pknoutrx2

Hi All
I have been considering the use of carbon 2mm seals in a bridge port. Engine will be used a little on the street and a little at drag strip, to put it in perspective 10000km will probably take me 3 years to clock up. Hoping prior learnings from porting will give me a carb / port combo to lay over in power at around 9000 so I can rely on driving it by feel for gear changes.
I'm not too concerned with the fact the seals will have to be changed time to time as I believe their are trade offs with performance stuff and it really comes down to what you choose to trade off.
Housings are new and don't really want to hurt them as you may understand.
To keep tabs on wear does anyone measure tip clearance through exhaust port with feeler or mark the end of the seal with a small dimple to inspect through the bridge for total height wear to catch them before they become un-captured by the bridge?
I'm just interested in how others have gone about knowing when it is time to freshen up before disaster.
Thanks in advance.

peejay

Apex height doesn't affect being captured (or not) by the bridge. By the time they would get THAT short, the engine would be impossible to start because the spring tension would be entirely gone.

That is the main factor, I think. When the seals get so short that the springs no longer hold sufficient tension, starting gets very difficult. And the seals bounce a lot, which kills them.

I've had good luck with Atkins ferrous apex seals (not sure if they are steel or iron) in similar conditions. The current set I have has done roughly 60k kms. The engine does need to be pulled down due to low compression but I feel this is mainly due to excessive chrome flaking. The housings weren't all that great to start with and I get the engines rather hot when racing which is the death of chrome. (It doesn't hurt that I am using pre-86 housings which didn't have chrome that was all that great to start with!)

The key to happy housing life IMO is ensuring that the seal to slot gaps are at the extreme tight end of spec. This keeps the seals moving smoothly instead of slapping back and forth. Once I started paying close attention to this spec, my housings look great with no chattermarking.

I do like your idea of putting a mark in the side of the seal for inspection. It would have to be some sort of cut and could only really be useful on a relieved bridge. I may do this on my next build.

WJM ROTARIES

I have been using the PTS 2mm apex seals and corner seals on all my BP motors with great results

j9fd3s

iTrader: (3)

there are tradeoffs to the different seals.

i built a 12A PP a few years ago (in 08!), and i used carbon for several reasons, the primary one being that its a 12A, so housings aren't replaceable. the second reason is that i didn't want to worry about seals at high rpm, although this has proven to not be a issue. the unexpected issue has been detonation, as it makes enough low rpm power to ping, already. its not a paranoia problem like the FD, but something to have in mind

you'd never know it has carbon seals in it, it runs great (engine was basically all new, and not new to me, but new from Mazda), so i'm quite happy.

second engine is a 13B P port. and we went with OEM seals, as they are well proven to work, and will be totally fine if he can keep it under 9k rpms.

third engine is a 13B bridge, and its the biggest bridge i've even even heard about, and since it needs a 1 piece seal, we went with carbons. in 2mm, as we're using S4 rotors. this engine may live a short life, as 2mm carbons seem like they leave no margin for error, and this engine is built from error. Mazda's race engines ran 3mm carbons, up until they went to ceramic

peejay

If I were starting with NEW rotor housings, I would go to ceramic, merely as a way of preserving the irreplaceable parts.

Yes, they are really really expensive, but then these cars aren't cheap cars anymore either.

Funny story - I rebuild the air compressor on the waste oil furnace at work today. It uses what look and feel like carbon-aluminum apex seals They're 2.2mm x 17mm x 34.13mm. The old ones were worn down to as little as 13.7mm high. They also cost $25 EACH.

j9fd3s

iTrader: (3)

lol, Mazda cannot have made that carbon material themselves, they must have tried a bunch of materials in the catalog, and that one worked.

just like Nippon Piston ring making the side seals, its literally just a piston ring that isn't round.

