interesting core teardown: 04 AT 34k original miles
12-05-2012, 12:03 AM
#1
kevin@rotaryresurrection
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interesting core teardown: 04 AT 34k original miles
Customer reported difficulty starting when COLD and absolutely impossible to restart when hot, as well as stalling at idle and vibration at idle. Indeed, as soon as I sat in it at idle it had the worst vibration I've ever felt in an rx8. I removed the engine and tore it apart, and found some interesting things I've never seen before.
This is severe carbon buildup on the chrome rotor housing friction surface. Normally this does not happen because the apex seal is sweeping across the surface thousands of times per minute and keeps it pretty clean. This carbon was so hard and thick (about 0.5mm in thickness) that the seal was lifting up off of the rotor housing and letting all the compression blow out.
Also I found significant wear and grooving in the compression-generating area of the rear housing above the trailing plug.
Here is some pretty significant chrome flaking.
Scraped off the carbon layer.
Apex seals are worn everywhere except the edges...wonder why that is?
Hmmm...this doesn't look quite right?
One of the 3 short apex springs on the rear rotor was broken. This normally does not happen.
Here is how the springs would normally sit when properly installed.
This is severe carbon buildup on the chrome rotor housing friction surface. Normally this does not happen because the apex seal is sweeping across the surface thousands of times per minute and keeps it pretty clean. This carbon was so hard and thick (about 0.5mm in thickness) that the seal was lifting up off of the rotor housing and letting all the compression blow out.
Also I found significant wear and grooving in the compression-generating area of the rear housing above the trailing plug.
Here is some pretty significant chrome flaking.
Scraped off the carbon layer.
Apex seals are worn everywhere except the edges...wonder why that is?
Hmmm...this doesn't look quite right?
One of the 3 short apex springs on the rear rotor was broken. This normally does not happen.
Here is how the springs would normally sit when properly installed.
12-05-2012, 12:09 AM
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kevin@rotaryresurrection
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How much side seal clearance?
HOW MUCH?!?! 15 thousandths...spec is about 2-4, I usually try for 2 at most. In other words this engine had 7-8 times as much clearance as I usually set with when I build.
More of the same on the front...
This housing looks a lot better when cleaned up than the rear did.
Now here it gets interesting again. As you can see here, two unbroken short springs on the front rotor are offset and not centered in the slot that they should be sitting in on the bottom of the apex seal. You can see that it's been riding this way since there is a set of shiny spots on the bottom of the seal that indicate where the tips of the spring have been riding. Thus, we can conclude that mazda installed these springs wrong when the (original, not a reman) engine was built new.
Another broken short spring on the front. Total count, two broken, the other 4 installed incorrectly.
HOW MUCH?!?! 15 thousandths...spec is about 2-4, I usually try for 2 at most. In other words this engine had 7-8 times as much clearance as I usually set with when I build.
More of the same on the front...
This housing looks a lot better when cleaned up than the rear did.
Now here it gets interesting again. As you can see here, two unbroken short springs on the front rotor are offset and not centered in the slot that they should be sitting in on the bottom of the apex seal. You can see that it's been riding this way since there is a set of shiny spots on the bottom of the seal that indicate where the tips of the spring have been riding. Thus, we can conclude that mazda installed these springs wrong when the (original, not a reman) engine was built new.
Another broken short spring on the front. Total count, two broken, the other 4 installed incorrectly.
12-05-2012, 12:19 AM
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kevin@rotaryresurrection
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The customer decided they wanted the nicest engine possible so he bought two perfect condition used rotor housings from me, I scrapped his chrome-flaked rear housing and took his good (but less than perfect) front housing in trade.
More new parts including cut to length side seals.
Everything else cleaned up nice...
Two thousandths, that's better...
Rotor seals installed:
Build...
Checking endplay initially, would have run as-is at 0.003 but I adjusted it to 0.0025 so it's perfect IMO.
Pressure testing the cooling passages...holds 20+ psi for 30 minutes and I call it good.
Checking endplay for one final time.
Put it back together with new motor mounts and the vibration is gone. It starts up perfectly cold or hot now (which is unusual even for a fresh rebuild with new rotor housings, usually they take a few days or weeks to start well when hot after a rebuild).
More new parts including cut to length side seals.
Everything else cleaned up nice...
Two thousandths, that's better...
Rotor seals installed:
Build...
Checking endplay initially, would have run as-is at 0.003 but I adjusted it to 0.0025 so it's perfect IMO.
Pressure testing the cooling passages...holds 20+ psi for 30 minutes and I call it good.
Checking endplay for one final time.
Put it back together with new motor mounts and the vibration is gone. It starts up perfectly cold or hot now (which is unusual even for a fresh rebuild with new rotor housings, usually they take a few days or weeks to start well when hot after a rebuild).
Last edited by RotaryResurrection; 12-05-2012 at 12:23 AM.
