seond generation RX7s have the highest coolant seal failure rate of all the rotaries, this has been fact proven to me over the years dealing with these motors and some conclusions can be drawn as to why they do fail, most commonly is lack of maintenance leading to cooling system issues and there is some ways to prevent total failures.

#1 failure is due to iron coolant seal wall breakage:


1st generation FB engines had the coolant seals inside the rotor housings which are made of aluminum, after the FC3S was introduced mazda switched the milling process to the irons because they felt it would help the coolant seals due to electrolysis of the aluminum, it had the reverse effect where the thin castings of the iron walls eventually became brittle after a decade of heat cycling and thin castings, which should have been revised after the change. the renesis RX8 engines have reverted the coolant seals back into the rotor housings due to the long term affects of the change that were noted in the earlier model 13B engines after some time passed.

so what can be done to help prevent premature failures of this flaw in design? well, there is no easy answer because one good shock of the iron material that has already been fatigued by age will break it. what commonly fractures cast iron is rapid heat displacement, meaning rapid cooling of a very hot material.

if you do happen to overheat a 2nd/3rd gen rotary, the best thing you can do is shut it off and let it cool down naturally. trying to cool down the engine more rapidly than a natural process can shock the metal and crack it. it does take more to break the coolant seal's seal than a little heat, but it really depends on the age of the seals, once they've been overheated all you can do is try to save the irons from fracturing which WILL kill the seals regardless.

since i am planning on moving on to other things in the near future i wanted to share my experience and possible ways of preventing these failures from occurring. one method while an engine is torn apart is by installing a sleeve to retain the coolant seals regardless if the iron walls do break:




working with stainless steel i have been forming ribbons to insert into the groove on the outside of the coolant seals to prevent the coolant seals from blowing out in the event that the older irons do break. this does take time because the thickness of the material is critical because it can put more pressure on the irons and break them more readily taking up more gap in the coolant seal valleys, since milling the groove will make the walls even thinner that is unpractical, i have been working with non OEM seal materials in varying thicknesses to try and get the best results which takes some time.

due to the cost of fuel increasing and the inevitable drop in incoming business my intention is to develop a hydrogen powered rotary based off a standalone EMS which i can tune to see if it is feasable to make an engine at most 50% reliant on fossil fuels, and possibly add in the twin charger idea in the process which runs on 100% fossil fuels when needed.

so basically my best advice is to not try to cool an overheated engine as quickly as possible, which is your natural reaction. give it a good hour if you have hit 230*F+ before attempting to restart it. and for those who care about possible preventative measures, the materials for the ribbon can be commissioned for about $3 a foot, a spot welder will cure the seam issue with some grinding of the sharp edges.

from my experiences only about 1 in 10 irons have sufficient castings on all edges for a reliable motor which will likely not have any iron wall failures. FD's have less issues with this due to less age and heat cycles but eventually will have more failures in time. also in my experience the front irons crack most often(6 broken front irons in my inventory) followed by the middle iron which has 2 possible sides to break walls on(7 in inventory with more than half breaks on the front rotor side) and lastly the rear iron(2 in inventory). this is because the front iron is the first to recieve cool air and water, hence most susceptible to shock cooling fractures.

it's a crap shoot as to whether you got lucky enough to have a good casting on a housing and very unlikely that the whole motor has good castings on all the housings, so this is a common issue to all.

 

i agree, if it gets hot, cooling it slowly seems to be the best. ideally you put it in neutral and coast or something.

it seems like if there is coolant and it gets hot, its ok, is when you loose water that it is disaster. for that reason its good practice to replace ALL of the coolant hoses with a new engine/major work.

 

what i dont understand is why the coolant seals were so thin to begin with. they could have doubled the size of the seals and just expanded the housing a couple of mm's to make up for the larger/wider seals. if they were made twice the size they are now.......they would probably last 3 times longer but the cost to replace them would be 3 times more as well.

either way, smaller seals= rebuilding more frequently= less money
larger seals= rebuilding less frequently-more money

you cant win with rotaries unless your racing.

 

It's not the seal that goes bad, but how they make the design into the iron. I know what Karack is talking about, since I rebuilt a few engines and the passage was broken off.

Coolant seals. are what worries me last, since I crack more apex's then rubber.

 

apex seals can be made out of different materials, cast iron by nature is a very brittle metal but it does hold up well which is why mazda made the OEM apex seals out of cast iron as well as the side seals as are piston rings in conventional engines.

the coolant seals really aren't the issue unless you abuse them, basically meaning boosting on a cold engine you can possibly break the seal and burn the o-rings which is a common problem on the FD3S engines i pull apart(keep in mind a completely cold engine there is gaps between the rotor housings and irons until the engine is warmed up and in its natural running state so the coolant seals are semi exposed on a cold engine). in FCs most commonly when i get an engine with coolant leaking into the motor you can bet 85% of the time that there is a broken iron and i usually quote for one broken iron in my estimates on FC engines.

so apex seal failures, iron dowel pin breakages and even coolant seal failures can be limited. when i do get around to building another engine for my TII i plan on using my knowledge to build a bulletproof engine for it to actually enjoy it once again. i know i really dislike rotary aviation/mcmaster carr coolant seals but in the long run looking back they can help seal in the event of iron wall breakages and will not burn up when boosting cold engines but the skirt chafing does bother me, giving the seals an average life expectancy of 3-5+ years in a daily driven application.

