Using the I-Rotary Apex Seal - F.A.Q.

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Lubrication and Pre-Mix

The I-Rotary Apex Seal (I-RAS) can be treated just like the Mazda OEM apex seal in all applications.

We strongly recommend the additional use of a high quality 2-stroke oil in the fuel to improve the longevity of the apex seal (Mazda’s or I-Rotary or any other aftermarket apex seal).

Importantly, the pre-mixing of a high-quality oil in the fuel will also help lubricate the rest of the sealing grid components and all the other internal wear surfaces of the engine.

Recommended Oil Premix Amounts in the Fuel
Using a Premium 2-Stroke Oil or Other Oil of Choice

For High Performance, Track-Day or Racing Engines
With or Without a Functioning OMP

Fuel Type

Milliliters per Liter of Fuel

US Fluid Ounces per US Gallon


(Pure Alcohol)

15-20 ml/Liter

2.0-2.5 oz/gallon

E85 Fuel

15 ml/Liter

2.0 oz/gallon


12-15 ml/Liter

1.5-2.0 oz/gallon

For Engines with a Functioning Oil Metering Pump (OMP)

Fuel Type

Milliliters per Liter of Fuel

US Fluid Ounces per US Gallon

E85 Fuel

12-15 ml/Liter

1.5-2.0 oz/gallon


10 ml/Liter

1.25+ oz/gallon


Apex Seal to Rotor Groove Clearance

The clearance or gap between the apex seal and its rotor groove as well as the consistency of this clearance across the entire groove is one of the most important factors in reaching the maximum performance, fuel economy and reliability attainable by any rotary engine.

This is the reason why the I-Rotary Apex Seals and the Mazda apex seals are made to such a high level of precision and accuracy across the thickness.

For maximum engine performance, the spacing or gap between an apex seal and its groove should be the same for every apex seal in that rotor.

It is also important that all apex seals have the same from whatever value is selected from the recommended range below







0.0762 mm

0.127 mm

0.003 in.

0.005 in.

The fundamental reasons for this clearance to have a minimum value are:

  • To minimize and / or prevent the apex seal from binding in the rotor groove.
  • To enhance the sealing capability of the apex seals during the compression and expansion strokes by allowing the gas pressure to travel through the rotor groove gap and push the underside of the apex seals toward the rotor housing. This effect is particularly important on the trailing apex seal.

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:

Good Rotor Groove to Apex Seal Clearance by Rick Engman
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 length of each of these I-Rotary Apex Seals. Also notice that the location of the witness mark is along the top of the I-Rotary apex seals which is next to the exposed area or ride height of the apex seal during operation. This engine had to be taken apart due to an issue with the side housing though the apex seals were fine

Bad Apex Seal to Rotor Groove Clearance Example
Example 2
Abnormal 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 as compared to the consistent wear witness marks of the I-Rotary apex seals illustrated in Example 1 which was assembled using a proper rotor groove to apex seal clearance.

In Example 2 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.).

For more information about this engine go to I-Rotary Apex Seals Damaged by Bad Rotor Grooves


Engine “Break-in” Procedure

I-Rotary Apex Seals often exhibit higher cold compression numbers than other apex seals. The engine can then appear to be broken-in and ready for tuning, however, due to the low wear characteristics of the I-Rotary Apex Seal, it is not.

In actuality, the apex seal surface that rides on the rotor housing has not fully mated and requires more time. Tuning for maximum power in this conditon significantly increases the likelyhood of engine failure.

Due to these factors, we recommend that the engine break-in periods be extended when using our seals.

Maximum performance will be achieved with a proper engine “Break-In” procedure. As far as we are aware, there is no Mazda-recommended or standard practice regarding the Break-In procedure for a rotary engine as there exists for high performance reciprocating piston engines.

In general, the break-in procedures for both types of engines (piston or rotary) are similar in that after an engine rebuild, the engine should be operated or driven gently during the initial period before an attempt is made at obtaining its maximum performance.

Many rotary engine builders suggest after a rebuild to run the engine for several hours (from 2-to-10+ hours) with a light load at 1000-2,000 RPM or just above the idle RPM.  Then, change the oil and the oil filter and run the vehicles for 500-1,000+ miles (~800-1,600 km) as easy as possible with minor acceleration events in the mid RPM range towards the later stages of these distances to allow the bearings, seals, and other wear surfaces to mate to each other.

The engine break-in procedure when using the I-Rotary apex seal may require a longer time to properly bed-in into the rotor housing surfaces than when using all other apex seals available in the marketplace, including the Mazda apex seal.  This is due to the much lower wear characteristics of the I-Rotary apex seals when compared to higher wear behavior of other apex seals, which makes the I-Rotary apex seal take longer than other apex seals to bed-in.

Engine “Break-in” Procedure on the Dyno

When attempting to tune the engine with the I-Rotary apex seals on the dyno (engine or chassis dyno), it is recommended that an engine go through any of the preliminary levels of the initial break-In procedure described above before a power tune on the dyno is considered.

