What are the downsides to having 3mm seals?
12-07-01, 09:37 AM
#1
Chicharrones Rule!!
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What are the downsides to having 3mm seals?
One of my O-rings is shot, so it's time for a rebuild.
I've narrowed it down to two places for said service.
One offers a 2mm street ported rebuild installed (they don't want to crate it...they want to install it themselves) for $4800.
The other offers a crated (read: self-installed) 3mm street ported rebuild for $3200.
All things being equal, why would I buy the 2mm street port installed for $1600 more?
Both of these are nationally known, well-respected builders.
-E
edit: For those wondering a search turned up a few things about 2mm vs. 3mm seals, but nothing specifically about what the downsides to 3mm were.
I've narrowed it down to two places for said service.
One offers a 2mm street ported rebuild installed (they don't want to crate it...they want to install it themselves) for $4800.
The other offers a crated (read: self-installed) 3mm street ported rebuild for $3200.
All things being equal, why would I buy the 2mm street port installed for $1600 more?
Both of these are nationally known, well-respected builders.
-E
edit: For those wondering a search turned up a few things about 2mm vs. 3mm seals, but nothing specifically about what the downsides to 3mm were.
Last edited by enuttage; 12-07-01 at 09:39 AM.
12-07-01, 11:03 AM
#2
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I am not an expert, but I do remember several people saying that with 3mm they can float away from the housings at high RPM. I don't know what they ment by high. They may have been talking about high as in 12-15k, but I really don't know. I am sure that someone here knows since it seems that there are always several people on this board that are getting a rebuild at any given time.
12-07-01, 11:17 AM
#3
Ex fd *****
I don't think 2mm or 3mm is that big a diff - either will break if the engine is improperly tuned 
. $1600 seems a very fair price for the install (assuming install is complete to the point the car is streetable) it is a major pain in the *** job. My local dealer wanted $2300 + Rebuildable Core (or+$750) for a MANA rebuilt and $3500 for the R&R, at Mariah I spent about $6K for Labor on my rebuild and Mods.
. $1600 seems a very fair price for the install (assuming install is complete to the point the car is streetable) it is a major pain in the *** job. My local dealer wanted $2300 + Rebuildable Core (or+$750) for a MANA rebuilt and $3500 for the R&R, at Mariah I spent about $6K for Labor on my rebuild and Mods.
12-07-01, 11:47 AM
#4
www.silverbulletrx7.com
I have heard the 3mm don't seal as well. Typically it's only a good thing to consider if you want to reuse your rotors but the seal slots a muffed up and milling them larger for 3mm would fix them up. Anyway I would say that you shouldn't go with a shop that only offers some sort of package deal that may or may not be what you want. Decide that first and then find a few shops that will do it. Then base your decision on cost and reputation. If it were me I'd go with Hurly seals. http://www.hurleyrotary.com/
12-07-01, 01:07 PM
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I've heard that a lot of the problems with 3mm seals are attributed to people doing them incorrectly. It's more than just setting the rotor on a flat surface and carving a channel in them. Find a shop that knows what they are doing (have done lots of them before) and you'll be happy you got them. I talked to one of the guys at Rotary Power in Gardena about it - he showed me a rotor that had 3mm seals on it when it detonated - the seals never broke but the surface of the rotor actually dented from the pressure. 
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12-07-01, 01:36 PM
#9
Super Snuggles
3mm seals have 50% more mass than a 2mm seal (by definition), and 50% more surface area, and therefore wear at an accelerated rate. The oil injected by the 13B-REW metering oil pump cannot compensate for the increase in friction, and doesn't distribute to the outer edges of the seal anyway, and the result is that the 3mm seals can (and will) drag and skip. Eventually something has to give, either the seal or the rotor housing. Brooks Weisblat lost his second engine, a Pettit-built 3mm seal engine, to low compression because of this problem. The solution is to run pre-mix in your tank and disable or eliminate the metering oil pump.
