Dynatard

[mrsmackpaul]

16 hours ago, fjh said:

Guess I was pointing out the cam timing is fixed! 

I dunno if this is 100% correct

Yeah I know in the standard parts department this is correct

However on racing type motor for a car you can dial in the cam shaft to make sure it is exactly correct

The use of off set keys to shift the cam slightly is used

Can this be done with a Mack motor ? I dunno, I guess it probably could be

Why would this be important ? well I guess if the cam is slightly retarded it would mean the exhaust valve is opening to late 

Would this be a real issue ?

I dunno, but clearly there are really good and really really bad Dynatards 

Something or a combination of things have to be slightly out and combined make a big difference 

To me the weakest part of the design has to be the rockers that from memory have no O ring to seal the oil in there, this would mean little to no retardation as the hydraulic lash adjuster would struggle to fill with oil and expand 

If this happens the retardation would be at the wrong time 

Anyway, just some thoughts 

 

Paul

[Joey Mack]

Well Paul, since you asked..  As far a cam degrees goes,, it may work. I wonder if setting cam degrees for better performance came later,,  also,, worn parts to me is an issue. IE;  worn piston rings causing lower compression, or the slave Pistons as you mentioned, add in out of adjustment valves, and how about gear selection when engine breaking ? Sometimes I think that because we are driving faster now, and have been driving computer controlled engines for 25+ years, ( Mrs. Mack not included ) that maybe the older systems that worked good back then, basically just SUCK for todays driving needs..  Thoughts 🤔 💭...

[mrsmackpaul]

Jo Jo I reckon your spot on

And our expectations have changed as well 

We were just happy to have any sort of engine braking once, now with modern engine brakes to compare to, anything from 40 or 50 years ago seems hopeless 

 

Paul

[Joey Mack]

Thanks Paul.. keep in mind, my response is not to discount or deny you.  You are very smart, i just set here thinking about the hundreds of performance complaints i have been asked to diagnose and fix when possible.  If your in an E-6 powered Mack and just got passed or out stopped by a newer KW or Pete.. no need to stare out the window thinking i need to get this ole truck turned up... It just aint there.. More thoughts 🤔 💭??

[Geoff Weeks]

I'll add mine with the caveat that I have never driven with one.

The design, in theory is a sound one, use a purpose designed "lump" on a cam to open the exh valve at the right time to"dump"compression.

Cummins touted this with the release of the ISX.

Problems abound with execution. How much lift can you have at TDC? how much mfg tolerance can the design have and still function well?

How much "extra"weight can the rocker system take and not float at high speed"

How well with the oiling system meet the demands that the system requires?

I can see all the potential of the design, but have no experience with the execution.   

[Joey Mack]

One thing that i was taught, and is obvious today, with Mack Engine brakes is simply, proper valve adjustment. As long as the engine is healthy and oil pressure is good, then you should get maximum engine braking,  I have a limited amount of full time driving, but i can say that Mack Engine brakes were not that strong, and when they went to Jacobs they were so-so, and still had to be updated for better performance... Now, that said... When Mack introduced the power leash in the ASET series, they made something.  You can literally stall the engine on the yard if you are aggressive with the throttle then the engine brake. It will also lock the rear wheels in semi slick conditions and sand on asphalt... 

[mechohaulic]

1 minute ago, Joey Mack said:

One thing that i was taught, and is obvious today, with Mack Engine brakes is simply, proper valve adjustment. As long as the engine is healthy and oil pressure is good, then you should get maximum engine braking,  I have a limited amount of full time driving, but i can say that Mack Engine brakes were not that strong, and when they went to Jacobs they were so-so, and still had to be updated for better performance... Now, that said... When Mack introduced the power leash in the ASET series, they made something.  You can literally stall the engine on the yard if you are aggressive with the throttle then the engine brake. It will also lock the rear wheels in semi slick conditions and sand on asphalt... 

can I get an AMEN . right on sir.

