Home rebuilt rotary engine not starting

Good Day!

I had a post about this a few months ago and can't find it now. Anyway, I rebuilt my S5 NA engine at home using atkins apex seals / oil control O-rings / and coolant jacket seals.

I got the engine to start by pouring oil into the combustion chamber through the trailing plug holes.

I ran the engine for about 4 hours idling and then high-idling. I was able to run the car up and down the street and it pulled well.

I took the engine out and had it wrapped up and drained (to use as a spare for our Chumpcar).

I decided to put it back in the car and do it right. (It was sorta kinda in there not really permanently before).

So, now I am back to trying to start this thing. It will not start.

Fuel pump is turning on. When the fuel pump is on, you can hear the engine "labor" a little when it is turning over.

I have spark.

I have timing set by way of lining up the CAS. This has never failed me before.

I hooked up a spare CAS and I can hear the fuel injectors firing when I spin the gear.

I am thinking it is because I did not clearance the apex seals properly to the housing width.

If this last item is the issue, how long will it take to break in (if I get it started)? Or should I just tear it apart now?

Do you have compression? Sounds like you have the other two necessary ingredients in place.

Tough to tell if I have compression. I can do a cold compression test. I have no idea what the numbers should be for a cold compression test on a rotary. I know the hot numbers need to be around 80 in order to start.

I can do a test and report back.

I'd at least look into checking if you have any compression at all. Maybe one of the apex seals got stuck.

Are rotary cranking-compression numbers different than piston engines? 80 psi sounds real low.

They are. IIRC even the regular measured compression with the engine hot is lower.

If you remove one of your spark plugs, it is soaked in gasoline after trying to start? If so, you flooded it and it will never unflood on its own. If it is flooded, perform the de-flooding procedure.

Is your ignition switch good? When I first got the rally car, the ignition switch "ON" position worked, as did the "START" position, but they did not properly overlap- you could turn it on and check things and they would appear fine, and you could turn it to start but it would cut power to some of the circuits which work in the "ON" position.

I'd try the de-flood procedures first, then maybe try pull starting it with another vehicle.

After my S4 rebuild I had to give it a tug behind a buddy's jeep to get it started the first time.

http://rotaryresurrection.com/2ndgen/tech_fuel_cutoff_switch_unflooding.html

I gots a fuel pump cut-off switch. I also have deflooded it a few times during this process.

As far as the compression, I will get a number tonight. I do not expect it to be awesome.

P.S. A properly broken in rotary that is kick ass built would have a number around 120 psi on all faces. I have heard it is time to rebuild at 85 psi. Both of these numbers are "hot".

I just am really curious if it is apex seal clearance if it will "run-in" or should I tear it apart...

Thanks!

Rob R.

Fully charged battery?

I'd check the compression first. If you've got something reasonable, try fresh plugs and a fully charged battery. Are you running the stock ECU?

Push start it. You will just melt starters trying to get a recalcitrant rotary started.

In my experience, if I wasn’t making decent compression, the starter motor would turn the engine several hundred RPM’s higher than normal.

You may not have a good baseline RPM number for reference but for me, tach and ear was all that was ever required to clearly “see” inside the engine.

The question is whether the compression will get better or do I need to tear it apart and clearance the apex seals to the chamber width?

Thanks everybody for the help so far!

I don't think you would want the apex seals to self clearance against the side plates, that would cause excessive wear I would think.. If it's convenient to get to, you may want to stick a boroscope/mirror into the exhaust ports and check that you can bounce the seals up and down. It should help you figure out whether you're bound up or not, but if you ran the engine in and it didn't feel odd, my guess is any jamming in there is temporary from sitting and you just need to pull start it after its nap.

It was difficult to start the first time too. It only has about 4 hours or so of running if I had to guess.

It is not broken in yet.

NOHOME wrote: Are rotary cranking-compression numbers different than piston engines? 80 psi sounds real low.

On a piston engine tester, that's pretty good. Compression drops off massively as RPM drops and the pressure of combustion is important for all of the seals (even more so than a piston engine because of the dual sided nature of things) which is why a compression test is almost meaningless if the engine is cranking too slowly. You should be able to turn the engine over with a couple fingers on the alternator blades.

wvumtnbkr wrote: I just am really curious if it is apex seal clearance if it will "run-in" or should I tear it apart...

It will but it will take a long time. You can sorta get away with not setting that clearance with Mazda seals because the corner piece is so small. But with Atkins seals, the corner piece is a significant portion of length. He did some testing and found that the Atkins seals "grow" after their first heat cycled, so you really need to set the end clearance to compensate.

I forget what I would set them to, it's been a long time since I've had to assemble a new engine Judge Ito posted his specs on rx7club and nopistons. I'd like to say .003" end clearance but double check.

I have never had an engine difficult to start when new. Setting the clearances correctly is crucial. They usually kick on the first turn of the starter after I remember to reconnect the fuel pump/computer/other...

In reply to Knurled:

Would you tear it apart or just let it run?

I would rather not spend the time and money to crack it back open if I just need to let it idle every day for 2 weeks or something.

Idling won't do much... need to run the sucker. If you had new bearings, there is something like 500mi or X hours of dyno time needed to seat them. By that tiem the seals should be seated.

If you clearanced them from the get-go, the engine is as good as it will ever be right out of the box. (Barring bearings of course - always use used bearings if you can help it)

I was an idiot and did not clearance them at all. I somehow brain farted on that step...

My guess is any damage that would have been done is already done by not clearancing them, so I would try to light it off and get it going by being dragged, and then try to use it as much as possible... Only tear it down if that doesn't work.

okay....

update time: Still doesn't start.

I checked compression with a regular compression gage with the valve removed. Cold engine (duh), open throttle plates, cas unplugged. The gauge is reading between 117 and 122 on all faces.

Lets step back a moment... I replaced the battery and got the starter checked out. I even rewired the starter so a relay uses the ignition switch as a signal for the solenoid (this REALLY helps rx7's start more consistently).

None of the above did much of anything except spin the engine marginally faster. I took out the spark plugs and replaced them with new ones.

Still didn't start.

I tried starting with fuel pump off, then fuel pump on, nothing.

Then I put some engine oil into the combustion chambers. Still nothing.

THIS is when I did the compression check. Maybe the numbers are artificially high because there was maybe still some oil in the engine.

My plan of attack at the moment is to:

drain the fuel tank.

Add NEW fuel.

Remove spark plugs and turn engine over (I will have some protection in place)

Check base timing and use the CAS that I have been using to verify spark.

Reground ECU (I realized the ECU is kinda sitting in its mount but not screwed down).

Then recheck Compression...

I will report back after I finish the above....

I predict success! Compression sounds fine. Fuel or spark is the culprit.