Anyone ever figure out why Mazda threaded the end of the Bolt so much? It only goes In a fraction of the amount that Is threaded.

 

Old bolts had a shorter threaded section. My two R5 13Bs had different lengths of threading. The short threaded bolts had rotor housings with three aluminum outcroppings around the spark plugs. The longer threaded bolts had semi-circle shrouds like FB 12As, which makes me think it's newer. This phenomena is only on the newer engines.



As to why, I can only guess that it's to try to prevent snapped bolts during high RPM running. Or they could make only one length of bolts and just chop 20mm from the ends for use in 12As (rather unlikely).

 

Do you have a picture of this Ted?