1996 Mazda Mx5 with ITBs - p16 video clip :)

I'm all for doing things relatively on the cheap Alex haha. Originally I was thinking I'd rather make this engine the good engine than plan to change it out so soon, but then those plans are kinda up in the air now….

Mark, yeah 20b parts are majorly expensive! Maybe I'll win the lottery one day….

I started cleaning up and measuring tonight... kinda wish I hadn't

First up, I removed the stationary gears from the housings and had another look at the bearings in better light. They've both got copper showing and the rear one is properly shot. I'm not sure how I managed to miss it before. I can only presume I just happened to look at the wrong light/angle.




Damn. While we're on bearings, on top of the shot front rotor bearing I can now see the rear rotor bearing looks fairly worn but ok for now.



Anyway lets look at the housings. The carbon sludge cleaned off the chrome pretty easily. I was a bit worried looking at the more dull surface below where the carbon was that it might be worn through the chrome to the aluminium, as I've seen in some 2 stroke engines, but after more close inspection I think it's ok.




There is some damage to the chrome on the front housing in the usual place, which the lowest section on the housing where the exhaust stroke happens. The Mazda rotary engine overhaul manual specifies that it's ok if the chrome is chipped as long as it's not more than 2mm into the housing. Mine is chipped just over 2mm in places but I'm not too worried. Having seen what runs in a 12a, sometimes chrome chipped 1/4 of the way across the housing! I'm not gonna let that little bit of chrome damage bother me.



The same front housing has an imperfection underneath where the water seal runs. It looks like a casting imperfection to me. Again I think think it's the end of the world, but it's another thing to add to the list of slightly dubious issues with this housing.



The rear housing had the same dull chrome where the carbon had built up, but had not chipped chrome which is good. On the downside it had this small but possibly crucial section of corrosion in the coolant gallery which extends most of the way under where the water seal will sit. This could well stop the seal from working properly and is a problem.



Moving on to the irons, having done an initial clean up this is the state of the corrosion in the front rotor due to the engine sitting with coolant in the chamber for quite a while.



I had a good go at cleaning it up, and made some progress but it still looks a bit of a mess.



The first test is to make sure the surfaces the rotors run on aren't warped, they can't be more than 0.05mm out of flat. On with the measuring, 3 of the irons surfaces passed the warping test happily, but the rear side of the centre iron was just on the limit in the intake area.

As the rotors rotate the side seals rub across the iron surface and this wears them down. This can create a step in the surface at the limit of where the side seals travel to, this was more of an issue with my irons.



The limit is a steep of 0.10mm. 3 of the 4 surfaces had side seal stepped wear of 0.12-0.14mm. The 4th was 0.10mm, so right on the limit. From what I've read I couldn't have them machine down this far without going through the hardened coating. Re-coating them wouldn't be cheap…

Before I could face trying to clean all that lovely carbon off the rotors I measured the apex seals next. All of them failed. They have enough depth left on them but they are unevenly worn, again just beyond the limits in the Mazda manual. The apex seals tend to wear n the centre more than the ends, and the limit is that if you put two seals together the gap in the middle should have less than 0.06mm, mine were over 0.10mm.



The rear rotor's apex seals also show some signs of corrosion/damage on their sealing surface.



After this I did face up to starting to clean off the carbon on the rotors. Generally they look ok, but one face of the front rotor has taken the brunt of that coolant leak and shows quite a bit of pitting/corrosion neat the apex seal slot.



After that I gave up for the night and got a bit despondent! It seems the whole engine is just either borderline or just over the wear limits. If it was just one of the components that was borderline I'd replace that element, but when it's every component in the engine it's a different matter.

I guess it leaves me with 2 options….

1. Chuck it all back together with some new soft seals, with a bit of chemical metal and RTV to help the water seals and hope for the best knowing that it probably wont last long. Start looking for another engine….

2. Give up and just hunt for a working engine to drop in straight away.

A third option could be to build this engine up properly, but I think realistically I'm looking at a replacement set of irons, oil pump, all new bearings and a complete hard and soft seal set. I just don't think it's financially viable.

Anyone know of a n/a 13b kicking about anywhere

That's a bit of a blow.
Not that my opinion is worth much, but I'd throw my weight in on a new motor. Even though it would be interesting to watch the refurb and build up of this one,
I imagine it will be silly money to do it that way and take a fair while, too. This car needs to be back on the road!

Throw it back together with some new tips and inner O-rings. Oh and some bearings. That bit of alloy missing near the O ring groove can be built up with JB weld. Remember I used jb weld on my centre plate that had corrosion pitting in the cast iron right next to the seal face. Worked so well and that was near the combustion chamber area too. Amazing stuff and would work well on this.
It is amazing how long a rotary will go on for when worn. If this engine didnt have a blown O ring then you may never have stripped it and it would probably be going strong.

If you throw this one back together then you can use the car at least while you build a super engine on the side :-) Plus you'll be practised!

