I-Rotary Apex Seals Damaged by Bad Rotor Grooves

Evaluating the apex seal to rotor groove clearance upon engine teardown can easily be done by looking at the wear pattern or witness marks created on the side of an apex seal after its use as seen below:

 3 Apex Seals showing good rotor groove witness marks

Example 1
A Normal I-Rotary Apex Seal Groove Witness Wear Mark.
This engine was assembled by the late Rick Engman.

Example 1 shows the witness mark caused by the contact of an apex seal with its rotor groove with a proper clearance of 0.089 mm (0.0035 in.) between the rotor groove and the I-Rotary apex seals. Notice the straight, uniform, and consistent witness wear mark across the entire upper section of each of these I-Rotary Apex Seals. Also notice that the location of the witness mark is at the top of the rotor groove next to the area of the apex seal exposed to the combustion gases. This engine was taken apart due to an issue with the side housing though the apex seals were fine.

 

3 Apex Seals showing Bad rotor groove witness marks
Example 2
These I-Rotary Apex Seals exhibit an Abnormal and Uneven Apex Seal Groove Witness Wear Marks due to Improper Rotor Groove to I-Rotary Apex Seal Clearance.
Notice that there are no straight witness marks, indicating that the rotor groove clearance was incorrect upon installation.

 

Example 2 is an image from a rotor set of I-Rotary apex seals used in an engine that failed on the chassis dyno due to an improper apex seal-to-rotor groove clearance.

As can be easily seen, the sides of these I-Rotary apex seals from Example 2 exhibit an extremely abnormal wear pattern. The fact that the witness marks on these apex seals do not look correct (straight and even) was a clue that something else was going on with the assembly of this engine.

The Story Behind the Story
of the I-Rotary Apex Seals from Figure 2

 

The 13B engine with the improperly fitted I-Rotary apex seals shown in Example 2 was assembled by an engine builder located in southwestern North Carolina, USA. Neither the condition of the apex seal grooves in these rotors, nor the measurement of the clearance between the I-Rotary apex seals and their respective rotor apex seal grooves was evaluated before assembly of this engine.

The engine exhibited cold compression numbers after a proper break-in procedure that were not as consistent from face to face, as is typically expected with the use of the I-Rotary apex seals. The compression numbers in one rotor were 107, 107, 118 PSI and in the other rotor 103, 123, 116 PSI. This was the first indication that something was not normal with the sealing grid of this engine. Although not totally sure, it is believed that the starting RPM used during the measurement of these compression numbers was around the 240-260 RPM range.

In contrast, the image below is an example of the type of consistency normally obtained with  I-Rotary apex seals or Mazda apex seals. The maximum variation is within +/- 1.5 PSI.

 

Compression Test Consistency Attainable Using I-Rotary Apex Seals.

Compression test results
Chamber to Chamber within +/- 1.5 PSI
Image courtesy of Joe Perez and Danny Perez

Notice the consistent compression value for every pulse achieved with the I-Rotary Apex Seals in a properly assembled engine. According to Joe Perez, who ran this compression test on his son Danny Perez’s world record RX-7 after a break-in and a few passes on the strip, this old type of compression gage always reads lower (by several psi) than other compressions gages available on the market.

 

 Compression Numbers of 1ST Engine Build with I-Rotary Apex Seals
After a Break-In Period of around 700 miles (with bad Rotor Grooves)

 

Rotor 1 (psi)

Rotor 2 (psi)

107 – 107 – 118

103 – 123 - 116

The owner, not realizing that these somewhat adequate but very inconsistent compression numbers indicated that there may have been something abnormal with this engine, decided to take the car to a chassis dyno to perform an initial performance tune.  The engine before going to the dyno only had ~700 miles of break-In. This car was being tuned remotely using a tuner from California, USA.

After a few initial baseline tuning passes on the dyno, the engine was incrementally stepped up in RPM at higher level of power. During the 8000 RPM pass, at around 6,500 RPM the engine suddenly hesitated and stopped increasing in power until ~7200 RPM where power began to climb again. The engine was taken to 8,000+RPM during this run at which point the engine regained power.

After this pass on the dyno, the engine would not start. Upon examination, the engine compression numbers were dramatically low. When the engine was disassembled, the I-Rotary apex seals were found to be bent in a concave or wrong direction. Since the apex seals were bent, the first assumption was that there was something wrong with the apex seals.

The engine was disassembled by the same engine builder located in southwestern North Carolina and the I-Rotary apex seals were returned to us. After an extensive examination, the only unusual finding was an extremely abnormal rotor groove witness mark left on the sides of the apex seals as shown in Example 2. This was communicated to the owner of the engine, but this observation was dismissed as possibly just another lack of culpability by a manufacturer.

2nd Engine Rebuild
with a 2nd Brand of Aftermarket Apex Seals

 

At the recommendation of the same engine builder, a different brand of apex seals, which had been given a cryogenic treatment by this engine builder was used when the engine was reassembled for 2nd time. Once again, this engine builder did not bother to check the condition of the rotor grooves or the clearance between the second set of new apex seals from a different brand and the rotor apex seal grooves.

