Why Apex Seals Fail

[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!

[Barry Bordes]

Originally Posted by 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.

Most rotary engines are built with OEM 2 piece 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.

I have not seen the sharp ends scrap the side housings.

That margin on the triangle protecting the tip looks like about .020" on the 2 piece and .040" on the three piece OEM seals.
See attached below.


(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!

I think we are addressing two different groups. I am trying to help the regular guy that wants to make a long-term dependable engine (usually with OEM parts).
You are working with racers that are pushing the envelope.

Although I test often for detonation with my TFX in-chamber sensor rig I have not experienced any detonation yet. Thank Goodness!

When your seals do fail where is the damage normally located?

Good luck with your Goopy seals and housings.
Barry

[j9fd3s]

Originally Posted by GoopyPerformance

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.

this is true, even the old timer SCCA autocross guys break seals when it gets too lean for too long.

the drag vs street vs road race thing actually is very important too. in road racing our warmup is 15 minutes, which is actually LONGER than the entire drag racing SEASON.

and street driving is again different, the WOT periods are short, but it needs to sit at idle and low rpm for a long time (traffic), plus mileage is important

there is nothing at all wrong with drag racing, 1000hp 13B is an achievement! it just requires a different engine/tune up etc etc

[vex]

As promised:

Apex Seal: Early in the development stage the RE used a composite one-piece apex seal made of carbon impregnated with aluminum. It was replaced later by a two-piece apex seal to provide better gas sealing, with the material changed to a stronger one in the form of cast iron.

The top surface of this apex seal that slides on the chrome plating shown in Fig. 8 is melted by electron beam and rapid solidified to provide an approximately 3mm chilled layer.

The chilled layer has excellent anti-friction properties since it contains a crystallization of finer cementite than is obtainable by ordinary chill casting. The base metal of the apex seal is accicular cast iron with bainitic structure. In addition to offering high strength and ductility to the apex seal, this structure gives increased wear resistance to its side faces (where it contacts with the apex seal groove walls) and its end faces (where it contacts with the side housing).

Apex Seal Temperature - Since lubrication between apex seal and trochoid is an important factor of engine operation, it was necessary to learn the apex seal's temperature distribution during operation with respect to oil film formation.

The amount of necessary lubricant for the lubrication between apex seal and trochoid surface has a close relation to the apex seal temperature, as shown in Fig. 9.

The suitable amount of the lubricant is that of when apex seal temperature begins to rise up due to the lack of the lubricant.

From this point of view, the apex seal temperature was measured to know how the temperature changes during engine running.

Apex seal temperature measurement was conducted by the following procedure...(omitted because it's not necessary for discussion)...[list=1][*]Temperature of bottom and top of Apex Seal - Temperature was measured at the top and bottom of the apex seal: as shown in Fig. 11, the temperature of the apex seal rises in accordance with the engine revolution, however at 5000 RPM with high load the apex seal temperature is reduced, because the combustion gas temperature is reduced by setting of richer mixture at high load. The temperature difference between top and bottom was below 10*C as shown in Fig. 11.[*]Apex Seal's Axial Temperature - Temperature was taken at the middle and both ends of the apex seal as shown in Fig. 12. It is to be noted that the heat flux into the seal flows to the side housing and rotor housing, indicating that the heat transmitted to the side housing exceeds the heat transmitted to the trochoid surface because of wider contact area of the end surface of the apex seal.[*]Temperature in Transient Condition - Fig. 13 plots temperatures that the apex seal registered when the engine was accelerated from 1000 RPM under no load up to 5000 RPM WOT and held at this speed for 45 seconds before it was decelerated to 1000 RPM under no load.

At 1000 RPM at no load, the apex seal's top was lower in temperature but became hotter during acceleration, and during deceleration it became less hot than the bottom.

If this is to be believed the main issues of expansion and contraction as well as heat flow is going to be through the side plates.

From the same report:

Side Housings: The side housing's inner wall is rubbed by the corner seal, side seal, oil seal, and rotor flank. This associated rubbed surface is in face contact and represents a considerable bearing area, with relatively generous supply of lubricating oil. Thus the side housing's operating condition is favorable compared to the rotor housing's.

However, as the engine is made capable of higher speed and power output, the thermal load rises, causing its operating condition to become less favorable, with the result that the oil seal lip in particular suffers increased wear, thus increasing oil consumption. To solve such problems, the plain cast iron surface of the side housing was softnitrided with resultant improvement in wear resistance and anti-corrosion.

(I'm putting in large portions so individuals can decide for themselves)

I'll work on getting some of the figures posted up for everyone's benefit. But just looking at them I see something rather interesting; As load is increased both BMEP and temperature peak at 4000 RPM and both begin to decrease proportionately to HP rating from 4k RPM to 5k RPM. If I'm understanding this correctly it correlates perfectly with what has been stated by others here.

Burning super lean even in low load conditions will increase the instantaneous heat in the chamber as well as the heat transfer into the combustion face material (as can be seen in another figure showcasing why iron wasn't used for the rotor housing).