3mm seals have 50% more mass than a 2mm seal... sound familiar? Well the 2mm seals will float under pressure, that is pull away from the surface of the rotor housing at around 8,200-8,500 rpm. You'll say that this is outside the normal range of use of the 13B-REW, and you'd be right. However, the increased mass of the 3mm seals will cause them to float at a lower rpm. How much lower is open to speculation, but when a seal floats, it can no longer shed heat, and sealing is compromised. One of two things can happen. Pre-ignition, which we know is a very bad thing, or the seal can warp and crack, which is also bad. The solution? Run ceramic seals instead, they're lighter and wear is negligible, and they will not float in the usable range of the engine. The downside, of course, is cost.
So what do 3mm seals gain you that 2mm seals don't? Improved strength? A negligible amount, at best. One or two pings of detonation is more than enough to take out a 3mm seal. In fact, 6 and even 8mm seals have been tried and discarded because of the reasons I list above, although they would last a bit longer against detonation. Nothing is 100% proof against detonation. Detonation is an uncontrolled burn that can flatten the compression dish or make a rotor roughly round. I've seen some impressive damage, both from my own engines and others. Apex seals are not going to withstand that kind of pressure (on the order of several tons per square inch) for long, no matter how wide they are or what they're made of. The solution? Don't detonate.
One thing I learned after buying into the hype on ceramic apex seals and buying a $1,900 set of 3mm 2-piece seals through Mazda Comp is that the money is FAR better spent on the fuel system. Ceramic seals don't withstand abuse that much better than the OEM seals. I know of one owner who lost a Mandeville-tuned Motec engine at only 10 psi of boost, with ceramic seals. They'll hold up to a few more pings, but that's it.
You are far better off spending your money on the fuel and ignition systems and leaving the seals alone. Many well known racers use the stock 2mm seals. Ask Brian Richards (M2 Performance) what seals he uses. They're fine in a properly tuned system to over 30 psi, so why should you have any trouble with them in yourcar? Unless you're trying to save a rotor and can machine it for 3mm seals, there isn't a significant enough benefit from running a 3mm seal to warrant the expense, and certainly not enough to unequivocably say that 3mm seals are better. They're not, in many ways.
If you want to believe that you bought some insurance against engine loss because you had 3mm seals installed, that's fine. If you think that ceramic seals will keep you from losing another engine, that's fine too. I and others know better. Spend the money on fuel management and you'll have accomplished more.
3mm seals have 50% more mass than a 2mm seal... sound familiar? Well the 2mm seals will float under pressure, that is pull away from the surface of the rotor housing at around 8,200-8,500 rpm. You'll say that this is outside the normal range of use of the 13B-REW, and you'd be right. However, the increased mass of the 3mm seals will cause them to float at a lower rpm. How much lower is open to speculation, but when a seal floats, it can no longer shed heat, and sealing is compromised. One of two things can happen. Pre-ignition, which we know is a very bad thing, or the seal can warp and crack, which is also bad. The solution? Run ceramic seals instead, they're lighter and wear is negligible, and they will not float in the usable range of the engine. The downside, of course, is cost.
So what do 3mm seals gain you that 2mm seals don't? Improved strength? A negligible amount, at best. One or two pings of detonation is more than enough to take out a 3mm seal. In fact, 6 and even 8mm seals have been tried and discarded because of the reasons I list above, although they would last a bit longer against detonation. Nothing is 100% proof against detonation. Detonation is an uncontrolled burn that can flatten the compression dish or make a rotor roughly round. I've seen some impressive damage, both from my own engines and others. Apex seals are not going to withstand that kind of pressure (on the order of several tons per square inch) for long, no matter how wide they are or what they're made of. The solution? Don't detonate.
One thing I learned after buying into the hype on ceramic apex seals and buying a $1,900 set of 3mm 2-piece seals through Mazda Comp is that the money is FAR better spent on the fuel system. Ceramic seals don't withstand abuse that much better than the OEM seals. I know of one owner who lost a Mandeville-tuned Motec engine at only 10 psi of boost, with ceramic seals. They'll hold up to a few more pings, but that's it.
You are far better off spending your money on the fuel and ignition systems and leaving the seals alone. Many well known racers use the stock 2mm seals. Ask Brian Richards (M2 Performance) what seals he uses. They're fine in a properly tuned system to over 30 psi, so why should you have any trouble with them in yourcar? Unless you're trying to save a rotor and can machine it for 3mm seals, there isn't a significant enough benefit from running a 3mm seal to warrant the expense, and certainly not enough to unequivocably say that 3mm seals are better. They're not, in many ways.
