Dynatard

[Mark T]

57 minutes ago, mackone said:

Hello,  I bought this service manual on ebay , and according to this it looks like all engines have the dynatard cam in the E6's, just giving an update,  thanks to everyone for posting and helping.

 

Someone PMed tat info to you

[mrsmackpaul]

I wonder if that is 4 valve motors only ?

 

Paul  

[mrsmackpaul]

Well my books arrived and I believe we are all slightly wrong here, no offence meant to anyone 

Well the book once proof read from Miss Molly 

 

 

Tells me that Dynatard motors, engines for the sensitive types have different heads with a recessed exhaust valve 

So after a quick glance at the book I  can see that one thing is obvious that is mentioned but not in a big way is timing 

It says to just line up TDC off the indicator on the front the motor indicator

Now me been me and knowing that this indicator is only a indication would mean that possibly a few degrees off here and the whole shooting match is tits up

So thinking a little more about this 

You can get offset key ways to line car motor timing up when building high performance motors

Now thats on precise machined parts, not a bit of tin pointing at a balancer

So Im wondering if TDC should be proven first to see just how accurate this indicator is 

Now a little more 

If only a Dynatard cam is fitted the motor would be retarded the whole time so it wouldn't run, the book says this as well

So with this new found knowledge quite a lot can be learnt

Timimg, valve clearance, good hydraulic lifters or hydraulic lash adjusters as the book calls them are important 

Not the things I was thinking of, good lash adjusters that aren't worn

good rocker that don't leak oil out the rocker shafts

All of these thing might only make a slight difference but combined might make a huge difference 

So now to find that elusive time for some experiments 

I do believe it might be a very plausible thing that some are as good as Jacobs and others are useless like mine

 

Paul

 

 

 

 

 

 

[MACKS]

Well keep us posted on your progress..

[1951 Mack LJ]

Any updates to bringing dynatards back to life.  My Mack 237 with dynatard holds good on hills with 30,000 gross.  Would like to get my E9-500 creating some engine breaking.

[mrsmackpaul]

I think parts still available in Australia 

 

Paul

[Geoff Weeks]

On 3/14/2023 at 2:16 AM, mrsmackpaul said:

I do believe it might be a very plausible thing that some are as good as Jacobs and others are useless like mine

 

Paul

 

 

 

 

 

 

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!  

[Joseph Cummings]

26 minutes ago, 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!  

I have a Dynatard on my R686 tractor, and I used to drive a R686 with a 750 Holmes on it with a Jake. As far as I remember the Jake performed about the same as my Dynatard. Then again comparing them is kind of hard, different loads, different hills, different amounts of wheels with operating brakes, hardly a scientific test.

BTW I was always curious about putting an exhaust brake on a reciprocating aircraft engine. A windmilling prop eats up a lot of airspeed. It'd probably be great for a steep dive

[Geoff Weeks]

8 minutes ago, Joseph Cummings said:

 

BTW I was always curious about putting an exhaust brake on a reciprocating aircraft engine. A windmilling prop eats up a lot of airspeed. It'd probably be great for a steep dive

Compression brakes don't work effectively on throttle governed engines. You could, with a hydromatic prop change the pitch of the prop to make the most of what you do have.

 It reminds me of an old Loony Tunes, where Bugs is in a aircraft making a nose dive toward the ground and stops just inches above the ground (and just hangs there in the air) and Bugs gets out and says

"Lucky for me this thing had Aiiir Brakes!" 

[Joseph Cummings]

9 minutes ago, Geoff Weeks said:

Compression brakes don't work effectively on throttle governed engines. You could, with a hydromatic prop change the pitch of the prop to make the most of what you do have.

 It reminds me of an old Loony Tunes, where Bugs is in a aircraft making a nose dive toward the ground and stops just inches above the ground (and just hangs there in the air) and Bugs gets out and says

"Lucky for me this thing had Aiiir Brakes!" 

Well someone who isn't me experimented a bit, and found that what ate up the most air speed was to cut off the mixture and have the throttle wide open lol.

Oh and BTW, that someone who isn't me did some experiments on spinning a Cherokee 180. It was hard to get the damn thing to spin, and really hard to get it to stop spinning. It took about 8,000 feet. Nothing like a Cessna 

[mrsmackpaul]

2 hours ago, Geoff Weeks said:

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.

