When I dropped the oil pan, there were dozens of little black pebbles on the bottom of the oil pan. All near the oil pickup tube. They sure look like they're made of carbon, and they are light and break apart easily with needle nose pliers.

What in the world caused this?

I'm attaching pics of one rotor as it came out of the engine w/o any cleaning. No pics of the pebbles.

 

I must say, this is an odd one. Parts of the rotor look way too clean. Have you done any engine cleaning lately, Seafoam, etc.? Do you pre-mix? What led you to dropping the oil pan in the first place?

 

'79 or '80 air cleaner assembly? The lid has a charcoal canister.

 

Interesting idea Jeff but how could the charcoal pebbles get into the oil pan? The only path I can see is if they were sucked into the oil fill tube vent.

 

this is a head scratcher. my first thought would be that they're small bits from a dry rotten oil cap...makes me wonder what the oil filter looks like inside as well. i think we need pics of the oil pan and the black pebbles.

 

Just a wild guess; I wonder if it's fallout from some kind of stop-leak or cleaner treatment?

Back in my 73 Satellite, I used to religiously use Pennzoil. When I eventually had cause to open the valve covers, there was a thick layer of crumbly black deposits everywhere that movement or pressure didn't prevent them from bonding. This stuff might be related to that effect.

 

I used seafoam & carb cleaner a LOT and the rear rotorhousing lost a coolant seal. That mighta been the rear rotor getting steam cleaned, don't recall which rotor it was.

1st gen air cannister.

It wasn't plastic from oil cap threads, cap is good.

I did use Amsoil Engine Flush a few times. It's a solvent you put in the oil, run for 10 minutes, then drain.

 

It's from the lid, dude.

 

Why and how Jeff? I don't have any smog equip, no charcoal cannister either. It's the repu motor.

 

I assume this is a 12A? If it was a GSL-SE the oil lines on those go and it could be bits of that line as well. can you verify if the bits look like carbon or rubber.
I've seen chunky buildup like carbon in the oil filler neck that could flake off as well.

 

74 13b with 3b plates and old school MAZDA script rotorhousings. OMP being used.

Black carbon that is brittle. Easily crushed with needle nose pliers. Not plastic which is more pliable but thanks for the info David.

I have an in-line oil filter in the return line (from oil cooler to rear plate) and when I removed and inspected it, it was clean. Years ago when the motor was being broken in, there were little bits of rubber in that filter, presumably from the oil control rings.

 

Can you get pics of these little *****? If you blew a coolant seal they may just be bits of carbon buildup that broke loose. Or perhaps something like that Bardahl's sealant used for radiators.

 

I took 2 pics but deleted them. Oil pan is now sparkling clean. They were just tiny little pebbles that were black and brittle.

I never used a sealer in oil or water systems. Just Amsoil Engine Flush in the oil a few times. Which works great for piston engines, piston motor runs a lot smoother afterwards. But negligible improvement when used with a rotary.

Anyways, I'll put the rotor seals together this weekend and try to have the motor built in the next few weeks.

 

I only mentioned the above because my brother's '78 RX-4 had carbon pellets in the oil pan. They got sucked out of the lid canister, through the intermediate plate nipple and down into the oil pan. Luckily it's soft so any small chunks would have gotten crushed by the oil pump without doing damage.