If you want to believe that you bought some insurance against engine loss because you had 3mm seals installed, that's fine. If you think that ceramic seals will keep you from losing another engine, that's fine too. I and others know better. Spend the money on fuel management and you'll have accomplished more.
12-07-01, 01:36 PM
#10
Super Snuggles
Originally posted by MattZeeTerror
the only bad thing about 3mm is they may set ya back a few more bills. On the otherhand you can run a much higher boost level then with 2mm.
the only bad thing about 3mm is they may set ya back a few more bills. On the otherhand you can run a much higher boost level then with 2mm.
12-07-01, 01:38 PM
#12
Super Snuggles
Originally posted by 95R2-89TII Ground Zero
I haven't heard of a downside to the 3mm apex seals. I know of a few guys that do nothing but praise them.
I haven't heard of a downside to the 3mm apex seals. I know of a few guys that do nothing but praise them.
From what I've seen here, there's a large amount of ignorance concerning apex seals...
12-07-01, 01:46 PM
#13
NYC's Loudest FD
OK, here's my knowlede on the difference between 2mm and 3mm seals:
2mm seals seal better because they are made from a harder material that doesn't wear out the housing like the 3mm's do, also they don't bow in the middle sometimes like the 3mm seals do, due to the 3mm seals sometimes not being able to withstand the high temps. They also last longer because they don't wear as fast as the 3mm's. I've done tests with a car with 2mm seals and 3mm seals as far as HP is concerned, the 2mm cars always made more HP, for example: a car I tested with stock 2mm seals made 450RWHP, and with the 3mm seals the same car made 400RWHP with the same combination and nothing changed, this is probably due to the better sealing characteristics of the 2mm seals. As far as the 3mm seals go the advantages of them are basically one thing, they will not destroy your housings or turbos IF you detonate because they are made from a softer material and will just basically disintegrate when knocking occurs. That's about what I know from personal experience. I also know that there are alot of cars out there making BIG HP with stock seals, as far as using the same springs with those seals I'm not sure, but I know as far as durability, better sealing, more HP, and less mileage wear, the 2mm's are the way to go, but some people need 3mm's due to the fact that they have race cars that don't drive on the street so mileage longevity isn't a concern with them. That's about it.
2mm seals seal better because they are made from a harder material that doesn't wear out the housing like the 3mm's do, also they don't bow in the middle sometimes like the 3mm seals do, due to the 3mm seals sometimes not being able to withstand the high temps. They also last longer because they don't wear as fast as the 3mm's. I've done tests with a car with 2mm seals and 3mm seals as far as HP is concerned, the 2mm cars always made more HP, for example: a car I tested with stock 2mm seals made 450RWHP, and with the 3mm seals the same car made 400RWHP with the same combination and nothing changed, this is probably due to the better sealing characteristics of the 2mm seals. As far as the 3mm seals go the advantages of them are basically one thing, they will not destroy your housings or turbos IF you detonate because they are made from a softer material and will just basically disintegrate when knocking occurs. That's about what I know from personal experience. I also know that there are alot of cars out there making BIG HP with stock seals, as far as using the same springs with those seals I'm not sure, but I know as far as durability, better sealing, more HP, and less mileage wear, the 2mm's are the way to go, but some people need 3mm's due to the fact that they have race cars that don't drive on the street so mileage longevity isn't a concern with them. That's about it.
12-07-01, 02:13 PM
#14
Super Snuggles
Precisely 50 RWHP... hmmm. While I do agree that 3mm seals do not seal as efficiently (mainly due to their 2-piece construction) as a 3-piece 2mm seal (13B-REW OEM), the same can be said of 2-piece ceramic apex seals, in either 2mm or 3mm widths. A 3-piece seal will always seal better. Still curious at to how you managed such perfect numbers in your "testing", though...
The premise that a 3mm stock seal will not damage the turbos is false. ANY piece of foreign material which passes through the turbos can damage them. Pieces of apex seal will almost certainly turn your Inconel exhaust turbine into a ragged pinwheel, and I've seen several examples. There is an assumption that a ceramic seal will disintegrate without damaging the turbo or rotor housing because of it is made of softer material, but I have yet to hear that anyone has proven this to be valid.
