Budget 12A SP build

[t_g_farrell]

I'm working on building up an aggressive street ported 12a to replace my
current stock port. The current engine is very strong and still has a lot of
life left in it and I intend to use it in another project.

What I have are 2 engines I've purchased over the past 2 years. The first
is a 12a that was rebuilt with a full Atkins Kit C for 75 bucks. This engine
died swallowing a bolt. You can actually see the bolt threads on the exhaust
port as it exited. Very entertaining, I'll get pics for you later. Anyway, for
the money and if it had been built with a full Atkins kit C then its well worth
it. The second engine is a original 12a that was just plain worn out
and had little compression in the rear rotor.

We will call the first engine A and the second B. Engine A I purchased for
$75.00 and engine B I got for $50.00. Since this is a budget build my goal
is to do a SP 12A for just a few hundred. So far I've got $125.00 into it.
I expect a soft seal kit to be about $120.00 and then I may need to get
few hard seals here and there. For porting I have some folks I can borrow
or make templates from. Might get this done for less than $300.00, actually
I have to because otherwise my wife will notice :D

So the the A engine looks like it really has all the new stuff from an Atkins
kit C. The apex seals are all like new as are most of the side seals. I'm still
disassembling it but I have to think I can save some coin reusing a bunch
of this stuff. The rear rotor is toast as it got beat pretty badly as it
moved that bolt thru its rotation. When I got the engine the rear rotor was
full of coolant. I flushed it with oil and wd40 and spun it with a my impact
when I first got it to flush it all out. Surprisingly the rear housing has no
big gouges or scores in it. I have to clean it up and measure it to make
sure its good still but it looks pretty good. The front housing and rotor are
in great shape. Reusable for sure. Too bad the rear rotor is trash because
I think this is an 83 rotating assembly.

The B engine is beat. All the seals are I'm sure out of spec and all the springs
are pretty beat as well. The good news is that its an 80 12a. I like this
because I want to use the side plates. Also the rotating assembly is in
good shape. The bearings are worn but just showing a lot of copper, no
scratches or weird wear marks on the eshaft.

So my plan is to use the rotating assembly from the B engine along with its
side plates and use the housings from the A engine as they have no flaking.

So heres some of my questions. I will be measuring all clearances and so
forth to make sure any reused pieces are in spec. I would like to try to
reuse as much of the hard seals from the A engine as possible because
that engine really wasn't run enough to even break in the engine. It sucked
down a bolt and blew its coolant seal shortly after being installed.

1. Can I reuse the apex seals given they meet spec?

2. Should I reuse springs? They all seem like new.

3. Most of the side seals came out intact. Use em?

4. The oil control rings on the rotors came out with no problem. Reuse?

5. The corner seals are mostly good. Reuse?

6. Can I pull the bearings from the A rotors and reuse them? They look
brand new, no copper at all!

7. Where the bolt went thru the exhaust port theres a gouge. I'll have to get
a picture up of that but I'm thinking the street port of the exhaust may take
care of it.

I will of course get a complete soft seal rebuild kit for the rebuild.

I know this thread is useless without pics. I'll get some I promise. I have to
clean things up this weekend and then take the pics.

[NoDOHC]

1. Can I reuse the apex seals given they meet spec?

Yes, but I don't like 3-piece seals. For the cost of new ones, reusing seems like a good idea. Be careful that the seals are not warped.

2. Should I reuse springs? They all seem like new.

I never had any trouble reusing springs, look at the apex seals springs closely, they wear on the ends and it is not always obvious.

3. Most of the side seals came out intact. Use em?

If they didn't get bent while removing (bends the weak direction are ok, but not in the strong direction - it will hurt the sealing surface).

4. The oil control rings on the rotors came out with no problem. Reuse?

Check how much of the edge is shiny (I think there is a spec in the FSM). Replace the O-rings for sure.

5. The corner seals are mostly good. Reuse?

There is no reason to replace good corner seals, just make sure that they aren't cracked.

6. Can I pull the bearings from the A rotors and reuse them? They look
brand new, no copper at all!

That depends on how they fit the eccentric shaft. you will have to mic them and verify that the oil film thickness is within spec. You will want to be ultra careful when pressing them out to keep them straight so that they don't deform.