[mrsmackpaul]

As far as I am aware, in Australia all E7 Macks came with engine brake and a Jacobs exhaust brake as standard from the Mack Australia factory 

It may not of been all but it at the very least it was most

I guess to me this points to even Mack acknowledging just how crap their engine brakes were compared to everything else into the 90's and beyond 

Yes Geoff, the science was good on Dynatard but the execution left a little to be desired 

And then you add a couple of million miles of use into the mix and worn parts etc and things really are not in Dynatards favor

Paul 

[Mark T]

27 minutes ago, mrsmackpaul said:

As far as I am aware, in Australia all E7 Macks came with engine brake and a Jacobs exhaust brake as standard from the Mack Australia factory 

It may not of been all but it at the very least it was most

I guess to me this points to even Mack acknowledging just how crap their engine brakes were compared to everything else into the 90's and beyond 

Yes Geoff, the science was good on Dynatard but the execution left a little to be desired 

And then you add a couple of million miles of use into the mix and worn parts etc and things really are not in Dynatards favor

Paul 

Little more to the exhaust brake part. One of the reasons was so with a Jake, the face of the exhaust valve would be "preloaded" allowing more lash in the setting of the Jake. This allows the piston to travel further on compression stroke and when the valve is bumped off the seat there's more effect.  You can get away setting the Jake a little looser than spec, but ....   Those exhaust brakes were also rough on the turbos. Up until the Power Leash, a working Dynatard had comparable power to a Jake.  Jake was just much easier to have in working condition. 

[mechohaulic]

3 hours ago, Mark T said:

Little more to the exhaust brake part. One of the reasons was so with a Jake, the face of the exhaust valve would be "preloaded" allowing more lash in the setting of the Jake. This allows the piston to travel further on compression stroke and when the valve is bumped off the seat there's more effect.  You can get away setting the Jake a little looser than spec, but ....   Those exhaust brakes were also rough on the turbos. Up until the Power Leash, a working Dynatard had comparable power to a Jake.  Jake was just much easier to have in working condition. 

On 1/19/2025 at 10:27 AM, Geoff Weeks said:

I have had very little experience with Dynatard, only enough to know when setting the valves, you must follow the instructions to the letter or your clearances will be off.

 I do have a lot of experience with Jakes.

 Jake's were designed for common rail fuel systems where the injector was triggered by a dedicated lobe on the cam. The injection timing is ideal for opening the exh valves for compression braking.

 This left Cat an Mack out of the picture because they used an injection pump and no injection cam or rocker.

 So to make a Jake work on those engines, they use a valve rocker on an adjacent cyl valve train to open the exh on the cylinder at TDC. Unfortunately it is less than ideal timing, so jakes are less effective on Cat engines then Cummins.

 Mack solved that by the Dynatard system, where the cam profile for the exhaust is customized with a "two lump" profile, the normal exhaust and a 2nd small one that could open the exhaust a bit at TDC compression with the hyd lash cyl at the rocker.

 I have 0 driving experience with the Dynatard, but am surprised to hear people say they were less good than a jake on the same engine! In theory anyway, by grinding the cam for the purpose, Mack should be able to idealize the opening time when the Dynatard is active, making it every bit as good if not better than a Jake on a common rail (Cummins, 2 stroke Detroit) engine.

 May be the "Lift" on the Dynatard side can't be high enough to be as effective? IDK but am surprised to hear people say it is less effective.

 May be they are judging "effective" by "Noise made" and not retarding power?  Opening the exh at less than ideal time make make more noise and less retarding power. Lots judge a retarder by how much noise it can make! They hate the hydraulic Cat "Brakesaver" because it doesn't make any noise!  

simple sentence :: an engine brake in principle slows a vehicle down by opening an exhaust valve AT THE PRECISE TIME . opening the exhaust valve which on combustion would force the piston down now uses the piston to create drag on the crankshaft NOT power stroke. speed the process up engine becomes a "boat anchor to drive train. the noise heard is due to combustion energy going out muffler system.  on a jake system , an add on unit is placed on top of rocker assy; reason for green spacer between valve cover and block. spacers(flat washer) are placed on top of the exhaust valve spring arrangement for the two jake plungers to open exhaust valve before compression .  the dynatard (flop at first introduction ::I was there ) utilized a modified exhaust rocker ; reason for the 3 "pregnant  bulges on rocker cover. when activated the modified rocker filled with oil reducing the valve clearance on exhaust holding valve open. adjustment was very critical . dynatard got a bad review due to people expecting to be thrown to windshield  from stopping / hold back ; didn't happen.  ENGINE brake no matter who's holds open the exhaust valve just before compression stroke.  exhaust brake is totally different. jake is called an exhaust brake ; technically wrong. exhaust brake goes on the piping system and is a valve closing exhaust system creating back pressure.  in the good days you wanted good fuel pressure (totally unrelated ) change your fuel filters. 

