Rotary Engine build Blog

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13b, rx8 builds, Side seal Clearance

9 Min Read

Rotary Engine REbuilds | Side seals and clearances

Rotary Engine rebuilds are not all the same..

...anyone can look up a few YouTube videos and start rebuilding your motor. The choice is yours. 

Performance is all about achieving the objectives on the path of the rebuild. This includes side seals and all the other seals.

All of our builds get the same level of detail as our racing builds, details matter. Mazda spent a lot of time figuring this out, we tend to stay with OEM side seals. If anyone has information that challenges the work / results of the Mazda engineers and builds a better version, by all means share that information. We are all about the results.

What side seals do I need for my rebuild? This is a highly subjective discussion as the Rx8 / Renesis has a side seal groove and mating angle to the corner seal exclusive to the Rx8 rotors.

Pull up the specs on side seals and you'll see a charts like these:

rx8 side seals
The corresponding letter represents the size needed for this specific side seal groove.
Rx8 side seal letter chart
Part numbers for the letter size of the side seal. The five part numbers represent a wide number of letters.
side seal tolerances for Rx8
Measuring the side seal clearance. The key here is to have the side seal compress and not bind up in the groove.
Side seal clearancing rx8 rotors
Look very close and you'll see that the side seal contours the corner seal. Precision tolerances = solid compression numbers / performance.

This chart is for buying the pre-cut seals from Mazda and installing them according to the letter referenced directly on the rotor face near the side seal groove.

Why are the side seals different on the Renesis motor? In the name of progress for compression, emissions and improving wear characteristics. The keyed groove is there to allow the side seal to move side to side for increased compression as well as to self clean carbon deposits (think of this as watching your windshield wipers). 

Clearances: The factory manual states that .002-.006 per side to be within spec. With all other Mazda rotaries, we like it to be tighter as the older rotors had the slotted groove. There is a lot of difference of opinion on the rx8 side seals and how to get them to work properly. 

Add to this that the Renesis rotary engine uses a side port exhaust, the reasons become clear. There is a lot going on with regards to heat and heat transfer. These little thin strips of metal do a lot of work! 

On motors that I am building, I like to set the clearance (tight) and then take another step, adding a contour to the side seal to better conform to the corner seal. We use diamond cutters that mimick the corner seal for accuracy. This ensures that they mate well and keep compression working well past the first 20,000 miles. Remember, there is a huge difference to assembly of a motor and building one. Again, the details matter.  

What process is the best? That depends on how you plan on driving the car. We know that the street cars will work well with the lettered pre-cut side seals, for racing and track day engines, we recommend a bit more precision. 

Most engine builds will do fine with the lettered pre-cut side seals, this is where a proper discussion with your engine builder makes the difference. 

Ready to start a conversation?

Topics:   13b, rx8 builds, Side seal Clearance

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