Topic: Lemony Rotary Rebuild, hard starting, won't idle

I need to reach out to the rotary guys for a moment with a problem I can't seem to wrap my head around.

After blowing up two motors in our 88 RX7, and finding the 3rd junkyard motor wouldn't build compression I got fed up and decided to sell the car. No one would buy it. So I got more fedder up and starting tearing down motors to see what I had. The first two motors where pretty much junk, but the third one I took apart looked darn good. So I decided to rebuild it. I'm reasonably intelligent, I have youtube, and a credit card. So using a Rotary Aviation rebuild kit I went to work.

The irons weren't lapped, they were just lightly sanded to "hone" the surface, per what some guy said online once. All new hard seals were used as well as soft seals. Much blood was shed. Much cursing was, uh, cursed. But the motor eventually went together. After putting the motor back in the car, it wouldn't crank for anything. Double checking everything, I realized I had "stabbed" the CAS wrong. Once that was corrected, I could get it to almost crack over. Thinking it might be a poor compression issue because of questionable housing/irons and new hard seals I put a little oil in the spark plug holes and it cranked. It ran but missed terribly, which led me to double check wiring and I found I had swapped an injector plug on the wiring harness. With that corrected as it stands now, the car will only crank with a little oil in the spark plugs, it runs but wont idle.

My thought is that the motor just needs to run awhile to, for lack of a better term, bed in the seals. But I wondered if there was something else I should check before I give myself lung cancer starting this thing full of oil every time.

Emily's Power for a Cure 1990 Mazda Miata (I Got Screwed 2014 Southern Discomfort)
Help in the fight against Neuroblastoma, a devastating childhood cancer.
http://emilyspowerforacure.com/

Re: Lemony Rotary Rebuild, hard starting, won't idle

This is basically the mistake I keep making in that after buying all the rest of the stuff I dont have enough money to resurface the irons and try to lap them myself.  It's hit or miss.  Some of them will get better after leaving them run in the driveway for a couple hours.  Often not. You can verify if its compression or not by removing the valve core from a compression tester and using your phone to video the gauge as you turn it over.  Its easier to see the individual hits on video.  If its 70 or less, you are looking at push starting after every pit stop.  As far as idle, I've adjusted the throttle cable sheath where it fits in the intake bracket so its pulling on the cable a bit and cracking the throttle.  You then adjust idle with the two nuts that secure the cable.

1990 RX7 "Mazdarita"  1964 Sunbeam Imp (IOE 2013 Sears Pointless) 2002 Jaguar x-type (Winner C-Class 2021 Sears Pointless)
Gone bye-bye
1994 Jaguar XJ12 (Winner C-Class 2013 Sears Pointless)  1980 Rover SD1 (I Got Screwed 2014 Return of Lemonites)

Re: Lemony Rotary Rebuild, hard starting, won't idle

Thanks Cheseroo. That gives me some insight.

Emily's Power for a Cure 1990 Mazda Miata (I Got Screwed 2014 Southern Discomfort)
Help in the fight against Neuroblastoma, a devastating childhood cancer.
http://emilyspowerforacure.com/

Re: Lemony Rotary Rebuild, hard starting, won't idle

Cheseroo has you pointed in the right direction.

I'll add that if you have near equal compression across all faces, even if it is 65-70, you have a runner.  If you have a couple of faces next to each other that are low, then you may have something like a stuck corner seal from improperly clearanced side seals.

The minute your borderline compression engine doesn't start on the first try, you now have a sub-borderline compression engine from flooding.  The flooding makes things seem much worse than they really are, and this effect is compounded on a rotary.  I'm guessing this engine will make plenty of power up top from the get-go, but may need to be push started out of the pit for the first race as cheseroo said.  Welcome to the club. 

So far, your experience with the rebuild doesn't seem much different than how it goes with us (including the cas and injector plugs), and we've been doing this for a while.

5 (edited by Crazybob 2017-05-24 10:50 AM)

Re: Lemony Rotary Rebuild, hard starting, won't idle

Well I pulled out the compression tester and I'm getting a very consistent 70 on all faces, both rotors.... so fingers crossed I'll just keep running it and see how it does.

Good to know even the rotary guys have these issues smile

Emily's Power for a Cure 1990 Mazda Miata (I Got Screwed 2014 Southern Discomfort)
Help in the fight against Neuroblastoma, a devastating childhood cancer.
http://emilyspowerforacure.com/

Re: Lemony Rotary Rebuild, hard starting, won't idle

Oh man, have I been here before. Like EXACTLY here.