After this 2nd engine was given a proper break-in period, the engine was again taken to complete the dyno map that had been started before the first engine failure with the I-Rotary apex seals. Compression numbers with a different brand of apex seals were found to be very low, yet the car was running, so it was taken to a chassis dyno session to complete the final tune past 7,000 RPM.

After 5 pulls on the dyno to only 7,000 RPM, the engine became harder to start.  At this point, the tuner wisely recommended that they stop the dyno session until the compression numbers of this 2nd engine with a different brand of apex seals improved to avoid the possibility of another engine failure, i.e., another set of bent apex seals.

After a substantial break-in period plus a road racing track session, the compression numbers never came up.  In fact, they became even lower.  These compression numbers were 69 - 61 - 68 psi in one rotor and 49 - 50 - 50 psi in the other rotor.  These compression numbers were obtained at around the 240-260 RPM range.

Compression Numbers of 2nd Engine Rebuild
with a 2nd Brand of Aftermarket Apex Seals
After a Substantial Break-In period plus a Road Racing Track Test Session
 

Rotor 1 Compression Nos. (psi)

Rotor 2 Compression Nos. (psi)

69 – 61 - 68

49 – 50 - 50

Note that these compression numbers were significantly lower than the initial compression numbers obtained with the I-Rotary apex seals.

Since this engine continued to perform poorly, even after several additional miles or kilometers of running, which also included a road racing track session, the owner decided to take the engine back to the same engine builder located in southwestern North Carolina and the engine was disassembled, now for a third time.

Detailed and Accurate Examination of the Engine Components after 2nd Engine Disassembly

At this time, the engine components were examined by a third party in the mountains of North Carolina, USA. It was discovered through this examination by the third party that the grooves in the rotors being used in this engine were in extremely bad shape. The center section of the grooves in these rotors only provided a 0.050mm (0.002 in.) clearance for the apex seals while the ends of these grooves, along the corner seal areas, there was an excessive clearance of at least 0.254+ mm (0.010+ in.). The conclusion from this examination was that this set of rotors should never have been used in an engine.

 3 Apex Seals showing good rotor groove witness marks

Example 1
A Normal I-Rotary Apex Seal Groove Witness Wear Mark.
This engine was assembled by the late Rick Engman.

 3 Apex Seals showing bad rotor groove witness marks

Example 2
These I-Rotary Apex Seals exhibit an Abnormal and Uneven Apex Seal Groove Witness Wear Marks due to Improper Rotor Groove to I-Rotary Apex Seal Clearance.

 

The lack of any witness marks that are straight and even across the entire upper portion of the I-Rotary Apex Seals from Figure 1 indicate these apex seals were installed in a compromised groove from the start. If the rotor grooves had ever been correct, the wear witness marks on all the apex seals would have shown a straight mark across the entire seal on both sides, given that the 1st engine assembled with the I-Rotary apex seals had an extended break-in period of around 700 miles before its brief time on the chassis dyno.

This fact precludes any possibility that the damage of the rotor grooves happened as a result of the dyno incident. If the rotor groove would have been damaged during this dyno session, the I-Rotary apex seals would have a straight witness mark across the upper section in addition to the strange side wear marks present on these apex seals.

The abnormal and aggressive wear patterns on the sides of the I-Rotary apex seals in Example 2 also clearly mirror the clearanced measured with the damaged rotors used in the rebuild of 1st engine with the I-Rotary apex seals and the 2nd engine with another brand of apex seals.  In essence, the clearance for these apex seals was too tight along the center section of the rotor groove with only a 0.050mm (0.002 in.) gap and had an excessive clearance at the ends of these grooves with a gap of at least 0.254+ mm (0.010+ in.).

The abnormal wear pattern along most of the center area of these apex seals is a clear indication that these apex seals were being pinched along this section of the rotor grooves. In contrast, the ends of these apex seals around the corner seal only show a minimum or no contact with their respective grooves in these areas. This large gap at the ends of the apex seals allows the seal to experience excessive movement as well as an increased leakage condition which will always result in a loss of engine performance.

3rd Version of this Engine
with a
3rd Brand of Apex Seals
and
A Different Set of Used but Good Rotors with Properly Clearanced Apex Seal Grooves

 

This engine was reassembled for a 3rd time with a used but a good set of rotors using a 3rd brand of apex seals that were properly fitted or gapped to their respective rotor grooves by the third entity who performed the initial test to discover the fact that the original rotors used in the 1st and 2nd engine rebuilds had damaged apex seal grooves. As far as we are aware, this engine is now running adequately given that the root cause of the engine issue was found.

It should be pointed out than even though, the 3rd version of this engine is running adequately until now, the compression numbers are considerably lower than this same engine after its 1st rebuild using I-Rotary apex seals (See Evaluation of the Progression of Engine Compression Number Table Below)

This engine after it was assembled for a 3rd time should have yielded the highest compression numbers to date. It had a set of used but good rotors with new apex seals which had been properly gapped to their respective rotor grooves, and the greatest amount of break-in driving time after three extended break-in periods on the other remaining internal components, plus a few road racing track sessions.

