Compression Test Results

[Koren]

Completed compression test, thanks to SprintRX8 for lending the tester. To me, the numbers seem bad, but I wanted to run through some things to make sure I didn't mess anything up. Firstly though, the numbers:

Front Rotor: 61 ,56, 60 @ 251 rpm on the display. Normalised results from the below website give the exacts same figures (61, 56, 60 still) at my elevation - 131 feet
Rear Rotor: 68, 70, 72 @ 252 rpm. As above.

https://www.calconic.com/calculator-wid ... 00252c7377

I warmed up the car first with a decent length drive, the guide i read said to let it cool 10 minutes but figured it'd be at least that long by the time I'd got everything sorted so got straight to it. I couldn't find the damn E-shaft sensor plug, but had read about disconnecting ignition and fuel fuses, which didn't work. Presumably that fuse stops the starter too (directly or indirectly). Instead i disconnected the coil pack leads and ran the tester. IS that ok or could that have skewed the results somehow? Also something I saw mentioned about turning the engine over with the plug hole empty first to make sure it's dry? I didn't do that either (forgot until after), does that make a difference? Lastly, the battery I used in the tester wasn't brand new, high quality, straight out of the packet like recommended (I thought I had one but apparently not). Is it worth testing again with a brand new Duracell? The one i used did read 9.5v on a multimeter. My gut instinct is that regardless of any of these, the fact that there's such a difference between front and back rotor is really not good.

[Nickp47]

My experience of the DCT testers (which I think you have used here) is that disconnecting the ESS is essential for accurate readings.
Forgot pulling fuses etc, all you need to do is have your foot firmly down on the accelerator to cut fuel.

A new, good quality battery is a good idea too.

I do agree however that although you will likely get stronger readings with the ESS disconnected, they will still be somewhat on the low side.

[30405]

Plugging those numbers in to

http://www.foxed.ca/indexmobile.php?page=rotarycalc

Your fronts min is 3.98 bar and the high on the rear 5.11
My understanding is that 1 bar difference is a fair chuck between rotors.

Have you given the car a good trashing Italian tune up? You can see increased compression after a good track day as you cook off the carbon.

[Koren]

I tried again following the above suggestions - e shaft plug unplugged, fuel fuse out, test lead clear of ht leads, pedal down. Seems even worse!

First rotor :

Cold - 54 61 59 @ 245
Hot Test 1 - 51 47 51 @ 239
Hot Test 2 - 54 50 52 @ 258

Rear rotor :

Cold - 73 73 68 @253
Hot Test 1 - 69 66 68 @ 245
Hot Test 2 - 68 67 68 @244

[BigPete]

Not looking good, will be even worse up to temp which is how it needs testing

[ChrisHolmes]

Have got any starting or running issues? If not then whilst the results are not brilliant you could well have many 1000s of miles left in the engine.

[Koren]

Not looking good, will be even worse up to temp which is how it needs testing

Ah, sorry, that was one cold test, two hot per rotor. I've edited to clarify

[Koren]

Have got any starting or running issues? If not then whilst the results are not brilliant you could well have many 1000s of miles left in the engine.

Yeah, hot starting is bad, and idle isn't great either. Maybe a bit of hesitation at low revs but still seems great if I put my foot down

[ChrisHolmes]

Have got any starting or running issues? If not then whilst the results are not brilliant you could well have many 1000s of miles left in the engine.

Yeah, hot starting is bad, and idle isn't great either. Maybe a bit of hesitation at low revs but still seems great if I put my foot down

Then unfortunately is appears to be rebuild time.

[Koren]

Oof, stalled on me at traffic lights. Dash lit up like a Christmas tree. Got it started again but seemed a bit shaky, kept the revs up and managed to get it back home. Well that escalated quickly

[SprintRX8]

Rebuild time Sadly or a good used engine from the likes of BigPete , Luke Murdock

[ChrisHolmes]

Oof, stalled on me at traffic lights. Dash lit up like a Christmas tree. Got it started again but seemed a bit shaky, kept the revs up and managed to get it back home. Well that escalated quickly

Rotaries are far less “spectacular” than piston engines when they finally “let go” often simply totally munching and scrunching one rotor and it’s seals whilst the other fights to keep the engine going and the damage to the the failed rotor therefore worsens. Unlike a major piston engine failure where things can smash out the block or cause horrendous rattles and bangs.

[Koren]

Rotaries are far less “spectacular” than piston engines when they finally “let go” often simply totally munching and scrunching one rotor and it’s seals whilst the other fights to keep the engine going and the damage to the the failed rotor therefore worsens. Unlike a major piston engine failure where things can smash out the block or cause horrendous rattles and bangs.

Do you think that's likely the case here? I enjoyed driving an rx8 but can't say I'm especially attached to this car specifically yet. Wondering if it's best to sell it on and get another (or maybe something else less stressful), or get the rebuild done.

Trying to get a feel for what prices broken ones go for vs recently rebuilt ones, anyone have a ballpark for that?

[Koren]

It all depends on the condition of the bodywork, not just the visible stuff but the shell underneath.

More 8s die from tinworm than from engine issues, these days.

Nordic Green is a rare colour, which may limit the demand or may make it more sought after.
That sounds like a contradiction but, while fewer people would be interested, if there's more than one then you might get a bidding war.