7. Where the bolt went thru the exhaust port theres a gouge. I'll have to get
a picture up of that but I'm thinking the street port of the exhaust may take
care of it.

Up to you, I was told my a good friend whose porting ability I respect that if you think that bigger is always better - leave the exhaust port alone.

I will of course get a complete soft seal rebuild kit for the rebuild.

I know this thread is useless without pics. I'll get some I promise. I have to
clean things up this weekend and then take the pics.

Cool, please do.

[t_g_farrell]

Wow! Quick reply. Thanks.

These are 2 peice seals so, all good except one of the small corner pieces
is broken.

So the oil control rings are not shiny at all and I assume that means they
are fairly new and reusable?

Is there an easy or trick way to push out the bearings from the rotor? I have
a large tool for pressing out various sized ball joints for trucks maybe I can
use that. Maybe some heat would help as well.

On the porting, I also think bigger is not always better but most of the
SP exhaust looked they would cover this area. Need pics for sure so you
all can advise me on that. I think I'll do the porting but haven't decided
yet.

[t_g_farrell]

I think I may use the A engine eshaft since the bearings are already matched
to that eshaft. I just have to get them pressed out carefully so I can reuse
them in the B engine rotors. The A engine rear rotor is toast and I'm having to
work pretty hard to get the hard seals all out. Mostly due to the rust that
formed when it sat with the coolant in it.

[t_g_farrell]

How do most folks get the bearings out of the rotors?

Favorite DIY methods or tools?

I know I can take them somewhere and have them pressed out but if I
can, I want to do it myself. More fun for me :D

[NoDOHC]

Atkins sells a kit for use in a standard press. That is what I use.

Please check everything for tolerances, you will thank yourself later.

Bearings are like $30.00 new (for 2) I think I would go that route, the chance of damaging them removing them is not entirely remote.

There should be a small ring around the metal part of the oil control ring that rides on the plate. I would expect this to be shiny (unless it rusted in the coolant).

If a seal is questionable, do yourself a favor and replace it. Better 1 seal than the whole rotor assembly.

How not to port exhaust (note many changes in taper angle and flow restrictions, early open and late close). Made 255 WHp at 10 psi.
http://i594.photobucket.com/albums/tt25/NoDOHC/P8310406.jpg

Much prettier exhaust port (consistent, near ideal taper angle, no avoidable flow restrictions, stock open and close timing). Made 216 WHp at 0 psi.
http://i594.photobucket.com/albums/tt25/NoDOHC/PA110558.jpg

[t_g_farrell]

... There should be a small ring around the metal part of the oil control ring that rides on the plate. I would expect this to be shiny (unless it rusted in the coolant).

If a seal is questionable, do yourself a favor and replace it. Better 1 seal than the whole rotor assembly.

Your referring to the 2 oil control rings on each side of the rotors right?
I'll be getting a full soft seal kit so I expect that will include the o-rings for the
oil control seals. The A engine oil control seals look brand new, no shiny area
at all. The B ones definitely look older and worn and are shiny about half way
across, probably out of spec as well.

Turns out I may be able to use the lighter weight rotors from engine A which
already have brand new bearings in them. They look almost new. In fact
everything from engine A is looking better than the B engine. The B engine side
plates have noticable grooves in them from the corner seals. I may use the
A engine front rotor housing instead of the B engine rear rotor housing which
has the chunk chipped out of the exhaust port top opening.

I'm thinking of trying out the Goopy housing resurface service. Its certainly
priced right at $125.00 for a pair.

[t_g_farrell]

Another question. My side housings show a darker coloring at the bottom
from after the spark plug hole over to where the exhaust would exit the rotor
housings? Is this normal? I'm assuming this heat from lean combution but is it
overheating damage? It certainly doesn't look like the typical iron overheat
damage they show on the mazdatrix site:

http://www.mazdatrix.com/pictures/faqpics/sidehsgs/burned.jpg

Otherwise they have almost no step wear, definitely nothing I can feel with
my fingernail. I still have to spec them out to make sure they are flat enough.

