I pulled a recent racing engine apart (blown front seal) and we found a very odd texture on the rotor housings that I have never seen before, a speckle pattern that is on the surface, almost like the chrome is flaking off or somthing? It was on both housings.

Take a look at these pics:




Housing from a previous engine on the right side to compare surfaces:







Have any of you engine gurus seen this texture before? and/or the cause?

 

Damian i have seen that before in an engine i pulled apart.

Questions
How many miles on engine?
Apex Seals?
OMP or premix?
And what kind of oil has been used to go into the engine for lubricating the rotor housings?

Looks like apexseal wear on the rotor housing. Like it's been sanding down the rotor housing. How does the apex seals look like?

I had that with hurley seals.

JT

 

thats not mazda apex seals for sure...

 

To me it looks like a softer metal welded to the housing surface with heat and friction and smoothed out by being run over with the apex seals.

I once got a little bit of that effect when some aluminum got into the engine from a blown turbo compressor wheel and housing.

My engine survived that, but when taken apart many miles later it looked like that on inside.

 

here is more info:

- 700 to 600 miles, basically break in miles plus a few track sessions
- stock Mazda 2 piece 2mm seals
- no omp, this is 100% premix for racin
- oils are redline, 40w racing for engine and redline 2stroke for premix

I have not seen this on any of our housings before, using the same oils

 

more info:

We just pulled the engine that was in the car as well, same seals, oil, breakin pattern, everything, and the housings looked basicaly perfect... nice and polished and smooth.

This leads me to think that these housings were defective, or sat somewhere or got exposed to somthing, that affected the coating?

thoughts?

 

An interesting side note that may be related:

We noticed that tips of the rotors looked like they were kissing the housings as there were marks and a polished look at the tips, here is a pic of what I mean:



There were not any noticable marks on the housings to suggest the rotors were hitting, however maybe it was just enough to pull metal off the rotors and make this odd texture on the housing surface? ...i am just speculating?

 

I suspect that might be your answer right there...

Are they early rotors in late housings?

 

Attached are a couple of photos of what the rotor housings looked like prior to the "speckling". They were brand-new with zero miles. I don't know what to make of it. I do know for certain that this engine used a 2pc 2mm Mazda apex seal as I'm the guy who did the engine assembly. The odd wear on the housings looks like what I've seen with some aftermarket apex seals. It happened to pair of housings of mine almost 5 years ago. I've never one time seen this with a factory apex seal, though. Also it's using factory apex seal springs. Nothing out of the ordinary on this build.

B

 

They're your grade-A, typical Series 6 FD rotors (with the machined faced; not the cast ones) in new Series 6 rotor housings. What's your idea?

B

 

Early (RX-4/5/1st gen etc) rotors and housing are slightly differently shaped. Most that have mixed and matched say that they have never had a problem, but some with early rotors in lates housings have had rubbing issues, so I have been told...

However, if it's all 3rg gen stuff, it cant be that...

does seem very odd...

 

hmmmm Damian

something thas been hitting the rotor housings that for sure. and the marks on the rotors would sugest that the rotors have hit the rotor housings, or that some kind of material has gotten into the engine.

was the engine loosing compression? was that why you pulled it out?

JT

 

I would say that the softer cast iron from the rotor is probably the softer metal welded to the chrome causing the speckling.

I have never had that kind of direct rotor face to rotor housing contact.

What kind of clearances are you running on your bearings?

Oil pressure?

What are you using for rotor oil cooling jets?
Too big clearance on bearings and too big rotor oil cooling jets could cause lack of oil film for rotor bearings (race rotor oil jets flow LESS than stock to preserve oil pressure for rotor bearings).

When I have over revved it has always been the usual side of the rotor tip contacting the side housing surface- I finally side clearanced the rotor tips on my last engine, though lowered the redline at the same time.

 

hey JT,

we lost a front seal (most likely due to a lean condition we were chasing down on the tuning side and possibly some bad gas), that is why we pulled it apart. As BDC mentioned above, I am pretty sure the rotors and housings were all matching 3rd gen parts, so I am confused on how the rotors could have hot the housings, unless somthing else was wrong that we dont see yet.