[Mark T]

7 minutes ago, mechohaulic said:

simple sentence :: an engine brake in principle slows a vehicle down by opening an exhaust valve AT THE PRECISE TIME . opening the exhaust valve which on combustion would force the piston down now uses the piston to create drag on the crankshaft NOT power stroke. speed the process up engine becomes a "boat anchor to drive train. the noise heard is due to combustion energy going out muffler system.  on a jake system , an add on unit is placed on top of rocker assy; reason for green spacer between valve cover and block. spacers(flat washer) are placed on top of the exhaust valve spring arrangement for the two jake plungers to open exhaust valve before compression .  the dynatard (flop at first introduction ::I was there ) utilized a modified exhaust rocker ; reason for the 3 "pregnant  bulges on rocker cover. when activated the modified rocker filled with oil reducing the valve clearance on exhaust holding valve open. adjustment was very critical . dynatard got a bad review due to people expecting to be thrown to windshield  from stopping / hold back ; didn't happen.  ENGINE brake no matter who's holds open the exhaust valve just before compression stroke.  exhaust brake is totally different. jake is called an exhaust brake ; technically wrong. exhaust brake goes on the piping system and is a valve closing exhaust system creating back pressure.  in the good days you wanted good fuel pressure (totally unrelated ) change your fuel filters. 

We're talking about the Stealth Brake.  They were and exhaust brake used along with a Jake. Sometimes, directly on the outlet of the turbo, and sometimes downstream under the cab. They were back in the E7 period in the later "90s before the E Tech.  PacBrake also had versions of them called the Super Pacbrake.  Not to be confused with a Super Jake (Caterpillar)  Like was pointed out before, E6s......they weren't very big displacement wise. So expecting one to work like a Cummins of the time is unrealistic. That's just based on size alone, let alone the better timing control of the exhaust valve opening during operation being triggered by nice big injector rocker on a Cummins.  

[mechohaulic]

thank you. as I have many times stated : this site is a wealth of info for ALL .  by '90's  I was out of dealership and private working.  my '93 Hino had an exhaust brake which helped. back in the '70's had installed/ worked on a number of install/ repairs of Jakes and dynatards ENGINE BRAKES . alot of hollow exhaust  push rods under recall were changed out.

[Geoff Weeks]

48 minutes ago, mechohaulic said:

sENGINE brake no matter who's holds open the exhaust valve just before compression stroke.  e

I disagree with this statement, it holds the exhaust valve open just before power stroke, it allows for compression but not power.

[Joey Mack]

No compression,,,,,, no boom,,,,,,  

[Geoff Weeks]

Jake on a Cummins, is operated (opening trigger) off the injector push rod, which is about 19 deg BTDC (yes it changes from model to model). If you open before compression, then you get no or very little resistance

It is the compression that provides all the retarding effort, by opening the exh right before or at the injection time, there is no or little ignition and by holding the exhaust off the seat, there is no power returned to the crank like there would be if the valve stayed closed, after the piston passes TDC.

Opening before compression, you have no compression, and little to no resistance to revolution in the crank.

[Joey Mack]

Too bad the engine braking wasnt simply cutting off the fuel. Then resistance we be optimal..  no need to crack open the exh valves..   

[Geoff Weeks]

29 minutes ago, Joey Mack said:

Too bad the engine braking wasnt simply cutting off the fuel. Then resistance we be optimal..  no need to crack open the exh valves..   

Not at all, new engines do just that, but cutting fuel does nothing to retard.

when you hand crank an engine on compression, then past TDC, the engine kicks even if it never fires. By opening the exh valve just before TDC you get all the compression effort but dump the "kick" after TDC.

The kick is caused by the pressure you built up moving the piston up now acting to push it down. by dumping the pressure, there is nothing to push the piston back down.

[Joey Mack]

Ok.. i guess i was thinking about how many junks bikes and trucks ive had that would die and slow down quickly, unless i pushed or pulled in the clutch. My Sportster is a prime example, the compression is so good it just slows the bike down fast..  

[Mark T]

9 minutes ago, Joey Mack said:

Ok.. i guess i was thinking about how many junks bikes and trucks ive had that would die and slow down quickly, unless i pushed or pulled in the clutch. My Sportster is a prime example, the compression is so good it just slows the bike down fast..  

That's the vacuum doing that. No vacuum on turbo charged diesel. ( well no enough to do that ) Even just the energy of the heat of the compressed air in a diesel counts for something, even without fuel. The little Cummins boy really was a genius.