drittens

I was reading about how some people get rid of the stock oil metering system and either premix or have a second container for 2-cycle oil....I assume the pump is actually in the block where the lines go in? Does anyone have pics/suggestions?

RX-4X4

Look in the FAQ and do a search for OMP removal. The FAQ covers it pretty well.

mazdaverx713b

iTrader: (91)

do not premix when using a catylitic converter!!!!!!!!!!!!!!!!!! you'll clog it and they're EXPENSIVE. the stock omp works fine. its on the right side of the block in the front near the bottom. it has two nylon lines coming from it and they go into the left side of the carb. pre mixing is done by guys who constantly run their engines hard or race. for normal or sporty driving the stock omp works great. the actual oil pump is chain driven by the timing chain and its located behind the front plate.

Aviator 902S

OK, this needs some clarification:

Pre-mix burns cleaner and lubricates better than that crud from the oil pan. 4-cycle oil from the pan is ideal for lubing bearings and carrying away heat and contaminants but leaves deposits behind when metered into the combustion chambers. Mazda went this route because it was convenient and somewhat idiot-proof. (Too bad some idiots are creative).

The problem is this: If you begin pre-mixing or otherwise arrange for 2-cycle oil to be used to lube your apex seals it will not only burn cleaner, it will also loosen the accumulated crud left behind by years of 4-cycle engine oil fed to the apex seals via the metering pump, which could clog your pre-cats. The expensive main cat doesn't clog because the pre-cats catch most of the crud. But the restriction in your exhaust will cause excessive heat upstream of the exhaust manifold which could do serious damage to the engine.

Best route is to first do an ATF treatment to the engine to loosen the built-up crud in the seals, then disconnect the exhaust and run the engine until the humongous cloud of smoke goes away. This will be very loud and smoky, but that smoke is a combination of burning ATF and contaminants exiting your engine. (You'll want to do a search on ATF treatments). Then simply reconnect the exhaust and run pre-mix--- it will have less clogging effect than the system that is stock on these engines.

The good news is that the pre-cats can be removed and then the crud can be cleaned out of them, after which they are re-installed. Mechanics have for years sold expensive main cats to unsuspecting customers on the premise that the main cat was "clogged", and then ripped the old cat apart for the precious metals inside.

The stock omp works fine, and a well-maintained engine will still last upwards of 150,000 miles. But that same engine running pre-mix or 2-cycle oil fed to the metering pump instead of 4-cycle oil will last up to 250,000 or even 300,000 miles given the same degree of proper care and feeding. The 2-cycle oil prevents apex and side seals from the type of clogging that causes loss of compression and engine destruction due to the resultant apex seal failure. Instead, the seals float freely on their springs, providing good compression and wear characteristics. It also greatly reduced the carbon build-up on the rotors. This carbon build-up causes pre-ignition, which destroys engines. The less build-up, the better.

These alternate methods are used in the racing community and by those who typically run their cars very hard. But they are also used by guys like me, who drive in a sane manner and know what it takes to make an every-day use engine last. Do a search on pre-mix systems, ATF treatments and on metering pump adapters. There's gobs of info on these threads.

trochoid

iTrader: (6)

There is NO timing chain. The timing is gear driven off of the e-shaft. The oil pump is chain driven, by a seperate gear, located behind the timing GEAR.

Aviator 902S

All true. And a sure sign of a half-assed engine rebuild is a oil pump drive chain that has more than 1/2 inch of slack in it. This would indicate that the rebuilder didn't bother to change it out and likely left worn thrust bearings in there too. But you'd have to pull the distributor (or crank-angle sensor) and go in with a borescope to confirm this.

rustnrot

I got two 12A MOP (Metering Oil Pumps) or OMP (Oil Metering Pumps)--you pick which verbage you like best, both the same thing--at the junkyard to take apart and look at.

I know there is a spacer that you can get that blocks the oil from the engine and has a fitting that allows oil in a new separate container to flow into the MOP (OMP) here http://www.rotaryaviation.com/oil_in...p_adaptors.htm.

What I would like to know is this---has anyone modified a 12A pump with a fitting and (appropriate block off) functionally the same as the $76 spacer (to be fair quite a nice piece of engineering for the price, really). I did find a thread here https://www.rx7club.com/forum/showth...ight=omp+drill installing a fitting and blocking off a 13B pump (poor quality photos I found hard to follow). The 12A pump is different so I was wondering if any of you Science Fair winners out there had done this mod?

Aviator 902S

I've been running that exact $76 unit in my stock '85 GSL 12A for two years now with excellent results. These adapters not only act as a block-off plate and provide a means of delivering the 2-cycle oil from the reservior to the omp, they also contain a small hardened steel drive shaft to complete the link from the engine to the stock metering pump so that this oil can be metered in the usual manner.

Any bock-off plate inserted between the pump and the engine would have to be thin enough that the pump's drive shaft would still remain in contact with the engine's drive unit. You'd then have to tap into the pump body to the main oil metering orfice where the engine oil enters the pump and thread a fitting into the tapped hole. Sounds like a relatively easy and not-too-time-consuming task. Just make sure your mounting bolts are long enough to accomodate the block-off plate or better yet, just JB Weld the hole in the pump where the oil enters from the engine and then tap into the passage downstream of the JB Weld. No block-off plate necessary.

Making one of these rotaryaviation-style adapters on a lathe and milling machine would likely take considerable time and money, rendering the do-it-yourself route more bother than it's worth. You'd have to source out and purchase the raw materials, measure the distances and positioning of all components, set up the machines to perform the machining and then finally make the part. This could consume an entire day--- not worth it to save a measily $76 IMHO.

I've posted at least a couple threads on this mod titled "Metering pump adaptor" or something along those lines. If you can dredge those up you'll find answers to any and all questions on the subject.