MDS hemi lifters

[raven3]

From the cut a way views posted by Chrysler of the MDS lifter all the parts are assembled concentric to the axis, except the cross release pin with compression return spring.
Is it the cross pin that rotates inside the lifter body.
The lifter cut a way shows the pin head cap orientation aligned with the side hole in the lifter outer body part, but the pin is slightly lower, longitudinally, towards the roller end than the side hole. Oil pressure is applied to the pin cap end to push the pin cross wise to open up the oil chamber under the plunger so the plunger will travel back and forth inside the stationary sleeve with each revolution of the camshaft.

A depiction posted by Chrysler shows the entire valve train with all sixteen push rods. The lifters are positioned more horizontal than vertical.
So the plunger is concentric with the stationary support sleeve. The gravity force on the plunger actually creates a line contact on the sleeve,
Since in reality the two mating parts are eccentric caused by the difference in diameter.

The noise folks complain about is at idle when the lifter are supposed to be solid with no oil pressure applied to the release pin head in V8 mode.
The occilating plunger could produce a flat line area on both the plunger and sleeve, if the oil film is ruptured.

Agree with SYN that the oil must be maintained very clean with a minimum carbon particles suspended in the lubricating oil.
The source of the free carbon molecules comes from the combustion process.

 

[Rustycowl69]

for what its worth, I have an ex state patrol 02 dodge Intrepid with HO 3.5L SOHC v6. When I bought it from State Surplus, it had a busted intake rocker. the roller had failed, turned sideways, and taken out the right cam. The story I got was that the engine was a quart low on oil, and the trooper was engaged in a long high speed pursuit. It seemed quite plausible, because the cam damage was extensive. It didn't look like it happened at idle speed, that's for sure. I fixed it and put on over 100k more miles since, with no problems.

 

[raven3]

Visited the RAM dealer.
Price on MDS lifter is $75, dealer stocks this lifter, this would indicate it is a failure part.
Price on non MDS lifter is $30.

To deactivate the MDS with 8 speed trans.
The speedometer must read more than 28 mph.
Push "gear-" button only once, on steering wheel
Then,push " gear + " button on steering wheel until gear selection on screen indicates 8.
The MDS is now deactivated and trans will shift in automatic mode up to 8 speed OD, until engine is stopped
or if the speedometer goes under 28 mph.
Then trans must be reset again on the move to deactivate, again.

 

[Limeybastard]

Sorry I didn't word that very well. I have a Magnaflow that makes it very obvious when my truck is in MDS. It's borderline annoying actually. Anyways my Eco light is on when I'm giving it very light throttle but it is running on 8 cylinders. Shortly after I can hear it kick down to 4. I do believe that the Eco light has to be on for MDS to activate...

I am not sure if its worse when MDS kicks IN or OUT with a magnaflow LOL

Forget vtec kicked in yo... 8 cyl just kicked in YO.

 

[raven3]

Have a stock exhaust system 2015
Recently had trans software update combined with rear axle recall.

Seamless from 8 to 4 back to 8 with 8 speed trans.
Unable to detect noise, vibration, engine load, whip lash, etc.

Agree the ECO light must be lite up for MDS to activate but maybe lite w\o MDS activated

 

[raven3]

The two nested compression springs located at the lower end of the MDS lifter are supposed to maintain zero slack in the pushrod.
When the rocker shaft is bolted to the head with cross release pin in default position, the two lower compression springs should
compress to totally eliminate any push rod slack.
The two nested springs at the lower end of the lifter and the valve closer spring in the cylinder head are in series in the valve train.
The two nested springs are only less than 1\2" outside diameter that fit inside the lifter body and must be weaker than the cylinder head valve springs.

 

[Limeybastard]

Have a stock exhaust system 2015
Recently had trans software update combined with rear axle recall.

Seamless from 8 to 4 back to 8 with 8 speed trans.
Unable to detect noise, vibration, engine load, whip lash, etc.