Compression Numbers of this Engine after it was re-assembled for a 3rd time
with a 3rd Brand of Apex Seals and A Different Set of Used but Good Rotors
With Apex Seal Grooves which Had Been Properly Clearanced

 

 

Rotor 1 (psi)

Rotor 2 (psi)

 After initial Start with

A light amount of running

(Unknown Test RPM)

83 - 95 - 95

108 - 105 - 105

After ~1,300 miles of Break-In

+

a few Road Racing Track Sessions.

(Test @ ~300 RPM)

 94 - 91 - 75

96 - 98 - 91

 

Evaluation of the Progression of
Engine Compression Numbers of this Engine
as a Function of the Three Engine Rebuilds

 

It should be highlighted that the highest cold compression numbers reported for this engine were obtained after its 1st rebuild with the I-Rotary apex seals, even though these I-Rotary apex seals were installed in an engine with damaged rotor grooves which did not allow the apex seals to freely move in their respective grooves during engine operation and where the internal components had the least amount of break-in time. The table below summarizes these compression results.

 

 

Rotor 1 (psi)

Rotor 2 (psi)

1st Engine Rebuild

with I-Rotary Apex seals installed in Bad Rotors

107 - 107 – 118

Only a 700 mile break-In Period

103 - 123 – 116

Only a 700 mile break-In Period

 

 

 

2nd Engine Rebuild

with a 2nd brand of aftermarket apex seals

but still using Bad Rotors

69 - 61 – 68

After a substantial break-in period + a Dyno Session + a Race Track session

49 - 50 – 50

After a substantial break-in period + a Dyno Session + a Race Track session

 

 

3rd Engine Rebuild

after it was re-assembled with a 3rd Brand of Apex Seals

+

Good Rotors with Properly Clearanced Apex Seal Grooves

83 - 95 – 95

After initial Start with

A small amount of running

Unknown RPM

108 - 105 - 105

After initial Start with

A small amount of running

Unknown RPM

 

94 - 91 – 75

After ~1,300 miles of Break-In

And a track session

Test Performed @ ~300 RPM

96 - 98 – 91

After ~1,300 miles of Break-In

And a track session

Test Performed @ ~300 RPM

 

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The Behavior of an Engine Experiencing an Apex Seal Binding Condition

Any rotor with a clearance of only 0.050mm (0.002 in.) between the apex seal and the rotor groove will almost always result in a condition which will bind the apex seal during engine operation, regardless of the brand or material of the apex seal.

Additionally, any engine experiencing a binding apex seal condition, or where the apex seal is unable to freely move as intended in its groove during engine operation, will not run smoothly and will likely exhibit a degree of hesitation. The level of hesitation experienced by this engine is a function of level of pinching force that restricts the movement of the apex seal as well as the RPM of the engine. The higher the RPM, the higher the level of hesitation.

If the binding force on the apex seal provided by a tight rotor groove clearance is excessive, as it would have been expected with only a 0.050mm (0.002 in.) gap, the likelihood of failure is vastly increased.

=====================================

Explanation of an Engine Failure Mechanism
Due to the Binding of an Apex Seal in its Rotor Groove

 

  • The lack of free movement of the apex seal, especially the trailing apex seal, will allow the hot combustion gases from the combustion stroke to leak or pass into the subsequent incoming charge, thus increasing the likelihood of pre-ignition and/or detonation in the incoming combustion chamber.
  • This condition will in turn result in an instantaneous and uncontrolled pressure spike into the incoming chamber. This uncontrolled pressure spike, if it is high enough, will cause the apex seals to bend without the requirement for an excessive high temperature condition to be present (no heat coloring on the apex seal).
  • Once a severe pressure spike is initiated in one chamber due to a detonation or pre-ignition event, the air-fuel mixture of each of the incoming rotor faces can ignite prematurely, resulting in all the chambers of this rotor experiencing uncontrolled combustion conditions. These uncontrolled combustion conditions will bend any metallic based apex seal, regardless of the apex seal brand, or fracture any brittle or ceramic based apex seal.
  • THE MECHANISM ABOVE IS THE REASON WHY MOST, IF NOT ALL, METALLIC APEX SEALS BENDING FAILURES HAPPEN IN ROTOR SETS AT ONCE (3 APEX SEALS BENDING or 6 APEX SEALS BENDING).

DISCLAIMER

These I-Rotary Apex Seals are competition components and are sold "As Is" and without warranty of any kind.  All implied warranties including all warranties of merchantability or fitness for a particular purpose are hereby disclaimed. Purchaser acknowledges that they shall be responsible for and bear any and all costs associated with the use of these I-Rotary Apex Seals. Purchaser acknowledges that installation of these I-Rotary Apex Seals may cause the vehicle to be unable to be lawfully used on public highways and assumes all risks and expenses thereof.

Extremely Important: Do not use these parts in any type of Aircraft or Flying Vehicle