Hi everyone,
I received an engine & transmission from Texas, they stated that it was able to rotate a few weeks ago! $1500 and a month later I got a frozen piece of crap that has been sitting outside in the Texas heat for decades! Oh well!
This throttle body was all locked up. I could not even rotate any of the throttle plates! I soaked the pivot points with WD-40 and slowly loosened the stuck parts. Now that I reached a point where things were moving again, I decided to learn all I could about these parts. So, I took this throttle body to pieces and will refurbish all the parts to get a functional throttle body and be able to adjust all the settings there are.

Here is the first picture, the bare throttle body after sandblasting.


throttle body after sandblasting

My first thing to do is to polish the bores with very fine polishing papers in the range of 600 grit and up.

Notice that there are what seems to be two O-rings side by side in each of the brass shaft bearings. I hesitate to try to remove them, I will protect them in place as I go forward.

My first question is about the small orifice at the top of the primary bore, it goes to the opening in the center between the primary and secondary bores. It sits just behind the primary plate when it is fully closed. Is it an air bleed or vacuum port?

Any info will help.

 

My next step is to find out the screw sizes used on the throttle body.
Here are two pictures of both sides:




This is the list of sizes, and the number needed:

M4x.7x10mm (1)
M5x.8 (5)
M6x1.0x10mm (2)

The thread length of the M5 screws might vary with the parts being attached. I will make some measurements soon!

I will be replacing the screws with SS bolts, either hex head or Allen cap bolts if they fit. That will look very nice.

 

I have picked a color and ordered it from eBay.


the reason for my choice is that I have a tricked out radiator cap in the same color and was looking for something to make it kinda blend in!


Say hi to the people out there Rex! Come on, don't go all shy on me now.

 

In my haste after the paint arrived, I proceeded to apply the base coat without masking off the bearings and shaft on the throttle body!

Also, I applied the base coat too heavily, resulting in drips and sags! I know better than to do that.


Top

first side

second side

After touchup

Before I applied the base coat I filed and sanded the mold lines off.
Spray paint does not like sharp edges and corners, these are the first areas for the paint to fail over time since they are the thinnest parts of the coating
So, I broke the sharp edges as I got rid of the other defects on the casting.

Now I will wait a couple of days to allow the base coat to cure, then start applying the topcoats in a much less aggressive manner!
If you think that there is not enough paint being applied, that is the correct amount of paint! Multiple light coats, please!

I will thread the screws into all of the used holes to remove some of the paint that got into them.

This base coat is very metallic looking, and it is necessary for the final anodized appearance. Cost for a can of each: $43
Pricey but worth it for something out of the ordinary!

 

Hi again,
Here is a problem that you might have with manifold vacuum ports!

I got my parts back from my powder coating person, going over it I tried blowing thru the three vacuum ports on the side of the middle manifold.

All three ports were plugged up, not with powder coating but with carbon!

The port that has the right angle to it was a problem to open up.
I tried pushing a Stranded Copper Wire through the obstruction, but it did not go too far after the bend.
I had a thought, yeah, that's rare, so I tried spraying carb cleaner to the port, that didn't go well!
After running my eyeball with water from the kitchen sink, my thought changed.
Now, my bright idea that came next didn't involve squirting carb cleaner in my eye.
Okay, how about putting acetone into the port with a drop on the end of a toothpick, Sounds kinda okay.


Blocked vacuum ports

After adding many drops, I was able to dislodge the deposits and clear out the port.

This port seems to be how the blowby gasses and evap canister get pulled out and added to the intake mixture.

Getting rid of the blowby gasses is important, it is one of the problems with internal combustion engines.
They kind of blow-up if allowed to get built up.

So, try blowing through the two smaller ports, unless you have an automatic, then the large port comes into play.

I am surprised at how many blockages I have come across in my 88 GXL rebuild!

 

Let's move this along,

The two studs that the air inlet tube attaches to with acorn nuts are made of regular steel.
As such, once in contact with the aluminum throttle body the steel reacts with the aluminum and forms a corrosive bond.

After 35 years they get quite frozen!
So here is what I did to get them free.

First, I applied WD-40 for three days in a row.
Added the two jam nuts and tightened them the best I could, open end wrench on the lower nut and a socket on the top nut.
There was a tip about going in the tightening direction first to break the bond. Put a large adjustable wrench on the top nut and hit it smartly with a ball peen hammer!

