Side Seal Clearance
 

The rotor rebuild kit I got came with uncut side seals. I used the method in the Mazda rebuild manual and inserted some 0.15mm feeler gauges to shim the seals back in the rotor while measuring the clearance at the corner seals and then sanded the long side seal to about .0020" clearance in the low part of the range that Racing beat recommends (maybe just for RX7?). The Mazda manual only has a max limit and it is .016", a big difference. "The side seal-to-corner seal end clearance should be .0015" to .0040" when using new side seals" quote from RB. Racing beat does also say "RX-8 Note: It is very difficult to measure this clearance in an RX-8 engine due to the taper on the outside of the seal. Side seals should be selected as Mazda recommends - by using the code stamped on the rotors." But they sell the RX8 rotor rebuild kit with the uncut seals...

Anyone have some advice on this one? I'm putting a lot into this build and don't want it blowing up from the seals being too tight...

Here's the info from the manual:
https://cimg3.ibsrv.net/gimg/www.rx8...0698ae2f6e.jpg
https://cimg6.ibsrv.net/gimg/www.rx8...e26b90c03d.jpg

Mazda only says the Maximum clearance, not a minimum. With what I have into this build I'm not against just buying new side seal from the side seal selection chart:

https://cimg7.ibsrv.net/gimg/www.rx8...60a598cd16.jpg

Thanks!

Well, guys no fast reply from here... I guess I'll just play it safe and just buy the pre-cut from Mazda.

I called Mazdatrix and asked them about this and they said that they never had great results, in the 30+ years of rebuilding rotoys, cutting their own side seals and that the pre-cut ones were "a million times better". They said they had a lot of compression issue with cutting them.

So I just ordered from them. The previous chart for sizing they said was outdated and it looks like they group 8 of them into one size.? Hope it still works as great as they are telling me since 8 of my 12 seal fell into this size.

https://cimg1.ibsrv.net/gimg/www.rx8...7be2578e68.jpg
Sizes I needed: N,Q,Q,R,S,S,S,T and J,K,K,L

I'll post compression reading after the build is done.

If anyone want the new long seals that I cut I'll give them away as I will most likely just toss them into a parts box and never use them.

the pro Renesis builders all hand cut their side seals

I could say more, but why state the obvious other than to say that in 15 years I never heard anyone ever refer to Mazdatrix as a pro Renesis builder. Like anything, there’s a way to do it right and a wrong way too. Go search on RX7Club to see the right way by setting up a rotor as a jig in a bridgeport.
.

I just want this motor to perform like a well built and reliable factory motor. Mazdatrix may not be a pro renesis builder but they did build reliable motors for years and offered me a reasonable solution to build a reliable motor. I'm pretty skilled and can handle cutting the seals to the correct length and angle but I have not been able to find a source for a gap specific to RX8 side seals or a procedure for measuring this gap other then what is in the RX8 rebuild manual which only shows how to check for a worn seal and to replace it with a pre-cut if it's out of tolerance. The RX7Club may show how to cut seals and the proper gap for an RX7 motor but since the 8 has the side exhaust ports I'm not convinced that the same gaps will work because the seals get hotter and may expand more and bind. I've built RX7 motors before and cut the long seals for them based on the specs from Racing Beats site but this would be the first MSP motor I've rebuilt that I'm replacing the side seals in and I don't plan to do this very often.

If you can point me to a thread or builder that can explain the correct gap and how to achieve it with the wedge shape side seal of the RX8 and the possible issue of the clearance being to tight with the side port exhaust that would be helpful.

Gear, a little bit of searching will point you in the direction of some reputable engine builders that can probably answer your questions. RotaryResurrection and Mazmart come to mind, the latter of which is who I had rebuild my Renesis. Results were amazing, as expected. Paul is a hell of a standup guy and Rick Engman probably has more knowledge about rotaries than many of us. Both of those builders I would say are trusted in the community, as well as others. I think shadycrew has a thread regarding some builders he trusts, as well.

Anyway, hope you reach out and they provide you with the information you need. Best of luck!

Links:
MAZMART - Your Wise Choice for Mazda Parts
www.rotaryresurrection.com

Well you’re on here asking this question, so where does your expertise on who might build solid RENESIS engines or not come from?

apparently you’re also not up to speed on how well an OE engine seals or not either, but ok then ...
.

He might be a little in over his head, then again I feel like most people who have at some rebuilt or helped their buddy rebuild the motor on their '88 NA FC think they have the ability to rebuild the Renesis. But, you know, who knows.

Best of luck OP! If you feel like you're not up to the task to do the job well, I would recommend transferring the labor to a skilled engine builder. Would be a shame if your brand new engine grenades because of a lack of knowledge and too much bravado. We're all guilty of it at times, just gotta know when to call in reinforcements.

over the same 15 year period the “it’s just another 13B” pre-Renesis rotary crowd has come and gone ...