The premise that a 3mm stock seal will not damage the turbos is false. ANY piece of foreign material which passes through the turbos can damage them. Pieces of apex seal will almost certainly turn your Inconel exhaust turbine into a ragged pinwheel, and I've seen several examples. There is an assumption that a ceramic seal will disintegrate without damaging the turbo or rotor housing because of it is made of softer material, but I have yet to hear that anyone has proven this to be valid.
12-07-01, 04:18 PM
#15
NYC's Loudest FD
OK, I meant 47.4HP to be exact, sorry I'd just thought I'd just round it out. What I meant by not damaging the housings or turbos with 3mm seals, I meant Hurley Engineering 3mm seals, NOT stock 3mm seals, at least that's with my experience. Sorry, I don't agree with the premise that a 3mm 2 piece seal will seal just as good as a 2mm 2 piece seal. Another reason that a 2mm seal will seal better than a 3mm one, is because a 2mm seal is meant to swipe and ride across the housings to seal better and not wear the housings due to the corner seals that a 2mm seal uses. Since the 2mm corner seals are two pieces they allow some swiping kind of movement and allowing that "swiping" motion across the housing, a 3mm seal cannot swipe and ride across the housing because it's being contained inside a 1 piece corner seal which doesn't allow it to move in that manner. The 3mm corner seal uses all of it's force to press against the housing and that's why it wears out the housings quicker as well, this also promotes less combustion chamber sealing.
Last edited by RX794; 12-07-01 at 05:14 PM.
12-07-01, 04:44 PM
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Well, we can all certainly go back and for with I know so and so who has 3mm and his engine lasted x miles and vice versa. ... And, there is certainly some validity in what both Jimlab & RX794 are saying but I'd like to offer one more statement....
While getting my car worked on at Rotary Power in Gardena, CA, because there is no waiting room and because it's so far from my house, I often sit around and chat with the owner who usually puts 3mm seals in his rebuilds. The quick history on the shop is that it's been around since '85 and the owner has been racing rotaries since well before that; he's also an incredibly skilled machinist that's made cams for Cosworth's Indy car engines and several high precision airplane parts.
He says that since he's been rebuilding engines, the ones in which he's put 3mm seals have almost always outlasted the 2mm seal rebuilds by a significant margin. He also likes to tell stories like the one I mentioned above where the rotor face dented before the seal cracked or how he's seen corner seals go before the apex seal when he's put the 3mm in. Granted, this may be attributed to his skill as a machinist (he was the person who explained to me that the channels are not necessarily straight across the rotor, but often time at a slight angle, and not necessarily the same angle for each seal), but it is fact, none the less.
So, take this info with a grain of salt, but I know that when the time comes for my rebuild, if I'm still on the rotary boat, I'll be getting 3mm seals done by Rotary Power.
While getting my car worked on at Rotary Power in Gardena, CA, because there is no waiting room and because it's so far from my house, I often sit around and chat with the owner who usually puts 3mm seals in his rebuilds. The quick history on the shop is that it's been around since '85 and the owner has been racing rotaries since well before that; he's also an incredibly skilled machinist that's made cams for Cosworth's Indy car engines and several high precision airplane parts.
He says that since he's been rebuilding engines, the ones in which he's put 3mm seals have almost always outlasted the 2mm seal rebuilds by a significant margin. He also likes to tell stories like the one I mentioned above where the rotor face dented before the seal cracked or how he's seen corner seals go before the apex seal when he's put the 3mm in. Granted, this may be attributed to his skill as a machinist (he was the person who explained to me that the channels are not necessarily straight across the rotor, but often time at a slight angle, and not necessarily the same angle for each seal), but it is fact, none the less.
So, take this info with a grain of salt, but I know that when the time comes for my rebuild, if I'm still on the rotary boat, I'll be getting 3mm seals done by Rotary Power.
12-07-01, 07:26 PM
#17
Chicharrones Rule!!
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Originally posted by maxpesce
either will break if the engine is improperly tuned.
either will break if the engine is improperly tuned
.
Originally posted by dis1
Anyway I would say that you shouldn't go with a shop that only offers some sort of package deal that may or may not be what you want.
