Apex seals
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Racing artist
Joined: Jul 2010
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From: Twain Harte California
Apex seals
I am rebuilding my 12A in my race car (83 RX 70) I have done a large port job (next bigger is bridge port) I fabricated a header two inch pipes into three inch pipe. I fabricated a intake to run a 44 MM weber IDF. I would like to know the differents that you get with the different apex seals. Stock one piece or two piece. Carbon or ceramics 2mm or 3mm.Where is the best places to buy these parts?
Joined: Mar 2001
Posts: 31,833
Likes: 3,232
From: https://www2.mazda.com/en/100th/
here is a rundown on seals. starting with construction.
2 piece; the triangle bit lets the seal change widths, so when the seal expands and contracts, it still seals.
3 piece; kind of academic, as these are custom at this point, but it can expand width wise too, so these seal the best, but are also fragile. the JDM tuners actually take 2 piece seals and cut em.
1 piece; the seal is a fixed length. there is now a rotor housing width to seal length clearance, and it needs to be set so that when the engine is the hottest, the seal doesn't bind, so the rest of the time you're running with too big a clearance, and loose power.
Materials;
there are basically 3.5.
ceramic. these are very strong, wear is very low, the seals are light. so they offer better performance, although cost is very high, and if you break one, it apparently does catastrophic damage.
carbon; these seals are very light, inexpensive, they have a self lubricating property, and are cheap. the light seal offers good high rpm sealing. these seals wear more quickly than any of the others, and are fragile, but probably won't do any damage when/if they go. its what all the racers used in the 70's and 80's. they are also very easy on the rotor housings
iron; this is what the stock seal is made from. it lasts a long time, and strong. they are also heavy, so they do not like high rpm.
the stock seal is iron with an electron beam hardening process, so each surface has a different hardness.
the after market iron seals have different processes and tend to be flexible where Mazda's seal is brittle. Mazda seal is also crowned, so when its in a running engine its flat, most after market seals are flat so they must be bowed when the engine is running. also the quality control isn't as good on the aftermarket seals, they need to be measured, and checked for straightness warping
so choices. ideally it sounds like we want a 3 piece ceramic seal, but there aren't any, and if there were it would be like $2000 for the set. the stock iron seals are $$ and not a great choice in a race car.
so this basically leaves us with the MFR carbon seal, which is 1 piece, but otherwise pretty ideal in a race car
2 piece; the triangle bit lets the seal change widths, so when the seal expands and contracts, it still seals.
3 piece; kind of academic, as these are custom at this point, but it can expand width wise too, so these seal the best, but are also fragile. the JDM tuners actually take 2 piece seals and cut em.
1 piece; the seal is a fixed length. there is now a rotor housing width to seal length clearance, and it needs to be set so that when the engine is the hottest, the seal doesn't bind, so the rest of the time you're running with too big a clearance, and loose power.
Materials;
there are basically 3.5.
ceramic. these are very strong, wear is very low, the seals are light. so they offer better performance, although cost is very high, and if you break one, it apparently does catastrophic damage.
carbon; these seals are very light, inexpensive, they have a self lubricating property, and are cheap. the light seal offers good high rpm sealing. these seals wear more quickly than any of the others, and are fragile, but probably won't do any damage when/if they go. its what all the racers used in the 70's and 80's. they are also very easy on the rotor housings
iron; this is what the stock seal is made from. it lasts a long time, and strong. they are also heavy, so they do not like high rpm.
the stock seal is iron with an electron beam hardening process, so each surface has a different hardness.
the after market iron seals have different processes and tend to be flexible where Mazda's seal is brittle. Mazda seal is also crowned, so when its in a running engine its flat, most after market seals are flat so they must be bowed when the engine is running. also the quality control isn't as good on the aftermarket seals, they need to be measured, and checked for straightness warping
so choices. ideally it sounds like we want a 3 piece ceramic seal, but there aren't any, and if there were it would be like $2000 for the set. the stock iron seals are $$ and not a great choice in a race car.
so this basically leaves us with the MFR carbon seal, which is 1 piece, but otherwise pretty ideal in a race car
here is a rundown on seals. starting with construction.
2 piece; the triangle bit lets the seal change widths, so when the seal expands and contracts, it still seals.
3 piece; kind of academic, as these are custom at this point, but it can expand width wise too, so these seal the best, but are also fragile. the JDM tuners actually take 2 piece seals and cut em.
1 piece; the seal is a fixed length. there is now a rotor housing width to seal length clearance, and it needs to be set so that when the engine is the hottest, the seal doesn't bind, so the rest of the time you're running with too big a clearance, and loose power.
