Rogue_Wulff

I previously thought the beehive oil whatever-you-wanna-callit was Mazda's biggest blunder in the 1st gen. WRONG!
The lack of any form of low oil pressure warning device (guage, light, buzzer) in the 1979 model RX-7 tops the list, for now. Story as follows:
My buddy purchased a 79 with rather low miles (under 100K) that looked to only need a few minor things, and a fresh coat of paint. It had been parked for quite a while, so the previous owner rebuilt the engine, to insure everything was up to snuff. Since the guy who was selling it has a shop that deals with only Rotary engines, and stated he rebuilt the engine, we took him at his word. He has a fairly good reputation for doing quality work.
This particular engine ran great, no signs of smoke, and only had a minor issue with starting when warmed up, which I just chalked up to apex seals not fully seated. After having acheived approx 500 miles on the engine, the hot start issue totally disappeared.
~6000 miles later, the engine suddenly developed a knocking sound. Not good. Pulled it out, dropped the pan, lots of copperish looking chunks. Really not good.
Took the front apart, and as the front cover came off, my heart sunk when I saw the pinched o-ring. I knew it had to come apart, and parts were damaged. As I broke it apart, and removed the rear iron, I couldn't beleive what I saw. The rotor was chewed up from hitting the rear iron. The rear iron had marks/grooves from the rotor gear. Side seals, corner seals, and apex seals all had damage from the dancing rotor.
Removed the rear rotor, and saw the bearing had spun, but only 3/4 inch or so. The e-shaft journal was dark blue.
All total, both rotor bearings are wasted, as the front bearing was beggining to chunk up, and probably would have spun very soon. Both stationary gear bearings are worn, but not too badly. Both e-shaft rotor journals are blued, rear is worse.
This engine died needlessly, all for the lack of a low oil pressure warning device. Worst part is, a manual guage was planned for install 3 days after the doomed sound started.
I am utterly amazed that a simple o-ring can cause so much damage, and the lack of an oil pressure warning ever made it to the production line.
At the same time, I impressed by the fact that the engine ran as long as it did, with very little (if any) oil pressure. This is compounded by the fact that this car has been to several open track events for "Play days", and driven rather hard after the intial break-in period.


Sorry for the long rant, but I just *had* to vent.

GavinJuice

did it not have an oil pressure gauge, i would think that would be the most crucial sensor to watch especially after a rebuild?

GavinJuice

oops i see you were planning, but not even an electrical?

Rogue_Wulff

In 1978, Mazda deemed a clock more important than an oil pressure guage. The rear housing is not even drilled for the stock guage.

GavinJuice

instead it came with a stereo.......psh

Rogue_Wulff

Radio/stereo was optional. Clock was placed where the oil pressure guage belongs, beside the tach. As my buddy said, "I could care less what time it is, I wanna know how the engine is doing". Besides, the damn clock doesn't even work 100% of the time.........
I know a lot of cars come without an OP guage, but they at least have a light, inspite of the fact that most people ignore it.

Naegleria_Fowleri

That is completely ridiculous. I didn't know they didn't come with an op guage. If I ever buy an SA, I know my first mod now.

Tranquil

iTrader: (1)

+1

and how accurate is my stock OP gauge? I was thinking of going aftermarket, but I said nahhhh.

gsl-se addict

iTrader: (3)

The SAs don't have any kind of oil pressure gauge or warning light. I just put a set of 3 cheap gauges when I had my SA (oil temp, oil pressure, amps). I would strongly recommend putting an oil pressure gauge of some kind on SAs. Doesn't have to be expensive/accurate as anything is better than nothing.

Rx-7Doctor

iTrader: (13)

The only thing they have is a low oil level warning.

ChasRX

I agree. What were they thinking? I tapped in to the banjo bolt (front-mount oil cooler line) for an oil pressure send when I swapped an '80 SA engine into my '81 chassis. I couldn't believe that the SA engine didn't have a tap. Feeling pretty humble, I asked the local Mazda shop mechanics when I couldn't find a place to thread my oil sensor into. They told me that the '79 / '80 models lacked such. That's just lame and unacceptable, so I immediately proceded to tap the banjo bolt. At least I'd get a reading as my stock OP gauge is consistent; regardless the accuracy.
I'd rate water temp and oil pressure as my top two most monitored.

aussiesmg

iTrader: (1)

I used a 25 pound low preasure warning light ,stock low preasure lights are only 5-6 pound, by then it's too late, with a big light fitting right in front of my face, (called a dummy light for good reason) It came on the engine got shut off immediately, saved my engine twice when oil lines failed on track days.

j_tso

iTrader: (2)

Like the temp gauge, it's not that great. It'll let you know when the **** hits the fan though.

rotarycrazy

iTrader: (8)

I need to get an OP for my SA since I am droping a FB motor in it soon that should be hopefuly not to hard to install.

perfect_circle

I<3 my FB's

trochoid

iTrader: (6)

I know the feeling. My very first rebuild, I forgot the front cover o-ring on a test build. 6 hours run time, mostly idling in the shop, I lost all 4 bearings and scored the e-shaft. Since it was basicly a practice motor, I wasn't too disappointed, but that was my best set of bearings.

Oh, and I did have have an opg that read 0, figured the sender was bad, oops.

Rogue_Wulff

I rigged up a similar light on another freinds racecar. Actually, 2 of them. I used low pressure warning light senders, and put one in the oil passage, along with a Stewart-Warner OP guage.
The other sender was installed in a block coolant drain location. Even a SW or atuometer temp guage won't give a warning when the coolant dumps.

The real ironic part about this SA engine dying such a horrible death, it still started and idled perfectly. About 2000-2500RPM, it sounded like 25 monkeys beating on the engine with hammers.
I dunno how it could run, with all of the apex seal, side seal, and corner seal damage.

aussiesmg

iTrader: (1)

It seems obvious to me, but who actually checks a gauge if you're driving at 10/10ths, a big bright light can't be missed. Hence shift lights are more important than tachs.

perfect_circle

thats cause the 7 never loses.

and the rotary is a marvel upon mere mortal engineering.

Naegleria_Fowleri

I prefer a shift buzzer myself, but how many people bought SA's to drive wide open everywhere? Not as many as what did to drive around a lot. It would still have made more sense for them to have it along with the light. The more indicators the merrier, right? At least the safer, I'd say. And if I were designing a sports car, I think I would want all the gauges and indicators possible to monitor as much as possible.

Rogue_Wulff

I agree. But even a 3-4 PSI warning light *might* have saved this engine. A rotor dancing around on the e-shaft, slapping the housings, is unacceptable as the only factory oil pressure loss warning.


This engine was my first to solo on the teardown, and would have been my first build. I doubt it be going back together anytime soon. Probably just get a running used engine to install, while gathering parts to rebuild this one. It looks like $1000 will be needed, in order to do it right.