Funny story - i went to the Mazda dealership today, and the parts guys were all complaining about how much the rotary stuff costs, all the seals and gaskets are $1500 at Mazda's list. back in the late 90's you would have gotten that, plus a PAIR of rotor housings, and back in the late 80's, you could have bought the irons and rotors too. he once showed me a packing slip from about 1992, and between 1992 and 98-99 the rotary stuff doubled in price

pknoutrx2

Cheers PJ for the reply.
Firstly must apologise had a big day yesterday so did not get to read/reply.
I had not actually measured how much wear was possible before the seal could move sideways but if the spring tension is low at that point I would have to agree the motor would most likely no longer start. My guess is the seal would be half worn at this point.
I'm gathering measuring the seal to slot through the exhaust may be worthwhile as well as a check on compression. I have pulled down a 3mm motor with near new housings that had .5mm on the rotor tips and although the thing did not pop rotors and housings went in the bin.
Have thought about ceramic but need to price them up, heard you need to be sitting down while doing this. Ha. Two piece ones would be nice though.

pknoutrx2

Thanks for reply WJM I had not considered these seals as I had always thought steel was an option for forced induction, mainly after watching the little yellow Datsun at the drags that I will assume these seals were developed in. Did awesome wheelies that car.
Have you pulled one down to inspect housing condition after use?

pknoutrx2

Thanks j9 for response,
I have previously considered how close I will be to getting away with Mazda steels but interested in trying something that could preserve the new housings, more so because I have always used preloved housings in the past. I have had steel Mazda seals in a 12a bridge before and quite honestly was impressed with their ability to handle the job.
Could you explain why the bridge engine could not have a two piece seal, I have heard this before but don't understand how it can be an issue when the corner piece can not go anywhere ( even when the housing is relieved) until the angled end breaks from the apex seal. Unless the bridge was extremely thin?

WJM ROTARIES

Yes have freshened up a few of them after 2 seasons of racing and seals and housings were all still good with little to no wear on either .Re used them and still running well .The pts apex seals are not harsh on the rota housings and don't break with detonation or high boost in turbo emgines

j9fd3s

iTrader: (3)

this particular bridge is HUGE. pic attached. i haven't actually checked to make sure i could, or couldn't use 2 piece seals, but the thing has an echo its so big.

the P ports have been really tame so far, but i have a feeling this bridge is going to be angry....

rx7jocke

Holy **** at that bridgeport!

BLUE TII

iTrader: (9)

That bridge is just silly.

Usually when I see a bridge that big the stock side port has been filled (like in a p-port) to maintain some intake velocity and suit the intake runner cross section.

peejay

Yeah, at that point it becomes a peripheral port that can use a standard intake manifold.

Doesn't seem to me that the closing line needs to be anywhere near that late, and I'd want to make sure the side seals don't stub themselves on the closing line (ports should never close tip-first, both for side seal life and for port flow when it's open) but heck, if it won't munch seals then run it...

j9fd3s

iTrader: (3)

it is quite a silly bridge, runners are hogged out too. hence the prediction of anger. its ok though, its going into a gsl-se we need to mow the lawn to find, and its going to go back and forth on a farm road once or thrice a year.

so its purely for fun. if we get all our ducks in a row, it could make it to sevenstock, but that's a lot of ducks...

and look at the bright side, we can likely inspect the apex seals by taking off the intake, pulling them out and measuring them :P

peejay

It'd be nice if the engines had access plugs like Subaru engines have for getting the wristpins. Pull the plug, remove a seal, rotate engine, remove another seal, etc.

Not practical in the least, but it'd be nice

Of course it seems that when I have to rebuild an engine it is because the side seals, not the apex seals, are worn out. Just as RICE RACING pointed out ten-odd years ago.

j9fd3s

iTrader: (3)

lmao, that is one of the funny things about the P port, i can take off the intake and see trailing plugs...

pknoutrx2

I'm not sure what you mean by angry but I have found that smaller bridges with carbs on the small side are generally angry engines that pig root much worse than larger combos. I'm not sure but assume it has to do with the ability for the combo to make power at low engine rpm, most likely an air speed thing. That massive port job may very well drive quite nice on the highway like a pp.
Three bond liquid gasket may very well be your friend whilst assembling that beast!

Back on to carbon seals I have decided that if I take this path it may be a case of keeping an eye on compression and swapping them out if any change is found. If coolant temp is kept in check they should do ok.