team420

HI!
Guess I got my own thread :D My bad for not reading the new members stuff... Sorry mods.

So my bud brings me his rx 8, I work on all his vehicles/toys, what have you. I am not new to wrenching, but am new to rotary engines, and have learned a lot by searching the last few weeks.
so... his rx8 stalls often after being driven just a few miles, and will not restart. Its hard to get started when cold, let alone warm. Thru searching.. I figure he needs plugs/wires/coils, but... I dont wanna tell him to go buy almost $200 in parts, and still have it stall, and refuse to start. So... I have looked over the engine, and did find a couple places that are likely causing a small vacuum leak. I understand that is issue # 1 on the "fix her" scale, but... she seems to spin a lil quicker than I feel comfortable with. But: that being said... I dont really know anything about how fast they should spin? Sounds like low compression to me when compared to a piston engine, but I understand that normal and acceptable compression is in the range of 97-120 psi? So quite a bit lower than a traditional piston engine.
My biggest concern is that she has low compression, and theres no sense throwing perfectly good $ out the window to polish a turd :D
I obviously dont have access to a rotary compression tester, but what I'd like to know, is if a regular piston engine compression tester will at least give me a good enough sense of, "ok, lets do plugs/wires, etc..."
In other words... even tho I wont be able to test each rotor face independently, will individual chamber readings be enough to make me feel all warm and fuzzy?

Sorry for the hijack :D And T.I.A. for any info.

E.T.A.: Sorry... forgot to mention its an 05 with around 100k(yeah, I know.... its why I'm asking) miles. A/T When she does run, she seems to run pretty well, till you come to a stop, then she gets all shuttery, and stalls, and wont restart. And before anyone says it... yeah, I know, fix the vacuum leak. :D

RIWWP

iTrader: (2)

A) Much harder time starting when hot than when cold is very typical of compression loss

B) If replacing the engine is in the cards, remember that replacing the ignition isn't a waste of money, as it probably needs that too Coils plugs and wires all fail easily, and can produce hard starts, stalling, shuddering, and other issues. They can also lead to many cascading failures, including cat failure leading to engine failure.

C) A analog compression tester can be used to check the compression, but only by jumping through hoops. Like removing the internal valve, video taping the gauge during cranking, then going back and doing the math to get the RPM of the test, and record the pulses individually to figure out which faces are which and what they are peaking at. Even a slight math problem and the results are going to be worthless.

D) A compression test that is either an average number for all faces on the rotor, a peak number for all faces on a rotor, or numbers without a cranking RPM... any of that makes a compression test completely worthless. What is good at 200rpm is ***** terrible at 300rpm, and mediocre at 250rpm.

E) New Owner's thread has details on compression scores and what they mean

team420

Thank you!

A) Its harder, but not "MUCH' harder. I kinda gathered that about the compression loss tho.

B) Replacing = not likely. He dont have the coin to do that, but... he just bought the car a year ago, and still owes quite a bit on it, so I may learn to rebuild these things, and have to buy some tools along the way. He's a good friend of mine, so as long as hhe buys the tools, and the parts, I'll do the rest for beer :-)

C) Exactly what I thought... I may research it a bit more, and see what I can figure out.

D) Kinda what I figured, but was hoping there would be a "redneck" way of making me feel warm and fuzzy :-)

E) On my way to read it.

Oh... I should also add, I live in Maine, kinda in the middle of no where, and there nearest mazda dealer is over an hour away. There are 0 mechanics around here that I would trust with a p.o.s. 85 ford escort, let alone 05 rx8. And since this thing stalls, and wont restart, it would have to be towed, each way, which would be more expensive than the compression test....

team420

Pix of the vacuum leak...





The other hose isnt much better.... but I didnt feel like taking it off :D

WTF?? LOL... who does this ****? I'm gonna "redneck" it proper in the morning, to at least eliminate vacuum leaks as a further problem.

RIWWP

iTrader: (2)

Yeah, not much point in trying to address anything else if the intake has a massive crack in it.

team420

I agree... but I'm also looking down the road....

Its been like this since he bought it a year ago... Prolly about 5-10k miles, it started giving him trouble, in december, so he parked it for winter, and has been driving his 4runner (I love me some 4runner love, I'm a yota boy at heart, as I own 3 of them :D)since. He tried to drive it a few times earlier this summer, but it kept dieing on him, and he presumably flooded it several times.... so I'm thinking about extra engine damage caused as a result of this....

I'm hoping that fixing this cluster of a patch job will have her up and running again, but my past experience, and common sense says otherwise......

BTW... tank you RIWWP for moving and changing the thread title :D


I found the fsm (dunno how I didnt find it when I searched last time) Lotta pages in that thing.... lol

RIWWP

iTrader: (2)

A crack that big in the intake tube would make it nearly impossible to keep the engine alive, and certainly will play havok with actually trying to produce power, so you may be surprised by the results when you get that properly fixed.

team420

Well... I got her sealed up. And... I am surprised. The hard start when cold is gone... she fires right up no prob, but.... when she's warm, she still dont wanna start :-(

I hope that maybe something is expanding when warm, and still allowing un-metered air in... but I doubt it. I'd also like to think that maybe its just a coil acting up when warm as the cel does flash after a few seconds of cranking... but again... I doubt it.
Looks like I'ma have to figure out the whole compression deal....

