DursRemote

Me and a friend are looking to buy a 1st gen RX7 to get into racing. We are going to look at one tomorrow, however it currently does not run. The owner says he can start it on starting fluid, but has all the cooling lines disconnected so can't drive the vehicle.

Being new to rotaries: how do we determine if this engine has a small issue that can be fixed with a rebuild, vs. if it's totally gone (needs new rotor housing, for example). With a piston engine, I'd bring the tools to check turning the motor over by hand and taking a compression reading. Does anyone have tips for us to check this car out?
Thanks.

misterstyx69

iTrader: (142)

unless you are superman you just can't turn the engine over by hand and do a compression check! (minimum rpm should be about 250 to do so).
If the car has it's starter hooked up then you can get a rough idea as to what the compression is.
If the car runs with starter fluid then it may be a fuel delivery issue.Common for these types of cars and especially a 1st gen.

Now,Rebuild?..you can only Guess at that.You can't tell; Exactly what it needs until you disassemble the engine,so I'd wait to do that before getting any parts..that is iF you buy the car and IF the engine needs to be repaired.

DursRemote

Yes, you're right I wasn't clear. First thing I do is put a wrench on the crank bolt and turn the engine by hand, especially in the case of an interference engine. Then I'll hook up the compression tester and turn it with the starter motor.
We are planning on opening up the engine no matter what, if we buy the car. If it has a fuel delivery issue that's no problem. The only thing I'm scared of is if there's permanent damage to a major component, like rotor or housing. Would a compression test eliminate damage to these? Does anyone have compression numbers to look for on the 12a, understanding that the engine has probably not run for a while?

Thanks for the response.

lduley

iTrader: (1)

In all honesty, if your wanting to build a race car, a 12a probably isn't your best bet, parts are getting scarce, and with that, the price is reflecting that.

Honestly you could ditch the 12a, part it out, and have enough for a running 13b with some change to spare

j9fd3s

iTrader: (3)

in piston terms, the rotary is non interference, so spin all you like, either direction is fine.

compression test can tell you something, the shop manual, which is here Foxed.ca - Mazda RX-7 Manuals gives a minimum spec, and in a race car you'd want as high as possible. if the compression is borderline, it probably will need rotors/housings, they are wear parts.

also the engine needs to have been running well to have good compression test numbers. i'm not sure why, but i would think that too much fuel can wash away the oil film on the rotor housings. so you might wanna put the lower hose in a bucket of water and run it for long enough to make sure it runs ok, and then compression test it.

diabolical1

iTrader: (3)

what sort of racing are you planning to do with the car? that might dictate what engine you can/should run in it.

12As are great engines, but we're at a point where parts can be an issue due to supply and demand. it's not meant to scare or dissuade you, more like a heads up.

as for being able to evaluate the hard parts, until you disassemble it, it's anyone's guess. as J9fd3s stated, you can get the accepted specs for compression from the FSM. chances are if the engine gets decent numbers, you're in relatively good shape and won't need to pull it apart. keep in mind i'm talking only about not having damaged parts. 12As are also quite notorious for running strong with ridiculous amounts of missing chrome, but i don't consider that damage any more. you'd be served well to do the same, so don't be alarmed if you see missing chrome whenever you do pull it apart.

DursRemote

This is going to be for the chumpcar race series, so endurance races between 7 and 24 hours. We are interested in the RX7 for a couple reasons, one of the big ones being that 12a-powered models are very advantageous in points. Using the 12a gives us plenty of room for upgrades, like intake/fuel/exhaust modifications.
In the interest of reliability, we will probably open the engine before the first race no matter what starting condition it's in. I understand parts are getting harder to find, but I've found rebuild kits online from atkins rotary and racing beat. What these kits don't have are the 'bigger' components like rotors and housing. I definitely do not want to buy a car and find that we need to replace those. If tearing it down and performing a rebuild will bring it back to ~factory spec, on the other hand, that is perfect.
What I'm getting from this thread: either need to get the engine running on normal fuel for a couple minutes and get good compression numbers from it, or pass and wait for a running car to pop up. Too bad this one is CRAZY cheap....oh well, sometimes those can be more expensive in the end.

Thanks for all the great replies.

j9fd3s

iTrader: (3)

you really won't know how the engine is until you tear it apart. basically all the housings aren't available new, but everything else is. irons and rotors are pretty easy and cheap to find, if needed. rotor housings are harder to find, but they aren't really big money, and it is possible to grind down a 13B housing too.

so i wouldn't pass on a car just because maybe you might think that there is a chance that the engine might have some wear. give it comp test, if its above failing, and even i'd think you're in good shape.

the 12A is actually the easiest engine to build in the world too, so its fun

ArmAnirx7

iTrader: (24)

Mazda RX7 ITA Race Car

just buy this one! All the work is done for you. I am sure you can pick it up for 4k. That is way less than what you are going to have to spend to set up a race car like this.