Guys, I have some mad skills and have successfully rebuilt rotarys and other motors with little or no issues. One of my flaws is I tend to cheap-out and try to save money. I did rebuild this same MSP motor 3 years ago and put almost 40k miles on the rebuild. I had a supercharger and water-meth on this engine but it started to get low compression because I cheap'd out on the rebuild and never did the side seals or lap the side housings. I always said that I would just pull it out in 2 years and rebuild it again anyways... Well 3 years later here I am rebuilding it. I see a lot of people come to this site with some great accomplishment and some with just a bunch of talk and BS. All I'm trying to do on this thread is find and document the correct procedure for cutting and clearancing Renesis side seals and so far I haven't got a strait answer. I'm patent so maybe someone that actually knows how to do this will post something or I'll just find the procedure and clearances and post it here myself. These motors are really not that complicated to rebuild.

That sounds great and I'm glad, but read the responses. I gave you two great resources, among others, that you can reach out to in order to get the answers you need regarding your side seals. (And any other questions you might have)

Thanks vlad0691, you're right you did give me something and I do really appreciate it:worship:. I just thought that maybe this has come up before and got posted somewhere already but I just haven't been able to find it. I did reached out to Mazmart who said they would check with their tech and send me a response. If they do I'll post it here and maybe apply it to my build if I don't have it together already.

I would try for somewhere around 2 thousands. The main thing is to be able push the side seal up and down without catching an edge on the corner seal. You dont want it to get jammed in the rotor. Like you said, I think mazda considers it out if spec at 15 thousands plus, which is huge. Almost all my seals are in the 0.002 to 0.004 range. This was a REW of course so take that for what it is...

FWIW.
Big update! After much trial and error and sacrificing about a dozen side seals to the Rotary gods I managed to get all my side seal to corner seal clearances to 0.002-0.003in. Grinding those seals was probably the most difficult part of my build...so far. In hindsight, I probably could've just went with the standard seals and been fine. But driving around knowing I passed up on some extra compression would drive me crazy.
This is a quote from the amateur builder who built the engine I am currently driving, which is the one he is referencing in the post. It has about 55k on it now, and was assembled with used housings. At about 12k I tested hot compression with a conventional gauge and the peaks were all above 120psi, and when I did peak hold, it was a bit over 130psi. I do not know the cranking speed. I believe he was going to use the Mazda method at first, but decided to grind instead. The engine runs very well overall. Here is the post:

https://www.rx8club.com/series-i-tec...-244370/page8/

Even if you cut them at 0.003 or 0.005", how much air could move through that gap when the motor is spinning at say 5,000 RPMs or 83x per second or 12 milliseconds??

Mazda obviously knows this answer, which is why they consider 0.015" max spec. I would think the flatness of iron is 50x more important than side seal clearance to the corner since the side seal is 50x longer than the width (just a guess).

kevink0000, good info thanks! And thanks strokercharged95gt! This is the thing I'm looking for, some clearance number, the method used to measure, and the long term results like great psi at 12k and a total of 55k reliable long lasting motor!

kevink0000, It looks like the smutterbutter build used a combination of mazda pre-size seals and some hand cut. Or was it all handcut to 0.002 to 0.003? And just to verify the method used to measure, was it the method from the manual with the two 0.15mm feeler gauges shoved infront of the seal before measuring at the corner seal?

Along with a set of long seals I also have a new set of mazda pre-cut from Madzamart so I'll most likely do the same as your builder and use the best combination or all hand cut.

Mazdamart did the side seal grouping different then what mazda is saying

Here are my seals needed and the part numbers they match to:
Mazda dealers numbers:
JKKL n3z2-11-C10D
NQQ n3z3-11-C10D
RSSST n3z4-11-C10D

Mazdatrix numbers:
JKKL n3z3-11-C10D (167.883 +0.0 to 0.02)
NQQ n3z4-11-C10D (167.883 +0.08 to 0.10)
RSSST n3z4-11-C10D (167.883 +0.08 to 0.10)

They grouped 8 different sizes into one and upped all of the other seal sizes by one size. Best to go to their site to get this: "https://www.mazdatrix.com/?s=side+seals"

I asked them about this and here is their responce:
"Back in 2008 or so, Mazda sent a TSB changing the scale to bump all the shorter seals up one size. They stopped at the NOPQ, holding those at the N3Z4 length. Since then, this is the way we built all our motors and found that the longer seals make better compression. (We have since stopped building motors and just sell the Mazda reman because it's usually less expensive and always has more new parts)
We have never seen that TSB again or any documentation to support the change, but it's what we used and have been selling. If you want to go with the shorter seals, obviously lots of engines are built that way since it's what all the documentation says."

All parts are here now except for one side seal that Mazdatrix is sending me.
https://cimg7.ibsrv.net/gimg/www.rx8...bf26298ab1.jpg
Chip's resurfaced and renitrided my side housings.
https://cimg8.ibsrv.net/gimg/www.rx8...19996228fe.jpg
...and some new rotor housings
https://cimg9.ibsrv.net/gimg/www.rx8...8eac72e2cb.jpg
...and all new OE seals from a Racing Beat kit I picked up on EBay for $900.

