Apex seal spring question
 

Hey All,

I'm just curious as to whether or not anyone has tried mixing and matching apex seal springs in various engines. I'm building a 12A right now and I'm working out some ideas that I've always wanted to try so that any beneficial information gleaned from this experiement can be applied to my next 13B project. Basically, I'm using this buildup as a test mule for a bunch of ideas I've had over the years.

So what I want to know is would it be a good idea to try using the smaller spring of the dual spring 13B's with a regular 12A spring for my own dual-spring 12A? I want to hear any ideas, thoughts or experiences (even better :D).

Thanks
1

From my experience:
Higher spring tension might improve sealing.
However, higher spring tension will also cause the seal to wear much much faster.
Is it worth it.

In REs all seals pressing to housings by gas pressure. Springs needed for start and low load perfomance(when gas pressure is low).(Overheated engine with dead springs wery dificult to start but under load it pulls strong).

yeah, i thought about this, too. however, i'm not overly concerned about it simply because i'm not using brand new rotor housings, so given the fact that i have no clue as to how accelerated the wear may be, i figured what hell, eh?

i'm not sure if i oversimplified this or if i'm just plain worng, but my thinking is that the wider (and heavier) 12A seals may show more wear with dual springs when compared to the Gen II and Gen III motors with dual sprung 2 mm seals - but i don't have the money to run extensive tests just to satisfy that curiosity.

i can't dispute what you said with facts or anything, but for what it's worth, i can say this ... the very first engine i built was put together with used (dead) springs (because i was young, broke and didn't know any better) - anyway, it always started fine and ran great when cold, but it would not pull past about 5500 RPM when up to temp.

I dont think the gas pressure theory is entirely accurate. Centrifugal force will keep it against the housing, except for the point in transition across the curve where it jumps off at high RPM with tired seals.

However.. The dual spring thing in the 12A.. you may wanna check the underside of the apex seal to make sure there is proper machining to keep the spring centered etc.. like on the dual spring seals.

Keep in mind.. that when the engine is tires and needing a rebuild.. the chrome liner is usually real thin if not worn through in areas. If you use dual springs.. I imagine the higher pressure is going to eat the remaining chrome real fast once it finds a spot to catch on.

Also.. If you have the time and inclination.. you could try a old school trick that takes some fine tuning.
Drill a hole in the apex seal groove and tap it for a carb Jet under the springs/apex seal. Then thread in a small carb jet to apply oil pressure on the back of the apex seal while running. THis applies cooling, lubrication, and additional sealing pressure to the apex seal.

good point. i actually didn't think of that, but i will try to do it if i do this double spring thing.
this is the first time i'm hearing of this trick. do you have any pictures of it?

thanks for the response.

by the way, i'm looking into coating the seals to maybe help with the wear issue a bit.

also, with the carb jet-thing, where is the oil pressure coming from in the rotor?

The eccentric shaft has oil flowing through the center to lubricate the Rotor bearings.. and the INsides of the rotors themselves are cooled by inside them, as they are hollow..
The Small hole you drill goes through the apex seal groove down into the cavity below.. then you tap and jet it carefully.
The only issue with this method is the sizing of the jet issue. Too bigand you have a mosquito fogger.. too small and you get no benefit... The real issue is the re-building of the engine repeatedly to change the jets.
The guru I know who does/did this regularly won many hill climb events similar to Pikes Peak etc.. and makes some very radical rotaries that I wont go into here.. BUT.. He did it on all his engines.. and I think it may have been mentioned in How to BUild and Modify your RX-7 co-written by Jim Downing.. Cant remember if I listed the title correctly..
Sooo Proper choice in the beginning is a kinda critical..

okay ... just want to clarify if i'm getting what you said - i know that the oil flows through the eccentric shaft and that the backs of the rotors are hollow and basically fill up with oil (really not being facetious about this, just stating) - but basically, is it the rotational inertia that forces the oil from the rotor, through the hole you'd drill?

this is good stuff, thanks.

You can coat them if you want, but you'd have to machine the seals first. Coatinng them will add a small amount of material to them. So you neeed to find out how thick the coating is before you do it so you can machine that much off the apex seals.

It is accurate. I have a Mazda training video that talks about the RX-7 and RX-8. It talks about the design features of the rotary and the new renesis engine, and it specifically mentions that the gas pressure helps put the seals against the contact surface. I'll see if I can find it and link to it. Its pretty impressive.

Click here

I think its being hosted by 87NA, so credit to him.

Actually No It is correct in the video.. and incorrect in your memory.
Watch it again and you will clearly see via the text and the animation.. It clearly shows that Centrifigual force and spring pressure hold the apex seal against the rotor housing, and the gas pressure holds the apes seal against the SIDE of the Apex seal groove.
The gas pressure that effects the apex, side, and corner seals is pressing against the specific seals in a lateral motion pressing them against the side of the respective groove. Not under the seals pressing them in a upward motion out of thier grooves.

Above and beyond all that... Excellent video. Gonna let my kids watch it. :D They tore down thier first rotary last weekend.. a spare 6-port that they are gonna rebuild.
They are 8 and 10 :bigeyes:
Evilaviator I think was here for the initial teardown they were doing he he he...

This is the reason why Mazda OEM apex seals are electron beam hardened on the contact edge.

Other aftermarket apex seals are not guaranteed to be built like this.



-Ted