In lieu of typing a million word post I will refer you to a thread I started on another racing forum when I had a similar issue, i.e full rebuild that was hard to start.  ***apparently I can't even link to a chumpc@r forum thread since the name is in the URL... very mature***

So if you want to read through this thread there is a lot of fantastic diagnostic/first start up info in it. It's called
"Rebuilt 13b immediately overheating! (warning rotary content)" and is on the other series forum.

Now, you have an 88 so that has a crank angle sensor, where my gsl-se has an old school dizzy but first and foremost check the timing.  And if you think you checked the timing and you know it's right, check it again.

long story short,my timing was off like 45 degrees but I didn't realize because I could get the motor going with oil in the spark plugs, and keep it running above like 2k rpms but it wouldn't idle and would overheat. I swore I set the timing right and chased fuel and spark issues for days before I checked the timing.  I was an idiot, don't be like me.

As far as the "fresh rebuilds won't idle until you bed in the seals". I believe there is some truth to this but I also believe this internet wisdom nugget also serves to give false hope that maybe if you sit there with the throttle body wedged open for two hours everything will be fine.  Check and recheck the basics. 

As a side note, I did the same as you, rebuild the motor with irons that I just lightly wet sanded.  My motor runs and pulls great.  The internet will have you believe you need 15 grand in parts overnighted from japan to rebuild your rotary.

ES-CAR-GO 1st gen rx-7 ( formerly Maz-Stache)
Real Hoopties 2012
Capital Offense 2012

7 (edited by Crazybob 2017-05-30 12:02 PM)

Re: Lemony Rotary Rebuild, hard starting, won't idle

I'll check out that thread.

I spent some more time on the car this weekend. Still having idle issues, but after correcting a couple small vacuum leaks I found, the car will start on it's own cold. Hot start and idle is still elusive.

Emily's Power for a Cure 1990 Mazda Miata (I Got Screwed 2014 Southern Discomfort)
Help in the fight against Neuroblastoma, a devastating childhood cancer.
http://emilyspowerforacure.com/

Re: Lemony Rotary Rebuild, hard starting, won't idle

Crazybob wrote:

I'll check out that thread.

I spent some more time on the car this weekend. Still having idle issues, but after correcting a couple small vacuum leaks I found, the car will start on it's own cold. Hot start and idle is still elusive.

Nice!

You seem like you know what you are doing but another one of my favorite rotary diagnostic tools is a good ole can of brakleen.

Start the car up and spray the crap out of the rats nest and general intake manifold area.  If it surges you got a vacuum leak.

ES-CAR-GO 1st gen rx-7 ( formerly Maz-Stache)
Real Hoopties 2012
Capital Offense 2012

Re: Lemony Rotary Rebuild, hard starting, won't idle

alex3000 wrote:

You seem like you know what you are doing but another one of my favorite rotary diagnostic tools is a good ole can of brakleen.

Start the car up and spray the crap out of the rats nest and general intake manifold area.  If it surges you got a vacuum leak.

How do you think I found them!

Emily's Power for a Cure 1990 Mazda Miata (I Got Screwed 2014 Southern Discomfort)
Help in the fight against Neuroblastoma, a devastating childhood cancer.
http://emilyspowerforacure.com/

Re: Lemony Rotary Rebuild, hard starting, won't idle

Just a quick update and thanks for the help.

Car starts better than she ever has cold, and with a little massaging of the fuel pump cut off cranks up hot every time. I've also managed to get the idle dialed in. I'm thinking we might actually have a runner.

Unrelated question for peeps who know these cars, I'm running a racing beat full street exhaust that I got of craigslist. It's not the true dual race one, but the street version. I got it off craigslist, so I'm not sure if its normal but the damn thing hangs way too low under the car. Is this normal for these? Any tips on tucking it up under the car better? The lowest point is where the header and presilencer meet. My thoughts are that either the header has gotten bent at some point, or the solid motor mounts are sitting lower than stock, but I'm really not sure.

Thanks guys!

Emily's Power for a Cure 1990 Mazda Miata (I Got Screwed 2014 Southern Discomfort)
Help in the fight against Neuroblastoma, a devastating childhood cancer.
http://emilyspowerforacure.com/

Re: Lemony Rotary Rebuild, hard starting, won't idle

I have that same exhaust but don't really have an issue with it.  Car is on cut stock springs and presilencer sometimes gets hung up loading/unloading on the trailer but not to any extreme degree and certainly a lot less than some of my other cars.

1990 RX7 "Mazdarita"  1964 Sunbeam Imp (IOE 2013 Sears Pointless) 2002 Jaguar x-type (Winner C-Class 2021 Sears Pointless)
Gone bye-bye
1994 Jaguar XJ12 (Winner C-Class 2013 Sears Pointless)  1980 Rover SD1 (I Got Screwed 2014 Return of Lemonites)