I Keep Bending Apex Seals
 

So first thing's first, this is a 6-port turbo GXL. I'm running a Haltech Elite 550 and LS coils with 9 heat range plugs all around. It's been turbocharged for a couple years, 1.5 of which it was just fine making between 296 and ~350whp. When I built the engine that year and a half ago I replaced the cast iron apex seals with RA classic seals. The front exhaust sleeve was a little flappy, but I figured it wouldn't cause any problems as long as the turbo manifold kept pressure on it.

Well, the exhaust sleeve flapped its last flap and sent a chunk into the turbine. This, in turn, caused a bunch of little inconel pieces of turbine to be thrown back into the rotor housings. The rotors and housings were jacked up, so I bought new housings and a pair of used 9.4:1 rotors. I also replaced the corner and side seals. The side seal clearance was set to 0.002". The car ran great during break-in, pulling good vacuum at 16 in/Hg. I still have the OMP but started using premix, about 2.5oz per 10gal of 91. After a few hundred miles I started introducing boost, and even at wastegate pressure, 8.9psi, I noticed that the engine didn't take well to it. Vacuum was down by a point or so. The EGTs weren't terrible, normally in the high 1600F range, barely tipping into the 1700s at the top end. After adding some fuel to bring the EGTs down, I tried some more pulls. The EGTs never went into the 1700s, but vacuum got worse, idle was weak, and the car was hard to start. Using a de-valved piston compression tester I discovered around 60psi on all faces on both rotors. I thought I toasted the corner seal springs from the higher-than-desirable EGTs, so I ordered the inconel FD springs, as well as new side seal and apex seal springs.

So a mere week after building the engine, I removed it and tore it back down to find that the apex seals had warped a good bit. That wasn't what I was expecting! The corner seal springs were a little flat but still in spec. I replaced them anyways. I got new RA classic seals and did a quick and dirty check of the apex seal groove clearance. Things were good from what I could tell. So, long story short, I installed the engine, broke it in for a few hundred miles, and ran into the same issue. EGTs were in the lower 1600s, AFRs are between 11.5 and 10.5. I'm also running 500cc water/meth (about 15% methanol). I even pulled about 4 degrees across the boosted portion of the lead timing map. Split is 10-11 degrees at around 9psi.

That's where I stand today. The compression isn't low enough to prevent it from starting, but vacuum is down in the 13s. The vacuum is slowly returning and starting is getting easier by the day, but I'm worried about hurting the new housings with the most likely bent apex seals.

I'm strongly considering ordering new S4 turbo rotors straight from Mazda to: 1) obviously reduce chamber pressures and 2) ensure the apex seal groove clearances are perfect.

I highly doubt I'm experiencing detonation or misfires. Nothing should have changed since before the rebuild. It ran great for a long while at 12psi on a hybrid turbo and later a S300SX-60 until the exhaust sleeve incident. The only real variable I'm seeing is the possibility that the used rotors I got are not within spec and I didn't notice while I did my quick and dirty clearancing. I suppose another variable could be that before my rebuild the side seal clearance was 0.006-0.007". That allowed for some blow-by and perhaps lowered the overall chamber pressure. Maybe? In any case, the old engine setup was just great. I don't know the EGTs from back then because I added the gauges as I was doing the rebuild. By the way, the probes are about 1.5" from the exhaust ports and centered in the runners.

So here's the question... could poor clearancing of the apex seal grooves cause the apex seals to warp? Or is it a sure thing that misfire/detonation/severe EGTs are the only things that could do this?

Thanks in advance!

-James

I forgot to add that the intake temps were low in both instances. They were low 90s at the beginning of a pull and upper 70s by the time I let off thanks to the AI.

if it was mine i would try a different apex seal. root cause is the RA seals come out of the box different enough that some people are fine and some people bend seals

fun thread from ~15 years ago, same problem though https://www.rx7club.com/rotary-car-p...report-285884/

Thanks for the link! Post #122 by rxeng sounds exactly like what I'm experiencing.