[SprintRX8]

https://www.ryanrotaryperformance.com/r ... ne-rebuild

[Koren]

Thanks, I also saw pages for Warren Court and Rotary Motion which aren't too far, and looked very reasonably priced. Don't really know how to choose one over the others. Rotary motion says "Our NO HIDDEN EXTRA GUARANTEE ensures you only pay for your chosen package. If, once your engine is stripped we find you need internal parts including Rotors, Rotor Housings, Engine Plates or the e-Shaft, we will replace these at no extra cost!" as well as free collection which sounds like nice bonuses.

[Koren]

It all depends on the condition of the bodywork, not just the visible stuff but the shell underneath.

More 8s die from tinworm than from engine issues, these days.

Nordic Green is a rare colour, which may limit the demand or may make it more sought after.
That sounds like a contradiction but, while fewer people would be interested, if there's more than one then you might get a bidding war.

I had rusty sills repaired already early in the year. Hopefully nothing else lurking. There's a leak in the boot I've been meaning to sort out, but I already have a project car (a capri) that gets worked on first usually.

[v-rex]

Thanks, I also saw pages for Warren Court and Rotary Motion which aren't too far, and looked very reasonably priced. Don't really know how to choose one over the others. Rotary motion says "Our NO HIDDEN EXTRA GUARANTEE ensures you only pay for your chosen package. If, once your engine is stripped we find you need internal parts including Rotors, Rotor Housings, Engine Plates or the e-Shaft, we will replace these at no extra cost!" as well as free collection which sounds like nice bonuses.

There's a list of specialists on one of the pages somewhere, and some aren't far from the ones you've already mentioned. So there is Essex Rotary and The Performance Shop (TPS) near Warren Court rotaries and I think there is Carl Hayward and I think another near RotaryMotion.

Also Luke Murdoch does the option of removing your engine, taking it to get rebuilt and then reinstalling, if you want to save yourself the journey, and of course he can supply used engines as well, so worth giving him a call.

Lastly in terms of deciding where to go if you decide on a rebuild. I would just ask alot of questions to the builder and don't take anything at face value, despite any reputation they may claim they have. Really make sure you know what to expect in terms of compression numbers, power, problems that might happen etc. As you've seen with the rebuild on your car already, cheaper isn't always better. There are some threads on this in the members section, so another great reason to join!

Lastly I've had my car over 13 years now from new and despite the horror stories you hear, it's been fairly good to me mostly and not really stressful, but actually alot of fun. Sorry to hear of your troubles, but it sounds like once the sills have been done and the engine, then the two biggest jobs you might face are done and it should be good for years after that with very little problems. (Touch wood)

[Koren]

viewtopic.php?f=25&t=36531

[Koren]

Lots to think about! Lots to research too. I was leaning slightly towards sell it's as a non runner to begin with, pretty sure I'll go for a rebuild without spending a fortune though now. Probably sell it in a few years while it's still a new ish rebuild.

[Koren]

A couple of people have asked me if I've tied it again since, and I kinda thought it wasn't worth it. The thought did occur to me that maybe I hadn't done up a spark plug properly or something, so I gave everything a once over, and tried it again around some local roads. It seemed a little unhappy at idle, but not as bad as when it stalled on Sunday. Could the symptoms I had be caused by a plug lead not making great contact or something simple like that? There is also a P0130 (Front o2 sensor) code showing up that I forgot to mention before. There was some oil in the airbox too, apparently that can a caused by overfilling on the earlier cars (it's an 04)? I guess the compression means it'll need the rebuild sooner rather than later anyway, so maybe best to do it while I don't need it much.

[Koren]

The problem with any car that's been through a few owners is that you don't know the detailed history.

It could well be that a CEL came up years ago that suggested a potential problem with the front O2 sensor.

Rather than fully diagnosing the issue (loose connection) the owner/dealer/garage just replaced the sensor, which appeared to cure the issue.

Only they replaced it with a generic aftermarket part from a motor factor that "fits all RX-8" - when Mazda couldn't even get the 231 and 192 engines to run properly with the same units.

All the symptoms you describe could be due to running with an aftermarket front O2 sensor - or any number of different causes, all unrelated to compression.

[Koren]

Oh, interesting! I'll definitely get that done first then see what happens!

[Koren]

The problem with any car that's been through a few owners is that you don't know the detailed history.

It could well be that a CEL came up years ago that suggested a potential problem with the front O2 sensor.

Rather than fully diagnosing the issue (loose connection) the owner/dealer/garage just replaced the sensor, which appeared to cure the issue.

Only they replaced it with a generic aftermarket part from a motor factor that "fits all RX-8" - when Mazda couldn't even get the 231 and 192 engines to run properly with the same units.

All the symptoms you describe could be due to running with an aftermarket front O2 sensor - or any number of different causes, all unrelated to compression.

I found a used one on ebay, the seller says :

"Hi,yes this is the original denso n3h3 mounted in 231ps version by mazda dealer"

https://www.ebay.co.uk/itm/184284206324

Is that right? I can't find anything to say that Denso were the original ones or not

[Nickp47]

Might be better trying a trusted trader, like Bigpete
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