Ok guys got a question for the rotary gurus. I had a 79 RX7 practically given to me the guy said he thought it had a blown water jacket seal. When u start it up it smokes like a bish but as it heats up the smoke dwindles off till you cant see it at all. It defintly has a sweetish smell to the smoke but if the seal was leaking wouldnt it continue to smoke pretty good? Also he said to replace the seal a rebuild is in order, he said that on that particular engine id prolly find the front rotor to need replacing. Is that true? And last question if a rebuild is required what site would you sugest for a reasonably priced kit?

 

I dont really believe the front rotor part, but the rest is correct. The reason it does not smoke once running good is the internal pressure is keeping the water out.

There are two things to do before a full rebuild is in order.

First do a check by running the engine with the rad cap off, if you get bubbles then you know it is the water seal, if not then

check the O-rings in the intake, There is a water jacket into it that can cause this problem

Next do a search for a how to do a repair that has been effective in many cars.

 

I think you should just give it away... say to me?

Sweet exhaust = coolant in exhaust. However, if it's not affecting the performance (meaning, it keeps running ;-) it's more likely the o-rings that seal off the coolant passages into the intake manifold.

Pop off the radiator cap and run the car... look for bubbles in the coolant. If there's bubbles then yes, possibly a jacket o-ring. If the motor has never been rebuilt, I recommend a complete rebuild (seals, springs, etc.)

Atkins, Mazdatrix, and many others sell rebuild kits from just gaskets up through complete...

Edit: Dang it Hades, you type too fast

 

Ok i coulkdnt find a trailer to take it the 200 miles home so i figured id try to drive it and see how it goes. It was absolutely freezing outside so it took a while to warm up, but by the time we hit the interstate she was warm and smoke free, running top. It went all 3hrs at 70-75 mph without so much as a hiccup. The next day i went out to fire her up and take her to my friends shop for some TLC, she fired right up smoked a few seconds and then practically nothing. Was the previous owner just way tooo damn jumpy is anthing really wrong with this thing? I'm going out tommorow to check the coolant to se if i ccan see bubbles when she runs, but how can I check the manifold coolant o ring? Iv never really worked on a rotary before. I know the principle but thats bout it, so try and make an explanantion user friendly. Also when its running maybe its just cause i smoke and my sense of smell is not so great but i really cant smell the sweet smell. An y ideas or suggestions are greatly appreciated.

 

Do the bubble test, if it passes then just watch the coolent level and dont worry about it.

 

If you have no bubbles in the radiator, and at this point in time, I don't expect you will, you will need to replace the intake o-rings. Let's demistify the rotary 1st. 95% of the car is like any other of that era, the other 5% is the engine block itself and it's internals. This means the carb and intake is nothing special either. You will need to remove the carb and intake to check the coolant o-rings, by the time it's apart, you will need to replace both o-rings and the intake gasket.

I make my own intake gaskets and o-rings can be had at your local parts store.

For your viewing pleasure, in my sig line is a link to the online FSMs, carb manual and other reading material. Download what ever you need.

 

Appreciate the info ill look into that when i go home tommorow. A question i searched for but just found info on different mufflers. Do rotarys need back pressure? On my Accord I fiddled with different exhaust combos and found a decnt bit of back pressure was required to get good low and mid power. Is the same true of rotarys? Also my substitute instructor for Fuel and Emmissions worked for Mazda and when i asked him about the compression ratio of a rotary he said it rises as the rpm's increase. I dont see how. The size of chamber doesnt chznge as the rpm's go up so how would CR go up?

 

Back pressure is a piston thing, bad for rotarys. Interesting question on the CR, I've wondered this myself, particularly in the 2nd gen FI engines with the dynamic intake effect. Have no answer for you.

 

the reason i asked bout the CR is, you know Blowers give great low end boost but start to lose efficiency higher up, well if a rotary starts out at low compression and then slowly goes up itd be perfect. Youd have great low end and as the blower starts to stumble the higher compression ratio would compensate. So youd have an all round awesome power band escpecially good for street courses. Right?

 

If there is a CR change, it would be minor at best. Nice thought, but I don't think it has any real world practicality to it.

 

If i remember right (I;m gonna have to double check with him now) that it went from like 9ish to almost 10.5. Again im gonna have to double check but he worked for a mada dealership for years and now teachs at NADC.

 

The intakes for the NAs and turbos are designed differently. I suspect that adding any kind of forced induction will reduce/kill the dynamic intake effect. This effect applies mostly to the 2nd gen NA intake systems.

 

Compression ratio cant change. How does that make any sense...
Doesnt the compression ratio just state the size of the combustion chamber when its largest compared with when it is the smallest?
This theory can work with piston engines because of the complex head designs available. But if Im thinking right, the only way for a compression ratio to change is if the size of the combustion chamber is changed, which is not done on any stock rotary engines.

Forced induction and the dynamic intake effect are a whole different boat, each one just has its own way of packing more air and in turn fuel into the engine. This however, doesnt effect compression ratio at all.

 

I said the exact same thing as you minus the stuff bout the variable intake junk (i have no idea what the later 7's are equipped with) It didnt make since how the combustion chamber size could change with an increase in rpm's. I'm gona have to track him down and get an exact explanation. When i find out ill post what he said. Iv tried checking other sources on the net but most just give basics on rotaries nothing really in depth.