However, there is one thing that's bugging me. The first set of warped seals was the same one that I was running before I had the broken turbine incident. I pulled the seals, checked for straightness, and put them back in to the engine. When the incident happened, the rotors got pinched at the apex, causing the seals to stick in place. There was no indication that the seals would not work afterward. Then there's the 14 years between Jon's (rxeng) incident and mine. I'm sure if there was a manufacturer defect it would have shown up some time in the last build.

I'm considering switching to OEM seals, but I'm afraid that if I encounter detonation I'll be out of my brand new housings. RA seals have worked very well for me up until I got new rotors and housings. I would hate to shell out double for other brands just to have the same happen to them.

I'm going to tear the engine back down and measure EVERYTHING, including the dish of the rotors. Wouldn't it be something if I received a set of 9.7:1 rotors? LOL

its more like the manufacturing tolerance. remember the seals have a length, width and height

Today I pulled even more timing from the boost portion of the map and increased the split to 14-15 at 8.7psi and over. I set the AI to come on sooner and reach full spray by 10psi. I made a half dozen runs at ~9psi. AFRs remained in the high 10s, mid 11s. EGTs were mostly in the upper 1500s F. There were a couple times where the rear rotor crossed into the 1600s.

The 1200cc primary injectors I bought used, so they could probably use a cleaning. I had adjusted the rear rotor fuel trim in low load to get the EGTs closer together. Doing this made the engine run smoother and AFRs read more consistently. However, it appears that I'm having to do the same in higher loads. So after the cleaning I'll switch the injectors from front to rear and take note of the EGT readings.

Anyway, after today's test runs the engine appeared to enjoy it! Vacuum at idle has improved by 0.5 in/Hg, and the engine is slightly easier to start when hot. It's not a vast improvement, but I'll take it! I've decided at this point to run it as is for the time being. I have missed too many autocross events because of this issue.

Lead timing is currently 14 degrees max at 10psi, sticking somewhat to Arghx's Rtek timing map for 9.4:1 engines. I'm just not increasing the advance as much in the higher RPMs.

Quick update: I just went out for a dozen pulls this evening. Vacuum is back up to 14 in/Hg and idle EGT is up to ~830F whereas it was ~755F earlier this week. Vacuum was in the high 15s when I assembled the engine both times. Let's see if we can get back to that level.

I'm going to call this a hard-learned lesson. A tune that works for an engine with poor clearancing might not work for a newer build. The timing must have been too aggressive and caused too high of a combustion chamber temperature.

Like I said, I'm going to run it at this boost level then increase it slowly after the 1000 mile mark while keeping an eye on the gauges. I will update this thread as new information comes up.

This is going to sound stupid, but I apparently had the ignition timing too retarded. How I found that out was I pulled the timing back a couple degrees more and the EGTs jumped. I went the opposite direction by a couple degrees and the temps kept dropping. Of course, I eventually got to the point where adding timing raised the EGTs again. So I backed off a couple degrees from there. I also switched to 93 and replaced my 15% water/meth mixture with 50/50.

Advance is now
21° at 8.7psi
17° at 10psi
11° at 13psi.

EGTs are mid to high 1500's depending on how many pulls I've made in the past couple minutes. I've only tested up to 10psi so far. The apex seals are still happy. I'll raise the boost incrementally and continue my testing.

The ignition timing seems pretty aggressive to me, but that seems to be what the car likes. I'm pretty sure I have the trigger adjusted properly. My timing light hits the marks on the crank pulley when I lock the timing at -5° and -20°, L1 and T1 respectively.

My Prelude is the same way. I started on the dyno with conservative timing, then advanced it to "standard" and still barely made any power. Another 10 or so more degrees and she started putting down real power. Weird.

you just have to give it what it wants. my P port is like this too, if you don't give it what it likes it gets angry.

