Why Apex Seals Fail

[alexyjay]

that's some good info. thank you.

[NoDOHC]

Ok, so I have a few pictures of my own to back up Barry's Theory:

Naturally Aspirated application - 13.2:1 AFR 28 degrees BTDC Timing failed apex seal in front housing at 5400 rpm in 4th gear - after 37 seconds at WOT in road load simulation mode on Mustang dyno.

This happened a while back, but my camera was acting up.

Here are the Apex seals:


The housing in which the seals failed:


Another shot of the housing in which the seals failed:


Here is the other housing:


You can see that the seals failed exactly as Barry predicted.

[Barry Bordes]

NoDOHC, check the remaining good seal under a microscope for a crack where the others failed.

Also what water pump are you running?

Did you bevel the spark plug holes? It appears that way from the pictures.

Barry

[88turboii]

mine had the same marks:



this was with RA classic seals, but they didnt break, it just had leaking coolant seals. it had 60k miles on stock turbo 15 psi, 7's and 9's plugs

[Barry Bordes]

Did you guys read the cooling mod thread?

http://www.rotarycarclub.com/rotary_...t=barry+bordes

This thread, (Why Apex Seals Fail) is a peek into one of the conclusions that we came too. We are already running engines with this cooling mod plus some others surmised from this and other tests.

Some think that this may be giving away too much valuable information. My thought is that it helps the whole rotary community.

What I have noticed is that individuals start using the info and forget to give credit to the originators. But that is life... you do what is right anyway.

Along that theme I would like to give credit to Carlos Lopez and Rick Engman for their thoughts on the subject. They are the community's Senior Rotary Advisors.

Barry

[vex]

Originally Posted by Barry Bordes

Did you guys read the cooling mod thread?

http://www.rotarycarclub.com/rotary_...t=barry+bordes

This thread, (Why Apex Seals Fail) is a peek into one of the conclusions that we came too. We are already running engines with this cooling mod plus some others surmised from this and other tests.

Some think that this may be giving away too much valuable information. My thought is that it helps the whole rotary community.

What I have noticed is that individuals start using the info and forget to give credit to the originators. But that is life... you do what is right anyway.

Along that theme I would like to give credit to Carlos Lopez and Rick Engman for their thoughts on the subject. They are the community's Senior Rotary Advisors.

Barry

I have. I posted in that thread starting on page 2 and page 3. Namely heat transfer and material expansion rates (roughly quoting the math unless you place the free edge of the fin within 0.00076 in then you have nothing really worry about for interference issues).

[NoDOHC]

Originally Posted by vex

How did I miss this thread?

Let me see if I can help in adding my schooling into the mix (Hurrah for Fluid Dynamics being applicable in all situations dealing with flow).

Fluid dynamics is applicable, but I think that heat transfer principles and metal expansion rates have more bearing in this situation.

Originally Posted by vex

What I mean by that is that if you have a single source flowing unevenly into the various passages the incompressible nature of the fluid is going to dictate that the area with the higher pressure is going to output the more mass of the fluid (all other things being equal). Consequently ensuring you're getting an equal flow rate prior to the passage entrance would be paramount.

Technically, all passages have the same pressure across them (all tied to the same hose on one end, all rising the same amount, all exiting to atmosphere) The issue is that all passages have different flow rates due to their differing hydraulic diameter. The flow rate does not need to be consistent, as there is very little heat to be rejected at the beginning of the intake stroke as compared to the compression region.

Originally Posted by vex

If however there is no leakage and the input is simply just feeding it through the water ports where the waterpump seals, then the issue is indeed hardware related. Consequently since we can assume a uniform pressure distribution (not only for this experiment but for the real world application) we can see that the differences is going to be directly related to the hydraulic diameter and boundary layer conditions of the passages. This provides us with an easy enough solution as well.

We can solve for the hydraulic diameter given the (measured) flow much more easily than we can compute the other direction. Once again, this is not important, heat transfer is much more important here. Fast moving water is not always better.

Originally Posted by vex

First and foremost; enlarging the hydraulic diameter of the passages will allow for a more unified flow condition between all ports in question. There remains however a finite amount of space to achieve that. The other option that can be excersized as well would be to instill a turbulent boundary layer on only some of the passages.

