Engine Question ?
 

I have a 88 RX-7 and the rear rotor is no good. There is no compression in it. The front one is good. It has compression and the motor runs on it. My question is are the front and rear rotors on the 13b engine interchangeable. I got another bad engine with the front rotor good and the back one fired the other day for really cheap. I was wonderin if its possible to take the front rotor and rotor housing and puttin it in the rear rotor spot. Is this possible. It looks possible to me. Any info will be much appreciated. I'm rippin the motor out at my school right now and i want to make sure this is possible.

Mike

If I'm not mistaken.. the rotors are exactly the same front and back... but, I don't know if there would be problems putting a used front in a used rear housing... I wouldn't think so if they are both in good condition.

Fikshun

i would take the front rotor and rotor housin and put it in the back of the other engine. I wouldn't just put the good rotor in it.

There are 2 or 3 major problems with this, though it can be done, but wont last long.

1) when your rotor lost compression on your good (one you're keeping) engine, it also tore up that rotor housing. This means you'll have to use the front one from the other engine with it's respective rotor. IF you have to pass an emissions test of any kind, forget it with 2 front rotor housings instead of a front and rear (there is a slight difference).

2) you'll be flipping that front rotor around backwards, whic is fine. What about the apex seals on it though? Theyre worn INTO that respective rotor housing a certain way, and if you flip em backwards (when the rotor is flipped) they'll no longer "fit", and you'll have mucho compression loss. THis means the egnine will be a BITCH to start, wont idle or run well, and wont last long. The only real option here is to try and keep the seals facing the same way the did up front (i.e. in relation to the housing theyre mated to).

3) when you take a rotary apart, even only one housing or 2, you tear water seals all to hell. You'll have to replace these with new ones, or risk having a crap motor that overheats and leaks water internally when you finally do get it back together. Also, by taking tension off the entire stack, you run the risk of rupturing one of the front 2 sets of water seals (on the front rotor you're not disturbing on your good motor).

Bottom line, this can be done, but isnt worth doing...you can buy the gasket kit for this engine (internal o-rings and external paper gaskets) for roughly $140, and a NEW set of upgraded 2pc atkins apex seals for $200, these are the items that make your engine work. You're gonna have it all apart anyway, why not do it right? Well, not "right", but, closer by FAR to right than what you're wanting. THis would be like an 80% rebuild...think of it as a re-ring kit for a piston engine, versus what you're wanting to do, which is get a piston and used ring out of another old ass motor and stick it into yours...it is so much better when you use new gaskets and rings...same with teh rotary with new gaskets and apex seals.

So i can do it but it won't work right at all. So your saying for about $340 i can do a 80% rebuild.

Mike

You can do it but at best it'll be piss-poor and you'll be real unhappy with how it runs.

FOr around $340 you can do an 80% rebuild, yes, the major components that determine how the engine runs will get replaced (apex seals, coolant seals). You'd wanna take all the seals and springs out of your 2 good rotors, clean everything up, and put it all back together with the new apex's and coolant orings. For 75 bucks more you can replace the oil o-rings too, and prevent it from smoking in the near future. By the time all this is said and done, you're getting close to what Id do for a basic rebuild.

So should i keep the same rotor and rotor housin with no compression and just rebuild it and not switch them.

You cant; you'll see why when you get it apart. They're fucked. Between the 2 motors, there are 4 rotor/housing sets; of those the 2 rears have no compression, and are of no use except for displays/paperweights. So you're left with 2 fronts, which you'll have to use. IF you dont need to worry about emissions, this is fine.

You'll also be able to examine the rotorhousings and apex seals and see how they're worn together, and you'll see why the apex seal and its matching housing would have to stay mated together like they were in order to maintain a decent seal. Even so, new apex seals are cheap, and it's too much work to do twice when your rig doesnt run for dammit.

how come i would have to worry about emmissions?
whats the difference
I don't have to worry but i'm just wonderin.

Thanks for the tips hypntyz7

the only difference in front adn rear rotor housings are how the "port air" ports route from the exhaust ports in the rotorhousings into the ports int he irons which lead to the intake...think of it as egr passages. Apparently if you switch them, or use a front where a rear should be, this cuts off that passage...

i got both of my motors out and tore apart. The back two were screwed bad the apex seals broke and scaped the shit out of the housins but the front one is good. Should i just buy new apex seals for the one rotor or both of them. I really only need gaskets and 3 new apex seals right.

base minimum 6 new apex seals and new coolant seals (gasket kit).

NEVER mix up apex seals, never...

so put new apex seals on the both rotors?
doesn't it only take 3 apex seals per rotor ?

For the final time, if you replace some apex's, replace them all. Otherwise you'll really kick your own ass when the ones you left stock break in 5-10k more miles.

Now, it's your car/engine, and you can do whatever you want, and rig up whatever you feel appropriate, but IM just giving you advice based on years of knowledge/experience. Yes, back in the day, I used to experiment with rigging too, and Im trying to pass the results on to you, but if you're the type that has to find out everything for yourself, then go right ahead. That's all I have to say on this subject, unless there are more/different questions being brought up.

Call up some place that sells engine parts and ask for 3 apex seals, and listen to their reactions...it'll probably be something like "you *do* know that there are 6 in an engine, correct? and you *do* know that you should replace them all, correct? well, ok, if that's what you want to do..."

whats the best place to order the parts i need from. i live in saskatchewan regina and theres not any places i can get parts from but the mazda dealership. they want $500 for a complete gasket kit and $57 each for new apex seals. Thats canadian i don't mind payin 350 for the new apex seals but i don't want to pay 500 for the gasket kit. Do you no of any good places i could order the parts from.

Forgive my interjection... :)

Kevin, do you know where mikealdcorn (and me, for that matter :) ) could find/buy silicone water jackets? I've seen mention of them in a few spots in the Forum, but never where to buy them.

I ask not knowing if mikealdcorn's interested in spending the extra $ on some extra insurance for his motor, but when my time comes for a rebuild I'll definitely be after silicone water jackets...

I get everything I need from atkins rotary in WA st. I think their apex's (upgraded 2pc) run the average person around $225/set of 6, and the gasket kit with coolant orings runs $140. That's all you *have* to do, but for less than 70 bucks you can get a new set of viton oil o-rings(the rubber part only, which is what needs replaced) and the e-shaft thermal pellet that replaces that dumbass thermowax deal.

You know, Ive never used a set personally, and ever seen any for sale, but Im like you, Ive seen em around. I think if I were on a hunt for them Id just start calling the usual engine retailers (those who sell rebuild parts as well, in contrast to myself, who uses someone else's rebuild parts) and ask them. Somebody somewhere is bound to know where to get em.