I don't think the gear has to back out much at all for it to contact the iron, so unless you used an interferance fit tap, then that might not give you quite enough retention. That said, I don't know how possible it'd be to have any sort of head on the screws, but with a head you could possibly safety-wire them in place.

 

^ That's a good suggestion, but there is no place for a head on the fastened so you'd have to use set screws. If you had a TIG welder, you could make a tiny tig weld between the screw and gear body, but that might crack over time from the vibration.

 

The reason why Racing Beat snaprings the gears instead of threading setscrews into the rollpin holes is because the rollpins have some spring to them, which is why Mazda used rollpins instead of bolts in the first place. The snaprings maintain that "give" while preventing the gear from having any means of escaping.

If you look at the SAE papers, the 9 pin rotors (85 and earlier, 12A for sure anyway) have loading on the stationary gears that goes up astronomically after about 8k, the '86-up 13Bs have 12 roll pins and the loading is MUCH nicer at higher RPM. So gentler loading = better life for the stationaries, and also probably = no need to retain the rotor gears.

At least, that's what I am banking on.

 

SDJ did a motor for me about 10 years back. They countersunk the roll pin holes in the gear, tapped the roll pin holes in the rotors, and then turned down hex heads as much as possible. Seemed to work fine, although one of the screws did become loose on me.

 

Holy crap TonyD89, that's some awesome stuff!!
I love this kind of stuff. Finding out how stuff works, and tearing deeper into things than you're supposed to (all the toys I owned as a kid ended up taken apart at some point )
Also, how did the apex seal groove welding turn out? Could something similar be done to repair rotor faces damaged by broken apex seals (i.e.: grind down any high spots and fill in the gouges)?

 

Thanks, I've done quite a lot of ripping things apart and f***ing with them also.

I think the final welded rotor product turned out pretty good though I have not run it yet.

Here's a quick run down. I don't mind sharing.

I welded on a junk rotor right at the corner seal and then tried to break it off with a screw driver. It broke pretty much like an unwelded one ( I did this also). Since this area is hardened at the factory I also put a drop in the middle of the groove and busted it off, taking a good amount of parent material with it. Neither seemed particularly easy or that, somehow, the area around the weld was significantly weakened (especially at the heat affected/stress area adjacent to the bead). From this I gathered that welding the groove was possible. Then it was just a matter of technique. The thin area over the corner seal is the hardest.


As far as welding the rotor goes, they weld pretty nice. But then again I consider myself an accomplished TIG welder. They are cast but weld more like a dirty steel (like hot rolled or structural) than what we would consider cast iron. They form a chip when machined instead of just a powder (like cast iron) also. I believe they are some sort of ductile cast iron/steel because they will deform, dent, and bend unlike cast iron yet have enough carbon for induction hardening at the corner seal. They are incredibly soft when checked on a Rockwell tester. I used a maraging rod whose best benefit is welding dissimilar metals and freezes off around 30 Rc., has carbon, and can be nitrided.

I roughed the groove back in using a 1/16" end mill in a Bridge port manual milling machine after centering on the corner seal bore. I then finish ground them in a surface grinder using a thinned down wheel. I also surface ground the weld to blend on the sides. I then used the ol' fake-o-metric (hand work, grind) to blend to the faces. I thought they came out really good.


A guy could probably fix damage elsewhere if needed. Just inspect well. I had one junk rotor that had a perfect impression of one of the long pieces of a factory three piece seal on its face but the real damage was seen when a simple scale was placed across the face. It only touched at he two sides and was incredibly dished around the seal imprint. If you look back at the junk rotor pics I posted you can see how I pried a side seal out because it was pinched in due to blown apex seal damage to the face.

 

I also have TIG welded apex seal slots to repair them in the past, seriously damaged slots from broken apex seals. A bit of pre-heat and some high nickel filler wire and you can't go wrong. Mill the slots to 3mm and you'd never know. I've also TIG'd gouged rotor faces then ground them smooth. The first rotor I repaired was about 3 years ago and as far as I know is still running fine in an FD.

Apparently the rotors are nodular iron. They are nicer to weld than the side irons.

 

Yeah, the rotors seem to be more "cast steel" than "cast iron".

From my experience, anything that dents before it breaks is probably weldable without the usual iron tricks.

 

I am intrested in this tool

 

unless you have rotors with the early 9-pin gear, then why?
.

 

I made it.