nycgps

iTrader: (1)

That sucks. if I have to replace my car's motor 4 times I think I will be mad pissed.



Now My motor obviously has a problem, but its so random that I afraid that I might not be able to get it fix under warranty. Grrr I hate this.

I still have my Geico's Mechanical Breakdown coverage with 250 deductible as the final option so ...

alnielsen

iTrader: (4)

Lets just say I have fallen out of love with the car.

Sleepy-z

Just to warn you they ship it with the flywheel still on it and you wont get it back unless they took it off, if they ship it without one they dont recieve there full credut back on the core usually.

alnielsen

iTrader: (4)

Thanks, the dealer has changed a couple of engines for me now and knows the routine.

nycgps

iTrader: (1)

if they really need to replace my engine, I dont mind to bring the stock flywheel back.

Spin9k

My 8s been now 3 1/2 weeks @dealer as well - waiting 4 the new engine implant. I wonder if I'm not just getting the rebuild of someone elses failed engine? I could have yours ... or his .... or that one ... or your #3 engine ... or .. or ...

Sleepy-z

Williams tech ran out of MT's so you will probably get one from us unless they have been holding the motor there at the dealer for 8 weeks or something. They ran out of motors about a month ago. Our first batch of 100 motors are brand new from japan, they are converted 6 spd AT's, we swapped the rear housing on them. So if its a MT they have the motor, we recieve the orders each day and ship them to the dealers in the afternoon, I shipped 6 today before I left.

We are getting a bunch of new rx7 3rd gen. motors soon also from japan, we have just started getting cores in this week too. I stil wonder how we will set the dyno up for one, we were kinda ghetto with the test stand setup. I can totally see a rx7 turbo bolted to the wall or something weird to make it work. We have ran 500+ rx8 motors now without any issues so I cant complain about the setup.

Renesis07

iTrader: (1)

wow, and I complain about my trans leak lol

Targatheory

Hey Sleepy-Z, I have a question for you,

You seem to be becoming very knowledeable with the rotary engines, and I think that's awesome especially from a Z guy.

This compression deal has been playing with my head, and I've looked for a straight answer but couldn't find one.

My question is, using a standard compression tester with the check valve removed, what "range" of pressure should I be watching for on the tester's dial? My gauge reads anywhere from 30 to 300, and I would love an accurate interpretation of what my engine is doing without dropping money at the dealer.

Is it possible to get as good a reading off a store bought tester (and without knowing cranking rpms)?

I would love to know what your buddies at work think.

Go48

I'm obviously not the Z guy, but here's my 2 cents anyway since I've been designing, building, testing and selling compression testers for rotary engines for 3 years now. Engine cranking speed at the time of the test is critical for normalizing the readings so that they can be compared to the Mazda specification. The lower the cranking speed, the lower the compression numbers. And the reverse for high cranking speeds.

Sleepy-z

Yeah crank speed matter for our compression numbers, I have no idea how to figure out the compression without the rpms. Our tester is mazda's own and averages the #'s digitaly to 250rpms I believe after cranking a few seconds. I haven't been in the dyno room for a few months now.

swoope

iTrader: (5)

guess is they are just going to use vacuum as a gauge to determine engine health..


beers

Go48

You can do something like this:

SoCmodder

just wondering, what year do u guys have?
cuz im thinking about buying an rx8, but after reading ALL of the problems that ppl are having before even reaching 40k miles....I'm not sure if its worth it. Right know I have a chevy lumina with 165k miles on it, and I haven't done more than replace the brake pads and rotors....along with normal oil and plug changes and stuff like that...

Sleepy-z

Well its a sports car for one with a unique engine, its not a made for daily driving lumina and wont always make 100k miles honestly. If I were to get one I would just get the newest one possible, 04-08 are all the same and the 09 has a few changes made on the motor. The thing about the rotary is if you know someone that knows how to rebuild it then essentially I look at the life span of the motor as the same thing as a 60/120k service on a modern engine. My z32 runs $1000+ for a 60k mile service, I could tear down a rotary in a afternoon, clean it up and have it rebuilt and running by night on my own.....assuming I have the tools. I dont even want to touch my z32 when it comes to 60k services.

RotaryResurrection

iTrader: (3)

Here is some more info about compression testing.

Cranking rpm is considerably important for accurate results. Spec for testing compression is 250 cranking rpm. IF you crank slower, you make less compression, if you crank faster, you make more compression. For some rx8s with the early starter (like mine) you may be turning less than spec RPM, which will reduce compression readings. Also if your battery and connections are not 100% you will get reduced cranking RPM. The upgraded starter (mid 05 and later, apparently) with the N3Z1 part number is supposed to crank the engine faster. I can attest that my early starter (N3H1 part number) does crank VERY slow compared to rx7 starters I have been around in the past, including my current rx7.

Also, at sea level you make more compression than at high altitude due to the atmospheric pressure. So if you are testing at 2000ft of elevation, there is a correction ratio that you can use to compare to the specified numbers for sea level. So in my area, compression numbers are always going to be a little lower than spec because of altitude.

