This section will concentrate on parts that are typical replaced during an engine rebuild. 

Apex seals:
[6 apex seals required per engine.]
Mazda OEM stock apex seals are the proven apex seals at the moment.  Mazda has changed from a 3-piece, 2mm apex seal to a 2-piece, 2mm apex seal.  The jury is still out on the advantage of the new 2-piece, 2mm Mazda apex seals, as there are stories about excessive apex seal warping on high boost (over 15psi) and aggressively wide exhaust ports.  Currently, we have several customers running these seals with very aggressively ported exhaust ports running over 10psi with no report of failures.  Some have blamed relaxed quality control specs on these new 2-piece, 2mm apex seals due to current RX-8 performance parameters, since the new RX-8 does not use forced induction / boost.

The older apex seal had an "electron beam hardened" leading edge, which K2RD had tested to be around 60C Brinnell hardness; the back end of the apex seal tested a softer 40C Brinnell hardness.  The harder leading edge allows for longer apex seal life, while the softer back end is easier on the apex seal groove in the rotor.  Excessive apex seal hardness can cause premature apex seal groove wear in the rotor.

Now, this fact becomes significant when we start talking about aftermarket (non Mazda OEM) apex seals.  Only in recent years have aftermarket apex seals offerings been significant.  Previous to these recent offerings, you only had Mazda OEM, carbon races seals not made for forced induction / boost, and ultra-expensive ceramic units that cost several thousand dollars for a complete set of six!

Hurley Engineering of U.K. was one of the first economical options over the stock Mazda OEM units.  Keep in mind that stock Mazda OEM apex seals were priced over $40 / each, and a set of six was approaching $300; current Mazda prices around $50 / each or more.  Hurley Engineering had their set of six apex seals for around $200, which made it an attractive option.  Hurley Engineering were touting their seals to break-in quicker and cause very little damage when they failed.  Most user experiences are consistent with their claims.  Now, this may sound like a good thing, but upon closer examination of these seals, this is not the case.  We theorize that the Hurley Engineering apex seals are made of softer metal / steel.  This would explain the Hurley Engineering claims.  Early engine failures seem to abound with these apex seals, and even though you end up with no or very little damage, I don't call doing early rebuilds an advantage.

More recently, Atkins and Rotary Aviation have offered their versions of apex seals.  Both are very economical options over the Mazda OEM apex seals.  Initial production from both manufacturers had problems with quality control, and premature apex seal failures were common.  These defects were supposedly fixed, and currently produced units are supposedly better.  Consumer experiences are still building, and the jury is still out on whether either can compete with the Mazda OEM units for reliability.  Atkins does not recommend "high boost" with their units, and those users who do not run more than 15psi should be okay.  Rotary Aviation have been touting their "700% stronger" apex seals, but having stronger apex seals does not necessary mean better.  Ideally, it looks like Mazda has the best design with the leading edge hardened, and it seems that none of the aftermarket options can offer a similar design at a cheaper price; the Mazda OEM apex seals are costly due to the intensive hardening process - Mazda did do their homework on R&D on their apex seals!

We won't bother even touching on ceramic apex seals, as even "cheap" ones are still over $1,000 for a set of six.  If you can afford a set of these, you've probably made your mind made up by now.

The subject of 3mm apex seals is highly debated.  Yes, the 3mm apex seals are stronger, but are they really that much stronger in real world testing?  In our experience, it is not.  They can give you a slightly larger safety buffer against failing under detonation, but they are not indestructible.  About the only valid reason to look at 3mm apex seals is if you insist on reusing rotors which have excessive apex seals groove wear.  The worn apex seal grooves in the rotors can be machined out for the thicker 3mm apex seals.  Be warned that precision machining is necessary to get proper apex seal positioning and sealing.  Sloppy or inferior machining will cause improper apex seal sealing and possibly apex seal binding!

Apex seal springs:
[6 apex seal spring sets (six longer, six shorter) required per engine.]
Check Mazda specs on tolerances.  For a tight rebuild, we recommend replacing the apex seals springs.  If you're on a budget, you can get away with reusing them.  Most high mileage engines are beyond Mazda specs, and reusing the old springs will not allow you to get top compression.

Corner seals:
[12 corner seal (rubber inserts) required per engine.]
The metal part of the corner seal does not normally wear significantly.  You can reuse the metal part, and the rubber insert can just be replaced.
Mazda part number for corner seal rubber insert:  N201-11-3220
Mazda part number for corner seal + rubber insert:  N326-11-C20A

Corner seal springs:
[12 corner seal springs required per engine.]
The stock FC3S corner seal spring is an old design, and we recommend using the FD3S corner seal spring.
Mazda part number for FD3S corner seal spring:  NF01-11-C24

Side seals:
[12 side seals required per engine.]
Side seals do not normally wear significantly.  If you do order new side seals, the new side seals are not sized for a drop-in fit; the new side seals need to be clearanced to fit properly.  We like to clearance the side seal to corner seal clearanced on the tight side (0.0015" to 0.002") for better compression on street engines.  Race engines can run looser clearances.

Side seal springs:
[12 side seals springs are required per engine.]
Side seal springs do not normally wear.  Old ones can be reused.

Rotor bearings:
[2 rotor bearings are required per engine.]
Used rotor bearings are more desirable then new ones.  If you do detect significant wear on your rotor bearings and require new bearings, you need to double the break-in period.
FC3S Pro - FAQ, Break-In procedure

Oil control metal rings:
[8 oil control metal rings (4 outer, 4 inner) are required per engine.]
Most times the oil control metal rings can be reused.  If the oil control metal rings mating surfaces to the side irons are entirely shiny, we recommend to replace them.  Most times, only part of the mating surface will be shiny.