Anyway I would say that you shouldn't go with a shop that only offers some sort of package deal that may or may not be what you want.
Originally posted by jimlab
3mm seals have 50% more mass than a 2mm seal (by definition), and 50% more surface area, and therefore wear at an accelerated rate.
3mm seals have 50% more mass than a 2mm seal (by definition), and 50% more surface area, and therefore wear at an accelerated rate.
Originally posted by jimlab
...there isn't a significant enough benefit from running a 3mm seal to warrant the expense.
...there isn't a significant enough benefit from running a 3mm seal to warrant the expense.
And...for what it's worth, the 3mm rebuild is from Pettit, who I tend to trust. They've been at it for a long time and my father-in-law (the co-owner of the car) used them when he lived in Atlanta many times when he was younger and buying pre-RX-7 rotaries.
Thanks for the helpful insight guys. I still don't know what I'll do. It'd be REALLY nice to see some hard facts on identical setups running different seals regarding reliability (total mileage before breakdown). Almost impossible to control this experiment, but if anyone has examples I'd appreciate it. The horsepower issue is not AS important. I'm not going to try and milk 400+ rwhp out of my car...
Thanks again. Any further insight is much appreciated.
-E
Last edited by enuttage; 12-07-01 at 07:29 PM.
12-07-01, 11:38 PM
#18
www.silverbulletrx7.com
I don't really have any more to add beyond what I already said. I just wanted to say "holy crap this is a great thread!" This is some of the best info I have read on the forum in a long time. I hope it gets stored some place. If I didn't have a policy of keeping my site to mostly first hand knowledge I would definetly devote a section to what has been said here Ok I'm done now...
cvs
Ok I'm done now...cvs
12-08-01, 12:55 AM
#19
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My 2 cents...
I have Hurley 3mm right now... Every Mag.: Sport compact car,
Turbo, Import tuner...ect. I've seen. The majority or RX's have been switched to 3mm.
The only one who hasn't was Adam Swaratari...excuse spelling please. And Adam has definifely got pletty of HP.
But still the majority is with the 3mm.
So that's why I use 3mm now.
I have Hurley 3mm right now... Every Mag.: Sport compact car,
Turbo, Import tuner...ect. I've seen. The majority or RX's have been switched to 3mm.
The only one who hasn't was Adam Swaratari...excuse spelling please. And Adam has definifely got pletty of HP.
But still the majority is with the 3mm.
So that's why I use 3mm now.
12-08-01, 01:12 AM
#20
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I use 3mm
I use 3mm Seals with 22 psi of boost and have gone over 5k miles with absolutely zero problems. Not sure if that has anything to do with anything, but they work fine for me.
-Dan
-Dan
12-08-01, 09:35 AM
#23
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ok i unsderstand that tuning the engine is better than putting 3mm but what if you can't tune the damn thing.
I can upgrade my fuel system with no problem. The problem is that i can not have it tuned, there are no competent shop around here and i don't want to drive 15 hours to go to the closest one.
Would 3mm be better in that case? I am looking for reliability, not hp.
Also, the mazda reman cost more than a street port with 3mm around here.
any suggestion?
thanks a lot
please keep this thread alive
puma
I can upgrade my fuel system with no problem. The problem is that i can not have it tuned, there are no competent shop around here and i don't want to drive 15 hours to go to the closest one.
Would 3mm be better in that case? I am looking for reliability, not hp.
Also, the mazda reman cost more than a street port with 3mm around here.
any suggestion?
thanks a lot
please keep this thread alive
puma
12-08-01, 10:32 AM
#24
Blow up or win
Less is more. Detonation will kill ANY seal, any size, any material. It's like a mini-nuclear bomb going off in your engine at exactly the wrong time. The shock wave pressure is mind boggling. Re-milling the seal groove for 3mm is VERY difficult to do properly, and it must be done exactly or the engine will be toast in a short period of time. It's very unusual to have to replace the rotors on a rebuild, but only a close examination and precision measuring of clearances can tell you if they can be reused. 99% of them can be, unless they've been damaged by - guess what - detonation! Spend your money on fuel management and a couple of quality knock sensors for each rotor. If you want reliability stay with 2mm, I personally think the Mazda engineers are pretty smart guys (except for a few things - duh...