The engine must also be tested when warm, to get accurate numbers. Rotary engines make more compression when they are cold, and lose about 5psi when they warm up. This is why some older rotaries in rx7s would be fine while they were newer, but as the mileage got up and they got some wear inside, they would have a hard time restarting when hot, but start fine when they cooled off. Because compression was okay when cold, but would drop just below a certain threshold (about 90-95psi) when hot, and tend to "flood". This condition actually isnt a result of too much fuel, but in fact not enough compression which then results in fuel not being combusted, and thus excess fuel, called a "flood".

Another reason why they must be tested warm, is because of the rotary oil injection system. We all know that rotaries puff a small amount of smoke when started cold. This is oil drain-off from the last time the engine ran, from the oil injection system. A little of this oil drains down and pools in the bottom of the combustion chamber over a period of hours, and then when the engine is restarted, this oil burns off in the form of smoke. If you shut the engine down and go into walmart and come out an hour later, there has not been enough time for the drain off to occur, so there is little to no smoke then. Well, this oil drain off that occurs when the engine cools down, also serves to fill in the gaps between the rotor seals and the housings, artificially and temporarily increasing compression. So for this reason you would get higher numbers on a cold engine due to the oil puddled in the housings. So you must start the engine and let it completely burn off this excess oil to get an accurate reflection of compression.

Finally the engine must be tested with the throttle body open. This allows the engine to take in more air, and a compression test is a measure of how much air an engine can compress, therefore this is important.

Sometimes people do tests and do not do them properly and so the numbers arent accurate.

The reason some dealers may not want to do tests (or be able to) is because a special tool is required to accurately test rotary engines, because each chamber shares 3 rotor faces, instead of only one piston face in a regular engine. Here is a pic of the mazda rotary engine compression tester.



As you can see, this unit measures and displays numbers for each face within a common chamber, and also the cranking RPM. This tool is quite expensive (about $1600 as of a few years ago) and some dealers may not want to pay for them.

I have personally owned one of these before, and it is quite a sensitive tool. I had to have mine serviced twice because it simply stopped taking readings, even though I always handled it with care. The company that manufactures and services them (American Kowa Seiki) is very slow and inefficient about working on them and so it is a big hassle. It is also expensive to repair, the starting cost is $275 to even look at it, and you can be without it for several MONTHS at a time.

Also I have noticed that they are not the most accurate/consistent tool in the world. For instance you might be testing one chamber on one engine. You might crank it and get results of 7.4, 7.2, 7.4 one time, and then clear it and test again immediately and get 6.8, 7.0, 7.3. And clear it and test again, and get 7.4, 7.6, 7.3. So the tool is not as good as one might expect (for the price) in my personal experience.

Over the years I have learned how to use a standard piston gauge ($25 at any part store) and read it just as accurately, probably more accurately, than the mazda tester. If I know that the engine is not blown (no broken apex seals) but I want to get an idea of the overall health/sealing ability, I simply test normally just as you would in a piston engine...put the tester in the hole and crank for 5-10 seconds to get a reading. This reading is the highest value of the 3 faces in the common chamber, but in general all the faces are within 5psi of each other so the highest number is still useful.

If I am testing to see if an engine is blown...well, I never have to do that, because I can hear it in how the engine cranks/runs. But if I were, I would remove the check valve from the tester and then crank the engine, observing the needle bounces. They should all bounce to about the same spot on the gauge, the actual value is irrelevant but the consistency is what is important. IF all 3 faces bounce to the same spot, then I put the valve back in and get an overall highest number...which is pretty accurate for all 3, because we already saw all 3 faces bounce to the same value.

I also have a computerized tester that I bought from some guy on rx7club a couple years back that is custom made from a data acquisition box/software plus a pressure sensor that goes on the engine plughole. It would measure the pulses and generate compression values and cranking rpm, and send that info to the computer display where it could be printed or viewed. However I have never been able to get the damned thing to communicate with my computer's "ports" appropriately so I have never been able to use it. But of course there is usually little question about an engine's condition once it gets to me anyway, so it is not a big deal that I know it's compression before rebuilding it.

Now...the mazda tester outputs values between 4.0 and 9.9 (as I recall), and most people dont know what these mean. It measures pressure in KG/CM^2. Most of us in the US are accustomed to compression test results in PSI, so we multiply this number by 14.223, or divide PSI by 14.223 to get KG/CM^2.

Most rotaries when new/near new give values in the 120-125psi range. Every once in a while you might see one between 125-130psi but that is rare. Rotaries drop compression slowly with mileage, and in the 105-120psi range is healthy for an rx-8 engine. It seems that somewhere in the 100-105psi range is the threshold where rx-8s begin having problems with idle/stalling and slight loss of power. The mazda spec for lowest acceptable compression in a renesis is about 96-97psi.

