Bart Vangampelaere
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| posted on 20/9/04 at 06:00 PM |
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I'd suggest being carefull with apex seal selection. If you are unsure: use Mazda ones. If you know the thing well enough, you can use something
else. But many racespec apex seals ARE NOT advisable for everyday use in a turbo engine. Just in case you don't have a clue what to do: Mazda
parts are excellent quality, the only drawback is that they are overprized.
BTW: the rebuild kit prices I listed include apex seals.
I still strongly advise for looking for a good used engine in a accident damaged car.
As for rotor housings breaking; they do wear off, and the chrome layer inside the trochoide will dissapear sometime. More importantly, if an apex
seals goes "kaboom" it can destroy the housing (I have a housing at home with a piece of apex sticking right into the chromed surface, and
cut flat by the leftovers of the remaining seals. All apex seals were shattered in that one)
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derf
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| posted on 20/9/04 at 06:39 PM |
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Very correct about the chrome wearing off the interior of the housing, but that happens mainly due to bad chamber conditions, usually from lack of
fuel or too high boost and lack of fuel.
As far as the apex seals go, the steel 3mm mazda units are probably the best ones on the market as far as longetivity. The 2mm ceramic racing beat
seals will take a beating from detonation and heat, but will wear out in regullar use, and have a max life of 20,000 miles. Expect that number to go
way down if you race or go on regular spirited drives.
Us talking about the damage that can be done sounds negative, but it is alot of lessons learned from others who messed up. Rotaries can have extremely
long lifespans. It's not uncommon to have a stock rotary with 250,000 miles on it in perfect working order and never have been fixed (not
counting auxillaries like altenator or power steering). The main key is to keep up with the regular maintenance and not neglect the engine, and it
will probably outlast the car that it's in.
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Jermyn
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| posted on 20/9/04 at 07:36 PM |
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Whoa! didn't realize rotarys were so expensive to rebuild. I guess I thought you could bore it out and just buy oversize rotors or seals like
you might do with a regular engine and pistons. But from what it sounds like...I am going to have to buy all new parts. Is that right?
In that case I might need to rethink this particular car. I was told it was junked because of a clogged, bad converter.... hence no exhaust. If I
can't get the car started due to the clogged exhaust, what sort of compression numbers should I be looking for out of a 99-106k mile engine?
Another factor is how long it's been sitting there. May have been a while. Should I try to spray some oil on the rotors before I test it?
Course, most of these late 80s cars have been at the scrapper for at least 2-3 years anyway.
If life is a race do you want to be the first one to finish?
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derf
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| posted on 20/9/04 at 08:21 PM |
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Standard compression on a wankle is around 100-110 psi, they cme from the factory with 125, but over the course of the first few hundred miles they
lose 15-25 psi. Any less than 110 and I'd be careful.
You also need a special compression tester to test compresion on all 3 chambers per rotor. Or you can just look real carefull at a regular compression
guage and if you see anything less than 100 etc... But it wont hold compression with a regular gauge.
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Jermyn
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| posted on 21/9/04 at 04:54 PM |
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My compression tester holds the amount untill I press the release. I would think that the 3 chambers of 1 rotor would all be the same amount due to
the concentric design. (or am I wrong) If so, how do you test the individual chambers? It's not like testing on a conventional engine where you
just screw in the guage and crank the engine a few times?
How much does this special compression guage cost?
If life is a race do you want to be the first one to finish?
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derf
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| posted on 21/9/04 at 06:56 PM |
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110 from racing beat, it reads all 3 compression chambers, and shows 3 different readouts. The thing is that the apex seals could leak showing bad
compression in 2 chambers or the side seals can leak showing low compression in only 1.
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Bart Vangampelaere
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| posted on 22/9/04 at 01:55 PM |
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when one paex would be bad, two chambers will be connected, therefor both will have bad compression.
it's best to meassure compression with a warmed up engine, especially if it's a bit older.
You can't use a compression tester for piston engines, as it'll keep the best chamber and show that figure. You might have 9kg
(don't know psi numbers sorry) on the tester but only have one good chamber. A solution is to screw out the valve that's in the tester
(not possible with all of them, but it's worth a look) and check. The gauge will then pulse. You should get equal pulses, in regular periods.