Enlarging the passages is not always the best solution. What racing beat is doing is much better. They are increasing the surface area that is exposed to the cooling fluid while also inducing turbulence which improves convective heat transfer significantly.

Originally Posted by vex

Why only some? Think of it this way: we have a large passage that is putting out a lot of fluid. The issue is attempting to balance the passages to output the same amount of fluid at the end of the day. To do this we can lower the friction a majority of the fluid is exposed to in the other passages, in essence allowing for a faster flow to be achieved on smaller passages, while the undisturbed boundary layer on the larger passage causes the flow to slow down when compared to the tripped boundary layer of the smaller passages.

Once again, consistent passage-to-passage flow will not make this problem go away. The issue is much more complicated than that. The heat transferred to the coolant in each passage needs to be equal to the heat generated in the nearby chamber and transferred through the aluminum housing. I am guessing that Mazda did some research on this, as the coolant passages on top of the housing (low heat rejection to the coolant) have restrictors in them.

Originally Posted by vex

The solution will consist of finding the appropriate balance of the two.

I admire your attitude and your desire to apply your knowledge to any problem, I just don't want you wasting a lot of time chasing wild geese.

[vex]

I think you're missing what I'm saying.

Originally Posted by NoDOHC

Fluid dynamics is applicable, but I think that heat transfer principles and metal expansion rates have more bearing in this situation.

Quite possibly and is something to consider. However the portion I was dealing with was the difference in the amount of fluid passing through the different passages. Not necessarily the heat transfer as this is two different issues of concern.

Technically, all passages have the same pressure across them (all tied to the same hose on one end, all rising the same amount, all exiting to atmosphere) The issue is that all passages have different flow rates due to their differing hydraulic diameter. The flow rate does not need to be consistent, as there is very little heat to be rejected at the beginning of the intake stroke as compared to the compression region.

Which I already stated.

We can solve for the hydraulic diameter given the (measured) flow much more easily than we can compute the other direction. Once again, this is not important, heat transfer is much more important here. Fast moving water is not always better.

Again, you're trying to tackle a different problem than to what I was referencing (not heat transfer).

Enlarging the passages is not always the best solution. What racing beat is doing is much better. They are increasing the surface area that is exposed to the cooling fluid while also inducing turbulence which improves convective heat transfer significantly.

Again, I wasn't discussing heat transfer specifically but balancing the mass flow between all passages. The heat transfer I did touch upon was coincidental and nothing more.

Once again, consistent passage-to-passage flow will not make this problem go away. The issue is much more complicated than that. The heat transferred to the coolant in each passage needs to be equal to the heat generated in the nearby chamber and transferred through the aluminum housing. I am guessing that Mazda did some research on this, as the coolant passages on top of the housing (low heat rejection to the coolant) have restrictors in them.

Again, I was only referencing the specific post I responded to.

I admire your attitude and your desire to apply your knowledge to any problem, I just don't want you wasting a lot of time chasing wild geese.

Asked and answered a question posted by Barry.

[NoDOHC]

Originally Posted by Barry_Bordes

NoDOHC, check the remaining good seal under a microscope for a crack where the others failed.

Also what water pump are you running?

Did you bevel the spark plug holes? It appears that way from the pictures.

Barry

I looked at it as carefully as I could and didn't see anything (I didn't want to get yelled at for using the magna-flux at work again).

I re-used that seal. I have over 2500 miles on the engine since the failure and have had no issues.

Stock water pump, stock radiator (a lot of fins are rotted out, I am replacing it).

I read this thread earlier and I found the tell-tale pattern on my housings, so I figured that beveling the edges was a good idea that may keep me from losing an engine. It survived 3000+ miles on the street just fine, but didn't survive the dyno run.

I should have backed out of the throttle and had the dyno turn the loading down, My coolant temp was about 125 C when the seal went. I went to the dyno since then and had no issues (with the temp under 115 C) I think that the spark plug boss grows too much relative to the unsupported housing around it. I have considered welding a brace in (parallel with the coolant flow) to keep the surrounding housing growing at a similar rate to the spark plug hole (although the spark plug hole has threads in it).

I like racing beat's idea - if I had this information before I rebuilt the engine, I probably would have done that.

[Barry Bordes]

Originally Posted by Barry Bordes

If you look closely at this photo you will see the Racing Beat type grooves in the this first iteration cooling mod.