+1 for slapper motor. My first 12a in the car in my signature had chrome patches missing from the housing that were about the size of the palm of your hand. Still ran ok. Only the apex seal cried enough.

Just check the clearances on the oil pump. I wouldnt worry about little marks from it having had something go through it- thats all they are..little scratches. It'll still pump oil fine if it has within spec clearances. You can also squeeze the oil relief valve thingee up in a vice as I did in the Elford engine so bumping up the pressure. Ask Era.

Remember- a loose, oil burning engine is a quick engine (or so say ford owners....) :-)

Just get it going and cane the f__k out of it over winter while on the side you can build up a sweet faster engine in the warm garage :-)

Also- look into alternative water seals- I have read of people using high temp insulated wire of the right diameter etc instead of o rings (this is for the outer seals only as they don't see anywhere near the abuse that the inners do as not dealing with combustion heat.

Excellent thread.

Sorry to read about the engine woes but well done on seizing the opportunity to upgrade at the same time.

I look away for one week and look what a turn this project took! Good to see you keeping at it!

Nope 'fraid progress has been a bit slow this past fortnight.

I've made some reasonable progress over the past few days though. I'd mostly been dragging my heels a bit because I'd promised myself I'd finish off the chassis issues before starting to play with the engine, and the chassis issues left were going to be those surprisingly time consuming and not especially enjoyable ones, haha.

One of those issues was to run the new fuel lines. With the rotary exhaust exiting on the 'wrong' side of the engine for the mx5, and knowing how hot rotary exhausts get, when I did the original conversion I re routed the fuel lines so that they would cross over the underside of the transmission tunnel and come into the engine bay on the opposite side. I did this with a mix of copper hard line and rubber soft line sections for the fiddly bits, I did ~9 months/10,000 miles driving with this without problem but about 18 months after I sold the car the braided lines split. This caused the small fire which was part of the reason this car was laid up.

This time I wanted to try and do a better, and more importantly, safer job of it. So I bought some 4m lengths of aluminium fuel hard line, so that I could make the lines one piece from right up near the tank all the way into the engine bay. I also bought some P clips and made sure the lines were well secured along their whole length, and added extra heat shielding where the lines would run anywhere near the exhaust. Belt and braces!




It turns out fuel lines are really hard to photograph! I took the photos mid way through securing them to the body, and did intact get them a bit neater. After that I put the gearbox back in (again kinda hard to photograph with the car on axel stands in a single garage….)



It took far too many hours but I'm really pleased with how the fuel lines run, they've got plenty of clearance to the gearbox and prop, and are also kept further from the exhaust than my previous set-up.

On the topic of lines I also got the rear brakes and lines installed.



That left me with 2 major jobs I wanted to sort before looking at the engine, 1. to fit the new shocks and check over the suspension before a final tighten up and 2. fit the gear lever and centre console. The shocks delivery has been delayed so no. 2 gear lever it is…

The old gear gaiter was a bit melted from the afore mentioned fire.



So I got a new one to fit. I also replaced the lower shift bush in the gear lever and both the lower and middle gear gaiters also, all pretty common mx5 parts that need replacing after a few years. I was making good progress so didn't really get round to taking any photos till it was done.



Interior properly complete! Woo!

Which meant about 6pm tonight there was only one thing to do. Mr Mx5, it's time to meet Mr 13b turbo engine!



I've basically not touched the engine since I picked it up. It's currently standard including all the emissions gubbins and original fuel injections stuff. The first job was to start stripping it all off, most of it wont be going back on, and I really need a bare block to work with so I can work out what the exhaust manifold/turbo location situation is.

This pile is all basically destined for the bin!



This is starting to look a little easier to deal with



Thats as far as I got tonight. I did do a bit of basic measuring and I was surprised to find that at the front rotor exit (where the steering column is most obviously in the way) the turbo manifold projects no further out than my current n/a manifold, so there's a slim glimmer of hope that it might even go in with the stock turbo location. That would be fantastic if possible, but I'm kinda doubtful it'll fit.

Either way my friend Ross is popping over tomorrow and hopefully we'll get chance to offer the engine up to the car and find out how far out we are!

So things are moving along nicely really. It feels like its getting closer now to road worthy, I'm starting to get a bit more excited about driving it again The only part I'm really missing now is the n/a light weight flywheel. I've got my eyes peeled for a good second hand one, I don't really wanna pay new prices, but nothing showing up yet.

I suppose when you read it back it's not bad progress! I guess maybe because I spent the last couple of weeks thinking 'I've just gotta finish these last couple of things, then I can fit the engine', yet those little things take much longer than you think. haha.

Yeah basically, I need to source a flywheel, make the turbo manifold/downpipe fit, fit the engine, fill it all with fluids and drive it to the MOT. Oh and cut a hole in the bonnet so the top mount intercooler gets air, not quite sure how that's gonna work yet ?