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we all read the 3mm vs 2mm apex seal debates...

Old 11-02-18, 10:36 AM
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we all read the 3mm vs 2mm apex seal debates...

One thing that I can't find is the sealing loss and frictional differences. I understand they exist, but how "bad"? I am working on a GSL-SE engine and while FC rotors would be nice, the funds spent on buying $400 used rotors could be spent elsewhere. It's not like 3mm apex seals were failing at 60k. There are plenty of high mileage 12A's. So what I am looking for is a rule of thumb number that for example a 3mm apex seal would be down on horsepower by 5% compared to a 2mm seal. Does such data exist?
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Old 11-02-18, 03:49 PM
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Originally Posted by Richard Miller View Post
One thing that I can't find is the sealing loss and frictional differences. I understand they exist, but how "bad"?
If this is some sort of data collecting thing for you, then fine. Otherwise, I wouldn't worry about it. My guess is the power gains you might see due to putting S4 rotors in a S3 engine would be attributed mostly to the weight you shed as opposed to the apex seals.

So what I am looking for is a rule of thumb number that for example a 3mm apex seal would be down on horsepower by 5% compared to a 2mm seal. Does such data exist?
Unless some private party conducted their own, valid, apples-to-apples experiments, I would tend to think such data probably doesn't exist. It would be pointless for Mazda to publish anything because from 1974 to 2012 there were major changes to the 13B engines that would keep you from isolating any changes, IF ANY, solely due to apex seal size.
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Old 11-02-18, 05:13 PM
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I would have expected a Mazda document that gave hard numbers from development. This was less data collection and diminutive returns estimation.

Thank you.
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Old 11-02-18, 05:51 PM
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Originally Posted by Richard Miller View Post
I would have expected a Mazda document that gave hard numbers from development.
They probably do have printed hard data. Whether or not it is available for our consumption, I don't know. If you search hard enough, or know the right people, you could probably eventually get to it. I have a few members in mind that you could ask if it comes to it, so there's that. It may lead you to something. It may not.

However if they exist, I would think, though, that it would be more technical stuff (friction and wear numbers, material comparisons, and that sort of thing) - as opposed to comparisons involving power production. I would offer to look it up in the old Rotary Engine book (I think I have a PDF copy somewhere), but I really don't remember if the S4 13Bs even existed when it was published, so that would probably be a dead end.
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Old 11-02-18, 07:13 PM
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Originally Posted by Richard Miller View Post
I would have expected a Mazda document that gave hard numbers from development. This was less data collection and diminutive returns estimation.

Thank you.
there was an SAE paper, i'll have to dig up the computer to look

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Old 12-19-18, 08:51 PM
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Dusting this off a bit. Reliability gets cited for 2mm apex seals. This confuses me slightly as I thing the 12a is the most reliable engine out of the whole group. What are the reliability concerns with a 3mm apex seal? Greater risk of chatter marks?
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Old 12-20-18, 06:58 AM
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3mm seals destroy the chrome, especially in 12As. They also are more likely to hammer the slots in the rotors out, making the rotors unusable. (These two problems feed themselves - bad chrome makes the seals chatter, chattering seals hurts the chrome...) A lot of times this would lead to broken seals as well, the chattering stresses them. I've pulled apart running engines with broken seals!

12As may have been super-reliable but when they were worn out, rebuilding usually meant replacing everything inside since the rotors would be egged out and the chrome on the rotor housings would be scrap. 2mm seal engines simply don't do that nearly to the level that the 3mm seal engines did. A 180k mile 2mm seal engine looks better than a 100k mile 3mm seal engine inside. Usually it cracked a coolant land out before it actually wore out.

The REAL problem is that these wear items are all NLA. You can't buy 12A rotors or rotor housings anymore.
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Old 12-21-18, 04:15 PM
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Originally Posted by Richard Miller View Post
. This confuses me slightly as I thing the 12a is the most reliable engine out of the whole group.
i haven't had any special luck with 12A cars, out of the 7 ive owned, ive had to put engines in 5 of them. considering a 6th, its fine right now, but its 33 years old, so its (over) due to start leaking from the dowel pins

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Old 12-29-18, 01:23 AM
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12As are great engines, but they are most definitely NOT as flawless as their reputation suggests. Of all the ones I've disassembled over the years, I'm not sure if I've ever seen one with pristine housings, but if I did, then it certainly was an outlier. Missing chrome and apex seals that were cracked or chipped were fairly common. Much different with the '86+ 13Bs I've pulled apart. Missing chrome was relatively uncommon with them.
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Old 12-29-18, 09:22 AM
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when i started at Mazda we actually stocked a pair of 12A rotor housings, and all the seals and stuff. now they stock FD engines
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