After the hit i put the same wrench on the lower nut and started hitting it in the other direction, after a few smacks it started to come out.

Here is a picture


The studs came out flawless.


I'm still in the process of cleaning and painting all of the steel linkage parts.
There are some white plastic bushings that the springs go on that are deteriorating due to UV exposure.
Riggs Vintage Mazda is sending me these along with functional diaphragm and thermowax valves.

Remember those O-rings in the throttle body which I was going to leave alone, nyet!
I was able to carefully remove them with a pair of toothpicks. Cleaned them up in mineral spirits and put some silicon grease before re-installing them.
They are not your ordinary O-rings; they have a groove on all FOUR sides. Wonder why?

The O-rings have probably shrunk over the years, there are nylon washers that go first onto the throttle shafts which should help keep any air from entering through the shaft bearings.
I am not going to worry about this.

I mentioned in another thread where my cruise control cable came off and jammed the throttle open. Happened twice, I thought that the cable stretched over time and needed to have the slack adjusted out of it.
On disassembly of the throttle body, I discovered that one of two small springs that are responsible to bring the throttle and cruise control cables back to rest was disconnected!
Without this spring to keep the tension on the cable it allowed the cable to fall out!
Once I removed the spring, I found the hooked end to be bent out of proper shape and it was lacking tension when I hooked it into position.
I found another pair of springs that have a little more tension to them, should fix the problem.

 

I ordered an 8x4x2mm O-ring, but it was too large and would not screw in.

The correct size for this O-ring is: 7mm OD x 4mm ID and is thinner than 2mm!
The space where it sits is 2.36mm wide. Perhaps this extra width it so that the O-ring has space to compress into?

 

Hi
I received the 7mm O-rings, they are thinner than the stock ones. With one installed there was no resistance as I screwed in the needle valve!

There is enough room to add a second O-ring onto the valve, now I felt a proper amount of resistance as I installed it into the throttle body.

So, use two, also my initial setting for the valve is 2 1/2 revolutions up from fully seated.

Here is a picture:

Idle speed adjustment valve

BTY, I put some silicon grease on the rings to keep them from drying out over time.

 

Hi everyone
While searching for some 25mm long Allen cap screws I came across these.




What do you think of these?

 

Hopefully you'll never have to touch it again, but Allen heads on my rx-7 would bother me. One more tool to use. As far as appearance, it's great.

 

Again, you have steel screws into aluminum body for years and they need an impact screwdriver to break them loose.
A 3mm Allan wrench won't strip out so easily and applies more leverage when removing the screws.

So, it's 50%/50% use and appearance. That's a win/win for me!

I have all the bits and pieces ready to re-assemble, just waiting on a working diaphram from Rigg's.
More pictures to follow.

Winter's Coming!!!

 

Yes totally makes sense and looks good, when you sell the car let me know 😂

 

Thanks for the complement, I do have it in my will, going to my Nephew. If he wants it!

I have a lot still to do, now mostly the rotting unibody and the exterior.

Back to business.


Primary throttle valve

The throttle plates have a bevel on the edges going in opposite directions on each one. So, it is important that they are installed in the correct orientation!

On the primary plate the small hole goes towards the bottom, but you can install it with the bevel going in the wrong direction!
Viewed from the back side of the throttle body, the bottom with the hole in it will pivot towards you. The bevel will be on the other side allowing the valve to open like a door without sticking.


secondary throttle parts

The secondaries go together in the same way. Note that the 0.7 stamping on the plates go up and to the front of the throttle body.
I did not keep track of which one went in which bore! I polished the edges and now I see light coming through in various areas around the plates when they are closed.
I am not concerned with this, I did the best I could when installing them.


Throttle plates installed

Remember to put a little thread locker on the screws while installing them!


Primary throttle stop

Here is the set stud for the primary plate, I am going to adjust it so that the instant the throttle plate starts to open I see some light all around the plate.
If it is closed too much, I feel that you will need an extra degree of opening before the plate allows more air through.
So, I will back the stud out until I have just the minimum amount of closure ( no light showing around the plate ).
Then turn the stud in until the amount of light starts to increase. This can only be done with the throttle body removed from the car!
If anyone has more info on this setting, please let me know. I am doing what I consider reasonable.




Here I have pictures of the fast idle cam and follower.

First, I found the cam follower to be frozen with corrosion, using a razor blade and WD-40 it came loose and rotated once again.

