Hi, last month when i opened my 20B i have never noticed 2 tubular dowel have smaller size at one end. All other tubular dowel have same size at each end, but this 2 dowel have .005" smaller at one end. I checked all hole and no smaller (same size for all hole).
Now, i don't know where i put this 2 tubular dowel with different size at one end.
Thanks for your help.

 

anyone

 

[QUOTE .......... All other tubular dowel have same size at each end, but this 2 dowel have .005" smaller at one end.

Yes,
These dowel pins are used on Rotor 1, & 3 upper pin position. To allow some "give" at the front & rear steel plates to prevent possibility of craking the plates in the event of pre-ignition.
When Detonation or heat induced Pre-ignition occurs, compresion pressures are violently elevated.
When the rotor reaches "Peak Pressure" at about crank angle 126* BTDC., the forces genereted propogate in the direction of the upper dowel pin.
These forces are generated outwardly through the Rotor Housing toward this dowel pin. This violent raise in presure, (a shock wave) passes through the Rotor Housing, and impacts the dowel, like a sledge hamer from the inside out, the Aluminum Housing gives, but the HARDENED STEEL Dowel does NOT.
When this occurs, knock shocks are generated, and the Dowel absorves the waves. Forcing it to momentaraly move.
This slight movement, or vibration causes the front, or rear steel plates to break or crack arround this area.

The slight reduction in the OD of the Dowel's in the area were they penetrate the steel plates, allows enough clearance, so when Detenation occurs, the shock induced movement of the Dowels, doesn't take the steel plates with it.

 

that's odd, these step pins were only on the front rotor on the ones i have seen.
reason: i was told, they allow for the front iron and rotor housing to align via the e shaft
which is supported in the thick iron, without the step pins a possible misalignment could
put a side force on the e shaft.
with a 2 rotor this is not a problem because there are only two bearings holding the e shaft
unlike the 3 bearings in the 3 rotor.
god did that make a bit of sense?
matt

 

All 3 rotor have this step pin?
If yes, i don't understand why nobody ask this question before.

 

all but the very late build ones
and this has been asked before
matt

 

Wow this is great info. I wonder how many builders have rebuit these engines not knowing this info especially since there isn't an english language version of the factory shop manual?

 

No just the front and rear rotor based on GT1-20b's reply

 

Uh, now (I think) asked this like last year...
Where have you been?


-Ted

 

and its not 1 and 3 it is front only
matt

 

I knew where these pins when i was unsure as to why, some builders say
to put unsteped pins in their place, I feel they are there for a reason and
think they should be used where mazda put them.
matt