Just got off the phone with the guy whos going to be rebuilding and tuning my fd - hes saying its likely the rotor housings will need to be replaced but i find this hard to believe as the car has only done 60k miles. surely the housings nitride would be fine after so few miles given theres no obvious damage.
If any builders could tune in and give me their 2c so i know if im being upsold thatd be great.

 

100k km seems to be the magic number when things start to get tired and he might very well be spot on.

With the mention of rotor housings and then nitriding, there seems to be a bit a bit of miscommunication happening. Chrome wear/chatter/cracks around spark plug holes on rotor housings wouldn't be out of the question, step wear on plates (or end/centre housings if you prefer), might be less of an issue at that mileage.

There used to be a cheap source of new S8 engines in kiwi a decade or more ago, which were little more than what 2 rotor housings cost over here now! If you could locate one of those, it probably would be a great alternative.

 

If your motor is just a little tired and lower on compression, the housings will likely be fine to reuse. If you blew the engine, you will most likely have one rotor housing that is gouged up by a broken apex seal and has to be replaced.

As stated, aluminum rotor housings have chrome surfaces. The irons (front, intermediate, end housings) are cast iron and have a gas nitrided surface from the factory.

But, if a shop is doing the rebuild work, many times they want to start with a 100% perfect engine that they can put their name on. They don't want to re-use parts and have something potentially bite them 6 months later and the customer points the finger saying "you built my engine with used junk!"

To give a point of reference, my RX-8 had 135,000 miles when I got it and the engine was slap worn out, had nearly no compression. Everything I can see and tell this was the original engine in the car. I put new seals in, cleaned everything up, re-used all the hard parts (irons and rotor housings) and have a solid engine with great compression. It's about 90-95% compression-wise of what it would be if I had got new rotor housings and had the irons lapped and re-nitrided, which wouldn't have been worth the money. It's amazing what all new seals and springs and hand-clearanced side seals can do for compression.

Dale

 

I've had two second gen turbo engines built by two reputable builders. New rotor housings and all new seals at the very least (mazda oem.)

Engine 1 from shop A tested at about 100PSI per face when warm (nothing below 100)

Engine 2 from Shop B tested in the high 90's with one face having an 11 psi difference from the others.

Each engine ran fine, but given the money I spent on rotor housings and even a center iron for the second engine, I was expecting compression to be 100+ at the minimum. I'm curious as to why that second engine didn't test higher, to be honest.

I think at this point, when it comes time to have the engine done in my FD, I'm just going to buy a new short block. I imagine those, being Mazda brand new, test significantly better than anything rebuilt.

 

The apex seals you are running, quality of oil, whether or not you are premixing, and how you drive the car all are contributing factors to how quickly the rotor housings wear. Many times they can be resurfaced. Post some pictures if you can.

 

Some of it comes down to how careful the builder fits side seals. A good, tight, exact fit on side seals makes a huge difference in compression. I do my engines to .003" EXACTLY on each side seal.

Mazda's spec is .002" to .0059" - that's a HUGE range.

By the same token, a Mazda-built engine won't have as tight or consistent a side seal clearance. Fitting seals by hand is very time consuming, they use pre-cut seals that get in the ball park but aren't necessarily the tightest fit possible. In other words, a new Mazda engine is good but not perfect - it really depends, some could be on the tighter side, some on the looser side, but they will all have good compression.

Of course, other factors like porting and the condition of the rotors comes into play as well.

A motor with tired compression - usually worn apex seals, carboned up, side seals worn into corner seals - may not be as easy to start and may not idle as well but when running at higher RPM they will typically seal well and make decent power. You need some RPM's to get the seals moving and improve low end compression. That's part of why Mazda upgraded the RX-8 starters, it would mask a weak engine by increasing crank speed and preventing no-starts when hot.

Dale

 

For reference this call was before i had even taken the motor in, he was telling me it was very likely that the housings would be shot. Motor has not suffered any form of catastrophic failure so the rebuild is essentially a freshen up to prevent such an event from occurring - motor was all factory ports.
Oil i was running was 5w-30 mineral, changed every 3000kms

 

unfortunately those days are over, youre looking at almost 14k nzd for a crate motor these days

 

Seems around the advertised rate here recently too. Guessing rotor housings would set you back around 2400 nzd. Got the impression the cheap engines were a deal for the Rx7 racing series over there.

You won't really know how things are until pulled down and oil injector failures aren't uncommon on these things. Also, if you didn't buy at auction yourself and it's anything like here, what you think you have and the mechanical reality have bitten lots of poor buggers locally......clock winders and cluster replacers abound in the second hand import market often giving cars a hefty haircut.

 

Would seem to be the case.
For anyone whose interested, heres the damage: Broken coolant jacket groove front and rear plates, flared apex seal grooves on rotors up to 2.09mm, worn housings with side wear and chatter marks (would like a second opinion on this)

 

Yeah those irons are DONE, classic failure of the coolant seal wall.

Rotor housings aren't amazing but they are re-usable. New housings would of course be best but those will work fine, I've built motors with housings not that nice that have been solid.

Dale

 

Bit of a shadow on the plate, must have sat for a fair while, possibly with water inside, $2600nzd for 3?

Housings, finger nail test below the exhaust port, otherwise not totally horrible - some have started to "resurface" them over here, but can end up with no chrome and junk if thin enough....a service like that locally?

Is it Banzai, IR or Ray selling those usd5.5k engines, suppose shipping, exchange and GST will screw you though!

 

How do you guys feel about using s5 rotor housings over s6? The price difference is substantial and ive heard theyre essentially the same

 

It's fairly common over here for exactly that reason. I understand the plating isn't the same, so not quite as durable....not aware of anybody actually quantifying the difference however.

 

I think they are pretty close if not identical. The S5 rotor housings do have an extra water passage for the turbos that has to be blocked off, Pineapple Racing has a freeze plug that fits that hole. Besides that it's plug and play.

Dale

 

From those pictures that motor is most likely not cost effective to rebuild. The collapsed coolant seal walls are usually the result of not changing the coolant regularly and severe overheating which will cause the seal to fail and combustion pressure will cave in the rust damaged wall. The rotor housings themselves may be resurfaceable if they didn't warp and measure in spec. S5 Tll rotor housings are nearly identical to s6 housings. The main differences are the additional coolant port that feeds the turbo (Mazda and other vendors sell a freeze plug) and the lack of the grooves for sealant just above the oil pan (makes no difference really). Later s6 housings also had an updated oil injector orfice but that also doesn't matter as you should be premixing anyway. Otherwise they are mechanically identical and usually significantly cheaper.

 

The only thing saveable are the crank and centerplate, otherwise im getting all new parts - the build goes on