Plt63

Hi,

Are we all sitting comfortably, then I'll begin.....

Having had a number of interesting cars over the years, I had an opportunity to get hold of RX8 for a bargain price. Manual 6 speed, black and red leather, 231 engine... I'm no boy racer (over 50) but enjoy my cars!o

So having now had the car for six months, I thought I would share my adventures to date (and obviously sneak in my own question too)...

Being In the UK, normal weather related issues had to be addressed....

Water in rear lights, scratched front light covers.... but nothing that a bit of common sense, foam draught excluded, a hair drier and metal polish plus elbow grease would my fix.

Then the ultimate distraction indicator needed some attention (flashing yellow airbag warning light). After a few attempts at diagnosis, tracked it back to the steering wheel clock spring being broken.

Next the stopping...... replaced discs and pads all round, serviced calipers. Fitting back pads back in was most difficult bit. Nice and smooth now...

Stereo on but no sound (not good), but all the lights and controls were on. Traced it back to the +12v trigger from the head unit to the boot amp. Anybody want to buy a second hand boot amp? Some clever former owner had put his own aftermarket amp in and blown the feed circuit in the header - just why do it?

New tyres all round, as got fed up of going sideways in the wet when accelerating! And it also scared the kids.....

Replaced exhaust with toyosports full system with decat.... two days later put the cat pipe back in ... FAR too noisy and attention grabbing for the boys in blue (and couldn't hear kids screaming as safety indicator). Also took smooth accelerating away, with not much more apparent power. Now sounds very good....sporty but understated!

Gearbox and back axle oil drain and change (noisy 2/3 gears, 6 speed manual).. noisy gearbox a bit quieter, and back axle LSD not anything like as twitchy!

Had some occasional starting issues when hot, so checking with published forum wisdom, replaced plugs, coil packs, leads. No real improvement....

Replaced starter with 14 tooth upgraded model.... brilliant when cold, not much different when hot!

Finally sussed it out, had K&N aftermarket filter (oil coated).... replaced with standard paper filter, then cleaned MAF sensor.... much better general starting and running all round!

So my advice....if you are not hands on with your car either.... avoid these like the plague, or get one with a full manufacturers warranty!

Would I have walked away it knowing this, and do I now want get rid of it? Nope..... love the sound it makes with high revving engine with proper read wheel drive handling! I smile every time I drive it....one happy bunny!

Right, after telling my little adventure story it's time for my question ....

Are there any known issues with engine electrical earth problems?

Why do I ask?
-With the new starter installed, if the engine gets hot (and ambient temperature is hot) car can be hard to start!
-So I park on a downhill slope, stick it in first, roll it up to about 5mph, pop the clutch and it starts straight away... no hesitation at all.
- All we're doing here is removing the starter load on battery (which is testing fine BTW)
- if it was engine compression, failing coils etc. It would be just as hard to start with this method?
- Is the updated starter putting more draw on the supply, which is reducing what's available for the coils?
- FYI also seeing some resistance on the circuit tester between the engine block and the battery negative (nowhere else shows resistance)
-Going to put a starter gauge earth cable directly between the starter motor mount bolt and the battery negative.
-Any comments or obvious things missed?

Thanks in advance for any help....

Regards.

Gravey

iTrader: (3)

Can you get a rotary specific compression test done on it? Hard hot starts is the most tell tale sign of failing compression.

Loki

iTrader: (1)

If it warm starts fine when you're rolling but not with the starter, and the starter is turning at a reasonable speed (220rpm or better), low compression is likely to blame.

The rotary has more compression the faster it turns in the 0-1000rpm range. Slow turning means more time for compressed gas to leak across the huge overall seal length. So when you pop the clutch at 5mph, you instantly go to ~1000rpm and have enough compression to fire up. When you turn the starter at 250-300rpm, that's not fast enough to build compression on an engine with less-than-healthy seals which leak more.

You can have the compression tested to be sure. It sounds like you're not at the higher end of "low" if it still starts warm after some cranking.

Plt63

Guys,

Thanks for the responses... will take the advice given.

I'm waiting to get the compression test done by a local rotary specialist, before going any further.

