FC_fan

iTrader: (2)

I have a disassembled t2 motor. I got it disassembled because the motor had blown out a peice of the metal water jacket area on one iron. anyway, one rotor definitely looks newer then the other. the newer one has what looks like very fine machined grooves all over the combustion faces and the other rotor does not. Does that mean anything substantial here? are these okay to pair together in a t2 motor (both rotors checked within all clearances and tolerances with a little room to spare)? and is there anyway I can check to make sure they are both t2 rotors and ones not an na or from a 12a or something? thanks, don't mind the surface rust in pics. for some reason it looks one hundred times worse then it is in actuality.

RotaryEvolution

iTrader: (30)

12a rotors won't fit because they're narrower.

typically original T2 motors had a smooth rotor in front and a rough machined face rotor in the rear, don't ask me why this is common but that is how i find most stock T2 motors to be.

just check the stamps to be sure the rotors are within 1 alphabetical letter of each other (ie one rotor stamped with a "c" and one with a "d"). if you want to be sure the rotors are the same compression you can check the depth of the compression pockets on the rotors.

Pele

iTrader: (28)

IIRC, S5 rotors are machined and S4 are cast. Check the weights as well.

http://mazdatrix.com/faq/rotorwgt.htm

RotaryEvolution

iTrader: (30)

the compression pockets are cast faces on the S4 and machined on the S5, similar to the outside faces.

the pictures all show rotor outside faces so i assumed he was talking about the rough milling on the rear rotors as shown in the second picture, which is normal. mazda may have had some underlying reason for building them this way as it is known that the rear rotor runs hotter and is more susceptible to failure during fuel cut situations than the front rotor. but with that said, there is no documentation from mazda about it or its importance so i ignore the differences and have seen no adverse affects from mixing rotors up. even the rotor weights have marginal impacts, i have torn down mazda remans that showed no signs or vibration or bearing wear that had rotors stamped 3 alphabetical letters apart(putting emphasis on the fact that these engines can take severe rotating assembly imbalances in stride).

FC_fan

iTrader: (2)

thanks guys. I never heard of the different finishes on them so wanted to be sure. also didn't realize that measuring the compression pockets would yield any differences between the two, probably should have figured that out. my rotors are actually the same letter so I think I am good. I saw on the pineapple racing site that rotor weight should be within 50 grams of eachother which means one letter grade. I would assume that in the long term, running an assembly with rotors more then one letter apart would lead to premature engine failure. it may run for 100k miles but maybe if the right rotors were used then it would had lasted longer so people should still stick to the one letter grade difference.

thanks for that mazdatrix link btw. one more question: should I have my assembly balanced? right now I am just building a stock s4 t2 using the s5 turbo and manifold. I have not removed the rotor bearings and the eccentric shaft is like new according to the tolerances. I want to try a medium streetport but not sure. I only have one junk iron to practice on and not sure I want to pay someone to do it for me so depends on how well the junk iron comes out I guess. somewhere in the future I plan on upgrading the turbo to something a little bigger but power goals will only be 300-350 rwhp max. so should I have it balanced for these goals? I only ask because mazdatrix says its mainly for high rpm engines or high hp applications.

RotaryEvolution

iTrader: (30)

unless you're shooting for 500+RWHP or an engine that sees over 9500RPMs/~8k sustained RPMs then engine balancing isn't going to gain you any real noticable benefits aside from slightly less bearing and iron face wear.

FC_fan

iTrader: (2)

that's what I thought, thanks. car is going to be somewhat daily driven and mostly a drift car but not really for intense competition. my housings are in used but excellent condition, my side irons are in great condition except the front iron. the front iron that came with the engine had a missing section of the water jacket area so I got another one from a member on here that was said to be in great condition. when I got it shipped, it had a 1 cm nic on the face but was within spec as far as depth and usable so I deceided I am still going to use it. maybe the lapping will give it ever so slightly more wiggle room for the tolerances.