Mazda (used) re-man engine teardown pics & scratched side housing
 

Hello all,

I just got my engine re-built after it started leaking coolant into the rear combustion chamber. The core was a Mazda re-man with only 36k miles on it. Never really ran right since being installed by a dealer, history of detonation/pinging in warm temperatures, symptoms of a vacuum leak somewhere in the LIM, and some problems with heat before new Koyo radiator was installed. Never severely overheated though, only hit 230 F a few times.

Rebuilder sent some pics that I wanted to share here.

1st is the apparent source of the coolant leak - rotor housing cracked around spark plug hole. Apparently both housings were cracked in that location, though only the rear one was leaking.

https://cimg4.ibsrv.net/gimg/www.rx8...e274f43645.jpg


https://cimg5.ibsrv.net/gimg/www.rx8...88f8e3eeec.jpg


Next up is the rear side housing (iron) with what appears to be deep scratches. They were too deep for re-surfacing and the part had to be scrapped, which was an unwelcome surprise for my wallet. I am at a loss as to what may have caused this. :dunno: None of my apex/side seals were broken. Rebuilder thinks it may have been assembled with this defect at Mazda. Anyone have any thoughts about this?

https://cimg7.ibsrv.net/gimg/www.rx8...a9bc8565cf.jpg

https://cimg2.ibsrv.net/gimg/www.rx8...8e579f67c4.jpg

Finally some gross rotors with carbon buildup.

https://cimg6.ibsrv.net/gimg/www.rx8...1c98ee704e.jpg

Also my OMP lines were apparently brittle from heat/age (car has 136k miles) and 3 of them cracked. Getting those replaced was also painful - those suckers are $40 each, apparently.

https://cimg8.ibsrv.net/gimg/www.rx8...e71be1ff45.jpg


This rebuild has turned out to be at the upper end of what I was expecting, and definitely more than I was hoping for - this core was pretty trashed. I'm in for new housings, a replacement used side housing, as well as all new bearings because the old ones were showing copper, in addition to the usual seals/springs.

But, hey, on the bright side, you should have a pretty good engine at the end of this.

I think we need to reset expectations around here for the cost of a rebuild. People keep throwing around numbers in the $2500 range, but almost never costs that little. $3500 is probably a more sensible floor cost.

Given my experiences, I would agree.

Yes, $2500.00 is a pipe dream for a reliable rebuild. The carbon on the rotors looks about normal but what is interesting is that the rotor coating that the S2's have does not appear to be there so it looks like Mazda uses S1 rotors in their S2 rebuilds. Which makes sense since they are rebuilt at the same plant.

the other wear is bad though too just by what I can see.

I don't know how coolant can leak from cracks around the spark plug hole as there isn't any coolant there unless the crack goes out toward the coolant passages.

Oh shit I missed that comment, :lol: Yeah that is not a coolant leak area.

Who is rebuilding your engine?

Well if you can afford it, new rotor housings should always be used if you want it to last. Those cracks are common on the Rene housings. Run colder plugs if you can.

won't even post what my last engine cost, still too painful to think about ....

.

Looks like a S2, as there are 6 OMP lines.

Sucks that you can't simply buy these rotors with the coating, and looks like not all rebuilds use them. Hopefully, when the time comes, I can reuse mine...

I assumed it is an S2 engine based on the OMP pic.

Yeah, I missed looking at that closely. Definitely the S2 one.

Yes, based on my pre-rebuild research, $2500 is the absolute minimum, if re-using housings and main bearings. This does not include installation/removal of the engine. With new housings, this becomes a $4k rebuild + installation, and it seems that $1k in unforeseen costs should be budgeted in as well. Of course with the amount of miles on my car, I sprang for professional oil cooler cleaning and flushing the oil lines, new heater hoses and belts. It adds up quickly, but I figured better to do it right if I'm going to go through the expense and trouble in the first place.

Actually that was me jumping to conclusions. :pat: Lucky7 Racing is doing the rebuild, and in a conversation months ago it was mentioned that coolant leaking into combustion chamber could be caused by a cracked housing. When I saw the pic I automatically assumed that it where the leak was, but after doing a bit of searching, that would have to be a pretty massive crack to go all the way to the cooling jacket. So it is probably unrelated to the blown coolant seal. I wonder though if the pinging caused the cracks. Either way, I would not have re-used those housings. Still mystified by the scratched rear iron though...

Got any pics of your bearings?

Regarding the S2 engine tear down shown here, I am guessing something foreign entered the intake at some point. The cracking at the spark plug holes are normal and they do pertain to temperature and warpage. They can be inspected and. modified and re-used if you know what you're doing and it's not too bad.
By the way, there are no different rotors for S1 vs S2 if you order new or get a reman engine. They all use N3Z1-11-B10C and N3Z1-11-B50C.

Paul.

No, they didn't send me any, and I was out of the country at the time of the tear down. I'm picking up the car tomorrow, so I'll see if they still have them around.

But I never ran it without the filter, unless this was done by a mechanic/dealer while I wasn't looking, or during the rear iron's previous life...:dunno:

So there's some residual value in those housings? If I can recover even a few hundred $$, that's still better than nothing!

Yes, you can resell them for budget builders

You also have to be mindful of the center iron life over time regardless of surface wear if you do multiple rebuilds. The siamese exhaust port divider has been known to fail and blow out over time.

Not all of the Series II have the coating. They started doing that shortly after Series II production. I remember the original post about this, with the date when they started. Sadly, mine was built prior to that date. I'd have to dig up that original post, I believe by ASH.

Well this is a reman, not an original engine so you would assume they would have the most recent part. But as Paul stated the rotors are the same and he rebuilds a ton so who knows.

when was the reman put together? I had heard that they are getting better, but not sure when they actually started getting better. Mine is nearing the end of the warranty, debating between having it rebuilt (prior to dying) or getting a reman (compression is a tad low, but seems to drive and pull just fine)...

I know they aren't the same engine but on the FD the carbon wings on the housings are from hotter section in the housing there, we fixed this on the FD by increasing flow around the spark plug holes. you can also run a little colder plug there. so what happens is this part of the engine heats up and the apex seals rock over this hump (the heat raises this part of the housing), eventually the apex seal cracks as it rubs over this spot and rocks and can ruin rotor slots.

Cooling in this area is essential and keeping the engine cool is a priority.

the grooves on the iron, we typically see this with too tight of side seal clearance to corner seals, when heated the side seal expands and pushes on the corner seal out of the rotor which puts pressure on the plates causing the grooves.

Cooler is not necessarily correct. You want to try and keep temperatures uniform or at least without a severe transient between adjacent areas

Not sure when this re-man was assembled, but it was installed at the end of May 2015.

Interesting, I read on RX-7 boards that the initial cracking around the spark plug holes is due to heat (thermal gradients). Then, when engine is warm, the crack expands and bumps the apex seal as described... About running colder plugs, I have seen no other recommended plugs, other than OEM spec for normally aspirated Renesis applications. Anyone care to chime in with a P/N?

I understand about the grooves/step wear - so it looks like the seals weren't clearanced properly? However the scratches look debris related, but this was the only engine hard part showing this kind of damage, which leads to the belief it might have been assembled like this.

I am sure it was rebuilt not too long before that, my buddy works at a dealer and they often have decent wait times on remans so I doubt they have them sitting around. When I got my last one it took my dealer (highest volume Mazda dealer in Texas) over a month to get it.