So i built a streetported 13b for my 1987 rx7 fc n/a. The front housing is a used fd housing that i got from atkinsrotary which read a 7:1 compression ratio, and the rear is a new housing with an 8:1 ratio, with brand new endplates. Atkins rotary tested it and said it would work fine.

I realize that when doing a build with used housings, it generally takes a bit of time for the seals to beed into the housing. I have driven approximately 600 miles on it thus far, changed the oil (10-w30), and even added some oil stabilizer in the hopes of slightly increasing compression...but it still does not fire up when hot (i.e. letting it reach operating temp and then shutting it off and letting it sit for 15 mins or so when i go get coffee or something). I essentially have to take out the bottom spark plugs + the fuse and crank the fuel out of the housings, then put he plugs back in. It fires up every time after that. Not to mention that twice already the threading on the spark plug breaks off in the spark plug hole and i have to extract it (it's really stressful, and i don't know why that happens, I torque it to 9 lbs like it says to).

Is there anything I can do so I do not have to do this deflooding procedure every single time my engine is hot? Perhaps using a different weight of oil?..Or should I just deal with this for however long it takes?

Anyways, anything helps. Thanks!

edit: drives great, revs smoothly, and idles at 750 rmps smoothly.

edit: sorry, poor title choice. I should have made it more specific "Engine has issues firing up when hot"

 

well my friend good luck to you. ive heard that you need to put more miles on the motor than that to get everything to seat. injectors good to go?

 

My car floods every hot start I do, I have 1,500 miles on my engine.

If you put in a fuel cut switch you can deflood it from inside the car.

I crank it and when it floods out I turn off the switch and keep cranking and when it fires up I switch it back on.

The switch is just a "bandaid" but it works.

 

Did you assembly the engine? Did you inspect the housings for wear? Did you use new apex seals? What were your side seal to corner seal clearances? What was the endplay measured at the flywheel?

I don't understand how the housings were tested. Housings are usually measured with calipers, straight edges, feeler gauges, finger nails, eye *****...but what is this compression ratio?


Where are the spark plugs breaking? Are you putting the socket on crooked and shattering the porcelain?

After 600 miles the compression isn't going to improve anymore...not enough to stop the hot start issue.

 

Injectors were serviced before i assembled the engine.

I assembled it. I received the housings from atkins rotary, they tested them with just a compression tester when i took the built engine down to them. It had no leaks and those were the compression ratios they gave me for both housings.

Brand new apex seals, brand new apex seals springs, brand new oil control rings. s4 rotors from the original engine. The clearances between the sideseals and corner seals were between 0.0022-0.0030 inches, all around on both rotors, with the angle of the sideseal to the corner seal being finished and lying flush with the sides of the corner seals. Endplay was 0.0016-0.0018 inches, i can tell you that.

I did not think to check the housings for wear because for one, one was brand new, and the fd housing had no scratches/flaking chrome, and I assumed atkins had measured/tested the housing before putting it up for sale...

I'm definately going to look into this fuel cut switch.

 

Uhm...

rotor housings have nothing to do with compression ratio. That is determined solely by the dish/bathtub in the rotor face.

Rotor housings do have a large impact on static compression itself, of course, since the chrome surface flatness determines how well an apex seal can seal against it and hold air pressure.

 

It depends on the condition of the housings. I have seen engines with more worn housings that continued to build compression slowly for 2, 3, 4000 miles until it finally hit a plateau. True, MOST engines with nice condition housings will be broken in within 1000 miles and pretty much "are what they are" at that point, but that's not always the case.

 

that actually sort of makes sense to me.

 

With the money you spent on the engine, I think it's worth spending a little more and having the compression tested properly, with a rotary compression tester. Especially since it runs and warms up and you'll be able to check it properly.

Then, armed with that info, go from there. I'm wondering whether the injectors you had serviced are really ok. Everything else in the fuel system stock and ok?

 

Alright good to know; I did not anticipate it could take that many miles. I guess ill just stick with it and see what happens in a few thousand.

Thanks for all the feedback guys, it was very helpful. Next time I build a rotary Ill try to avoid used housings.

 

And atkinsrotary does have a mazda compression tester that they tested it with, that's why I was so confident with my build when they told me the numbers were good. However, I realize now the importance of a compression test on a hot engine vs. a cold one. It is unfortunate how expensive rotary compression testers are, but I suppose I have no other choice.

edit: I don't want to sound like i'm blaming them for my anything, they're a good bunch of guys.

edit: When the injectors were serviced they sent me a chart with the difference in flow before and after service, but i'll take a another look. Everything is stock in my fuel system.

 

k, just to be sure...I thought you just got a housing from them. You built the engine yourself, no? So the housing may very well be ok.

