Yippie, New Rotor Hou$ing$!... Maybe NOT
08-15-17, 01:21 PM
#1
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
Yippie, New Rotor Hou$ing$!... Maybe NOT
brand new rotor housings out of the Mazda box. awesome foundation for a premium higher power build...
well, one of them is although it takes two.
the first item on my 6 page Spec Sheet generated for incoming motors and outgoing builds is... rotor housing width.
our motors are pretty weird as the top of them is relatively cold (incoming charge air) and the bottom is hot. the poor old aluminum housing has to deal w both and maintain clearances.
aluminum is HIGHLY sensitive to heat.
eventually warpage occurs. Mazda requires builders to measure the housing at the top and 3 spots near the lower plug.
more than .0024 diff and the housing will often give up the outer coolant seal under load.
i measure everything, including new housings, especially when they are going in a balanced clearanced new rotor higher power motor. actually though, i measure all housings.
so what do i find? one of the new housings is .002375!
the cutoff on rebuild motors is .0024 and i am starting out at the cutoff?
not really so back it goes to Mazda and just a heads up to all of you to check housing width.
a couple of other measuring stories...
conventional wisdom is you can use rotors marked one letter apart.
i recently weighed two rotors that were one letter apart and they were 65 grams from each other. i never look at letters... they go on the scale and anything approaching over 40 gets retuned.
finally, how about the "Rotor Land Protection" spec? yes, there really is one and it surfaced and bit one of my motors/customers and provided another learning experience. i bought a set of rotors for a customer motor that spec'd out fine. i did notice a bit more thrust width to rotor housing clearance but it was on spec for a race clearance. eventually the customer had an engine problem... after taking a closer look at the rotors i found they had contacted the side irons.
as you may know the thrust surface touches the side irons but the rotor side face does not. it is "protected" by the thrust ring and the measurement is around .009 the failed rotors were around .003.
it appears someone skinnied the thrust width but did not skinny the rotor width.
08-15-17, 03:15 PM
#2
Please excuse my skepticism, but, how do you explain these rotor housing dimensions? I'm sure your answer is I dunno, but based on the machining process it's difficult to understand how this could happen unless the upper and lower housing faces are not parallel. I'd take additional measurements at 3, 6, and 9 o'clock positions and try to develop some reasoning behind this odd measurement.
08-15-17, 03:56 PM
#3
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
the measurements are what they are and i really don't care about the how. the fact is the housing is already over .002+ off. it doesn't make any diff what any other widths are on the housing.
and, yes, it is weird for new to be not on spec and that is why i posted it. if you are working w new housings spend some time w your micrometer.
and, yes, it is weird for new to be not on spec and that is why i posted it. if you are working w new housings spend some time w your micrometer.
Last edited by Howard Coleman; 08-15-17 at 03:58 PM.
08-15-17, 09:26 PM
#4
Old [Sch|F]ool
NEW stands for Never Ever Worked!
Oddly enough while I do measure rotor housings so I can accurately adjust apex seal length, I have never encountered one that had more than .0005" variance.
Oddly enough while I do measure rotor housings so I can accurately adjust apex seal length, I have never encountered one that had more than .0005" variance.