 

ya a couple of the t2 rear irons ive had all had signs of erosion in that vunerable spot pointing to the imminent doom. i had to get a few diff irons before i found one that was in real good shape in the thin areas...

 

I guess thats the reason why they move it back to rotor housing on Renesis engines ...

 

0866-23-025

as for dual fuel H2,, where is this massive and expensive and heavy tank going to fit in an rx7 ?

dedicated LPG ( propane ) is the answer,, and some of us have been doing it for a while
my FC rx7 ( 6 port/turbo hybrid ) is around the 300 rwhp mark on a V trim and costs aus $25 to run for 200 km
the LPG brute ute i built ( b2000 with hybrid 13b with turbo ) runs 286 rwhp from an S trim hifi highflow and also returns similar economy

these are both with ancient impco mixers

gas vapour injection ( i have also fitted on of these ) will work with better low down power an less pressure drop with potential for a 30% increase in further economy
--but have limitations in injector flows with only 4 keihin injectors to around 220 rwhp

 

to each their own, my idea is for the vehicle to produce it's own hydrogen which has been done but has been muffled due to improper techniques which have varying results, namely because the ECU doesn't know how to tune for it or cheesey small setups which produce little to no measurable ignitable hydrogen.

i have only seen one other rotary use the method but it was more of a marketting scheme for him to sell his car for more money without any results on paper, on the stock fuel system and stock ECU which likely resulted in poorer fuel mileage, not increased.

i still am a little skeptical, even if it doesn't work eventually more stations will carry E85(85% ethanol, 15% fossil fuel) which is renewable anyways so i'll be working in either direction. hydrogen is more volatile and risky but nearly 100% free. E85 burns cool, clean and safe but is equally as expensive as fossil fuels if not more and will match it as it rises, very similar with LPG, it has been more expensive than 91 octane for some time even with increased fuel mileage it is a wash, something i would like to try and derail.

this is a reverse osmosis thinking of the way most hydrogen powered cars are derived, they are basically designed to use the hydrogen to create electricity to power an electric motor. this is the reverse of what i am aiming at. just whether it can breach the negative gain threshhold is the question deriving power from the alternator to create hydrogen, drawing power to make fuel to feed on itself, which of course the gasoline can help with.

 

Sorry if this is not the direction you want to go but is it possible/practical to weld the iron where it was damaged and then machine the weld flat with the rest of the iron to make a seal?

Very interesting what you are doing btw Karack

 

you'll find that cast iron is a very unique material with low bonding properties for welding material onto it. the issue is that even with a nickel alloy it will eventually break off again, even quicker with steel welding materials. you could epoxy it after welding material to build it back up to help support the weld but in the end it is just a temporary fix, the method i am testing isn't aimed at but i am in actuality testing the sleeve method with an engine with a complete set of broke irons.

cast iron is one of the most difficult materials to work with, and anything applied to it has to match it's expansion/contraction properties or the repair simply will crack again and again. the best idea would be to just recast the housings with thicker walls, but then they need to be cut, threaded and re-nitrited which would be costly to produce.

many will say it's easier to just replace the broken irons but eventually everyone here will find that used irons won't be available forever and new irons at $600 each, isn't always what people's budget allows for.

the only other missing thing from the equation is reconditioning the rotor housings, some people mill the chrome off to even the surface but this weakens the surface because it is now thinner and will wear quicker and re-chroming requires specialized tooling and an expensive process otherwise it will not bond to the steel sleeve or be true to seal against uniformly.

the best alternative is to epoxy the thinner walls to help support them from breaking and to protect them against rapid cooling as the metal is not directly exposed to the water jacket any longer. sometimes i do this, but generally i do not, mainly because my builds are priced as cheaply as i can price them which only allows for me to spend so much time doing them. sadly most people would prefer a dressed up engine with decent tolerances to a rough looking engine that has a few reliability mods built in instead. if it was up to me i would rather build $2.3k motors all day long that were bulletproofed instead of the $1350-1450 motors that are standard.

 

LPG is aus is half the posted price of 92 RON petrol ( and is 100 + RON octane )
currently 72 cents per litre while 92 RON is $1.44
98 RON petrol is 12-20 cents per litre more , call $1.60 per litre at my local

if LPG mixer isset up with a lambda feedback correction commander and solenoid they can return economies not unlike a petrol car litre per litre

i have an FC with around 300 rwhp,,( 15 psi )
and it costs about 20 L per 100 km LPG
( 17/22 litre per 100 km highway/city )

this is not all that far off other petrol FC's around me,, tuned for 11 somethings AFR and 15 psi of boost
( 18 litres of 98 RONpetrol per 100 km )

the reason for this is i can run close to stoic at full boost,, unlike a rotary petrol motor

considering the cost of 98 RON petrol,, i am doing OK --yes?
i am also EPA clean,, having past standard applied even to post 2005 vehicles

 

We have Propane commonly available and several Propane conversions are available for OBDII engines. Most allow dual fuel capability. I spent some time with a fellow last week who had a 2009 Ford F150 converted to Propane. Pretty nifty.