What confuses me is the engine starts so easily when bump starting, no significant engine rotation and very very slow vehicle speed. The engine speed must obviously be very low in this situation?

Additionally it is worse to start after an extended period of idling before stopping engine. Oil Fouled plugs?

Also still don't fully appreciate the basics of why the hot starting for rotary engines is more problematic than cold starting?

Understand the basic low compression as underlying cause, but what makes it worse when hot? Is it oil temperature reducing viscosity therefore sealing? Different metal expansion rates? Seal surface areas vs displacement? Plenty of experience of piston engines previously....

Any recommended external references that can help my understanding here?

Thanks again....

Regards.

gwilliams6

A UK post from RotaryRevs in Yorkshire

Low Engine Compression
Low compression is an issue the RX-8 suffers from more and more as the cars have aged to the point where their average mileage is quite high. It’s one of the main reasons that you might developed a hot start problem and can be extremely frustrating to deal with.

There are a couple of reasons your RX-8 may develop Low Compression issues, the most notable of which is the wearing of internal engine components.

In theory the RX-8’s Renesis engine should be capable of running for well over 250,000 miles and in some cases around the world, they have! Unfortunately the engine does not respond well to the type of driving that the cars are subjected to here in the UK. By that, we mean idling in traffic, short runs day-in and day-out particularly can cause peculiar patterns of wear to various internal engine components such as the stationary gear bearings, apex seals and rotor housings.

It doesn’t help that failing ignition coils also exaggerate the wear on those internal components as un-burnt fuel that left behind from incomplete ignition causes a condition known as ‘bore wash’. Oil doesn’t stick to petrol, bore wash is literally the un-burnt fuel washing away the oil layer designed to lubricate your RX-8’s seals and the resulting lack of lubrication causes a chattering and thus excessive wear to the seals and other internal components as well.


Apex Seal wear, is the primary cause of low engine compression.

Due to the way in which apex seals are lubricated, the centre of the flat seal surface often wears faster that the outer edges. Over time this causes a gas leakage which runs past the seals because the developing ‘bowed’ edge doesn’t sit correctly against the flat edge of the rotor housings.This wear can also severely damage the rotor housings as well.

After the centre of the seals has worn, it can leave the seal edges raised slightly. These prominent edges then cause more pressure to be applied (and to a smaller surface area of the housing) causing the housings to ‘chip’ and score. The wear often means that they cannot be reused when the time comes to rebuild the engine.

In some cases the seals just wear out naturally, the level of vertical wear exceeds the point in which the apex seal springs can no longer take up the slack causing further gas leakage and thus less compression. Though this kind of wear does not often show until well past the 100,000 miles mark, and when it does, is normally pre-cursed by another type of failure.



Each cause of low compression, results in the same symptoms, most common an inability to restart the car at operating temperature (within 3-5 minutes after the vehicle has been switched off, it will refuse to restart and will need to be left to cool down for at least 15 minutes in order for restarting to be possible). Other symptoms can be low power output accompanied by an uneven idle level. Eventually these will develop into cutting out at idle and then refusing to start at all.

Unfortunately the only effective fix for low compression, is to have the engine stripped and fully rebuilt or to replace the engine altogether. For more information, contact us or read online more about our engine rebuild services.

http://rotaryrevs.com/about.html

Loki

iTrader: (1)

About vehicle speed: in 1st gear idle speed translates into what, 3mph? Say you bump it at half that, 1.5mph. That's 400rpm. The starter turns at 250, so you're still ahead. You could bump it at 1mph and still get better engine speed than the starter.


About hot relight: metal expansion primarily. When hot, the housings expand, increasing the seal clearances slightly. Normally this is ok, but loss of compression, by definition, brings your engine to a point wherr the clearances are acceptable when cold, but not acceptable when warm. The problem is that total seal length in a rotary is ginormous. In a piston, the seal length is the circumference of the piston ring. In a rotary the seal length is the perimiter of the entire rotor face. It's huge for the same combustion volume. So if all of those seals open up ever so slightly from the housing expanding, the increase in leakage is large. As things cool down, the clearances close and the engine is able to start at starter speed.