I tested the thermo wax in boiling water and it ended up protruding a total of 8mm, so I assuming that it is working correctly.

With a few pieces of the primary throttle plate linkage in place I was able to determine if the fast idle cam was adjusted to the center of the cam follower.
You will see the contact point between the cam and follower, they need to be aligned very well!
I used a magnifying headset for a close look.


diaphragm delay valve

This is out of assembly order, but I have this picture of the delay valve.

Do not confuse this with the check valves used elsewhere on the engine.

The delay valve takes 9 to 15 seconds to release the vacuum on the diaphragm before the No.2 secondary throttle valve is fully closed.

 

My RX-7 rev's up to 3000 RPM every time I start it when cold
Yep, part of the accelerated warm up process. Start the car with the clutch pressed in, and the car in gear if you don't want it to do that.
From IceMark

To me having the cold engine go to 3000 rpms for a few seconds does not shorten the warmup time at all!

I think it is to perform a particular function on a cold start.

I think it might have to do with pulling the vapors from the carbon canister. They accumulate when the car is off, so overnight is when the most vapor is captured.
In the morning upon starting, it revs to 3000 to allow the purge valve a little time to pull the vapor from the charcoal into the engine to be allowed into the primary intake along with any blow-by gases to be burnt as you drive.

At idle, just a small amount of vapor is allowed through. This is because of the Venturi effect on the small hole at the top of the primary throttle bore, just to the back of the plate when it is just slightly closed. Think fast idle cam.

When the rpms go above 2000 the effect is much more vapor is pulled into the dynamic chamber’s primary intake.

I traced the purge valve lines into the throttle body through the black spacer block behind the body.
The bottom of the two small lines which move the vapor end up going into the hole centered on the back of the body between the three throttle plates.
The only thing this hole goes to is the small hole at the top of the primary bore.

I can't figure out how the top port on the purge valve functions when vacuum is applied to the spring and membrane in the valve.
Both small ports on the valve have only pin size holes in them, I am guessing that these restrictions limit the flow of vapors and the pull on the membrane.

All this is just me trying to understand what is going on in the throttle body.

Any comments or corrections are appreciated!

 

I don't know much about all of this so, thanks for the write up.

From what I have read in other posts, at least in part, the accelerated warm up is to start up the catalytic reaction in the exhaust faster.

 

Okay, that sounds right, anything to get the cats working faster is a good thing.

 

I got some of the parts mixed up as I refinished them, so I had to refer to my complete throttle body to complete the assembly.



These are the two small springs the keep some tension on the cable attachment part.
Please note that they are a mirror image of each other and only fit their particular part of the cable attachment!
I will not be showing you where they go yet, I am still waiting on two plastic bushings that go on this shaft.
So this will be an assembly order check only.


Plastic bushing

I am starting with the primary throttle shaft on the thermowax side of the body.
First on the shaft is this thick plastic washer.
You can see how well my $47 paint is holding up!


Cam follower and throttle stop assembly

This goes onto the shaft next; the silver stop goes against the plastic bushing.


Bushing for the spring

This metal bushing goes against the black cam follower.
Note: when I do the final assemble all these parts will get either silicon grease or oil.
I also will spray WD-40 dry lube on all the linkage when finished.
The threaded areas will get some anti-seize also.


Spring bushings that I will be replacing.

inner plastic bushing on the metal bushing

Note: there is no washer between the metal bushing and the cam follower.


primary shaft spring attachment point



Bracket orientation

I did not get a photo of the part of this bracket where the spring attaches to it, sorry!



Cable attachment piece and black spring bracket

This is the orientation for the two pieces, this spring bracket is for the two small springs I mentioned at the top.

All that's left is the SS nut and flat washer to complete this side of the primary shaft.

Please let me know if I made a mistake!

 

These parts of the linkage go onto the stationary shaft on the thermowax side of the throttle body.


The spring goes onto the fast idle cam (no washer between the cam and body.)
The round end of the spring goes onto throttle body attaching point.
The other end of the spring goes where the picture shows on the FIC.


There is a groove on the shaft where this weird "C" clip is installed!


Then this stop bracket goes on next, followed by a washer and in my case a 4mm Allan cap screw.

This is a good time to center the cam follower to the indexing line on the cam!

 

Onto the other side of the primary throttle plate, the side with the diaphragm.


This is the shaft that we are going to assemble.


Here is the spring and plastic bushings attached to the throttle body.