There is no second hump on a dynatard cam 

They look almost the same as a non dynatard cam

When dynatard is off the exhaust doesn't follow the cam because it can't 

The exhaust valve is shut and as such it can't travel any further

When dynatard is on, the effective push rod length has increased and as such the valve must follow the cam and the exhaust opens just before TDC

If we think about the dynatard and all the bits that need to work and be reasonably oil tight and in good working order it is little wonder that there are lots of issues with them as they age 

Reducing the valve clearance would help as the effective travel needed is reduced to achieve a good result

Having said all of the above I feel timing is also critical, as is good mechanical clearances on the rockers gear

The little piston in the lash adjuster can't extend fully if it can't be supplied with oil under pressure 

There's a lot to getting dynatard working fully, more than most of us understand 

 

Paul

[Geoff Weeks]

Paul, I agree with all you say, I was just pointing out is or should be as good as a jake on a common rail fuel system and better then a jake on a injection pump/nozzle system, where the jake is operated off an adjacent cyl valve gear.

[Geoff Weeks]

the 2nd "lump is at the side in your picture and only comes into play when the lash in the system is reduced.   It is still the same operating principle where the exh is opened on compression near TDC.

the lash adjust is similar to Cummins STC injector. The effective length of the push rod is changed and that changes the timing and/or travel of the rod.

Edited Sunday at 06:18 PM by Geoff Weeks

[mrsmackpaul]

That's hardly what I call a lump, but for the sake of keeping the peace you can call it a lump 😆

 

Paul

[Geoff Weeks]

Just now, mrsmackpaul said:

That's hardly what I call a lump, but for the sake of keeping the peace you can call it a lump 😆

 

Paul

Don't want you coming over and giving me a lump upside the head!

[mrsmackpaul]

[mrsmackpaul]

5 hours ago, Geoff Weeks said:

Paul, I agree with all you say, I was just pointing out is or should be as good as a jake on a common rail fuel system and better then a jake on a injection pump/nozzle system, where the jake is operated off an adjacent cyl valve gear.

I think the issue is there is so many spots for oil to leak in the rocker gear and the oil pressure is say 60 psi at best, once the rocker gear is worn a bit oil can easily leak out the rocker shafts 

This means the little ram in the lash adjuster never gets its full oil pressure

Also timing must be critical as the lobe change is tiny 

 

Paul

[fjh]

13 minutes ago, mrsmackpaul said:

I think the issue is there is so many spots for oil to leak in the rocker gear and the oil pressure is say 60 psi at best, once the rocker gear is worn a bit oil can easily leak out the rocker shafts 

This means the little ram in the lash adjuster never gets its full oil pressure

Also timing must be critical as the lobe change is tiny 

 

Paul

Fuel timing has no bearing on the dynatard 

[Geoff Weeks]

1 minute ago, fjh said:

Fuel timing has no bearing on the dynatard 

I think he was talking cam (valve cam) timing.

[mrsmackpaul]

29 minutes ago, Geoff Weeks said:

I think he was talking cam (valve cam) timing.

Yes I am

[fjh]

15 hours ago, mrsmackpaul said:

Yes I am

Guess I was pointing out the cam timing is fixed! I believe the issue is the amount the valves can be opened and the displacement of the engine! The engine can’t get rid of all of the compression with such a small bump on the cam ! Oil escape  on the shaft is a factor as mentioned thou! Valve adjustment is important I have experienced if you set tight or under spec the better the braking effect! How ever the Tighter the set the more mindedful you have to be to over speed!

[Geoff Weeks]

16 hours ago, fjh said:

Fuel timing has no bearing on the dynatard 

Not what you said, tho

[fjh]

3 hours ago, Geoff Weeks said:

Not what you said, tho

True my bad! Just don’t like to cause a fuss!

[Geoff Weeks]

I don't know, if I'm not careful Paul may make the trip to put a lump on the side of my head!😄

[tjc transport]

38 minutes ago, Geoff Weeks said:

I don't know, if I'm not careful Paul may make the trip to put a lump on the side of my head!😄

never happen. 

he is too smart ....and dont want to hurt his hand...