1985 13b differences
 

I have located what the owner thinks o be a 1985 Mazda 13b to swap into my sandrail. My question is, what are the differences between the 1985 and 1986 mazda 13b's? I found that compression is the same but the 1985 weighed more, so it revs up slower from what I understand, but are there any other differences I should know about, and would the power be similar ( I will be swapping my Dellorto 48 DHLA and custom exhaust onto it from the blown motor).

The easiest way to compare the two engines is to read through the '86 training manual. The engine section details all of the internal changes that were made.

http://mazdarx7.iougs.com/training.shtml

The major changes include 2mm, 3-piece apex seals (instead of 3mm, 2-piece), lighter rotating assembly, and engine mounting would be from the front cover instead of the center iron. Overall, they're very similar engines, so if both run the same intake/exhaust setup, you can expect similar results.

Thanks for the info, that helps. Are the apex seals in the old ones better since they're thicker and less pieces? Since this will be my 3rd motor going into the buggy I'm really wanting to find something that will last for a while so I can just enjoy it.

How hard is it to rebuild a 13b?

Better in terms of what? Durability or performance, or other...?

In relation to what? To a 12A rotary, or to a reciprocal engine?

I meant in general. I have never rebuilt one but mine is blown and I don't have $3000 sitting around. I have done a lot of work to the car and would like to try this. What special tools would be required?

Answering in a general way, makes it so in a way that requires a very long and complete answer and I don't really have the time for that.
Anyway, I think a good way for you to have an idea of what that is, is to check this topic:
https://www.rx7club.com/new-member-rx-7-technical-256/rotary-idiot-993291/
There you'll find some videos, that show how to rebuild a 12A engine, and some information about the 13B rebuilding process. Rebuilding a 13B is not very different from rebuilding a 12A, and so by watching those videos I think you'll have a good ideia of the work and materials/tools needed for that process.

from what I've found it's not to difficult to rebuild the 13b (I watched Aaron Cake's video on You Tube and it was great), but the kits cost between $500 and $1000 and I was able to pick up this motor for $400 with a distributor with both ignitors, an intake for a holley (that's not for this motor so it'll be going up for sale soon), and some other parts that made it more than worthwhile for me since I found a guy around here looking for blown 13b's to rebuild that paid me $300 for my 2 blown ones so it was pretty much a swap of 2 bad motors for 1 good one.