JonathanC

Still no start: Today we tested each spark plug to actually see the spark, and also tested compression.

Each spark plug has a spark. The front-TRAILING spark plug had the weakest spark, though. All others were some shade of bright blue; the front-trailing was yellow and not bright (still a spark, though). I've read the trailings aren't important, so can't imagine that would prevent the car from starting, but am now thinking about replacing coils, wires and plugs (since this seems to need to be done regularly anyway). BUT --- the car started before with these same coils, wires and plugs.

Compression. Getting three "strokes" of compression in each rotor. The rear does seem to be stronger than the front, which is worrisome, but the front definitely has three pulses (I'm using a standard compression gauge and just watching it move and trying to guess.) Putting some oil in the front rotor did seem to improve the compression. But there's still some compression (and they became equivalent when I put the oil in, so I've a hard time thinking that this is preventing it from starting.

Another note is that the trailing plugs both had a lot of gas in them from flooding, as I think it's harder to clear those in the regular deflooding ways, so we removed them both and dried them.

Another note, the trailing sparks start about 4 seconds after the cranking starts, but the leading start pretty much right away. So this is helpful to determine the wiring is right.

Still no start.

Air, fuel, compression and spark, but no start. What's the deal?

JonathanC

I checked out this page, RX-8 Help, and now I'm thinking it's generalized low compression.

I compression tested again (again using a regular (not-rotary) compression tester) and get 58PSI on the rear rotor about 56PSI on the front rotor at 220 RPM. This is FAR below the required compression to start, so would completely explain the motor not starting. (we are at 5300 feet above sea level which does make a difference according to Foxed.ca - Rotary Compression Calculator, but I don't think enough to let it start )

Remember, this is a completely new rebuild, and the compression is equivalent on both. So is this expected? Could we have done something wrong that would lower the compression (but not eliminate it) equivalently across both rotors and all three "chambers"?

Thanks for your help.

Reoze

Not nearly enough information to start diagnosing where you went wrong in the rebuild process. What kind of apex seals and springs did you use? Did you reuse your housings? Rotors? How do you know they were within spec? Did you figure out the cause of low compression to begin with? Otherwise how do you know you resolved the issue?

JonathanC

When we got the car it would not start. We injected oil in the combustion chamber and actually did get the engine to run for a few seconds, so that showed us that everything was OK (except something internal).

Upon taking it apart, the main problem was that the front bearing had worn out, and an apex seal had broken. There are/were some scratches on the housing, but we showed them to two different experienced RX8 Mechanics and both said they were ok. (very shallow). the eccentric shaft was deeply scored, though, so we replaced it and several components in the front stack.

We rebuilt with seals and springs and everything else from Atkins and replaced everything. It's our first rebuild of a rotary engine, but I've done pistons before. So we were really careful and meticulous and checked tolerances on the apex seals, etc.

Yes, re-used housings and rotors.

We just tried putting 10 more CC of oil into each combustion chamber, apparently not enough vacuum to suck it up from a cup, so I injected in. It definitely sounded more like it wanted to start, but still didn't. Funny thing is that when we first put the engine back together and tried putting oil in it, the vacuum did work well enough to suck it in. So something has changed.

Reoze

Atkins seals are known for having inherently low compression. If the entire rotating assembly was worn that badly I would have expected the housings to wear in a similar pattern. Do you have any pictures of the engine while you were rebuilding it?

JonathanC

Well, we did not check the spec on the internal dimension of the housing. But when putting the engine back together it seemed quite tight in there.

The rotors and housing weren't work, it was only the eccentric shaft and the front stack (because of the bearing that spun)

here's a pic of the rebuild




Yes, rebuilt it in the living room

Here, for example, is a picture of the spun bearing.





Also, here's a pic of some of the wear on the rotor, which was not much at all.

BigBadChris

iTrader: (4)

New coils, plugs and wires? If not, when was the last time those were changed?

Reoze

They wouldn't cause ridiculously low compression numbers like that. Though I'd definitely want to get a second opinion with a rotary specific tester rather than trying to eyeball a mechanical gauge like that.

