Hey Watson, I've got it! What do you have Sir? I have THE reason for essentially all the "random" engine failures. The key bit of info is the clutch pulsing. This ALSO explains why the BSD seems to have a longevity effect on the engine. Mazda has/had a problem with the thrust bearing clearances in their early series of 1.8 liter engines in the Miata. No BS in those motors, but the SAME type catastrophic engine failures resulting from excessive crankshaft end-play.
Ok, here's my theory and rationale:
The main culprit in these failures is the crankshaft thrust bearing. The thrust bearing is loaded heavily in the DISI turbo MZR from the BS angle-cut drive gears AND the HD clutch required to hold 280 lbft of torque against the AWD system and 3500 lb car. As such the thrust bearing wears, allowing excessive crankshaft end play and resulting side loads on the HEAVILY stressed connecting rods. A bit too much thrust bearing wear = too much side load on the con rod and Zoom, Zoom, BOOM, rod (pick one) and/or piston collapses from the off-center load and there you have it. Explains everything! Even why some new cars GO and some BLOW for no "apparent" reason.
I say EVERYONE concerned about their engine should check the crankshaft end-play per the FSM and see what they have. I don't have the reference right now, but it is a few thousandths of an inch. It COULD be another series of engines have the "incorrect" thrust bearing clearances at initial assembly.
ALL the failed engines to date can be checked for this clearance before the crankshaft is removed. I would wager that Mazda Japan already knows about this! The Miata crowd is very diverse and pursued their engine failures up through MNAO and got results. I should have checked mine when I had the pan off recently, but wasn't even thinking about it. I'll be checking it real soon though. It can be checked externally without removing the pan.
I also recommend jumpering the clutch switch so you can start the car WITHOUT pushing in the clutch. I have ALL my manual trans cars jumpered....
Ok, here's my theory and rationale:
The main culprit in these failures is the crankshaft thrust bearing. The thrust bearing is loaded heavily in the DISI turbo MZR from the BS angle-cut drive gears AND the HD clutch required to hold 280 lbft of torque against the AWD system and 3500 lb car. As such the thrust bearing wears, allowing excessive crankshaft end play and resulting side loads on the HEAVILY stressed connecting rods. A bit too much thrust bearing wear = too much side load on the con rod and Zoom, Zoom, BOOM, rod (pick one) and/or piston collapses from the off-center load and there you have it. Explains everything! Even why some new cars GO and some BLOW for no "apparent" reason.
I say EVERYONE concerned about their engine should check the crankshaft end-play per the FSM and see what they have. I don't have the reference right now, but it is a few thousandths of an inch. It COULD be another series of engines have the "incorrect" thrust bearing clearances at initial assembly.
ALL the failed engines to date can be checked for this clearance before the crankshaft is removed. I would wager that Mazda Japan already knows about this! The Miata crowd is very diverse and pursued their engine failures up through MNAO and got results. I should have checked mine when I had the pan off recently, but wasn't even thinking about it. I'll be checking it real soon though. It can be checked externally without removing the pan.
I also recommend jumpering the clutch switch so you can start the car WITHOUT pushing in the clutch. I have ALL my manual trans cars jumpered....