Too retarded ignition can be bad aswell.
I always make sure that spark is before TDC at all times and never after. So for instance with 10 degrees of split I don't run any less than 10° of advance.
This is to avoid the trailing plugs pre-igniting the following rotor chamber which can happen at high rpm with coils that provide a long spark duration like the ign-1a's

j9fd3s - yeah, I'm pretty much going with the flow on this. I'll let the engine tell me what it wants, at least as far as exhaust temps go for now. When I get her on the dyno I'll see how that relates to torque figures. I feel like we're about ready to hit the rollers.

John - that's a great tip. Aaron Cake mentioned that he levels his timing out around 10° in the higher boost columns, so that seems to coincide.

So I moved from 10psi to 12-13psi. AFR and EGTs remained about the same, but after several back-to-back pulls I noticed a drop in idle vacuum and EGT. Starting is a little more labored.

I suspect that the 9 heat range plugs might be a little too warm and the plug holes are expanding and lifting the apex seals. They say all over the forums that 9 range plugs are fine to 350-400 or whatever hp, but things may be different for high compression engines. I ordered a set of 4 BR10EIX plugs.

If the engine survives until the winter I'll break it down, put in fresh apex seals, and clear out the water jackets around the plugs. The casting was a little ugly there. I just forgot to do anything about it before I assembled the engine.

I'm going to get this figured out, dang it! :D

the JDM guys switch to the cold plugs a lot sooner than we do here, although it does depend on how you drive. if you're on the banking at Daytona for a day you need the cold plugs, if you're just sitting in traffic, it doesn't matter...

Just anecdotally - I've also bent some seals recently, and spoke to Brian Nickel and also another rotary turner on Orlando. Both said don't pull the engine. Go drive it around on the street normally for a few hundred miles as it may start building compression again. They said they usually take their race engines, put them in street cars, go break them in and the compression dips, then as they start to beat on them it comes back up after a few hundred miles. It's somewhat bizzarre but I've now heard it from two sources one of which I very much trust...

That said, I pulled the engine and put stock 2pc mazda seals back in it and had the irons lapped by chips motorsports. Had 100+ psi compression with just one heat cycle and zero miles. I've got about 300 miles on it now. Going to check compression again at 500.

I think I warped the seals by having a coil issue that resulted in the coils melting due to exceeding duty cycle causing the leading plug to not fire, which in turn it got really hot. when I checked compression front, and rear all faces were low (75psi)

j9fd3s - The Japanese may be on to something there. I do feel like switching to colder plugs would be a wise move. She doesn't see a whole lot of casual driving. I only autocross for the time being, but I foresee some track time in the near future.

F1blueRx7 - That certainly gives me hope! I think I've already mentioned that if I drive around on low boost the issue starts to resolve itself. It happens quicker if I go WOT a lot. I'm glad I have some confirmation from others. We already use spinning triangles to go fast and make fire, so what's one more bizarre aspect in the grand scheme of things?

That sucks you warped your seals too. It's frustrating. If your issue was what you suspect, you might have dodged a nasty bullet. I'll take warped seals over replacing my housings, rotors, and turbo again. Please let me know how it's going after you cross the 500 mile mark.

Switch to cold(er) plugs, but there's more to it than that---- get the full length spark plugs with a resistor. An inductive ignition setup that uses CAS for timing benefit from the 'R' in the part # ;).

I've posted about this before...... had a very in-depth convo with Ari Yallon about this many years ago. Long story short, run the proper plugs for the application. NGK R6725 or (my favorite) the Denso Iridium IRE01-31. Keep the motorcycle/snowmobile plugs where they belong. One source for the plugs here:

Spark Plugs 93+ RX-7

I’m sure it’s been well covered on the forum, but in addition to the NGK R6725 platinum rotary plug, there’s also the R7420 Iridium plug

They also offer a set of iridium plugs specific for the Renesis; R7440A (21mm leading) and R7440B (19mm trailing)

https://cimg8.ibsrv.net/gimg/www.rx7...6e32296e9.jpeg
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https://cimg9.ibsrv.net/gimg/www.rx7...1be8cfe7d.jpeg
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I switched from OEM 9 range plugs in trailing and leading, to 4 R7420-10.5 at 340rwhp, never looked back, expensive? yes, but I am still on the same set since 2014 (have cleaned them a couple of times) No cold/hot start problems, running OEM FC3s coils.