Oil control springs:
[8 oil control springs (2 outer / front, 2 outer / rear; 2 inner / front, 2 inner / rear) are required per engine.]
Most times the oil control springs can be reused.  If there is significantly wear, replace them.  I believe the Mazda spec for shiny wear spots from the normally copper plated surface is 0.5mm wide.

Oil control o-rings:
[8 oil control o-rings (4 outer, 4 inner) are required per engine.]
These o-rings should be replaced.  Some vendors offer aftermarket Viton o-rings for better sealing.

Water jacket o-rings, inner:
[4 inner water jacket o-rings are required per engine.]
We use McMaster-Carr teflon encapsulated silicone o-rings for replacements for the inner water jacket o-rings.  These o-rings are priced right around $10 / each and are cheaper than the stock Mazda OEM part.  These are stronger and reusable versus the stock Mazda OEM part.

Water jacket o-rings, outer:
[4 outer water jacket o-rings are required per engine.]
These o-rings should be replaced.  Mazda OEM is recommended for use of these outer o-rings.  At under $10 / each, they are still reasonable from the Mazda dealer.
Mazda part number for water jack o-ring, outer:  N326-10-B720

Summary of (above) o-rings and seals:
Type: Quantity: Required? Mazda part number: Price:
Apex seal 6 Required N351-11-C00C $60 / each
Apex seal spring, long 6 Highly recommended N326-11-C06C $10 / each
Apex seal spring, short 6 Highly recommended N326-11-C04A $8 / each
Corner seal, rubber insert 12 Required N326-11-C22A $3 / each
Corner seal, complete 12 Inspect - replace if necessary N326-11-C20A  
Corner seal spring 12 Replace with FD3S part NF01-11-C24  
Side seal 12 Inspect - replace if necessary N3Y1-11-C11  
Side seal spring 12 Inspect - replace if necessary NF01-11-C17  
Oil control metal ring, outer 4 Inspect - replace if necessary 8871-23-180
(set includes one inner and one outer)
Oil control metal ring, inner 4 Inspect - replace if necessary 8871-23-180
(set includes one inner and one outer)
Oil control spring, outer, front 2 Required, most likely if original 1011-11-353A  
Oil control spring, outer, rear 2 Required, most likely if original 1011-11-363A  
Oil control spring, inner, front 2 Required, most likely if original N225-11-351  
Oil control spring, inner, rear 2 Required, most likely if original N225-11-361  
Oil control o-ring, outer 4 Required 8341-11-343 $22 / each
Oil control o-ring, inner 4 Required 0820-11-341 $12 / each
Water jacket, outer 4 Required N326-10-B72 $10 / each
Water jacket, inner 4 Required (Use McMaster-Carr part) $10 / each
Rotor bearing 2 Inspect - replace if necessary 1011-11-111  

Miscellaneous o-rings and seals:
Type: Quantity: Mazda part number: Price: Notes:
Tension bolt "stat-o-seal" sealing washer 18 0839-10-455 $2 / each  
Rear stationary gear o-ring 1 0813-10-555A $7  
Oil filter pedestal o-ring 2 9954-10-1601 $5 / each  
Dowel pin o-ring 4 N3A1-10-B73 $10 / each  
Front oil cover o-ring 1 N231-10-174    
White Teflon support ring 1 N326-10-C15 $5 Kouki FC3S only!
Front oil cover gasket 1 N326-10-502A $20 Kouki FC3S only!
Lower intake manifold coolant o-ring 2 8527-13-113 $10 / each  
Front cover oil seal 1 0820-10-605 $5  
Rear oil seal 1 1668-10-556A $15each  
Pilot bearing 1 N326-11-D03 $15  
Pilot bearing seal 1 1881-11-404 $5  
All parts are highly recommended to be replaced.

Type: Quantity: Inspect: Mazda part number: Price:
Oil pump chain 1 Deflection according to Mazda specs N326-14-151  
Torrington needle bearing, front 2 No scoring on needle bearings, bearing race intact 0813-11-5058  
Thrust bearing washer, front 1 No scoring on washer faces 1011-11-501  
Thrust plate, front 1 No scoring on plate face    
Eccentric shaft front spacer 1 No mushrooming of edges; should slide easily on eccentric shaft    
Stationary gear, front 1 No chipped or damaged teeth on gear N370-10-E00C
(includes bearing and oil seal)
Stationary gear bearing, front 1 No copper showing; copper exposed on "seam" OK 0820-10-502B (standard)
N350-10-E02 (oversized)
Stationary gear, rear 1 No chipped or damaged teeth on gear N370-10-E10B
(includes bearing and oil seal)
Stationary gear bearing, rear 1 No copper showing; copper exposed on "seam" OK 0820-10-502B (standard)
N350-10-E02 (oversized)
Side housing, rear 1 No excessive scoring on chrome surface    
Side housing, center 1 No excessive scoring on chrome surface    
Side housing, front 1 No excessive scoring on chrome surface    
Rotor housing 2 No excessive scoring on chrome surface; apex seal triangle assist piece groove OK    
Rotor 2 Check all seal clearances; no excessive damage on rotor faces, especially near apex seal grooves    
Eccentric shaft 1 No excessive scoring on bearing journals (2 stat gears, 2 rotor)    
Inspect all parts - any part not passing inspection should be replaced

Questions?  Comments?  Click here to contact us!