black93RX7

Finally took my motor apart today and found 5 broken corner seals and 1 broken side seal.

The motor only had 6000km's on it and was rebuild last summer.


The motor had always registered 60psi compression since it was first tested after a break in period of approx. 1000km.

Last week I adjusted my timing and it started to run really bad above 3500 rpm, I couldn't find any other cause so I decided to pull it.

What was interesting is the builder used 2 different types of corner seals. One was the old style one piece type without the rubber insert and the other was what looked like a Hurley seal, also a one piece type. Each rotor had two different types of corners seals. Only the old mazda corner seals broke, none of the Hurley's (if thats what they are) broke.

It seems the builder just used whatever he had around. Has anyone ever heard of someone doing this before?

The cause of the low compression may have been from the end plates which were in poor shape since they had not been lapped. I was under the impression they were.

The motor was street ported, dowell pinned and had 3mm apex seals. All the apex seals looked fine. It also had new rotor housings last summer.


I am going to lap and ceramic coat the end plates and install all new corner seals and coolant seals.

Anyone have any advice as to what corner seals to use or any other advice reguarding the rebuild? Currently have a T-78 and am planning on running up to 25psi.

By the way the last motor only boosted 15psi max.

Zero R

iTrader: (1)

I would run one piece corner seals. I have had good luck with both mazda factory seals and Atkins 2 piece apex seals.

Wankel7

Just wondering...how much power did you make?

black93RX7

388 rwhp @ 14psi

this was while running only the leading plugs

Zero R: I am planning on staying with one piece corner seals, however the mazda ones are the only seals which broke. Is it strange that so man y corner seals broke and no apex seals were damaged?

Could pre-detonation be the cause as a result of high air intake temps? or would it be more likely a result of a timing issue?

thanks

t-von

iTrader: (8)

It seems that the side seal clearance was too tight. Due to heat expansion if the clearance is set too tight, the side seals will stretch and put to much stress on the corner seals causing them to break at their weakest point. The solid corner seals usually hold up better in this situation.

Chris Ng

Don't mean to intrude in your fourm black93rx7... I'm sorry to hear about your motor and what you found inside it.. Adam claims to have a lapping table, unfortunately if he does decide to use the table he has, you would probably end up with housings that are in worse shape than before.. if you check out the device he uses to lap housings, you can figure out why.. basically he laps the plates on top of another plate.. you can't do this because if the other plate is not perfectly flat, neither will the plate being lapped.. not to mention the unequal pressure that is applied to the plates being lapped..

Anyways, as for your corner seals.. I belive T-Von is correct.. I have motors built at the shop, and at no time have I ever seen any of the side seals clearenced.. basically they are taken directly out of the package and inserted into the grooves.. 2 motors we have disassembled, including mine, had a broken side seal due to improper clearencing.. either the side seals will give, or the corner seals will.. were you running 2mm or 3mm seals in yoru motor? and were you running stock seals or his own brand seals? improper clearencing of the slots could also have played part in this..

Hope everything works out for you and you get back on the road soon.. make sure you double check your plates for out of tolorence step wear before you decide to re-use them...

Zero R

iTrader: (1)

While I agree to check side seal clearence, (detonation usually even if small will chip the apex seal corner), I'm not sure I follow Chris. I'm not sure what type of side seal your talking about, but I have yet to see a seal I can take out of the package and have it even remotely fit with the corner seals. Usually 2-4mm needs to come off then start clearencing by hand. Are you referring to Adams seals in particular?

It's important when you do this rebuild you check and recheck. Any time saved rushing through will quickly be lost on another teardown.

Maxthe7man

It depends on the rotor and what series it is.. The FD rotors in my motor took maybe two swipes of the seal on my sanding block to fit, they would have gone at zero clearance but they would have bowed slightly and probably broken quickly.. But I find on series 4 rotors, it takes significantly more sideseal cut to get them to fit.. Then I have had Series 5 rotors that need alot shortening as well..
Leaving the rubber out just leaves an unsupported void, I am not a fan of that, and the porting I have seen on motors that has been done to, does not warrant leaving it out..It appears to me to just be laziness rather than having any kind of performance benefit..Max

BNA_ELLIS

Not Laziness considering the rubber only takes seconds to fit.
If you port large enough it's better to leave them out otherwise they will come out on their own accord, and make a mess of your engine doing so.
Personally to me it seems impossible to be able to fit side seals without moving a fair amount of material first.

now

iTrader: (1)

anyone who has ever purchased new side seals would know that there
is no way to install them into a rotor with out doing some sizing of the
side seals, they will not fit in right out of the package its impossible!
matt

Zero R

iTrader: (1)

Max I'm not trying to doubt you here but I have built tons of S4-S5-RE-REW and 20B motors, I have never seen a seal come out of the package and take just two swipes. What seals are you referring too.

Kahren

iTrader: (13)

if you are porting the motor where the rubber can fall in then please use the solid corner seal. leaving the rubber out shoudlnt be an option. like Maxthe7man has stated that it weakens the corner seal, i tend to agree with that statement.