Thanks for all the input, guys! I'm going to take all of this into consideration. I'll give the plugs I bought a shot, then when it comes time to replace them I'll take a good look at the examples y'all provided.

Today I was able to make a couple runs at the local autocross before I lost enough compression to have to go home. This time I was only running 9psi. I'm about to break it down and do an inspection. I'll let you know what I find. Something is definitely off. I never had this problem with my old rotors and housings.

it likely won’t be long then because those BR10EIX plugs are known to erode and build up deposits quickly, but I suppose it depends on how much it’s driven.

https://www.rx7club.com/single-turbo.../#post11743171

"The hypothesis that I advance is that as the spark moves down inside the plug and/or onto the nose insulator's surface, it becomes effectively more shrouded, cooler and delays flame front travel into the chamber which, for all intents and purposes, "retards" the timing and may slow the overall burn rate as well. This offers one possible explanation for poor or inconsistent power--and that which occurs without an apparent misfire (may also produce high egts too).

Given some thought, one may see where it possibly has other tuning implications as well. This is, of course, solely conjecture on my part, but if a motor were tuned to say, the ragged edge, while using well worn plugs, what might happen if fresh set of "good" plugs were installed on that same tune? Would there be enough of a performance difference to potentially put the engine in peril? I don't know. Just some food for thought....?

Dont use the BR10EIX

I used to use them. Dropped the ground strap into my engine twice. First time engine survived, second time the strap dented the rotor at the edge and pinched a sideseal- had to rebuild engine.

Now I use Mazda speced plug.
I buy from Mazda Motorsports, but they are available through other vensors for about $18ea.

from Mazda Motorsports site-

000-10-R601-11
@ NGK SPARK PLUG/11.0

Notes: R6601-11 S&P PORT

RX-7
RX-7 TT

Can you post a picture of the bent seals from your first build? I'm curious to see how much yours bowed. I have some pictures of mine using my desk as a flat surface but I'd like to get a known flat metal surface before I really post the picture because I'm sure I'll get opinions.

Okie dokie, so I've just out of the blue decided not to use the BR10EIX plugs. Weird, huh? :D

I don't mind dropping cash on good parts. I've come this far, so why not, eh?

Blue TII - Hey, they're only $14.99 from Mazda Motorsports! It seems as though they don't have anything warmer than an 11 plug. I do drive my car around town a fair bit, so I'll see about getting a warmer version elsewhere. I like the idea of not having to worry about a grounding strap. I keep reading good things about the R7420, but I think those have grounding straps. And they're much more expensive. And they require thin-walled sockets.

I noticed that Denso's and NGK's websites are identical. Even the phone number at the top is the same. Does NGK own Denso now or something? Anyway, I think I've made my choice. I'll start with R6601s.

I haven't removed the engine yet. I'm taking a little break since I used my long weekend to resurrect my Odyssey. I might start this weekend.

I did, however, dig my old apex seals from the trash. Luckily the trash truck is running late this week. Here's a pic of the warpage:
https://cimg6.ibsrv.net/gimg/www.rx7...d6904763ad.jpg

You can easily make out the gap towards the center of the seal. In addition, all of the seals have a slight bow along the other axis. It's almost unnoticeable--maybe a thousandth or so--not enough to really bind in the groove of the rotor. Sorry, I don't have a machinist's straight edge. The glass is the best I can do for now.

I'll make sure to get lots of pics when I tear the engine down. I want this well-documented for future reference.

the R6601 is available in -8/-9/-10/-11 maybe a buck or three more than Motorsports is typical retail