Early model 4 port 13b, can I use a later model 13b e-shaft?
 

I've got the components a early model N/A 4 port 13B (water control o-rings in the rotor housing) that I'm putting into a 73 RX2. I bought the components from a friend about 12 years ago and have since lost touch with him.

The port is an aggressive street port, "It's about as big as you can get w.o doing a bridge port," so I really want to be able to use it. However, I'm missing the rotors and the e-shaft. I have some early model 13B rotors lined up, but I can't seem to find any info on the interchange of the e-shafts. Everything I've read says they're interchangeable from 86 on-wards, but i'm not seeing anything about interchanging 86 and later e-shafts into a pre 86 motor which is a bummer since I see a ton of later model e-shafts for sale, but I don't see much for the earlier models. Can a late model e-shaft be used in an early model 13B? If so, do I need to do anything special with the counter weights?

Thanks in advance.

i'm using one from 86. also get the thermal pellet from RB or mazdatrix.

100% interchangeable

.. but if you take the 86 onward shaft, you also need the 86 onward front pulley bolt
( and mod or fit thermal pellet delete as hinted above )

no other changes required

if you change the rotors to late rotors
( for less mass and more gear fixing pins, 2mm seals and 0.7mm side seals )
then you need the appropriate front and rear masses

and it is also a good move to delete any chain tensioner ( very early 13b ) and get the short chain and cogs ( and the GSL-SE or s3 12a high volume oil pump )
and mod the rear oil reg for 90- 100 psi ( in lieu of crank jet mods )

these mods will make the NA engine more sustainable, and sweeter at higher revs and HP

so you *can* use the later 13b rotors? My reading suggested that there was a geometry change in the 86 and older rotors that made them not a wise choice in the early 13B rotor housings.
If so, that's great news since it opens up the field of rotors to consider.

Thanks so much for the info. I'll be starting a build thread here shortly if you're interested.

I built an engine for a friends repu and it is an older engine with water seals on rotor housings and it has 87 rotors and counterweights.truck is turbo also and has no issues.

My motor on my car is a old school 13B with gslse rotor and e-shaft. As long as you have the proper balance it shouldn't be a issue.

it is the early rotors in post 86 housings that whack at hi rpms

2mm apex late rotors in early housing may not be exerting the same seal pressure on the housing when at the least perpendicular
but it isnt really an issue especially on NA's

I knew about this and since a thread is started about it,....My set up will be old school 13B housings with S4 NA rotors. It's going to be Semi-PP Bridged fully balanced and will be seeing high rpm's maybe boost later.

Does anyone know how much to take off the face of the rotors?

you dont ..
it is only those making "12C" or "12D" engines that have to take down the face of 12a rotors
.. when used in post 86 13b housings
( i.e using FC or FD plates and the post 86 13b housings taken taken down to 12a width and land for oil O ring machined )

similar for those trying to run GSL-SE or rx4 13b rotors in the post 86 housings

at revs the rotor face will whack on housing face near the narrows

... been there.. took pics..

late rotors in early housings needs no mods

So what you are saying is with the combination of old school 13B housings and post 86 rotors it will automatically be clearanced for high rpm?............and the other way will need the face clearanced.



Thank you for clearing that up for me Iv been very curious about this because iv read that post 86 rotors will whack the old school housings. Wish i could find the thread where i read that and post it's wrong. Looks like the OP may have come across that thread also.

it was always, early rotors in late housings that was the issue

im pretty sure as far back as i remember it was me putting up the warnings.. and the pics
it wasnt till after the fact i found the JHB paper outlining exactly my observations

the engine concerned ( that i took pics of the clash )
was pulled down more than 10 years ago
one of two engines that i pulled in and out of the car ( rx2 ) so i could drive daily and race at the strip mid week

pretty sure i kept one housing for the laughs
and i am absolutely certain it was s4/5 housing and GSL-SE rotors