 

hey BlueTII,

here is what I typically run on my race engines:

>>What kind of clearances are you running on your bearings?

I usualy run the mazdacomp race rotor bearings (part # 4801-11-111)

>>Oil pressure?

I run the mazdacomp racing high pressure regulators, I think they are 115psi regulators, this compensates (over-compenates really) for race oil jets I use in the e-shaft and deeper grove race rotor bearings.

>>What are you using for rotor oil cooling jets?

mazdacomp racing jets (part # 8553-11-411)

I also use a solid thermal pellet in the front of the e-shaft.

Keep in mind that over the handful of engines we have pulled apart over the last 4 or 5 seasons, we never have seen this, we usualy see very nice surface wear on the housings and seals, and I have kept the lubrication 'system' fairly stable, so I have a hard time pointing to any of those items as the cause... but obvisouly can't rule any of them out yet :-(

 

Cast iron ... softer?

Softer than what? Not steel. not even close. more brittle, yes.

 

Rotors are soft as ****. Best described as ductile cast iron or cast steel. Very soft cast steel. Brinnel one out sometime. They weld fairly easily, which is something that can't be said for cast iron.

 

>>Rotors are soft as ****.

I disagree, based on my experience, f*ck is much softer than rotors, no contest ;-) LOL


I wish there was a way to salvage the rotor housings, those were new housings ;-(

 

LOL, most things are softer than the chrome of the rotor housing that I was referring to. But not a good hard f@#k! That is harder.

Your build sounds great to me too Damian.

So, the sparkly rotor housing and the rotor with wear on it near the rotor tips were from a motor that lost an apex seal.

Perhaps it was bits of apex seal between the rotor and the housing that caused the wear on the rotor face as well as the little scratches seen on one of the rotor housings and then of course the sparkly material on the rotor housing.

I noticed with the new stock 2mm seals that I had to clearance the rotor slots wider to get into the minimum clearance.

If you fail to do this it could cause binding and the apex seal will break lengthwise when the rotor expands with heat and pinches the apex seal preventing it from proper movement.

Hmmm... Were both rotor housings from that engine sparkly or just the one that lost the rotor?

 

The sparkly one was the good housing and the normal looking housing lost the rotor correct?

Also, is that a crack in the chrome above the exhaust port?

 

>>So, the sparkly rotor housing and the rotor with wear on it near the rotor tips were from a motor that lost an apex seal.

Yep.

>>Perhaps it was bits of apex seal between the rotor and the housing that caused the wear on the rotor face as well as the little scratches seen on one of the rotor housings and then of course the sparkly material on the rotor housing.

Both housings had the 'sparkly' thing on them, so it was not related to the apex seal going since the rear seals were all fine, only 1 front seal went, and it was just the tip that broke, very typical style from detonation from running a bit lean, so I do not think it was any clearance issues?

>>The sparkly one was the good housing and the normal looking housing lost the rotor correct?

The sparkly one was from a bran new housing set, in the engine that lost a front seal, but both front and rear housings looked the same, so it was not related to the seal going. The smooth shiny surface housing was from a previous engine to compare against.

>>Also, is that a crack in the chrome above the exhaust port?

Yeah, it maybe, ill take a look at that later this week.

 

Racing Beat says so, but I've put 12A housings up to Series 4 housings and they were identical all the way around.

I get the suspiscion that they were intended to be different, but in actual production there was no change. That or the housings I compared to were early production S4 units that were still built to the old specs.

Having one thing in the docs, one thing in the real world, is not uncommon, since the docs tend to get written well before actual production takes place.

As far as the rotor housings seen here are concerned, it definitely looks like metal transfer has been taking place. How much premix was being used?

 

>>How much premix was being used?

I use 1oz to 1 gal, redline 2 stroke racing oil. I am pretty religious about the premix, always added before the gas goes in, either in the tank or the fuel jugs we use, using the gas to help mix it as the gas goes in. It it possible we missed some premix, however the rest of the surfaces (irons, other seals) all looked very well lubricated....but I can not rule it out as the cause.

 

did you by any chance sand blasted the manifolds or engine parts prior to assembly?

 

nope