Materials;
there are basically 3.5.
ceramic. these are very strong, wear is very low, the seals are light. so they offer better performance, although cost is very high, and if you break one, it apparently does catastrophic damage.
carbon; these seals are very light, inexpensive, they have a self lubricating property, and are cheap. the light seal offers good high rpm sealing. these seals wear more quickly than any of the others, and are fragile, but probably won't do any damage when/if they go. its what all the racers used in the 70's and 80's. they are also very easy on the rotor housings
iron; this is what the stock seal is made from. it lasts a long time, and strong. they are also heavy, so they do not like high rpm.
the stock seal is iron with an electron beam hardening process, so each surface has a different hardness.
the after market iron seals have different processes and tend to be flexible where Mazda's seal is brittle. Mazda seal is also crowned, so when its in a running engine its flat, most after market seals are flat so they must be bowed when the engine is running. also the quality control isn't as good on the aftermarket seals, they need to be measured, and checked for straightness warping
so choices. ideally it sounds like we want a 3 piece ceramic seal, but there aren't any, and if there were it would be like $2000 for the set. the stock iron seals are $$ and not a great choice in a race car.
so this basically leaves us with the MFR carbon seal, which is 1 piece, but otherwise pretty ideal in a race car
2 piece; the triangle bit lets the seal change widths, so when the seal expands and contracts, it still seals.
3 piece; kind of academic, as these are custom at this point, but it can expand width wise too, so these seal the best, but are also fragile. the JDM tuners actually take 2 piece seals and cut em.
1 piece; the seal is a fixed length. there is now a rotor housing width to seal length clearance, and it needs to be set so that when the engine is the hottest, the seal doesn't bind, so the rest of the time you're running with too big a clearance, and loose power.
Materials;
there are basically 3.5.
ceramic. these are very strong, wear is very low, the seals are light. so they offer better performance, although cost is very high, and if you break one, it apparently does catastrophic damage.
carbon; these seals are very light, inexpensive, they have a self lubricating property, and are cheap. the light seal offers good high rpm sealing. these seals wear more quickly than any of the others, and are fragile, but probably won't do any damage when/if they go. its what all the racers used in the 70's and 80's. they are also very easy on the rotor housings
iron; this is what the stock seal is made from. it lasts a long time, and strong. they are also heavy, so they do not like high rpm.
the stock seal is iron with an electron beam hardening process, so each surface has a different hardness.
the after market iron seals have different processes and tend to be flexible where Mazda's seal is brittle. Mazda seal is also crowned, so when its in a running engine its flat, most after market seals are flat so they must be bowed when the engine is running. also the quality control isn't as good on the aftermarket seals, they need to be measured, and checked for straightness warping
so choices. ideally it sounds like we want a 3 piece ceramic seal, but there aren't any, and if there were it would be like $2000 for the set. the stock iron seals are $$ and not a great choice in a race car.
so this basically leaves us with the MFR carbon seal, which is 1 piece, but otherwise pretty ideal in a race car
Joined: Jun 2006
Posts: 4,815
Likes: 24
From: Columbia, Tennessee
Well basically its the width of the seal groove bore on the rotor tips. Youd have to have 12a rotors milled to accept 3mm seals which I think only came standard on some very early 10a/12a engines and Renesis. Not sure of the actual benefits... Although Id think thicker equals stronger. Could be wrong.
Joined: Mar 2001
Posts: 31,833
Likes: 3,232
From: https://www2.mazda.com/en/100th/
the 68-73 engines were 5mm, the 74-85 engines are 3mm and everything after that is 2mm, so for a 12A, you really only have the 3mm choice.
the only time you change apex seal size, is on a 2mm seal engine with worn out apex seal grooves, and people mill them out to 3mm.
the only time you change apex seal size, is on a 2mm seal engine with worn out apex seal grooves, and people mill them out to 3mm.
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Rot005
Joined: Apr 2013
Posts: 103
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From: Texas
I am rebuilding my 12A in my race car (83 RX 70) I have done a large port job (next bigger is bridge port) I fabricated a header two inch pipes into three inch pipe. I fabricated a intake to run a 44 MM weber IDF. I would like to know the differents that you get with the different apex seals. Stock one piece or two piece. Carbon or ceramics 2mm or 3mm.Where is the best places to buy these parts?
Have you tried 3mm super seals from Aviation Rotary? I've seen these seals perform under brutal load ( 6.8 to 7.2 sec at 190+ MPH) over and over they behave like a champ.
Let me know!
Joined: Mar 2001
Posts: 31,833
Likes: 3,232
From: https://www2.mazda.com/en/100th/
for a stock 12A i'd expect an idle jet between 50-65, and a main in the 170-190 range, other than that though its hard to say what will work, as each engine is different, and there is more than one combination of jets that will work
