I have my FD torn apart in the garage for some attention and a few upgrades, im going to compression test and rebuild if necessary as well. Here's the thing, I put it away pretty well flooded, what kind of compression numbers can I expect from an engine that is flooded but otherwise healthy? What compression numbers when flooded would indicate time for a rebuild?
The motor was running good before flooding, just typical issues with junk vacuum lines.

Thanks in advance!

 

If it's been a while, the fuel should have evaporated and found it's way out the exhaust/intake, but will have washed out any oil clinging to the chamber walls. Why don't you go ahead and test it and post your numbers up.

If it was washed out and is now sitting I would get a little 2 stroke oil in there and spin the engine to protect against corrosion/stuck seals, but that will give you false high compression readings by filling in all the little gaps.

 

if its been a while who knows? less than ideal though.

this one time (this was in 2006-2007) we had an Rx8 come in running on 1 rotor. we compression test it, it fails. the numbers were all 5's. we call mazda and they told us to put coils wires and plugs in it, and recheck. we do. after running for a half hour or so, we pull it apart, and recheck.

it passes the compression test. numbers in the mid 8's.

 

Its been a few months since its run now, I premixed the last tank an oz/ gallon with factory omp so that may have kept some lubrication on things. I will be testing it as soon as the weather warms up a little. I'll test it without oil in the chambers and with, hopefully that will tell more or less how healthy it is. I'm assuming it will be okay, I have no reason not to plus its a reman in a 76k car

 

With the condition of the lubrication film completely unknown, it's not really predictable what the compression would read.

Best bet is get it running then follow proper procedure and check the compression. That will allow you to use the readings to evaluate the condition of the engine.

 

Spark plugs and wires have nothing to do with the compression since they are not even supposed to fire during the compression test
Rx8s tend to have weaker starter motors especially in the early models
And this is probably what was the story there.

 

If it was running one rotor due to lack of spark on that chamber, that chamber would be flooded, giving the low initial compression test result. When ignition was restored, and the combustion chamber flood-cleared, compression came back to normal.

 

Testing once back together would be ideal, however thats not what is available. I'd like to test it apart, as is. If anyone has experience with flooded compression numbers I could reference, I would appreciate the information. If there is no reliable way to test compression on an engine in this condition , oh well.

 

Running on one rotor is one thing.. having around 5bar compression in both chambers is another story

 

did you read what i wrote? we didn't change the starter.

 

I read what u wrote.. starter speed can vary with the battery Voltage hence different compression readings at different speeds. Will the compression be affected when a lot of fuel washes off the oil film? Absolutely. .. will it be 8.5 bar vs 5? Hell no . I in fact fried my ecu with the injector drivers were dumping all the fuel i had in the engine. Washed off the oil real good.. vacuum dropped from -420mmHg to -250mmHg. That is the extreme case when the oil film is washed off. Would that reflect to such low compression? Hell friggin no

Next time i blow a motor i wont rebuild i will change plugs lol

 

i wouldn't have believed it either, except i saw it happen.

 

When people are trying to unflood an engine they remove top plugs and turn the engine over and the excess fuel comes out of the spark plug holes...

Why don't you just turn it over without the top plugs in it, which will get rid of any fuel residue or whatever, add some ATF into spark plug holes afterwards to help build compression, then reinstall plugs then do your compression test..

 

im well aware of deflooding procedures as well as using oil to help build compression.

however, ideally to get good numbers, you would test a warm engine, recently run engine, that isn't my case.

I am just looking for someone who has experience with compression numbers in a situation like this (no recently run, previously flooded, engine stripped to shortblock), what to expect for numbers or ways to obtain more accurate numbers and what compression is acceptable from such methods to help decide if its a good time to freshen up my engine or not.

 

I bought my 50K mile RX-8 for $1,200 because it was diagnosed by Mazda as blown engine from no start condition, low compression test, cleaning, low compression testing, new ignition components, still no start.