So how bout a little more info regarding LPG conversion on an FC?

Thanks!

Jack

 

great info in this thread.

 

as i said, i can understand propane(LPG) in non US countries because the price of fuels outside the US is insanely high and has been forever(because we're greedy bastards) but around here LPG has been more costly than pump gas for as long as i can remember and will continue to be as will just about any alternate fuels with the exception of E85 BUT it has less energy by volume as fossil fuels.

i remember when methanol was less than $1 per gallon and that was just a few years ago when i first started using auxiliary injection, then it shot through the roof to nearly $5 a gallon making it more expensive than pump gas and burned down that avenue as an alternate. i'm sure ethanol will also once they know they have people hooked and also follows the price of diesel(because everything in the world is moved by truck or car or train at some point so EVERYTHING goes up when fuel prices rise). ethanol is just a slightly less harsh fuel to use with most fuel systems versus methanol.

so it really does sound like a good idea for you, for me it sounds like alot of work just to get away from reliance on pump gas which at the end of the day is a good idea but still not good enough for me to look into as a real alternative. i also would bet if a chunk of the population switched to LPG that the prices would rise because of supply and demand such as methanol/ethanol did. ethanol was also a very cheap alternate fuel which has nearly tripled in price over the past 4 years or so, why? because fuel prices hiked and people started looking into alternate fuels. there's billions of cars on the road and realistically not nearly enough alternate fuel sources to switch at this time. hydrogen derived from water is one of the most readily available renewable resources on the planet.

i also don't want to to go through several motors to figure out the tuning curve of LPG when pushing 400-500WHP versus 250 which is much more flat. not that it isn't a real accomplishment using an alternate fuel in force inducted applications and cheaper than E85, it's just too marginal for me to bother with while fuel prices are all near equal.

 

Not to forget the crappy coolant sitting in the average engine for too long time.
Eating away the material. I have such an engine sitting here. The housings are
looking nice inside but that damn coolant almost destroyed them to the point of no return.

Lots of **** building up inside the housing, corrosion pits everywhere on the housings side surface. Even on the coolant seal area.

I mean nice for the owner if he saves some money by not changine the coolant.
But not nice for the engine, it will get damaged. And the owner pays the bill multiple times back for his ****.

Makes me sick, super nice housings on the inside and the sides are horrible.


Reminds me of my friend with his impreza, using the cheapest no name oil and coolant ... Explained it to him, but he means "Oil is oil".

 

the pitting in the rotor housing seal surface can be epoxied, run over it with a razor blade to flatten it out then run over it with a sanding block to deck the surface after it has cured(mazda actually uses this procedure on porous castings as i have seen housings right out of the box filled and decked where something got into the aluminum casting to cause pockets in the metal). pitting in the iron valleys is pretty much normal even in engines that have been well maintained.

the other tip is to not use tap water to mix with the coolant in the cooling system, the minerals will cause electrolysis which eat away at the aluminum. always use distilled water in the cooling system.

 

https://www.rx7club.com/alternative-fuels-249/could-i-run-propane-through-rotary-761118/
ask anything you like in that thread

 

just to throw some stuff in on the subjects.

As far as pitting goes on a rotor housing and depending on severity of the pitting epoxy is not always the answer. as you stated previously metals expand and contract at different rates and so does sealing compounds so there can be long term effects if using this method that's why i tig and resurface the bad ares.

Now on the coolant you can use tap water but keep in mind that it had all the minerals in it as well as who knows what from pipes and your hose ect... but Nitrate is the key component to protect your engine. you can pick up nitrate recharge kits and throw them in you coolant to get the nitrate levels back up.
Nitrate coats all your internal engine parts and prevents the electrolysis process from eating away at your metals as electrolysis happens when electric current is passed in the cooling system splitting molecules. The molecules then try to re attach them selves to the opposite charge say a positive looking for a negative (your metals) but Instead it eats at the nitrate and neutralizes in which the reason for the nitrate recharge when it runs out. This is a common accourance with diesel engines as the cylinders create great amounts of kinetic energy and with out nitrate small pin holes can eat right threw a cylinder wall very fast. All other engines do create kinetic energy but depends on the engine. Just remember to keep your nitrate levels up. they make nitrate test strips at most auto stores. hope this was helpful to prevent future failures

 

Great thread! I have been guilty of using tap water in a pinch, but I flush my coolant system on a pretty regular basis for one reason or another, but w/ 140k I don't imagine it makes too much difference@this point.

Also, someone mentioned the "thin areas" on the 13b coolant seal castings, where are those exactly? I'm putting together components for my replacement build and I'd like it to be as "bulletproof" as possible.

 

tap water is fine but make sure your nitrate levels are up