did notice that the SBC lifter cup has a smaller diameter hole vs the HD lifter cup. There could be a difference in lifter spring rates too but never checked them out on a spring tester.
Just my guess anyway.
Like I stated in my previous post, there are a lot of differing opinions and theories on this topic. Your theory on the oil pressure is certainly plausible with one exception...
Where you state "The added oil pressure will assure the lifter cup stays planted against the holding clip equaling basic zero lash" is not correct. Let me explain. The lifter plunger/cup should never be "planted" against the "holding" clip during operation. If it was that would mean one of two things. 1) You have no preload adjusted into the lifter, or 2) the lifter has "pumped up" beyond its design intent. When you adjust in any amount of lifter preload (i.e., .100, .120, .140 etc.), the plunger should never get any closer to the retaining clip during operation than that amount (except as required to compensate for thermal expansion). If it did you would likely have a valve that would never fully seat when closed.
Make sense?
Last edited by 2black1s; Aug 9, 2013 at 03:58 PM.
Road Captain
Joined: Dec 2009
Posts: 570
Likes: 4
From: New Mexico
Makes no sense at all. If the lifters were pumping down at idle they should immediately pump back up off idle when oil pressure rises. Which is what happens when you start your car sometimes. Although now that I think about it I haven't had a car do that in years. You think it would be consistent. If they bled down once when the motor was idling hot they should do it every time.
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Stellar HDF Member
Joined: Jan 2013
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From: Illinois
Makes no sense at all. If the lifters were pumping down at idle they should immediately pump back up off idle when oil pressure rises. Which is what happens when you start your car sometimes. Although now that I think about it I haven't had a car do that in years. You think it would be consistent. If they bled down once when the motor was idling hot they should do it every time.
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HDF Community Team
Joined: Jun 2006
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From: san antonio
I think we all agree that oil does not compress. A lifter has four basic parts; check ball/spring, body, socket and plunger (some refer to the socket/plunger as the piston). The piston moves up and down with the pushrod inside the lifter body and the body moves with the valve. The up/down movement of the piston allows oil to enter and fill the cavity below the piston via the check/ball spring until the cavity is full. At this point the piston stops moving independent of the body, the check ball closes off the entry of oil from the oil galley and the piston moves with the body and the lifter effectively becomes a solid lifter.
The only way oil can escape the lifter cavity is between the outside of the piston and the inside bore of the lifter body. Poor quality control that results in excessive clearance between the lifter piston "skirt" and the lifter cavity bore, or clearances that develop from wear or a weak or broken check valve spring will allow such leaks. These leaks are commonly referred to as bleed down.
The reason lifters like the Woods directional, HQ Blackops, Gaterman and the new S&S lifters are so much better than the others is the precision fit of the four basic parts of the lifter. A Woods directional lifter can take 30 minutes to an hour to bleed down after adjusting as compared to say an OEM lifter that will bleed down in 5 minutes, or less.
I have attached a link to a video that better illustrates my poor attempt at explaining lifter hydraulics. The video is generic as there are variances in the four basic parts of a lifter but I think the basic hydraulics of the lifter are clearly illustrated.
Elite HDF Member
Joined: Nov 2010
Posts: 3,846
Likes: 173
From: Simi Valley, CA
Makes no sense at all. If the lifters were pumping down at idle they should immediately pump back up off idle when oil pressure rises. Which is what happens when you start your car sometimes. Although now that I think about it I haven't had a car do that in years. You think it would be consistent. If they bled down once when the motor was idling hot they should do it every time.
Last edited by 2black1s; Aug 9, 2013 at 09:26 PM.