Note that previous versions of rotary would continue running normally well into the 90psi range...95-90psi was the threshold for hot startup problems/flooding, and 85psi was the mazda lowest acceptable limit for compression in pre-renesis engines. My only guess why the limit was changed, is that the engine management system of the renesis is more complex and unable/unwilling to cope with a lower compression engine (thus the car starts dying at stoplights and doesnt make proper power), whereas the older less complex/less precise fuel injection systems on rx7s could handle the reduced compression fairly well.

Any of you can run your own compression test if you are curious about the engine's health in your car. The only drawback is that the plugs are more of a bitch to get to on the renesis because it sits so low, and so far back in the engine bay. It is actually easier to get to them from under the car, but then you have to jack it up and get it on stands, and climb on the ground which is no fun either.

Simply remove both trailing sparkplugs, and unplug the crank angle sensor on the front of the engine at the very bottom, below the crank pulley. This keeps the computer from injecting fuel and producing spark while running the test. Note again that the engine must be fully warmed up prior to the test. Thread the tester into one hole and get in the car, depress throttle fully and crank for 5-10 seconds solid, then shut the key off and go obtain the reading from your tester. Release the pressure and repeat for the other rotor. The front and rear should not be off by more than 15-20psi MAX. I usually like to see differences of less than 10psi. The rear chamber will almost always read less than the front chamber, as it wears out sooner in most rotaries.

Hopefully this post will be helpful in understanding compression tests on rotaries.

nycgps

iTrader: (1)

RR, Great read ! learned a lot.

Oh one question, why is it the rear rotor wears faster than the front? Is it because of the way coolant route? or something else ?

Spin9k

That's good news indeed if the Mazda tester output numbers you speak of are the same that Sleepy-z has in-house for testing rebuilds. Sleepy quoted me 9.5 numbers for 5 of 6 faces (warm) of my new engine, and I thought that was good, but not sure exactly. But now... that would be ~135psi and I must admit it does seem a bit spunkier than the original, (at least in the midrange). I'm still babying it during its 600 mile breakin, so it's a bit hard to gauge.

Sleepy-z

Thats pretty much the same tester we use in the pic, ours looks a little different. Funny thing is we had a pile of 20 or so motors sitting out tagged as failed friday from the last few days, I have been off the line checking in cores and shipping and had to ask why in the world are so many failing? Test room guy said low compression in either the front or rear. I said has anyone figured why? They assumed it was someone building using the wrong parts but they just keeped building without trying things. I told him to check the compression tester, reverse the sensors, he did it and it turned out to be the problem....people were po'ed since now they have to retest all the motors but the issue was MGS(mazda gasket sealant) that was clogging the sensors making false reading(low readings). Just thought it was funny, I knew I should have bet the bosses, they were blaming the people on the line but there isn't really any reason on why they ran fine but failed compression, when there is low compression its obvious and they sound bad running.

RotaryResurrection

iTrader: (3)

so...do you do any assembly, or just organization and shipping stuff? I am curious what side seal clearance they are setting the remans up with (or if they are even measuring it).

Targatheory

Just out of curiosity, when will the general public ( like me) be able to just send off a motor to have it rebuilt by Mazda ( you guys, sleepyz)? And is your existence part of the reason that Mazda won't do compression tests anymore?

Sleepy-z

First for the side seals, there are 4 different sizes that we use, they are already cut. There is letters stamped on each side seal location of the rotors and we just use whatever side seal goes with the letter. I have done the rotor building position a few times, I actually challenged the japan worker who is the fastest builder once but we never got to do it . I am in the "floater" position, which is pretty much the best position you can be since I have freedom to roam. I am the only person who handles of shipments coming in and going out under the parts boss but when people are out sick I have to work the line that day. I have been trained to work every position on the line, kinda hard to remember each position but I dont mind it.

The reason why we will do compression tests is that the dealers are not always doing them proper or sometimes either not doing them or giving us the data. Some complain about the costs involved also. And the "public" is already sending theres out to us, I dont know if your wondering if you can ship it direct and bypass the dealer or what though? I imagine you can always purchase one retail through a dealer if you wanted and put it in yourself, I dont really know the policies on that. As of now we handle the MT motors, Williams tech has about 150 AT's to ship off still but we recieve every single core.

Jedi54

iTrader: (7)

Note to self: invest in a compression tester and charge all the locals.

thanks for the heads up Sleepy, I appreciate all that you're doing for us.

EdwardsB

^good point, they are cheap too!

RotaryResurrection

iTrader: (3)

cheap? how do you figure?

When I got mine used a few years ago I think I paid a grand for it. I have seen then go for as little as 800 used. New they used to go for over 1600 and are probably more than that now. The last time my digital tester went bad, I sold it for $350 to a buyer in europe, non-functioning.

Even the old school style that prints out a chart (like a polygraph) are hard to get and cost a lot.

Exactly how are they cheap again?

Unless you were referring to a standard piston tester...which takes some experience to be able to read. You have to have a quick eye to be able to discern whether the bounces are going to the same spot on the gauge or not. I actually have 2 dedicated gauges...one unmolested which allows me to test the highest pressure, and one modified to let me observe the bounces.