Given the nature of the defects and what the SAE paper has stated concerning a stock configuration it can be intimated that failure of the Apex Seals is going to be derived from lean conditions increasing the heat of the combustion chamber beyond design constraints. The result; heavy thermal loading of metalic parts.

To tackle thermal expansion and any subsequent interference from the Apex Seal and side housings will need to be evaluated on merit (I will actually be attempting a simulation here shortly to test just that).

[NoDOHC]

Good post Vex!

I especially like the way you tied Barry's theory to other's experience.

I can tell from my last dyno session that the more the timing was advanced, the more quickly the engine overheated. The closer I ran to max power AFR, the more quickly the engine overheated.

In my previous dyno session, I ran all the way to 9,000 RPM without severe overheating at 11.2:1 AFR and 22 degrees of ignition timing (I also only made 175 WHp).

I was making 175 WHp by 5,000 RPM on my next run, but the significantly more optimum AFR and 28 degree ignition timing proved too much for the engine.

Last time I ran for hours at optimum AFR with no issues, but I couldn't advance the timing enough to make much power as the engine would overheat immediately.

Basically, there was no difference in the engine internals between the dyno pulls, but keeping the engine from overheating was key in keeping the engine intact. There are those who would claim that the advanced ignition killed the apex seals, but I think it was more a temperature thing, as I ran 38 degrees of total advance at my last session, but I couldn't get past 4,000 RPM without overheating. As long as I stopped when the coolant temp hit about 115C I saw no problems with seal failure.

Interestingly enough, the only time I ever got to 9,000 RPM in 3rd gear on the dyno without overheating was when I was running 17:1 AFR.

[Barry Bordes]

A couple of observations.

Detonation can be a cause of breaking apex seals but it is not a root cause.

Leaning out at high boost and too much advance can be a root causes, but how many of us run conservative maps and still have problems? There is something else going on.

Also, no one has brought up the warping of apex seals. Using OEM I haven't seen this. Can anyone share their experiences with this problem?

Barry

[vex]

Originally Posted by Barry Bordes

A couple of observations.

Detonation can be a cause of breaking apex seals but it is not a root cause.

Leaning out at high boost and too much advance can be a root causes, but how many of us run conservative maps and still have problems? There is something else going on.

Also, no one has brought up the warping of apex seals. Using OEM I haven't seen this. Can anyone share their experiences with this problem?

Barry

My only experience of warping apex seals comes from when I was running OEM 3-piece seals. They didn't warp enough to cause failure before the 'fire control ring' let go, but they tended to warp concavely (ie The center of the seal moved to be closer to the eccentric shaft). I doubt this would cause the failure we're seeing. Convex warping may prove more of an issue; and may be indicative of the material selected for the seals.

Also the leaning out of the AFR does not necessarily have to be in positive pressure to cause the issues of thermal induced mechanical interference. Note that the SAE paper only took the motors up to 5000 RPM for 45 seconds. They were not in positive pressure, but were loaded. The result can be the same and is dependent upon the AFR and the resultant flame front temperature.

If you look at the picture I posted previously, I would assume that the peak temperature would appear at the peak temperature at normal operation (assuming timing remains constant and the fuel itself is adjusted). This means if we're running lean AFR at normal timing the result is going to be increased temperature at the Leading spark plug boss, where we may, or may not have appropriate energy transfer.

[Barry Bordes]

Vex from what I have read they seem to be talking about softer seals that warp or bow in the apex groove causing the seal to jam and thus lose sealing ability... but it can be straightened to be possibly used again.
Barry

[vex]

Originally Posted by Barry Bordes

Vex from what I have read they seem to be talking about softer seals that warp or bow in the apex groove causing the seal to jam and thus lose sealing ability... but it can be straightened to be possibly used again.
Barry

I don't think material hardness is going to cause this Barry. Thermal properties would, but material hardness works both ways...

[j9fd3s]

Originally Posted by Barry Bordes

A couple of observations.

Detonation can be a cause of breaking apex seals but it is not a root cause.

Leaning out at high boost and too much advance can be a root causes, but how many of us run conservative maps and still have problems? There is something else going on.

Also, no one has brought up the warping of apex seals. Using OEM I haven't seen this. Can anyone share their experiences with this problem?

Barry

i can see detonation breaking things, however on an iron seal NA engine, you can let it knock and ping all day and it'll take that abuse for a while. it will come apart, but not right away. with carbon seals detonation is a problem. i built a carbon seal PP engine, and everybody was warning me about detonation. which seems weird, its non turbo. although i actually have gotten it to detonate/ping a little. it makes the same bird chirpy detonation that the Rx8 does, similar conditions too, 1800-2200rpm, mid 14's afr, 18BTDC timing. throttle is around 40-60%

the SAE papers are on NA engines, and they point to the root cause being temperature related. when you add the turbo this doesn't change, except that you can have "conservative" maps and still be too hot.

so the question is what is too hot? and when is it too hot? note this is going to vary with the apex seal. we know the stock seals want about 900-950c EGT at peak power with a max of 1100c.

warping is a symptom i think. i don't think i've seen it, but i really don't have a good way to tell.

mike