It's not as accurate as a real rotary tester, but it's worth a try.
Another idea would be to hand turn the engine, if possible with exhaust off. You must hear the "plops" from the compression. They should
all be equally strong. If you don't hear the right number of pulses, an apex is bad.
Using a light, you can also check the apex's through the exhaust openings in the housings. Every apex must be undamaged, and it must be
possible to push them in a bit with a screwdriver.
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Jermyn
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| posted on 22/9/04 at 03:03 PM |
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My compression tester will allow me to remove the valve. With that in mind, I should then be able to watch the pulsations on the guage to get a
somewhat accurate readout.
Which spark plug hole should I be using? Top or bottom? or does it matter?
Doubtful the scrapper will let me cut off the exhaust to get the engine warm so I could check the compression. Will a squirt of oil in the chambers
give me an idea of what I can expect the compression to be if the engine was warm?
The other car was known to run at the scrapper about 6 mo ago but the fella said it smoked a little on startup. Isn't this true of all rotarys?
Won't run now due to bad fuel pump.
If life is a race do you want to be the first one to finish?
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Jermyn
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| posted on 22/9/04 at 03:11 PM |
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Just out of curosity...why is the 4 port engine preferable to the 6 port?
Also, didn't convertible Rx7s have som other engine designation that was slower than the gxls and gtus?
If life is a race do you want to be the first one to finish?
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Jermyn
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| posted on 22/9/04 at 03:13 PM |
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Sorry....new question. Someone told me that wiring problems are common to RX7 and they often short and burn.
True or False?
If life is a race do you want to be the first one to finish?
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derf
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| posted on 22/9/04 at 06:11 PM |
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1. Sorry....new question. Someone told me that wiring problems are common to RX7 and they often short and burn.
2. Just out of curosity...why is the 4 port engine preferable to the 6 port?
3. Also, didn't convertible Rx7s have som other engine designation that was slower than the gxls and gtus?
4. My compression tester will allow me to remove the valve. With that in mind, I should then be able to watch the pulsations on the guage to get a
somewhat accurate readout.
5. Which spark plug hole should I be using? Top or bottom? or does it matter?
6. Doubtful the scrapper will let me cut off the exhaust to get the engine warm so I could check the compression. Will a squirt of oil in the chambers
give me an idea of what I can expect the compression to be if the engine was warm?
7. The other car was known to run at the scrapper about 6 mo ago but the fella said it smoked a little on startup. Isn't this true of all
rotarys? Won't run now due to bad fuel pump.
Ok here are my answers:
1. Yes there were a few electrical problems, and I'm sure that a car or 2 burned, but not in any higher numbers than any other model car and if
a few burned I would consider them flukes, to the point that I am forgeting you asked about fires. They did wire some of the relays in a bad way, and
it was common for fuses to burn out. I think there was a recall done and this was fixed on pre '88 cars.
2. 4 larger ports provided less turbulence to the intakes air stream, aloowing slightly better hp numbers in stock form (almost negligable), and after
tuning one some minor gaines are noted.
3. Possibly, Ive never heard f it though, but it's still possible.
4. Yes, it will work. I never wrote to remove the valve, but I thought it you should have known that I was thinking it, you need to be more psychic.
5. Top, it does matter, not sure why but it does.
6. It's possible, but I wouldnt trust a squirt of oil to be anything near accurate, Not recomended.
7. Yes they smoke a bit on startup, this is because the seals havnt warmed up and taken their full "warm size", which allows a bit of oil
to seep into the combustion chamber, and you get smoke. Dont take this as youre gonna run out of oil if you drive it a small distance. The average
rotary uses 1/2 quart over 3000mi.
