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Got into a back-and-forth in another forum that produced the following suggestions/recommendations.
I'd dearly love to hear if any of you Oracles have an opinion on this course of action.Facts: 85; FB; 1.1L;
Owner (me) Reports: Cranks, but won't start - Customer says vehicle may have new spark plugs and oil. It appears as if the
starter wants to start the motor but the engine doesn't turn over.
Tech Comments: The engine was flooded at arrival we removed and cleaned the spark plugs and let vehicle sit over night so the engine could
air out any fuel left in chambers. We also noticed that the spark plug wires were not routed properly and we re-installed the wires after re-installing
everything we found that the engine only has 25 psi compression.
Specification is 85 psi minimum. Recommend owner take the car to a Mazda rotary engine specialist to inspect and possibly rebuild the engine if needed.
Forum (not 1st gen RX) Comments Received -
Forum Comment 1: Needs a rebuild if those compression results are accurate. A kit can be found for $1000 more or less assuming
all the internals are still good. I paid $1700 to have a short block rebuilt (I did the tear down and motor reinstallation)
Forum Comment 2: I’m assuming the compression test wasn’t done while the car was at operating temp or with a rotary tester? Otherwise
yeah you’ll get an inaccurate low reading like that.
Usually when a rotary sits a long time and you have no idea what it could be the best and cheapest (although not safest either) is to
pour some MMO (Marvel Mystery Oil) in the combustion chamber then jumpstart it with new plugs. I’ve done that a few times and it
works every single time.
A compression test should be done with a rotary compression tester to determine the engine's health. Each face of the rotor will give you a compression number. There will be three in total. The test should be done with the engine at normal operating temperature and the throttle should be wide open.
You can put the MMO into the engine via the carb if you so choose. This is the easiest way. You can also go through the leading spark plug holes. You can also use automatic transmission fluid. The detergents in it will soften the carbon and can help free stuck seals. The seals, apex, side, and corner, will stick from non use. The apex seal spring can flatten and then its rebuild time.
You need to determine if you have proper spark. You also need to read up on a proper deflood procedure. Also, if you remove the plugs and crank the engine over, you need should note if the pulses sound even or if there's a pause and then a pulse. This is where I would start.
Even with an incorrect compression tester 25psi is a low reading, not enough to start it. I would try MMO let it sit for 24hrs or longer. I don't rec ATF, as I used this which worked, but in the long run deteriorated the oil control seals causing lots of smoke and a rebuild.
Stop taking these 2 cars you bought to piston mechanics. Either do the work yourself or find some legit rotary mechanics in your area. Both of the cars you have posted about in the build section and here are probably runners with some maintenance done to get them running well. Since your are in Kalifornia it's hard to say if they will pass emissions but probably not unless you dump more money and time into them.
so this one time at the dealership, we had an Rx8 come in that was running on one rotor, and we compression tested it with the tester, and the one rotor was in the 8's and the other was in the 5's, bad.
the tech, called Mazda and Mazda had us replace the coils, plugs and wires, the experienced guys, were unsure how that was going to fix a bad motor, but its Mazda's dime, so ok.
the tech, Mike#2 replaced the ignition system, fired it up, ran it for a while, and re-tested the compression, which was now fine, both rotors in the 8's.
moral of the story? the engine needs to run ok to have compression.
your 25psi might be low, but if its even, it'll (eventually) run and once it runs well for a while compression will come up.
this other time at the dealership we had a car come in with a bad piston engine, and 4 of the tech decided to test it, and all four of them had different readings with their 4 different testers....
How much MMO should I use; and, I should leave the car to rest for 24 hrs after introduction of the MMO before starting?
Does the process you recommend still require me to drag it down the street to jump start it, or can I just start it with the key in the garage to listen for the pulses?
They are both Cali cars, the running one has already passed emissions.
I want to do the work myself. I am merely trying to ascertain what work needs be done.
I am going to reputable mechanics recommended by other reputable mechanics in the area; even
though, as you say, they are "piston" mechanics - which sounds pejorative; but, what do I know.
It has been hard finding a rotary mechanic, even at the local Mazda dealership they shrug.
https://www.rotarycompressiontester.com/ for the tester. The reason that people here are talking down about piston mechanics is that most of the time they see the rotary engine as a failure and/or black magic. For me it's the other way around, while I have never rebuilt either I'm WAY more comfortable around a rotary just because I have many more hours around one.
To answer your questions about compression how does the engine sound? three even pulses? If so, you may be in decent shape. Have you tested ignition and fuel to make sure both are functioning? I honestly don't know what you have done.. sorry if you have already confirmed this.
Make certain your battery is in good condition and fully charged, all ground connections are squeaky clean and that you have good strong spark at the plugs. Verify fuel pressure and flow. Don't forget to turn the engine several revolutions by hand after putting the MM oil in the chambers to more evenly distribute it. Start with clean plugs.
In my experience, the fuel has to be cranked out of the engine with spark plugs out, ignition unplugged, fuel pump off, throttle preferably wide-open, for anything to change. Piston engines have piston rings that allow the fuel to drain by and into the oil pan. But on a rotary, the seals around the combustion chamber have no gaps or clearance. The fuel has nowhere to go. I believe this is why letting it sit works on a piston engine, not-so-much a rotary, but I could be mistaken.
While you are cranking the fuel out through the spark plug holes, listen to the whoosh sounds, if they all sound the same and are all evenly spaced apart. You're probably okay on the compression side of things.
07-20-20, 11:10 PM
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