Agree the ECO light must be lite up for MDS to activate but maybe lite w\o MDS activated

So you are saying you have no idea when it's operating in 4cyl mode or when it changes? Must be the 20W oil that you use [emoji12]

Sent from my SM-N910T using Tapatalk

 

[raven3]

Yes, transition is seamless
Last 8 speed software update changed the feel slighty.
Use 5w20 PP
Only transistion to 4 cylinder with speedometer > 28 mph on the flat at constant speed.
Engine has 4k miles on it.

 

[raven3]

Have an idea on the MDS valve train design.

What if the rocker arm was pinned to collapse with an electro magnet to engage the pin and disengage the pin.
When the pin is disengaged with power on the electro magnet, the valve remains closed while rocker pivots on the pin that is constantly oiled.
The push rods could be adjustable in length to minimize clatter asis done in many OHV engines.
The lifters are now all solid fixed, no moving parts
The rockers are easy to access by removal of plastic cover.
The adjustable push rods are accessible by removing only the intake manifold.

The current configuration requires removal of the cylinder head to service lifters.

 

[R.L.K.]

I like the way you think Sir .
The current design is more complex than it has to be , I can't come up with a reason for this .

 

[raven3]

Back in the day this current design would have called a "Rube Goldberg.
It's way too complicated.

Harley Davidson clone engines all use adjustable length push rods with no issues.

Suprized the aftermarket folks have not jumped all over this valve train
configuration.

 

[raven3]

The issue with two compression springs in series, lifter spring, valve spring is a resonance phenomium
were at times the two springs are in phase with other and at other times the two springs are out of phase as a function of the driving frequency, i.e.
The chamshaft rpm.
It's called a two degree of freedom spring \ mass mechanical system.
At a resonant driving frequency the lifter roller mass could actually be bouncing on the camshaft lobe based on the internal lifter spring and lifter mass. This action would damage the lifter roller and camshaft lobe mating surfaces.

 

[raven3]

Some research on the MDS Hemi lifters indicates there has been three design changes.
Group 1 design covers 2006 -2010
Group 2 design covers 2011-2013
Group 3 design covers 2014-2016

There are several after market manufactures that furnish MDS lifter kits including the retainers, including Elgin Industries, Engintech & melling.

Interested in the method of sealing off the oil chamber directly below the plunger.

The design change may have included a change in the spring rate for the two nested compression springs in the lifter base.

After the engine is stopped, oil can drain from the chamber directly below the plunger through the release pin seal (probably steel to steel).
When the engine is started again this chamber must fil with oil to create a hydraulic lock so the lifter is solid.

The two springs at the base of the lifter are compressed to maintain contact of all mating surfaces, including, camshaft lobe/lifter roller, lifter dish top/push rod & pushrod/rocker.

The source of the non pressurized oil fill is from the rocker in the cylinder head.
The oil must gravity flow through the hole in the push rod to the top of the lifter, where the orientation of the push rod is more horizontal that vertical.
It could take a while for cold thick oil to reach the lifter upon start up.

Noticed the retainer for the non MDS lifter is a spring wire, while the retainer for the MDS lifter is a C clip.

Still on the search to find the cause of the so called noisy hemi.
Believe the source of the noise is an impact of steel on steel , not scraping.

 

[Hemi395]

Some research on the MDS Hemi lifters indicates there has been three design changes.
Group 1 design covers 2006 -2010
Group 2 design covers 2011-2013
Group 3 design covers 2014-2016

There are several after market manufactures that furnish MDS lifter kits including the retainers, including Elgin Industries & Engintech.

Interested in the method of sealing off the oil chamber directly below the plunger.

The design change may have included a change in the spring rate for the two nested compression springs in the lifter base.

After the engine is stopped, oil can drain from the chamber directly below the plunger through the release pin seal (probably steel to steel).
When the engine is started again this chamber must fil with oil to create a hydraulic lock so the lifter is solid.

The two springs at the base of the lifter are compressed to maintain contact of all mating surfaces, including, camshaft lobe/lifter roller, lifter dish top/push rod & pushrod/rocker.

The source of the non pressurized oil fill is from the rocker in the cylinder head.
The oil must gravity flow through the hole in the push rod to the top of the lifter, where the orientation of the push rod is more horizontal that vertical.
It could take a while for cold thick oil to reach the lifter upon start up.