Maybe a stupid question...but you're sure the right injectors are in the right spot (primary vs. secondary). I'm so rusty on a lot of stuff - someone correct me if it's even possible to switch them by accident.

 

Just rent/buy a cheap piston engine tester and remove the schraeder valve. I'm also guessing that the numbers you mentioned earlier were in kg/cm2, which are the units on an official Mazda compression tester.

7 kg/cm2 = 97 psi
8 kg/cm2 = 114 psi

But as mentioned already, if Atkins tested another engine to get these numbers, and then sold the housings to you, it doesn't mean that much. You need to compression test YOUR engine. Or did Aktins build/test your engine?

 

I built it, and since I live relatively close to Atkins (about an hour drive) and do not own a mazda compression tester, I took it down and they tested it.

Those numbers are very helpful, I never understood what they truely meant in the past, but you have made it clear to me. Thank you. I apologize for my mechanical ignorance.

I may as well at this point just install a fuel cut off switch and see what happens in a few thousand miles.

 

If your engine has 97/114 psi compression, that's good. It's usually the low CR turbo engines that flood, but a high CR NA can too. The start maps on the stock ECUs are very rich under hot conditions.

 

Very valuable information thank you.

I'll see what I can do with all of this information that everyone has provided.

Thanks everyone!

 

On a stock 2nd gen engine (regardless of year) it's impossible to "mix up" the injectors because they are all the same on the same engine...there are no differences between primary and secondary on the same engine.

I guess it might be possible to have the primary injector PLUGS switched (rear plug on front injector) which could cause some issues, but I doubt it. These harnesses are usually pretty stiff at this point in time and it would be hard to re-route any wires to a wrong position.

Then again, I've seen some "interesting" stuff on rotary engines brought to me for repair...

 

Ah...I see. They didn't give you a compression ratio, they gave you a static compression test in kg/cm^2. As noted already your numbers are not perfect but certainly acceptable.

Now, if you had this test done when you first built the block, I can tell you what probably happened. I've seen that atkins does "compression tests" on their rebuilds that they send out. BUT they do it on a cold engine that was just built and has never been fired. As we all know there are assembly aids and lubes in a fresh built engine, and similar to adding oil/atf to a flooded engine, these will artificially raise compression numbers. Also testing a cold block will usually give you artificially high numbers, since the rotary loses a few psi of compression when hot.

I've discussed this with Dan a few times and it's my opinion that these "tests" they do are useless and the numbers absolutely inaccurate for those reasons. To some degree, he agrees, but says that it is just something they do to see that there are no major problems before sending it out the door and that they don't expect them to be accurate per se.

So if those were the artificially inflated numbers pre-startup with assembly oils etc. inside and on a cold block, then your actual numbers today with the engine running and on a hot block are probably 10% lower or more. That would put you in the low 90's or high 80's which would explain your flooding issues.

You don't need a rotary compression tester to get an accurate assessment of the engine's compression levels. Where the rotary specific tester shines is the ability to show you each individual face within a common chamber, which shows you if you have a chipped or cracked individual seal. On a fresh build you can safely assume that this is not the case...you just want to know an overall view of the highest compression generated in one chamber, which a modified piston tester will do for you. I have instructions for this on my website in the tech section if you care to look.

 

Oh that is very interesting, all of that. I think I have learned more about my rotary in this thread alone than in my whole process of building it (that really is just following procedure).

Also, Dan told me they tried to eliminate any artificial compression within the engine block before the test (just like you said, oil inside the block and whatnot).

Anyways, what's done is done. I will definately check out your website for that modified compression tester.

Thanks so much!

edit: I don't think its anything injector related. It has a brand new wiring engine wiring harness from mazda, and like he said, it is indeed stiff and all of the connectors fall into place where they should be.

 

Last time I checked my TII compression it was under 90 psi on both rotors and holds around 10-12mmhg vacuum at an 800 rpm idle. I have and always use a fuel cut switch and still have never had any issues with it starting because of flooding. It starts after the 2-3 revolutions whether it's 90 degrees or 20 degrees out. If I ever buy another 7 it will have a fuel cut switch. Just my 2 cents.

EDIT: My first rx7 was a 1988 SE, it didn't have a fuel cut switch. I have had fond memories of having the girlfriend wait in the passenger seat while I pulled the fuel injector fuse to deflood it.

 

I think your problem is just residual fuel pressure leaking past the injectors, racing beat or mazdatrix has a setup that goes into your supply and return fuel line that has a small jet that bleeds the residual pressure in your supply line off into the return line so as to keep it from pushing past your injectors

 

sounds like switched injector clips, a fuel pressure issue, inoperative leading coils, faulty AFM or water thermosensor.

 

Actually, turns out it just took some time to break in. About 1000 miles on it thus far. Fires up every time now.

Thanks for all of the feedback guys, I appreciate all of the help.