Paulc19

rx7 GXL T2 swap with microtech lt9c ecu running stock boost
did a compression test, here are my results:
95, 75, 75 rotor 1
95,95,95 rotor 2
shows 1 apex seal going bad. Having to eyeball this because i'm using a regular compression tester without the Schrader valve so idk if it is better than that in reality but regardless.
I have 0 problems with the engine. drives like a champ, no starting problems like what I had with my NA (which was well and truly fubar). no sign of bad idle, slightly low oil pressure (20 idle 55-60 @3k says stock oil pressure gauge) gas mileage is 13 city, 20 highway which I would call standard (correct me if I'm wrong), oil consumption is minimal, id say about 1/4 quart every 3k miles when I do oil change, and often no sign of lower oil at all (probably because of premix going into the system and ending up in the oil pan?) and obviously no big cloud of smoke on startup signifying excessive oil consumption.
Ive been digging for a long time now and everyone says if a seal is gone its supposed to run like dog sh*t, so why isn't it? even my tuner didn't notice anything abnormal when I first tuned the car.
hell, I'm not complaining why it doesn't run like a$$, but I am curious as to what the science is behind this?

dguy

iTrader: (8)

Minor chip or potentially a compromised corner seal, and the other solid faces are masking the issue/when you get into boost you cant tell. Throw it on the dyno and you'll see its lower than you expect.

Paulc19

so then how long should I run this motor for? Is it possible for me to do only a partial rebuild? I'd also like a second opinion on the matter before I do anything like that so I'll know what to look for when I do.

doug910

What do you mean by partial rebuild? Just replacing one apex seal?

The biggest risk of running on a bad apex seal is that it can destroy your housings and/or rotors. If you plan to do a rebuild where nothing is held back i.e. brand new housings, brand new rotors, brand new irons, then sure, just run this engine to the ground. But if you want to re-use the core, I think most people's recommendation would be to just rebuild it sooner rather than later. That way you can just get a soft seal kit and a hard seal kit, and have another worry free 100k miles at reasonable power levels. It does not make sense to save $200 at the time of rebuild by only replacing a few of the apex seals only to have to be worried about your other apex seals going bad and destroying your engine within the next 10k miles.

Paulc19

good point. rather spend the money now and save money in the long run. what I mean by partial rebuild is just replacing the apex seals, corner seals and springs.though I guess it would make sense to do everything else in the long run while I have the motor apart. would a basic rebuild kit from rotary aviation or Atkins do the job or do i need to look at a full rebuild kit?
this car is just something I use to put around town in, go to car shows and show off at the moment, so it doesn't see really high RPM too often throughout the week. just the occasional pull here and there but I'm pretty light on it.

Pete_89T2

iTrader: (4)

There's really no way to accurately predict how long the motor will run as it is now, nor is there any accurate way to determine how re-usable any of the internal engine parts (i.e., housings, plates, rotors, etc.) are now without dissembling the motor. So if the motor is running well now, and if still starts fine hot or cold, I would keep running it as-is. In the mean time, to get piece of mind on those compression numbers, I'd also see if you can borrow/rent or buy an actual rotary compression tester like this one - https://rotarycompressiontester.com/ and test it again to get accurate numbers before even thinking about opening the keg.

Not sure what you mean by "partial" rebuild, but if you were thinking of just replacing all the soft & hard seals, and reusing everything else, that could be feasible, but as stated above, there's no way to know what condition all those "everything else" parts are in before tearing down the motor, and cleaning/inspecting the parts.

Paulc19

I plan to eventually own a compression tester like this since I want to do more work on rotaries in the future. I have a burning passion for these engines, its why i want to ask all the questions to keep mine alive . so in practice, how accurate is the compression test using a mechanical gauge and removing the schrader valve?

doug910

Just fyi - you can't rebuild an engine without replacing the coolant seals and they're included within the soft seal kits. Luckily, the soft seal kits are pretty cheap ($200 for OEM on Mazdatrix) and you get a bunch of other gaskets you should be replacing anyways. When my coolant seal blew, I got the master rebuild kit from Atkins (w/ OEM parts) which runs about $1400. In hindsight, it comes with a bunch of stuff that you don't really need so I could have saved some money and bought each component individually from Mazdatrix. Then again, it was my first time and I didn't want to forget anything. You can also save money by going with Atkins branded stuff but I guess do your research before you determine if it's worth saving a few hundred bucks right now.