12-05-2012, 12:07 PM
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kevin@rotaryresurrection
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Also I should note that the customer did the "decarb" procedure twice, as well as took it out and ran it hard for a few days, per my advice before giving up and bringing it to me. As you can see neither of these procedures helped the carbon buildup much.
12-05-2012, 10:40 PM
#7
Wow .... thanks for posting this ... I spy an rx7 motor in one of the pictures (tall injector holes on the center iron is how I've been able to distinguish rx8 and rx7 motors ... also the front cover is different, and I think the gasket setup for it? )
also thanks for your contributions in general .... I wish there more threads like yours out there and I think most of the rotary (RX7 too) community would agree with this. (and your rebuild service as well)
also thanks for your contributions in general .... I wish there more threads like yours out there and I think most of the rotary (RX7 too) community would agree with this. (and your rebuild service as well)
12-05-2012, 11:24 PM
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kevin@rotaryresurrection
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Wow .... thanks for posting this ... I spy an rx7 motor in one of the pictures (tall injector holes on the center iron is how I've been able to distinguish rx8 and rx7 motors ... also the front cover is different, and I think the gasket setup for it? )
also thanks for your contributions in general .... I wish there more threads like yours out there and I think most of the rotary (RX7 too) community would agree with this. (and your rebuild service as well)
also thanks for your contributions in general .... I wish there more threads like yours out there and I think most of the rotary (RX7 too) community would agree with this. (and your rebuild service as well)
Pictures!
12-06-2012, 03:11 AM
#12
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I wonder if this 04 had the MSP16 ECU re-flash?, what was MOP condition like?, nozzles and oil lines?
Naughty Mr Mazda assember...I wonder if he still works there?
BTW: Thanks for great info!
Naughty Mr Mazda assember...I wonder if he still works there?
BTW: Thanks for great info!
12-06-2012, 08:27 AM
#13
RR what are your opinions on decarbing and premixing. Obviously their superfluous if the engine wasnt built to spec to begin with but would they actually be of any use in situations like this where carbon is excessive? Ive been premixing with valvoline 2 stroke since ive got my 8, decarb about twice a year although its effect is small if any. And every once in a while i premix with MMO because of its cleaning properties, effects of that arent noticeable (again minimal if any).
12-06-2012, 04:59 PM
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Yeah I always figured my first original engine (lasted 22k) was probably the last one built on a Friday after a 60 hour work week in Japan and my last reman (lasted 27k) was built on a Monday after a weekend in Vegas 
12-06-2012, 06:59 PM
#21
RR what are your opinions on decarbing and premixing. Obviously their superfluous if the engine wasnt built to spec to begin with but would they actually be of any use in situations like this where carbon is excessive? Ive been premixing with valvoline 2 stroke since ive got my 8, decarb about twice a year although its effect is small if any. And every once in a while i premix with MMO because of its cleaning properties, effects of that arent noticeable (again minimal if any).
as for premix, it helps to coat the housing so crap does not stick on as easy.
most crap came from gasoline, so pick a better, newer station ...
hey RR, thx for the pics! ya think the build up has something to do with the improper springs install? thats what it looks like. like u said u never seen crap like this before and this engine's springs were not installed correctly
Last edited by nycgps; 12-06-2012 at 07:05 PM.
12-06-2012, 07:19 PM
#22
when u soak hot parts into tub of hot decarb mixture, it desolves the crap on it fast, but most people thought those thing works like detergent and the longer it soaks the better. i seen big *** machines use pretty much the same kind of solution and heat to clean parts. the key point is it has to be hot hot.
as for premix, it helps to coat the housing so crap does not stick on as easy.
most crap came from gasoline, so pick a better, newer station ...
hey RR, thx for the pics! ya think the build up has something to do with the improper springs install? thats what it looks like. like u said u never seen crap like this before and this engine's springs were not installed correctly
as for premix, it helps to coat the housing so crap does not stick on as easy.
most crap came from gasoline, so pick a better, newer station ...
hey RR, thx for the pics! ya think the build up has something to do with the improper springs install? thats what it looks like. like u said u never seen crap like this before and this engine's springs were not installed correctly
Lucky for me I havent had any compression related issues since I've owned my 8 (knocks on wood). Just trying to see if their are any real ways to keep carbon away from my engine or am I just wasting money on seafoam. I think RR may have proved seafoam to be ineffective. Good thing i've been filling up with 93 at the same Mobil station for over a year now.
Then again I think that being an automatic really factors into this situation. More than likely this engine might not have seen high rpms throughout much of its life and RR's suggestion to drive the car hard wasnt enough to combat all the years of carbon build up off of this engine. Like you said nycgps, carbon might be able to be broken down under excessive heat which is why I continue to drive my car at high rpms every once in a while.
Last edited by GK1707; 12-06-2012 at 07:23 PM.