RIWWP

iTrader: (2)

Typically hard hot starts when cold starts are fine can be traced to either engine compression loss or fuel pump failure.

With compression loss, it is exactly what you noted, the housings expand more than the rotors when hot, which creates a bigger gap between the seals and the housing making compression plummet.

With a fuel pump failure, the fuel pump is too hot to pump, either partially or completely.


However, the very big difference between these two failure methods is more in how the engine shuts off and how soon you can re-fire it.

It's typically the fuel pump if:
- The engine shuts of by itself while running
- The shut off is abrupt with no RPM droop
- The shut off is usually under higher fuel demand points
- It is impossible to immediately refire, usually waiting about 20 minutes lets it fire right up

It's typically the engine compression if:
- The engine is shut off by the driver
- or if the engine shuts off by itself, it shuts off from idle with a slow drooping RPM loss until it stalls
- It is possible to get it refired within the next 5 minutes or so, even if with great difficulty



A really weak starter can slow down a start more due to heat soaking, but it's not typical.

team420

Well.. when I shut it off after its up to operating temp, and turn thhe key back on, I can hear the pump kicking on, so I presume that means its working. Also... it seems to stall more when coming to a stop, as opposed to a higher fuel demand situation.

I initially suspected compression loss, so I'm gonna go with my 1st impression.

Now I'll just have to get crafty to get those #'s :D

team420

So I had to pull this thing out of my shop last night to make room for another vehicle that needs work. She fired up and ran great for about 5min, then thhe sputtering and rough idle began. I let her sit for a good 20 min or so, then I notice steam coming from somewhere near the pass side headlight. My buddy then says, "oh ya, she's been leaking coolant over there too"
Well that woulda been nice to know before I started checking her out....

So any common spots in that area where they leak? I'm almost starting to think that she leaked out a bunch at one point, and my buddy refilled without burping it, and now she's air bound? Temp needle gets to just below halfway on the gauge, and dont move after that, But after running more than 5 min, she def starts to run like ****. No cel codes either.

team420

She's not air bound. I'm just gonna tell my bud to get new plugs/wires/coils. Even if it has low compression, it should still make the car run better.
What're the chances his cat is clogged and causing this? I dont really think its the case, as the car is fully warm before the issues. If I pull out of the driveway with a cool engine, she runs fine till warm. Then she starts sputtering and loss of power till she just bogs down to nothing.

team420

Towed the car the hour away to the nearest mazda dealer, and had compression tested.

rotor 1 = 6.1/6.2/5.9 kpa x100
rotor 2 = 5.3/5.0/5.7 kpa x100

Well below spec... basically motor is spent....

I'm gonna start looking into whats required to rebuild these, as mazda wants $8k for a new motor... lol The car isnt even worth that.

found a couple used motors for $2k-$4k, but... a used motor is just as likely to have the same ****....

Thoughts/opinions welcomed....

RIWWP

iTrader: (2)

Mazda list price for a reman had been $2,001, it just went up to $3,300. That dealer is just trying to get another $4,700 in markup.

With the price hike, even the "cheaper" options are going to climb I imagine, but give Rotary Resurrection and Mazmart a call.

team420

I'll look into thhem, but honestly.... at this point... I'd feel better, and my buddy would feel better if I rebuild it myself....

Assuming thats even possible....

Gotta look into it a lil more..

I been really busy lately, so just havent had time to source all the info/parts.

My real question is.... will the chamber be spent as well? Or just the apex seals?

RIWWP

iTrader: (2)

You won't really know till you start tearing it apart. You will need to replace all seals, gaskets, o-rings, etc... at a minimum. I think there is a rebuild kit that includes all of those for around $700. But, what parts you can re-use can vary widely. With compression numbers that low, I'd guess that you are going to end up replacing at least the rear housing, and probably the 2 flanking irons. Just a guess, and I'm not knowledgeable on the intricacies of figuring out what you can get away with re-using.

Rebuilding the engine yourself is not to be undertaken lightly. It's a "simple" engine with very precise measurements and clearances, stack order, etc... Doesn't take much to destroy your freshly rebuild engine as soon as you turn it over. Not trying to scare you into avoiding it, just trying to emphasize how important it is that you research the hell out of it before you attempt it. Lots of information on the forums here if you start digging for it. Anything posted about engine rebuilding by Charles R Hill, RotaryResurrection, and 9krpmrx8 is reliable. Anyone else (myself included) should be at least taken with a grain of salt, if not entirely suspect.

9krpmrx8

iTrader: (46)

You won't know until you tear it down but if you have never rebuilt a rotary before I highly recommend against it. If it needs new hard parts (rotors, housings, or irons) it will cost a grip even if you do it.

team420

Yeah... I pretty much figured it wasnt gonna be easy....

I have never rebuilt a rotary before, but have rebuilt engines. I know its a whole different animal, but ya gotta start somewhere....

I intend to research fully before I start on it. My bud is in no rush.... Snow will be flying soon anyway, and he wont drive it after that.

I'm mostly concerned about special tools that may be needed to do thhis job...

I'm not about to spend a small fortune on tools I'll likely only use once....

9krpmrx8

iTrader: (46)

Well, to do it right you will need some specialty tools.