No, I specifically told you where to get the cutting answer and then we got into you telling us you got the incorrect answer at Mazdatrix claiming it was correct. You need to factor in some differences of the Renesis, the primary one is the side seals run a lot hotter than the 13B and the length expansion needs to be accounted for.
.

I believe Smutter was able to use some of the seals he had already bought to get the clearance where he wanted them. He then bought some long ones to grind. I don't know more than that really.

As far as how important clearance is: I say very. Piston ring end gaps can be responsible for 5-10% (or more) HP and torque difference on a freshly rebuilt piston engine. I read a paper that a 350 got a 50% reduction in blow by from going to .016 from .025 in piston end gap and the aforementioned 10% increase in torque.

Our engines are very leaky, with I would guess more than 25% leakdown when fresh and broken in. Probably more. Worn out piston engines are about that.

Also, combustion gases can recirc into the intake stroke on adjacent faces through sloppy side seals, something a piston engine does not have to contend with.

Our chambers are small, (200cc or so) , and seal area is very large compared to a piston engine, so any way to restrict leakage should be pursued when rebuilding in my opinion.

So I ended up just buying pre-cut but I went with the suggested sizes that Mazdamart suggested. I did measure the gaps and they all looked good. All were between 0.006 in and 0.004 in.

Here's the first start:

...and a hot start at 241 miles later:

I'll do a compression test at 500 miles and post that here too. I'm putting together this Instructables TR-01 DIY Rotary Engine Compression Tester to get a good diy compression reading.
This build is looking really good though. I want at least 1000 miles on it before I put the SC and WMI back on it.

https://cimg8.ibsrv.net/gimg/www.rx8...9ed5e7aa17.jpg
Two 0.15 mm feeler gauges to space the seal as the manual says and then measure the gap at the end

https://cimg9.ibsrv.net/gimg/www.rx8...5fe64feadd.jpg
Pre-cut side seals

Sounds good. Glad those OEM seals were as tight as they were. Congratulations on the build!

Great work on the rebuild. Once the motor turns over and idles and you don't see fluids going all over the place, its definitely a sigh of relief.....

what do the ends of the side seals look like though; i.e. the shape where they intersect with
the corner seal?
.

They look like the old seals I took out (only not all worn out) they're cut flat on the ends and to an angle that seams to best meet the corner seal at the center of the side seal cut.

Here's a picture I had:
https://cimg4.ibsrv.net/gimg/www.rx8...9929168036.jpg
closeup of the new pre-cut side seals

Thanks strokercharged95gt, The startup did go pretty smooth. Like you said, if you don't see fluids all over the place you can calm down a little bit! Only issues I had were self-inflicted. Plugged in the power steering wires backwards (white-black), not keyed different so glad that didn't blowup. Also I didn't push some of the plugs in all of the way while I was laying out the wiring harness on the engine, so in case I didn't like the routing I could unplug them easier, forgot to push a couple all the way in when I was done so I got a check engine light for an intake issue and a limp mode for the oil injector. Fixed the wiring and I was in business! I also replaced the transmission at the same time as this rebuild with one I replaced some the synchros and bearings in. It started leaking the other day and then got stuck in 2nd gear. Ended up being a bolt that fell out right next to the neutral switch. Had to use my mad skills to fish the collar, that bolts against the case to keep the linkage straight, back to the right spot and spin it around with a mini screwdriver, then get the bolt to thread back in, all without seeing what the hell I was doing! All good now!

Well the method I mentioned for you to go try and find on RX7Club puts the same curvature on the side seal end as the corner seal. The way it was done the clearance is only at the closest point between that flat end surface and the round corner seal. It’s a bigger fap on either side of that though. I figured it must have been that because it’d require using a round wire gauge to measure clearance rather than a flat feeler gauge. The Renesis is much more sensitive to leakage than the previous 13B. Again it comes down to the higher compression ratio coupled with the intake/exhaust port rephasing that Mazda did on the Renesis that I’ve been talking about recently in some other threads. It will be ok for a while, but not really optimum. A fresh engine is always nice regardless. I’ll 2nd what Stroker said; always that little bit if uncertainty starting up a fresh enter for the first time.

I see your point Team, the actual sealing point is very small, "the closest point between that flat end surface and the round corner seal", so matching the curvature of the corner seal would solve this. Seams very difficult to do a good job at this, even with a good jig and some mad skills! and if Mazda built these engines from the factory like that then I would definitely do it that way. And as you mentioned too about "it’d require using a round wire gauge to measure clearance rather than a flat feeler gauge" to get a measurement between those clearances. I also think that the Renesis side seals move differently then the 13B side seals since the Renesis side seals have a tapered surface on one side and may move side to side and change the contact point at the corner seal slightly. Which is the main reason for measuring the clearance with two feeler gauges shoved in the side.

Looking at how some people have made jigs to help match the curve looks to be a great way to get the most out of it like you mentioned:

https://cimg1.ibsrv.net/gimg/www.rx8...4fb3e89889.jpg
A nice jig

https://cimg3.ibsrv.net/gimg/www.rx8...ea61ed5a6d.jpg
Really hard to see but here's a pretty good picture I found of the results