I think my seals are blown; do I rebuild or go with a 302, rb20det or something else?
 

Hey guys I have been wondering why my rx7 refuses to start once it's hot and won't start again unless I leave it over night. I'm assuming this is the seals, and will require a rebuild? So how do I check compression just to make sure that's what it is? If it is the seals which I'm pretty sure it is, what do you guys think is the cheapest/easiest way to go from here to get max power out of my car? I'm lucky enough to have a guy a block down the street who has built rotaries for mazdas racing team and specializes in roataties. But the problem is a rebuild will prob run me around 2-3k with that money I could drop a 302 in there and get twice the power! Or I could rebuild it myself for prob under 1000? But will take allot of time and research. I know you guys may not be fans of pistons but I truly just want something cheap and fast and do it in the most efficient means possible!

Thanks for reading my long ass post :)

Also are there any tips on how to get it running again once it's hot? I would like to drive it a little bit before I tear the whole thing apart. Thanks :)

You can do a compression test easily enough with a standard compression testing gauge. You can get the highest number by leaving the shrader valve in place. By this I mean you will see the highest compression of one face of each rotor by this method. The second method is to remove the shrader valve and watch the needle jump with each face of the rotor. This will at the very least tell you if you have weak compression on one or more face.

Unlike a piston engine the rotary wont show very high compression at cranking speeds. 110psi is considered very good for an NA engine. Anything below about 85psi would be considered low and is much more likely to cause starting issues.

On the topic of a piston engine conversion, i suggest you do a lot of research. You may find that to do it right the conversion will end up nickel and diming you to death. But that also depends on your expected power level.

Hot start sometimes requires wide-open throttle - - that's why the cars came with the "hot start assist" assembly, which many people remove to simplify their bay.

make sure your carb is well tuned, get a regular compression tester and crack see if when the needle jumps it goes anywhere below 85.

how do I check if it was removed?
 

Im not sure if the guy had removed it? It could be the reason its not firing. Do you know how I would check if it was removed?

It is a motor driven assembly that is in the engine compartment, drivers side, near firewall, right above the steering box and attached to the rear of the shock tower. All it does is pull the throttle cable.

When the car is running - does it have "normal" power or does it seem really weak?

i dont think it does anything after its warm, last i checked it opens up when you use the choke to hold the throttle open till it warms up

The hot start assist only functions when the engine is warm and the key is in the start position. There is a small wire connection on the starter that leads up to a temp activated switch.

I am local and willing to take a look at it and answer a few questions for u

Im not sure It cranks over a whole bunch but doesn't fire, it just keeps trying to start and after a few tries it will almost start then die.

Have you tried a big hill and popping the clutch in second gear OR pull it with another car? If it does have low compression this can help.

Either your timing is off, or you have fuel running into the carb after shutdown (common issue).

If your timing is correct, then read this article on causes of after shutdown flooding: http://www.nellump.net/peri/epi/firs...odedCarbs.html



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One issue could bethe inner O ring that keeps the water out of the combustion chamber
 

One problem could be the inner O ring that keeps the water out of the combustion chamber. It's happened to me more than I care to remember. If you want to find out if the inner o ring is toast, read on.

When engine is cold, remove the leading plugs and coat the threads liberally with anti-seize compound; if you notice a dribble of water coming out of either plug hole, you're already looking at what is almost 100% an inner o ring problem. In fact you could coat both the leading and trailing plugs while you're at it; it's cheap insurance.

Once it's hot, remove the leading plugs and see if water dribbles out. If so, bad inner o ring seal. The reason you want to coat the plugs with anti-seize is that since the rotor housings are aluminum, there's a chance that when you remove the plugs on a hot housing, you'll remove the threads that used to be on the housing which is why you shouldn't change your plugs on cars with aluminum heads (or rotor housings) while they're hot.

Up thread is an excellent way to test the apex seals but if you're going to test them hot, you guessed it, put anti-seize on your plugs while it's cold and before you test for compression.

One final thing, when you start the engine cold, does it run on one rotor for a bit and then the other rotor kicks in? That's also a bad sign. It means water is leaking into the combustion chamber and it's taking a couple of turns to push the water out and then that rotor runs. There's a FAQ on this site on things you can do to try to get the inner o ring to seal again, I've never tried it but I've seen people who've done it and one guy got over 50K out of his motor and for all I know, it's still running.

Also, check the basics, is the timing correct, are both sets of plugs firing, the leading and the trailing, but mostly the leading. Is the carb getting enough gas, do the accelerator pumps work, are the floats at the correct level? Does it have the correct plugs for your model car? Any vacuum leaks, cracked vacuum lines? Did this start all of a sudden or did you buy it this way?

Good luck and keep us posted.

Look like he gave up and put it up for sale

If the problem is indeed water leaking into the housings, then grab a bottle of Alumaseal (be specific). Half a bottle should do it for you. Stuff is a miracle worker! :)




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The plugs are correct to my knowlage, the carb is actually saturated in fuel once I turn it off so I know it's getting that. But I think that the idle mixture is causing too much fuel to enter the engine when shutting off/reving down and causing it to flood and making it difficult to start again. How would I go about checking for vacuume leaks? I bought the car in this condition

Exactly what's happening to me. I think this is the solution!