Due to the inherently low wear characteristics of the I-Rotary Apex Seal, it is also recommended that the power tune procedure on the dyno be performed using a higher number of runs on the dyno than is typical with the other types of apex seals.

This dyno procedure should start at the lowest values of RPM and power settings possible, methodically increasing these values in small step increments before any attempt is made at obtaining the maximum power at the highest RPM and wide-open throttle position.

This increased number of runs or cycles methodology will provide a better chance for the I-Rotary Apex Seal, as well as any other apex seal brand, to mate or bed-in to the internal surfaces of the engine, especially the rotor housing.  Any apex seal that is not properly mated or bedded in with these internal surfaces, regardless of the brand, will singificantly increase the possibility of engine detonation or pre-ignition, which in turn, will typically result in an engine failure with bent apex seals.

As reference, we have found it useful to review some of the established piston engine break-in procedures from reputable sources.  Some of these include:

Mahle recommended piston ring break-in procedure

Piston Rings 101: Break-in Procedure - with Lake Speed Jr.

How to Properly break in your new engine with Lake Speed Jr

LA Sleeves 2 Stroke Break-in Procedure

LA Sleeves 4-Stroke Break-In Procedure


Adding Fuel during Deceleration

(Extremely Important)

It is extremely important that a certain amount of pre-mixed fuel continues to flow into the engine during the deceleration phase of the rotary engine, especially if the engine is not using the Oil Metering Pump (OMP).

The addition of fuel with a pre-mixed amount of lubricant during deceleration events, such as coasting the engine from 7000 RPM with the foot off the throttle, allows the entire sealing grid to remain lubricated during this event. The addition of the pre-mixed amount of lubricant during deceleration events is extremely important when the engine is being tuned on the chassis dyno after the completion of a dyno run. All apex seals, regardless of the brand (Mazda’s or all aftermarket apex seals), will benefit from the addition of pre-mixed fuel on deceleration.

Please note that if the engine is using a Mazda stock ECU, this ECU is programmed to cut the fuel in deceleration to improve gas mileage. You will need to disable this feature on the Mazda ECU to allow the fuel to continue to flow during deceleration. You will also need to make sure that the addition of fuel on deceleration is programmed on any other aftermarket ECU.

Rotor Housings

The best performance results for the I-Rotary Apex Seal are obtained with new rotor housings.

Important: It has been found by several engine builders that the dark surface treatment or residue left on the chrome trochoid inner surface of the NEW Mazda rotor housings should be removed for the best performance of any metallic apex seal. This surface treatment or residue was not present on the chrome surface of older housings.

To remove this layer, use 400-600 grit Silicon Carbide sand paper and, preferably by hand, gently sand the rotor housing inner surface in a manner that does not create grooves in the surface. This sanding process should also not affect the flatness or squareness of the Mazda inner surface. Continue with this sanding step until the inner surface becomes brighter or shiny. Then, clean the inner surface thoroughly as well as the rest of the rotor housing to remove any residue from the sanding process. Continue cleaning the chrome surface until your cleaning cloth or paper towel no longer shows any residue.

Used rotor housings can be used but must be inspected to make sure that they are:

  1. Within the width dimensions recommended by Mazda
  2. Not heavily shrunk or distorted along the leading spark plug area
  3. Not distorted along the exhaust port
  4. Have a good chrome surface that is smooth, with low wear, free of scratches and without any chipping along the edge.

When using used rotor housings, it has also been found by several engine builders that sanding and cleaning the trochoid inner surface of the rotor housing, as mentioned above, may improve the life and performance of any metallic apex seal.

Use of a used rotor housing that is not as described above will damage any metallic apex seal, lowering its life.

Important note: to our knowledge, not a single rotor housing has been damaged by an I-Rotary Apex Seal. With normal conditions and normal lubrication the rotor housing chrome surface will be in excellent condition after using our apex seals.



The best performance results for the I-Rotary Apex Seal are obtained with new rotors.

Used rotors can be used but must be inspected to make sure that they do not have damaged or mis-cut apex seal grooves and that the proper apex seal groove clearance can be obtained.

Use of a used rotor with damaged or mis-cut apex seal grooves will damage any metallic apex seal.


    What Springs to Use

    I-Rotary Apex Seal Model

    Spring Part Number (P/N)

    13B - 2mm - 2pc.

    (Mazda P/N: 0000-01-9113-ST)

    Mazda P/N N3H3-11-C06 (Outer Spring)

    Mazda P/N N3H3-11-C04 (Inner Spring)

    Renesis - 2mm - 2pc.

    (Mazda P/N: 0000-01-9116-ST)

    Mazda P/N N3H3-11-C06 (Outer Spring)

    Mazda P/N N3H3-11-C04 (Inner Spring)

    13B - 3mm - 2pc.

    Mazda P/N:  1757-11-304

    12A - 3mm - 2pc.

    Mazda P/N:   1011-11-304B


    Buy from Our Distributors Here


    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