<... I can imagine that this back and forth hammering would tend to open up the slot ... what causes this to be worse in some engines than others ... Lynn, Leon, do you see this in racing engines?

Perhaps we should entertain the notion that we're plowing new ground here.  Rusty and Ed got what - 100 hrs or so?  Rusty's seals were worn, the slots wallowed out beyond specs, Ed's slots wallowed out beyond specs, etc.  Granted  both engines were built from cores, but didn't both have a pretty good handle on "where those things had been"?  40k - 50k mi in a car shouldn't do much anyway. 

So we're banging up these slots and seals in 100 hrs of really hard usage.  How long is a racing season?  Maybe 100 hrs or so counting qualifying and everything?  Then what?  A new engine?  A "soft" rebuild like most of us seem to be doing?  Lynn?  Leon? 

Is it possible we're hitting a wall that Mazda perhaps knew about all along but had no reason to discuss at any length because nobody was apt to get there.  We do seem, after all, to be asking more from these engines than even the racers.

Does this make sense at all? ... Jim S.


Russell Duffy wrote:

Hi Jim,

 

First, Tracy's/Bruce's new seals are certainly available in 3mm, and at the same price of the 2mm seals.   From what I've understood (or thought I did), the 2mm seals actually "seal" better than the 3mm seals.  For a street engine, (idle, emissions, etc) that's clearly better, or Mazda wouldn't have changed to them in 86 (I think).  I don't think there's anything really wrong with running 3mm seals if you want to.

 

I'm more interested in what causes the slots to open up.  If Bruce is correct, and they're just bent outward, then I guess the force of combustion is causing this???  Imagine when the plug fires, there's a huge force created.  That force would push outward on the two apex seals that border that particular rotor face.  When the next face fires, the seal that was previously forced backwards, is now forced forward.  I can imagine that this back and forth hammering would tend to open up the slot.   I guess the real question is what causes this to be worse in some engines than others.  The obvious answer would be that it's worse in engines that produce lots of power, for long periods of time. 

 

Lynn, Leon, do you see this in racing engines?

 

If all the above is true, then I can also see far more stress being put on the seals as the slot widens.  Imagine the seals slapping back and forth rapidly.  What happens if a tiny bit of carbon, sand, etc manages to get in the apex slot, and then the seal is slammed into it.  Wouldn't that offer the opportunity to snap a brittle seal?  

 

To add to this SWAGing, I would also like to mention that Ed is not alone with his observation of excessive wear on Hurley seals.  My engine probably had 80 total hours on it before the oil cooler incident, and there's a remarkable amount of wear on the sides of my seals.  These were in new rotors, and the apex slots are still at new specs, so it wasn't caused by out of spec slots.  Leon may have a point about dust in this case, since I didn't run with a filter, and half of my running time was on the ground.  

 

At some point, I'm going to measure one of the old Hurley seals to see just how much of a groove was worn in them.  Just from looking at them, I can tell that it's much more wear than the Mazda seals in the old (??? miles) engine in the box in the garage.  Suffice to say that I'm happy that I have the new seals in my current engine.    

 

Cheers,

Rusty (firewire hard drives biting the dust left and right...)