Damaged core of a 13B engine

RX8 Project – Part 3, Engine Autopsy!

Rather long delay since the last post on this project mostly due to a server problem it took a while to resolve.

So here it is, the autopsy of a failed RX8 engine. First here’s how the engine looks freshly removed from the car.

RX8 13B Engine
13B Engine Complete
13B-Left Side
13B-Left Side

 

 

 

 

 

 

The 13B rotary engine really is rather small and while it is true to say it is a comparatively light engine (I’ve heard figures around 130kg though I’ve not checked this) it is a solid lump with very little space inside. It’s also worth noting the four spark plugs at this point – this engine has leading and trailing plugs and actually fire the chamber twice during combustion phase which is a little unusual for an engine.

13B Engine stripped to core
13B Core

Here’s the next stage, strip all the supporting components from the engine. So the alternator, aux drive belt, manifolds, ignition coils, clutch and anything else bolted onto the main block.

13B Stripped Components
All the bits removed

So when you get to this point you will (if you haven’t already) realised the flywheel must be removed to break down the engine any further as the engine is built as a series of layers with long through bolts. These through bolts are all located under the flywheel hence why that needs removing.

13B Flywheel
13B Flywheel

The bad news here is that the flywheel is held on by a single very large nut, this nut is 54mm across flats. I have no idea what torque it is tightened to, but it’s very tight, very fine pitch and is installed with thread locker adhesive.

The first problem is locking the engine solid. I actually  used a section of steel between two of the the clutch bolts and then another bolt through one of the bell housing bolt holes. Obviously the steel must be installed across two bolts so it doesn’t cross the nut you’re trying to remove. Alternatively proper locking tools can be bought but the ones I could find were quite pricey. As for the actual nut I ended up buying a 54mm impact socket which on its own was about £30.

54mm Socket Vs Pint Glass
54mm Socket Vs Pint Glass

For the actual removal I tried a long 1/2″ breaker with a big cheater bar and ended up shearing the end off the bar! The bolt didn’t budge! I ended up convincing a mechanical fitter where I worked who was well into cars to stay a little late one night, borrowed the company van to get the engine up to the workshop and borrowed his largest 1/2″ drive air impact gun to remove it. After a bit of an argument the nut eventually moved!

13B with flywheel removed
13B with flywheel removed

Next I took off the sump, while I could have done this earlier I was largely resting the engine on the sump so it made sense to leave it in place. This moment was a huge warning of what was to come!

Very contaminated oil
Oil/Water!

So, apparently this was once oil! Judging from what came out it was something like 90% or more water at this stage suggesting a serious internal failure of a water seal. This is a known problem in these engines and if caught early is repairable. In this case unfortunately the engine had still been used for some time after the warning signs started appearing with the previous owner running the car until it wouldn’t idle at all or restart when warm. Expectations for the engine were not high at this point!

It’s worth pointing out at this stage you need to find a way to prop up the engine vertically to disassemble from the flywheel end. Again a guy at work helped me out here by building me a custom engine stand from offcuts in a quiet moment but other solutions could be used. the positions I used were the rear pair of air con mounts.

Seriously rusty rotor
Well that doesn’t look good!

On opening it I was met with this sight. Again this confirms very large amounts of water getting inside the engine. Several parts of the engine are cast iron and so will rust for a pass-time when exposed to water. Add to that the total lack of lubrication offered by the water and engines will basically overheat and the bearing surfaces will eat themselves alive.

Badly damaged rotor bearing
Badly damaged rotor bearing

Notice the scoring on the internal bearing surface on this rotor.

E-Shaft Heat Marks
E-Shaft Heat Marks

Here is the lobe on the eccentric shaft that the rotor locates on. This photo clearly shows the the lobe has experienced excessively high temperatures to such an extent the shaft has discoloured.

Damaged E-shaft
Damaged E-shaft

And the final shot shows the amount of scoring on the shaft. Clearly everything is not well.

13B O-Ring Failure
13B O-Ring Failure

So this is what actually caused the damage. These o-rings seal both the water from the combustion chamber (red) and from the outside world (black). As can clearly be seen in the photo the outer seal has degraded to the point of failure. The really unfortunate aspect here is is this seal failed at any point over most of its length the engine would leak coolant but this wouldn’t actively damage the engine. What happened here is the point of failure was above the sump so as the water leaked out it filled the sump with more water than oil progressively ruining the engine. The inner seal in this engine had also failed and this means that once the coolant is hot and under pressure it leaks into the combustion side. This is a common cause of the warm idle and restart problems.

More signs of running without oil - chatter marks in the housing
13B Housing damage

So this was the final nail in the coffin for this 13B engine, both rotor housings were ruined with significant chatter marks, scoring and chipping of the hard chrome surface and these cannot be restored because the only people that have a specialist surface grinder to finish the hard chrome surface in the correct profile is Mazda. So at this point virtually everything needs replacing, effectively this is buying a new engine and costs a huge amount of money. for a £300 car it just isn’t worth it.

So now project moved onto what reasonably priced alternative engines could be fitted for less than the cost of replacing the proper engine….

More in part 4!

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