It didn’t seem to help much to alleviate the growth problem as I had hoped.

The next set of mods included severed fins and larger balanced passages.

[project86]

Barry,

You said you were using reliability mods.. What mods exactly were you using? Ported? etc, etc, Just curious

[TitaniumTT]

It seems to me that the stain is in line perfectly with the fin. It appears to me that the fin has kept that area from growing. Effectively retracting it as the rest of the housing grows. Looking at the 16x and the renni, they seem to aleviate some of this material. I'm wondering if this is in an attempt to not contain it, but to let it grow a the same rate. Thoughts?

[vex]

Originally Posted by Barry Bordes

If you look closely at this photo you will see the Racing Beat type grooves in the this first iteration cooling mod.

It didn’t seem to help much to alleviate the growth problem as I had hoped.

The next set of mods included severed fins and larger balanced passages.

Barry, as NoDOHC mentioned I do not think balancing the flow in the passages will help alleviate the problem. The issue I believe may be compounded by too high a temperature difference in the cooling surfaces (IE across the passages). Physically speaking you have a large temperature difference on the lower half of the engine while the upper half is more nominal.
Increasing the engergy transfer around the spark plug hole I believe will yeild more results than not.

Something else to consider is that the cooling of the combustion walls is not necessarily the root cause of the problem. I'll have to do some research into the material properties when I'm back home, but could it be the atomic structure of the materials developing fissures over time due to heat cycling? For instance would voids and imperfections in the casting develop the same event?

Originally Posted by TitaniumTT

It seems to me that the stain is in line perfectly with the fin. It appears to me that the fin has kept that area from growing. Effectively retracting it as the rest of the housing grows. Looking at the 16x and the renni, they seem to aleviate some of this material. I'm wondering if this is in an attempt to not contain it, but to let it grow a the same rate. Thoughts?

It's a possibility, but has anyone actually analyzed the stain itself? Do we assume it's a discoloration of the Chrome lining or do we know if it's a Carbon impregnation of the Chrome? Additionally do we know how deep the discoloration is within the Chrome? I ask as that--I believe--will dictate the environment and conditions of the failure. If it's a discoloration of the Chrome caused by too slow an energy transfer through the matrial adjusting the cooling will help, if it is a thermo-mechanical interaction that causes the issue, perhaps modification to the cooling passages to allow easier expansion and contraction would help. From what I see thus far it's a lot of conjecture--can anyone do this testing?

[vex]

So I did a little more research and I think this modified picture is quite enlightening. Sorry it's hard to make out but it's the best I can do with GIMP at the moment.


We now have flame fronts with angles of eccentric shaft and the temperatures at those flame fronts that match up with the chart. I have a few more pieces of information that I will be posting throughout the week coming from SAE paper 860560:
Material Technology Development Applied to Rotary Engine at Mazda
by
Takumi Muroki and Jun Miyata

[GoopyPerformance]

This is a very interesting post but the title "why apex seals break" may be misleading.

Lets be careful and not add to much theory and 1000 dollar words and confuse some of the laymen who are just coming to the rotary scene.

We all know that the web is full of data but gotten to the point that true information is lost or siphoning out the good stuff becomes almost imposable, with that in mind lets keep this forum
nonsense free.

Now the specifics on why this post can be misleading is because the breakage on the end of the long part (hypotenuse) only happens on OEM 93-94 2 peace seals.

Also the end tip on the OEM seals gets within a few thou of the irons of either side, where the sharp tip may catch the iron when the engine detonates and rotor tip hits the irons. We see this often with drag cars pushing 40+ lbs of boost. Cutting the rotor faces
alleviates some of these issues.

(Aftermarket seals including ours have a larger Side peace than OEM.)

This also happened on engines with fresh new housings and new OEM Apex seals.
Therefore if the apex seal cracked (hypotenuse) it happened when the engine leaned out or detonated, these are drag cars which never get any road millage where the (hypotenuse) area can slowly crack then one day let go completely.

Even if the hypotenuse area of the apex seal was further inward or even if you used a 1 piece apex seal, leaning fuel, TOO much advanced ignition or detonation are still why apex seals break.

We have been working on Apex Seal technology for almost 10 years with collaboration from engine builders both stateside and Puerto Rico and agree this breakage (hypotenuse) end tip break off is primarily a oem seal issue.

Glory to GOD!