I know I need pics. I can probably get them up tonight.

[NoDOHC]

Your referring to the 2 oil control rings on each side of the rotors right?
I'll be getting a full soft seal kit so I expect that will include the o-rings for the
oil control seals. The A engine oil control seals look brand new, no shiny area
at all. The B ones definitely look older and worn and are shiny about half way
across, probably out of spec as well.

Turns out I may be able to use the lighter weight rotors from engine A which
already have brand new bearings in them. They look almost new. In fact
everything from engine A is looking better than the B engine. The B engine side
plates have noticable grooves in them from the corner seals. I may use the
A engine front rotor housing instead of the B engine rear rotor housing which
has the chunk chipped out of the exhaust port top opening.

I'm thinking of trying out the Goopy housing resurface service. Its certainly
priced right at $125.00 for a pair.


At $125 each, I have a few that I might send in myself. It makes even more sense to get 12A housings done as they are getting harder to find.

If there is no shiny place on your oil control rings, they are likely new. It sounds like engine A really was a recent rebuild when it ate the bolt.

Eating bolts is not that uncommon, I have a 90 4-port that ate a bolt (all seals were still ok, rotor and housing = junk).

[t_g_farrell]

Heres the A engine when I got it:

http://lh4.ggpht.com/_yHWw1b7rWdc/TRABLo59Y7I/AAAAAAAAAf0/KRj6R1ZZ3Io/s640/IMG_0012.JPG

This is what all the oil control rings looked like.

http://lh6.ggpht.com/_yHWw1b7rWdc/TRABL-u224I/AAAAAAAAAf4/EEBbAy0F_xI/s640/IMG_7933.JPG

The rotor bearings (like new, mostly silver with a touch of copper at the seams)

http://lh4.ggpht.com/_yHWw1b7rWdc/TRABMENzAfI/AAAAAAAAAf8/TEebP6tfkTU/s640/IMG_7936.JPG

The damage the bolt did to the rear housing as it left the exhaust. I'm thinking
porting will take care of it. If not I'll use one of the other housings from engine B.

http://lh5.ggpht.com/_yHWw1b7rWdc/TRABMp6KyaI/AAAAAAAAAgA/agh7zg04uOU/s640/IMG_7938.JPG

The right rotor shows a dent in the top edge of the combustion indent. None
of the apex seals got damaged and none of the apex seal slots looks
damaged. I think I can use the rotor? Opinions? Remember its a budget build.

http://lh6.ggpht.com/_yHWw1b7rWdc/TRABM3dS53I/AAAAAAAAAgE/dKVnkDlOx38/s640/IMG_7940.JPG

[t_g_farrell]

I think I should explain the goals of this build. I call it a budget build because I
don't want to sink a lot of money into my 1st rebuild. This is a learning exercise
for me and if it works well when I'm done great. If it blows up in a year,
no biggie. Normally, if I was doing a full rebuild like this it would be with near
perfect parts and all new hard and soft seals and springs. My next rebuild
(see I know there will be another) will be of much higher quality.

The other thing going on with this is that the engine its replacing in my SA,
I will be keeping for another project. The current ignition, intake and exhaust
can all be reused with this rebuild. Just some small jetting changes for the
Dellorto. If the engines blows, I can just swap the stock port back in. I like
doing it like this because it will keep a lot of unknowns out of the equation while
I try to get my rebuild started and running the first time. Baby steps. Gotta
walk before you run.

[NoDOHC]

Those pictures reminded me, you have to keep the rotors separate on a 12A (they are different). I had forgotten that.

Let me put the porting to you this way, you can always take more out later. You can't easily add it back. Small porting is your friend.

Intake port cross section should not exceed cross section of intake runner feeding it.

Later close is only better if it greatly improves flow, don't dig a corner upwards just to match the majority of porting templates on the market today. I prefer the port to follow the shape of the rotor (quicker close = optimum dynamic charging, maximum port area without expense of compression displacement).

Exhaust port should increase in cross-sectional area.

[t_g_farrell]

Excellent advice on the porting. I'll definitely keep it in mind when planning the
ports. Since I'm using the later 12a irons I do get a little larger intake runner
size.