I got it to fire up on 1 rotor with starting fluid and a 200A battery charger/starter and after running for 30sec or so it spat the carbon out of the other rotor and started running on both rotors.

I railed it at redline for a weekend with premix/injector cleaner and its been fine since.

It is easy to get side seals stuck with carbon from the exhaust port on the RX-8... especially if the ignition is faulty or weak.

The key in j9fd3s story is they replaced the ignition components and got it to run on both rotors.

If there isn't combustion pressure from a running rotor there is nothing to push the seals back out from their carbon encrustation (the springs are very weak and sacked out from exhaust heat on RX-8 anyways).

 

Anyone?

 

I understand you want to do a compression test so you know about where the engine is in its life span, but you are introducing too many variables for it to give you a definite picture of its health.

Really, to get a feel for how far along an engine is you really have to do compression tests in a very controlled way (Mazda compression tool or aftermarket that takes cranking speed into account) and it sure would be helpful to have many baselines through the engines life done exactly the same way.

However, in my experience if it was flooded it is probably very low on compression to start with and needs a rebuild.

 

If you stand on your head with a 6" adjustable crescent wrench tucked firmly between your cheeks while reciting Ch 2 from Yamamoto's book on rotaries you should get exactly 102 psi compression. Without Ch 2 read aloud you will get 98 psi.

/thread

Just test the darn compression and let us know what you get!

 

Finally got a break from the cold weather and did the compression test. 25*f outside, just in case anyone is curious. I filled the combustion chambers with 2 cycle oil and turned the engine over by hand a few rotations before starting. Front compression ~70 +/-2 psi on all faces. Rear ~90 +/-1 psi on all faces. I tested the front with both top spark plugs and the bottom rear in which resulted in a slower turning speed than the rear rotor which I tested with just the top plugs in. Battery started to get low so I didn't go back and test the front again after. So I set the battery on the charger and Im going to test the front again soon without the rear bottom plug in, hopefully it picks up a few psi. Regardless looks healthy enough to run!

 

Dude #1 get rid of the gen II pic from your sig. Everyone knows you love your FC but you are in the FD section now and it's confusing as hell and also blinding the **** out of people trying to reply and help you.

Your compression numbers are terrible, 70 on front rotor and 90 on rear and you're celebrating? I'm not a mathematician, a financial analyst and that's a serious range. Normally 5-10% is acceptable in piston engines between cylinders if I'm not mistaken. To me being over 20% different is not a good sign. Are you always premixing or rely on the OMP? Maybe the front isn't getting oil but the rear is. Also potentially everything you wrote is useless and it is almost certain that you have wasted everyone's time if you introduced a variable of different # of spark plugs installed at the time and different battery charge while doing the test.

In any case like everyone said repeatedly while you went on your merry way, it was probably completely dry if you've had the car in storage for a while, at worst you should have just pulled the plugs, pulled the fuel pump relay and turned the motor over a bunch of times to get the fuel out and let it sit over night, turn it over again and let it sit again to be perfectly sure it's dry. No clue what you were talking about when you were asking for flooded compression test numbers, nobody does that. Plus each gauge reads different, and there are other factors like battery strength, temperature of the motor and whether the throttle is opened or closed while doing the test.

Now you have introduced oil into the mix which will give you falsely high readings of which nobody can calculate. In fact you may have forgotten to put oil in the front causing the difference. You also mention it's a reman engine in a 76k mile car, but never mention the mileage on the reman. If you don't know the mileage, then can you actually prove the engine has been replaced? And why are you doing a compression test if it ran so good? As often as these engines have engine failures, if it's not blown it's running, and I'd keep running it unless you have a million dollar turbo you are trying to spare.

You may want to charge your battery, try the procedure I mentioned to get rid of fuel in your engine, leave only 1 plug in on each rotor, and add more oil evenly to the front and rear to cover the second variable you previously created and then try the compression test again. The real concern is the over 20% variance between rotors. To me it sounds like you may have stuck seals or worn seals or housing on the front rotor, if the test was run correctly, which I do not have much confidence in based on your actions, so you have something going for you if you take your time and re-do it correctly.