Noticed the retainer for the non MDS lifter is a spring wire, while the retainer for the MDS lifter is a C clip.

Still on the search to find the cause of the so called noisy hemi.
Believe the source of the noise is an impact of steel on steel , not scraping.

So they changed the lifter design in 2014? Might be why the owners manual changed its wording about 5w30 from "don't use it or it will explode" to "its OK to use it when 5w20 isn't available". Very good info.

 

[R.L.K.]

LOL ! I've been running Redline 5W -30 for over 4500 miles , no issues at all and smoooooooth and quiet ! LOL
I haven't noticed any explosions, maybe I missed it , I have bad hearing , been working on turbine engines for 25 years , LOL !

 

[raven3]

RLK
Understand RL can used for gas turbines, also, since the POE is good for really high temperatures and very cold temperatures.

 

[R.L.K.]

RLK
Understand RL can used for gas turbines, also, since the POE is good for really high temperatures and very cold temperatures.

Lol , 4th generation turbine oils are approved for 900+°c flash and 750°c constant usage for 12 mo. or 300 flight hours , which sometimes is 450 hrs total with ground operations .

 

[raven3]

Finally figured out how this MDS lifter works.

The upper section is like a conventional flat bottom hydraulic lifter, except instead of a hole through the body and corresponding side hole through the plunger, the lifter is feed oil through the top hole in the push rod seat from the oil hole in the push rod with gravity flow rather than oil pump pressure flow, as with a conventional side fill hydraulic lifter.

The top hydraulic lifter assembly with flat bottom, slides into the main steel body with a very close fit, similar to the close fit between the plunger and top hydraulic lifter body.

The two holes on opposite sides of the main body allow pressurized oil from the oil pump to apply pressure on the ends of two round caps located 180 degrees apart.
The oil pressure pushes the caps inward against the force of one compression spring located between the two caps. With the two caps pushed inward the top hydraulic lifter section is allowed to move downward in the direction of the camshaft follower roller against. the force of two nested compression springs. In this mode, the top hydraulic lifter is allowed to slide up and down within the main body driven by the camshaft lobe.
In this mode the engine is now firing on four cylinders, 1,2,4,7.
When the oil pressure is released by the solenoid valve in the oil passage circuit the two caps default to normal position , locking up the top hydraulic lifter from movement within the main body. Now the entire main lifter is solid and the engine is firing on all eight cylinders.

The plunger in the top section lifter only slides with within the top lifter body section when the engine warms up or cools down to allow for heat expansion, normally, .02'-.06". This the normal function of a conventional hydraulic lifter.

This top section lifter can leak down oil through the ball check located at the bottom of the plunger like any other conventional hydraulic lifter.
However, since the top lifter gets oil from the push rod by gravity flow it could take a while to fill up the small chamber below the plunger.

POE base motor oil is polar which means it clings to metal surfaces better than conventional group 2oil or even group 3 or 4 oil. This might explain why there is minimum start up clatter using RL.

If the top hydraulic lifter is sluggish to return to the default position by compression spring force the main lifter roller could cause noise impacting the camshaft lobe, until the side latching caps return to default position by compression spring force.

It is really important to maintain very clean motor oil, since the top hydraulic lifter has to slide up & down inside the main lifter body with close fit, while in 4 cylinder mode at a frequency equal to the camshaft rpm. The lifter is more horizontal than vertical so the wear is accelerated by gravity force.

Still investigating the source of the infamous hemi noise.
Still investigating two degree of freedom spring\ mass configuration comprised of the lower two nested lifter springs and the valve return spring. Both springs are in series which can cause resonance issues.

Dodge/RAM is now on the second design change of the MDS lifter, since original 2006 design.
Last design change was 2014, previous was 2011.

 

[R.L.K.]

Wow , great info to read Sir .
@.raven3 Sir , I could read your post for hours , you paint a picture with your writing , your understanding of systems are exceptional and you are very good at explaining how things work . I hope you sir are an educator, our youth today could use insight like yours running a classroom.

 

[R.L.K.]

Just read your profile , retired mechanical engineer , well that explains it ! Still you should look into doing some sort of teaching !