I still have to decide which housings to use. First I have to get everything
all cleaned up and measured to see what parts are even good:)

[t_g_farrell]

Not much new to report yet. I've been cleaning rotors, housings and irons.
I think I can reuse the dented rotor. It seems fine other than the dent near
the combustion indent. I was able to get all the side seals out of it and the
rest of the rotor appears fine.

I think most of the A engine can be reused except for the rear iron. I think
the rear iron from the B engine is actually in better shape. There is some
mild stepping at the spark plug side but I'm thinking it will be in spec. I have
yet to get some feeler guages for thousandths of an inch. The A engine irons
are all Ys whereas the B engine irons are Rs. Is it ok to use the R iron with
the other Y irons? Now that I cleaned em up I don't see huge differences
between them.

The stationary bearings don't look new like the rotor bearings. Some copper
showing on the lower part of the bearing and at the seams. They don't look
that much different from the ones in the B engine, which had a lot of hard
miles on it. Thinking I may need to change those out.

I pulled the e-shaft oil jets and they had disintegrated o-rings in them. I
think I can safely say those were never replaced.

I'm thinking about doing the oil pressure mod to the regulator where you
mash down the tip to get it to about 90 psi and shim the front one. This
will be a SP with spirited driving and some track days. Is it worth it? I don't
think I need to do anything with the e-shaft jets other than new o-rings.
I can't see having extra pressure being a problem as long as my lines and
cooler can handle it.

[NoDOHC]

If the dent has not deformed any seal grooves, the only thing that you need to worry about is the balance. That will probably be fine, as street ported engines don't typically make much power over 8,000 rpm anyway.

As to the oil mod - I have never done it, and to my understanding it is intended for high rpm operation. Your street port will not be likely to operate much outside the standard rev range, so I don't know that it is necessary. As I said, I have not done it and have never had bearing trouble from overrevving (redline at 9,000).

As I said before, check tolerances on everything, the FSM is an excellent resource.

[rxtasy3]

tim, the wear on the oil control rings look really good, can reuse. if u reuse all the seals and springs associated with the rotors, they all should remain with/be put back where they came from. good luck with ur first build and hope it turns out to be a good running/long lasting engine. i myself only have 2 builds(same engine) under my belt and hoping to do more in the near future. so far have bout 80k on the 2nd build.

[t_g_farrell]

Micheal thanks for the comment on the oil control rings. Unfortunatley I
didn't keep the parts sorted as to what rotor they belonged to because I
thought I wouldn't be able to use the original rotors :banghead: Now it
looks like the original, lighter rotors can be used. I'll just make sure
everything is within tolerances when I put it back or replace it. The hard
parts are all so new that none of them show any wear at all. Especially
when compared to the other engine I tore down which was beat to death.

I think I'm going to do the street port by porting the secondaries fairly
aggressively and leaving the primaries pretty much stock except for
smoothing the area near the edges of the port openings a bit for better
flow. I've been doing a lot of reading on nopistons which has been very
educational. I want to maintian as much of my low end as I can but get
a good bump in hp once I hit the higher rev ranges. The exhaust ports
haven't decided on yet but I'm still reading.

Heres one question on the exhaust porting. Do you port the inserts at all or
just get close the edges of the end of the insert and shape it out from there?

[NoDOHC]

I usually pound them up as much as possible with a punch and hammer (until they are tight against the housing) and then polish them to 600 grit or so (minimizes radiative heat transfer from exhaust gasses, improves flow, makes slightly louder).

Constantly increasing cross-section is your friend for the exhaust.

For the intake, don't bring the port up any more than you absolutely have to if you intend to keep some semblence of low end. Raising the far edge (furthest from the housing) gives much greater performance improvements than raising the near edge and you can raise the far edge quite a bit without changing the port timing.

[t_g_farrell]

So are you saying for the exhaust you want a megaphone or cone shape with
no bump or waist in the middle? In other words you don't want anything thats
like a venturi on the exhaust.

It looks to me like if you follow the angle and contours of the stock insert
and carry that onto the housing as you port you end up with the classic
D shaped exhaust port. Good idea ?