 

Snook, you're the kind of pretentious person that makes people hate this forum. Congratulations. Take your opinion elsewhere.

However regarding relevant portions of your post:

I just bought the car this fall drove it home and didnt even put it on the road knowing it needed attention. So it sat since then, starting it up amd moving it around the yard now and then.

The car didn't run great but it ran, idled well and had typically been starting well. It flooded, likely due to the slew of minor things the car had wrong amd sitting.
Typical FD, toasty engine harness, broken sensors, cracked and missing vacuum lines, the list goes on.

I have no idea what kid of condition the injectors are in but they're being sent out for cleaning regardless. They also could have been contributing to it flooding.

The entire purpose of this thread was to give me an idea what to expect, not solid numbers. Looks like that was unrealistic. I'm over it. Numbers aren't great but okay. When I test again, consistently, I'll post the results.

The car is running factory omp plus I premixed an oz per gallon im the 3 tanks I've actually put in the car since owning it.

The engine is a reman because it has a Mazda reman tag on the front of the block, serialized and dated.

I would have prepped the car better for this work (deflooding etc) but I thought it would be sitting outside for the winter and only got it in a barn between snow storms this fall. On top of this I work full time, attend college and work an internship. My time is limited on making sure everything is perfect ahead of time. I work on the car when I can.

Adding oil to the combustion chambers was suggested by others on the forum, which made sense thinking about fuel wash removing oil from the walls. I oiled each face of each rotor.

I'm aware that my numbers aren't great. But i am assuming the front rotor will pick up a bit when I rerun the compression test. Also I'm assuming the numbers will be significantly better once the car has actually run, correctly for the first time in several months.

 

From racingbeats website
"- Normal compression - 110-150 PSI
- Minimum acceptable pressure - 75 PSI
- Maximum acceptable pressure difference between chambers - 20 PSI"

That leaves compression right at the border line of failure. However this is with non ideal conditions.

Rebuilding a rotary engine before destructive failure is by no means a poor decision. I fail to see how it is adventageous to run it until it blows, The price of a rebuild kit is cheap compared to having to buy new housings, irons and rotors.
In fact I will likely rebuild if I don't see a significant rise in compression of the front rotor.

 

Gave it another go with a fresh battery today and both lower plugs out today. Between 100-110 psi on the front rotor, 110-120 rear. Engine's healthy, that settles that.

 

I'm not really an A hole, I responded that way on purpose because..
The issue is that you didn't provide helpful or complete information, you knowingly cut corners on the test, you asked for something that doesn't exist and didn't listen to any advice from people that posted. What do you expect the reaction to be?

Good thing is you know your car has a reman, but don't know the mileage.
Rebuilding the engine could be a good idea before it blows up, if the parts in the reman are actually good. Seeing as how you dont know the mileage it's hard to say the condition or if the parts will be reusable. At one point new housings were being used. The date on the block may help you research the quality of the remans during that time and if new or used rotors and housings are likely installed. On the flip side it doesnt matter if the engine blows and internals get damaged if you are going to go the reman route again. If your comp. numbers are accurate I'd be hesitant to go with another reman, but that's up to you to research what quality is being put out now. What is the date on the block?

Its also good that you are premixing on your own. I suggest replacing the omp lines with SS or I believe theres also a clear version so you can see if oil is being fed by the OMP.

 

I didn't see your latest reply before you posted...there you go. Scratch everything.

Replace the Fuel Pulsation Damper while you're in there and the injector o rings and bungs. Also any gaskets that arent metal or look worn. Probably a good time to do the simplified sequential if you can get rid of the emissions solenoids and replace the vacuum lines with silicone if not and put in a metal AST if not already. I'd also put in a pop off valve on the output side of the intercooler and set it to your max boost so you can save your motor. It's like a second wastegate in case yours fails or it gets overloaded with improper boost control or on a cold night with boost spike or boost creep. Every FD should have come with one stock. Every modified FD should install one now.