Even though I was bummed when I found out my coolant seal blew 6 months after purchasing my FC, it's actually kind of nice now because I learned a new skill of rebuilding rotaries while having a bullet proof engine to enjoy autox/track days/cruises for the foreseeable future. If you don't have any events planned for your car for the next few months, I would just rebuild it now if I were you so you don't have to worry every time you drive the car. Sucks the fun out of driving when you're paranoid.

lespaul166

I do want to address the elephant in the room here that no one seems to want to acknowledge. Everyone says "oh reusing your keg, just a rebuild kit"

If its up there in miles (hell even above 100k) there is a very good chance several engine components are bad. When I tore my 112k keg apart for a rebuild like youre talking about, my housings had TONS of edgewear, large spots where the chrome had been worn away. My center iron had a big crack in it, and my outside irons had excessive step wear. My rotors and e shaft were ok, but my e shaft bearings were out of spec. So far this rebuild has cost me around $5000, more than I paid for the car. Now I am using new housings (1500), lapped and Renitrided irons (750), new S5 rotors (500), full Pineapple rebuild kit (1500), and a street port job (750). But even buying used housings and irons will drive your cost up, as these parts are starting to be unavailable used, especially TII irons, most guy are starting to hoard them rather than sell them. I also tore a 130k keg apart for parts and the housings were completely shot on that one too.

Paulc19

I bought my engine from a guy who didn't know how rotary engines worked and didn't want to touch it. he owned a shop and bought it off of a friend because he needed the cash. the previous car it was it had a really bad electrical problem because of a shotty wiring harness and sat most of its life anyways, and the motor that was in it (the one that's in mine now), was an s5 and the car was an s4 so it was swapped into it at some point (that car had about 70k miles on it). He told me that there were only a couple thousand miles on the motor if that, and it makes sense in my mind. when I bought it it came with a boat load of parts and practically a whole s4 engine that was the previous motor in the vehicle (they started to bridge port it when i bought it so who knows, i might finish the job and have a bridge port block if I can spare the cash).

JerryLH3

iTrader: (11)

How accurate it is can vary. What it isn't doing is telling you the engine RPM during the test, which can sway the numbers a little bit when they are normalized to 250 RPM.

Anyhow, you're somewhat local to me. I have an RCT v5.2. PM me, maybe I can make a trip and then you'll know where you stand after a rotary specific compression test.

dguy

iTrader: (8)

I wish I had taken photos during teardown of an engine that I just took apart that I was a dumbass about and had some minor detonation while it was on my engine dyno. Had similar compression numbers (down to the 45 range on 2 faces though), still made 265 at 10ish PSI. One of the apex seals on the rear rotor was in 3 pieces with a 4-5mm chunk out of it, thankfully they were Atkins so there wasn't damage other than a few burrs on the apex seal slot. I'll take some photos of the seal and rotor and post them up tomorrow or something.

Paulc19

I just pm'ed you. I looked at my fsm and it says 85 PSI @ 250 rpm minimum compression. Seeing as how I get the feeling like my starter is going bad, im probably not making that 250rpm mark.

Paulc19

so thanks to Jerry, i got my true compression results on rotor 1 (the bad one): 75,115,80. Ill definitely want to rebuild the motor sometime this year, but considering how i took this car on a 2k mile road trip with minimal wear, I think for now i can get away with it. gonna keep an eye on it though, if Im getting 115 on one rotor face it probably means the housings and irons don't have much wear on them (correct me if i'm wrong). whatever the case, ill be ready for a rebuild, and it will be a good excuse to get a few upgrades and clean the bay out while I have the engine out of there.
also Mazda spec is 85psi minimum. but I checked on the racing beat website and they say anything under 75 psi will give you problems. how accurate is that?