Chris Ng

my bad regarding the clearancing of the side seals.. Perhaps at that point in time he had already grinded the seals down and just put them back into the package to hold them.. just what I've seen when I have been in the shop speaking with him.. and no doubt If adam decides to post anythign in this thread he will knock me about the clearancing of the side seals.. at which point I'll mearly bring up the point of using hockey tape in lieu of electrical tape ...

As for the corner seals, I think there may be some confusion.. I don't belive what he ment was that adam used stock corner seals with the rubber inserts missing, although we can confirm that 2 of 3 motors we have pulled apart were missing the rubber inserts (one motor, all the inserts were missing from both sides of the rotors, and on another motor, only one side of the rear rotor were missing the rubber inserts).. adam proudly showed me a bag full of stock mazda 3mm solid corner seals from the earlier motors that he managed to get from mazda old stock..perhaps this is what he used along with another brand of corner seal?

Anyways, appologies for the confusion with the side seals...

t-von

iTrader: (8)

The Rx8's pre-measured side seals are the only ones that may fit straight out of the package.

Maxthe7man

depends on how many seconds you intend on spending pay attention to detail on the motor I guess... I am not fan of overporting enough like that, you may as well go bridge and run all the seals the motor was intended to have along with decent cranking compression..But in the cases of what Chris is referring to, not putting the rubbers in corner seals, on motors with stock ports or basically close to, is just laziness..

Sideseals, I know it doesnt happen alot, but occassionally you will get a rotor where they need a very minimal amount of material removed.
Mazda has 12 sideseal lengths they use at the factory, the side seal stock that they sell as replacement side seals, is a hair longer than the longest sideseal they would use at the factory and encounter in a rotor..I found out you can buy precut sideseals, but you would also have to be able to identify the length of the seal, which is a trick I am not gonna give away in this thread.. So they just sell the stock to make it easier for global parts sales and to let people run their own clearances. I know myself sometimes it seems that you have to sand for ever before they even come remotly close, but on my own motor, it was very minimal work to get them in there. It would have been pretty easy to over cut them, if I would not have eyed them up before cutting them down, since I am use to sanding for a couple of minutes before even trying them.

rx7_turbo2

Sorry to hear about the shitty senario.

I've been part of about 3 tear downs of RX-7 Specialties motors, and all the things you mentioned seem to be par for the course, as far as I'm concerned. It sucks, but think about how much more power and how much stronger the motor will be when you build it yourself. Take your time, check all tolerances, and build something you can be proud of when your done. The other day I told someone who also got what in my opinion was the **** end of the stick from them, live and learn. Adam always wanted me to tell others to give him a shot before making a judgement of them, you gave them a shot, make sure you tell people what you thought.

Zero R

iTrader: (1)

I'm aware of the different sideseal lengths and so on. I prefer to measure and fit each one some are close but still never a drop in. I wont put any "preclearenced" pieces in the engines I build that way it's all on me.

black93RX7

I have been trying to decide if I should just replace the broken seals and put it back together, just to get the car back on the road or get new rotors and go back to 2mm seals.

Either way I will replace the coolant seals and o-rings.

Will a bit of wear on the plates cause a significant compression loss?

rx7_turbo2

That's hard to say. Everyone's idea of "a little wear" might be different. The service manual should have a spec on how much wear is ok. Somebody here probably knows it as well.

Zero R

iTrader: (1)

At the very least if you want it back on the road replace the corner seals with one piece units. Replace corner seal springs. Replace the side seal springs and reclearence the side seals. Leave them in their same positions and you could get by enjoying your car till summer is over and then do the whole thing. If it were me I would say, Hell I'm 90% there! Just check and lap the plates and put new side seals in. One more week at most and then it doesn't need to come out again.

Maxthe7man

yeah me too, but the precut seals are spot on to the factory tolerance, good for people that dont have the time/tools/patience..Just dont expect any North American Mazda parts counter to be able to order them..

Do you have a set of "3mm" rotors?... If so, go back to 2mm rotors and seals, that alone will probably net you back in the 90's from compression, Basically thats all I changed on the last 3mm motor I had to resurrect, even with somewhat questionable housings used it gained about 25 psi or so before break in from just the rotor change, even though it was dropped to 8.5 rotors from 9:1..
In my best comic book guy from the simpsons voice, please consult page 44 , top center paragraph of the racing beat catalog....

bobybeach

I might be lazey! as i have leave them out. I couldnt understand the need for them. Ive asked two rotor specialists on weather they were needed, they had mixed opinions on the subject.

two of my engine that have blown on me from age detination or revs. Spun bearings brooken apex seals and cracked rear plate, But none of them, having pulled them down showed any failure or damage to the corner or side seal. both these engines were not using the insert.

Has anyone considered the porting might be to large so the side seals are unsuported causing them to break when they callapse in and hit the end of the port.

GUITARJUNKIE28

i just pulled a motor apart last week and it had the exact same thing!! a bunch of broken corner seals and one broken side seal...i'll ask the guy who built the motor.

black93RX7

Thanks, I would like to know