[Edited on 22/9/04 by derf]
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Bart Vangampelaere
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| posted on 24/9/04 at 08:17 PM |
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quote:
1. Sorry....new question. Someone told me that wiring problems are common to RX7 and they often short and burn.
Never heared of that personally, so they won't have been any more prone to self-detonation as any other cars
2. Just out of curosity...why is the 4 port engine preferable to the 6 port?
The 6-port engines use a configuration with 4 main intake ports (2 per rotor, 1 in each side housing) and two aux. intake ports (above the main ones
in the end and front plate) The aux. ones are opened only when rpm rises. This is either controlled by pressure (sleeve valves in the housings,
operated via a tube from the exhaust) or vacuum (butterfly valves in the manifold), depending on either USA (cats, sleeve valves) or EU spec (no cats,
butterfly-valves). This will increase torque in low rpm area's, due to a smaller intake runner.
The 4 port engines (pre RX-7 13B's, or later turbo ones) don't have this. The turbo compensates for the lower torque of a Wankel engine.
The big advantage is that they can be street ported (or bridge ported) a lot easier then a 6 port engine.
this might help a bit:
http://www.mazdatrix.com/faq.htm
check "porting"
A common problem with 6 port engines in USA specs is that the actuators stuck. Obviously not a good thing. A EU-spec intake manifold can be used, and
will be a better choice, if you can get one (no problem overhere, of course).
3. Also, didn't convertible Rx7s have som other engine designation that was slower than the gxls and gtus?
No. At least not that I know of. In Europe the coupe's were sold with 150hp non turbo engines (S4) and either 185/200hp turbo ones (either
S4/S5) BTW: S4: 1986-87, S5: 1989-1991 In 1988 some where S4, some S5.
The convertibles were all turbos.
But I do know S5 non-turbo verts were available in the US. These had 165hp.
4. My compression tester will allow me to remove the valve. With that in mind, I should then be able to watch the pulsations on the guage to get a
somewhat accurate readout.
more or less, you should at least be able to see the pulsations, which give you an idea of the engines condition.
5. Which spark plug hole should I be using? Top or bottom? or does it matter?
The reason why it matters is because one has a smaller hole at the inside. The plugs basicly fire in a small chamber.
6. Doubtful the scrapper will let me cut off the exhaust to get the engine warm so I could check the compression. Will a squirt of oil in the
chambers give me an idea of what I can expect the compression to be if the engine was warm?
Not very accurate. What about unbolting the exhaust?
7. The other car was known to run at the scrapper about 6 mo ago but the fella said it smoked a little on startup. Isn't this true of all
rotarys? Won't run now due to bad fuel pump.
Hmm... Most will smoke a bit because of seals warming, but it could aswell be a bad oil-ring or something. Smoke can be ok, if it will dissapear soon,
but it can also mean many costly parts...
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derf
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| posted on 27/9/04 at 01:17 PM |
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Thanks for making it easier to read.
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Bart Vangampelaere
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| posted on 27/9/04 at 08:40 PM |
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quote:
Originally posted by derf
Thanks for making it easier to read.
you're welcome, you now know how to do it in the future
on a serious note: if you look at this thread it somehow looks like rotary engines aren't very reliable, or difficult to work with. For
clearity: the Wankel rotary engines are not unreliable nor hard to live with. I really like a rotary much more then a piston engine. And since I
drive both, I know what I'm talking about!
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derf
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| posted on 1/10/04 at 05:15 PM |
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yes, and with 9 moving parts, it's not hard to track down problems either.
IMHO wankles are better engines than traditional piston engines. their design allows full time "on power" where as a piston engine only
has power every 2nd rotation for 1/2 a rotation.
When my locost is done it will be my 3rd rotary powered car. It's just a shame that more cars aren't rotary.
On another note, remember the old comercials from mazda "rotaries go round and round while pistons go up and down" I always thought that
those were cut sayings.
[Edited on 1/10/04 by derf]
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Jermyn
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| posted on 2/10/04 at 06:57 PM |
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I went to the scrapper yesterday. The compression test I did with my standard meter seemed to show 1 good compression number followed by 2 not-so-good
numbers. This was just on the first rotor. I didn't bother to check the second. 
I think I'll have a talk with the scrapper on Monday and see if we can negotiate a lower price. Maybe just for the engine/trans alone, since
I'll have to rebuild them. I think I'll keep searching for a running GTU in the meantime. Is there a difference in the axles/uprights for
the two?
If life is a race do you want to be the first one to finish?
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