Did you make sure to properly gap the side seals? If they were binding then that could definitely cause some major problems.

MIGhunter

Did I read that right? Your using a regular compression tool to check the compression? It's my understanding you can't get real numbers this way. Try to borrow a rotary compression tool

JonathanC

Yes, using a regular compression gauge.
I realize this isn't he best way to test compression, but not sure where I'd get a rotary compression gauge.
And there's lots of examples of it working:

My pressure doesn't get above 60PSI

There seem to be two ways of doing it. I did it by taking the valve out of the tube of the compression tester, which allows you to see the needle bounce up and down for each face. and after the first rotation it's consistent and you can read it pretty well. The other way is to get the reading of the "whole rotor" by leaving the valve in, but this doesn't tell you if each face is compressing properly.

The only strange thing is that the compression is low across both rotors. I'm still hoping for something that will fix it that will not mean I have to pull the engine out and tear it down again (or get a new engine).

9krpmrx8

iTrader: (46)

A piston compression tester will show you if the engine is toast, it just doesn't tell you the whole story. But 60psi is fucked either way.

JonathanC

Yeah, I'm inclined to agree.

What could go wrong to have low compression across both rotors?

9krpmrx8

iTrader: (46)

Faulty batch of seals, upside down springs, improperly cuts seals, or out spec rotors, housings, or irons.

Despite what the internet says about rotaries having less parts than a piston engine, etc. Rebuilding a rotary is not simple.

Reoze

At this point there's no use speculating, pull the engine.

me2151

I just recently rebuilt my motor and it wouldnt start either. I had multiple issues but the main two were compression(atkins cryo seals and solid corner seals) and my fuel pump was bad( only primed 30psi). I replaced my fuel pump and put atf into the service ports of my intake(the 2 nipples on the lower intake manifold) while bumping the motor over with the starter. It needed alot of atf and once it was going it ran rough until i was able to driver around 50-75 miles. expect lots of smoke and many chances for it to stall. Mine now starts cold every time on its own and warm most of the time(still breaking it in and i need new spark plugs from fouling out my old ones). I currently have 150 miles on my motor and its worth every penny.

9krpmrx8

iTrader: (46)

Your freshly rebuilt engine still hard starts when hot and it's worth every penny? I don't think you know how things are supposed to work.

JonathanC

me2151, what do you mean by "a lot" of ATF? More than 15cc?

I figure I should try one last effort to get it started like that before pulling it. How much oil is too much?

9krpmrx8

iTrader: (46)

When it's enough to liquid lock the engine and do even more damage.

JonathanC

�� ok. So manual says 10-15cc. So twice that? 4x that ?
also thinking of doing it with 2-stroke oil instead of ATF. Does it matter?

and doesn't there need to be enough room in there for some gas and air?

JonathanC

Got it started today! found a mechanic who works on RX8s and he suggested WD-40, so we sprayed it in through the spark plug holes on each side, and bumped it around. quite a bit in each lobe. and it started.

I'm not sure if it unstuck something or if it just provided some liquid to help create the compression, but either way it did the trick.

BUT … it only ran for a minute and then died. But while it was on, it ran really smoothly. More troubleshooting tomorrow on why it stalled out -- likely there's still something really wrong, but it was a nice moment

Reoze

If the compression is *that* low then it's possible that it stalled while the idle was settling down due to the lack of airflow coming into the engine.

Besides that, you're looking at your standard troubleshooting.

Spark, air, fuel. One of the 3 isn't sufficient.

9krpmrx8

iTrader: (46)

There is definitely something seriously wrong. You can keep wasting your time, but you are just in denial.

JonathanC

Pulled the motor and it turns out that 3 side seals were stuck in their grooves. One partially in the rear rotor, and two almost completely in the front rotor. This is what was causing the low compression.

So now I've started a new thread about what my next steps should be:
https://www.rx8club.com/new-member-f...groove-265532/

Thanks for all your help!

9krpmrx8

iTrader: (46)

Next step = new rotors and another rebuild. This is why having someone who knows how to determine if parts are within spec is so important. This cannot be said enough.