The 13B Rebuild Chronicles :: Chapter 3 :: Rotor Dry Assembly

15 02 2009

Last week I finally settled on which rotors to use. After purchasing numerous set (on eBay) I finally found one (out of six) that was acceptable for use.

The first two I bought were in rough shape. They had heavy carbon deposits and badly worn bearings.

The second set were the wrong year (and hence the wrong weight and compression ratio). The eBay seller had listed them as 86-88 rotors, which is what I needed (even though my car is an 83 GSE-LE body and engine, the rotating assembly is from an 86-88 13B engine). Upon receipt of the rotors I was excited at first. Taking them out of the box they looked great. Clean and shiny, great looking teeth and bearings. But something was wrong…too shiny. Hmmm. I looked closer and found that the shiny appearance was a result of a textured surface reflecting the light ie. CNC mill lines running the length of the rotor faces. 89_91_Rotor

Up until 88 Mazda cast their rotors. From 1989 onwards they started milling them, so you can easily see the difference in the surface texture (see above photo). What the heck? This guy had sold me the wrong rotors! Pissed me off at first. Then I made lemonade. The 89-91 rotors are lighter weight (about 9.5 lbs compared to around 10 lbs) and higher compression (9.7:1 compression ratio compared to 9.4:1 on mine) and are therefore more valuable as they are a popular performance upgrade on 13B engines.  So, I popped them back on eBay and sold them for a $100 profit, and used the dough to order my third set of rotors.

The third set finally arrived and were gorgeous. Both rotors still had their original gold tone on them, and were in overall close to mint condition.

So, today I then began sizing my new side seals.  I pulled out my set of new Atkins Rotary side seals and set to work.  In order to trim the seals down I got two pieces of fine sand paper (from an orbital sander so they had an adhesive backing) and stuck granite_sanderthem onto a granite slab. I used 150 grit and 220 grit paper. I found that the seals were much longer than needed and would have taken me way too long to trim on the sandpaper, so I took a grinder with a fine grain wheel and inserted it into my bench-mounted vise. I used that to do the bulk of the trimming and them fine-tuned it using the sandpaper.  I trimmed all side seals to between 0.002″ and 0.006″.

Because each side seals is slightly different size, I used two folders to keep track of each rotor and taped each side seal onto them. Here’s how it looked when done.


Grant Boshoff
Thrust Motorsports




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