This is the bracket that the spring attaches to.


First assembly parts onto the shaft.

This is the assembly order for this shaft.



Here is where the plastic washer goes!


The spacing on this assembly is 14mm, to be adjusted as needed!

 

Hi again,

Back to the thermowax side of the throttle body.


Note the two plastic bushings on the arm

secondary shaft

bracket #1

bushing #2

linkage #3

link to primary, needs washer & cotter pin

bracket #4

SS washer #5

Lost the picture of the SS Nut #5!

I coated all of these parts with silicon grease, but used anti-seize on the final nut.

Bracket #1 & Linkage #3 are interesting. They provide movement of the primary throttle plate before any movement of the secondary plates is allowed.
Does anyone know the reason?

My painting of the parts in black or silver provides a clear relationship between them. Also looks nice.

The rest of the parts go on kinda easily, does anyone need pictures of these being installed? I don't mind, this is fun for the old guy!

Going forward I will try to adjust the throttle body to an approximant setting before installing it onto the dynamic chamber. "DYNAMIC CHAMBER" sounds scary!

Please let me know if you found any of this of interest.

 

This is described in the FSM, page F2-35. I have some reservations as to how correct the FSM is here, but I can answer the question.

The reason you want the primary opening before the secondary plates has to do with engine operation near idle. The primary plate delivers approximately 1/3 of the max airflow of the throttle body. The two secondary plates deliver the other 2/3 of the airflow. Engine idle with a good compression engine uses very little air through the primary plate pinhole, idle air adjust screw on the BAC, and the various air-bleeds. Small changes in the flow at the primary plate can result in a wide rpm range change. With this, we are allowed to finely adjust the fast-idle cam throttle setting in its full range without adding airflow from the secondary throttle bores. At WOT, the difference in degrees makes little difference in the airflow of the throttle bores.

My question is not with how the throttle body works, but how the manual describes the adjustment of this degree separation. It says "If clearance is not within specification, cam adjusting screw to get the proper clearance is obtained." I've read this a bunch of times and it doesn't make any sense. There is no screw that makes this adjustment that I have found. The only adjustment I have found to change the degree of opening is by bending the little dog that goes between the little fork prongs on the secondary shaft linkage. I'm sure we as a community could design one for fine tuning this secondary opening timing, similar to the fast idle cam adjust, but I don't think there is a reason to do so. I am also differentiating this adjustment from that of the bump stop screws for the primary and secondary throttle shafts. These are the painted ones that you should never touch under any circumstances. The throttle shafts should rest against the bump-stops so that the throttle plates completely close, but are not allowed to smack into the walls of the throttle bores. I reset my throttle body, after changing it from not knowing better in my younger days, using a dial indicator and adjusting the bump stop with the throttle plates fully closed so that the respective throttle plates barely move the needle on the indicator.

 

These threads are great. Even if you don't get much interaction on them now, they live forever and can be referenced later!

 

This sounds correct, on my untouched throttle body (I bought the car off the show room floor in 1989!) there is no light shoeing around the throttle plates!

On my rebuild I have light showing in certain areas around the plates. This is probably due to my polishing the rim on the plates unevenly.
How much this affects the idle quality I will find out. I am sure that the idle speed adjusting screw will compensate for the gaps in the plates.

I received the plastic bushings that I needed and will continue with the rebuild.

 

I just received the two plastic bushings from Riggs Vintage Mazda.

Here is where the two small springs come into play.


Square end attachments

I installed that last black bracket 180 degrees off!
Here are two new pictures with it installed correctly:

Spring attaching bracket orientation

Bracket points to the main spring attachment bracket!


Hooking up the large spring that goes onto the plastic bushings seems to be the most difficult part of reassembly. I had to fiddle around until I finally got it right!

The two small springs pictured above were a close second in terms of difficulty.

After I got them in place I noticed that there was very little tension that these springs applied to the cable attachment parts!
Is this correct, or do the springs need to be tensioned another full revolution to do their function?

Once I installed the bracket where it belonged it added 180 degrees more tension to the springs! Good to go now!

What do you think? Any response will be appreciated!

 

From the factory there is a sealant around the edge of the throttle plates to minimise clearance and air flow at idle. By polishing the throttle plates and bore you have removed the sealant and increased clearances. This may result in high and unstable idle and possibly throttle stickiness once you reinstall. It is a common occurence on rx7s and other Japanese cars of this era that were not designed with close tolerances in the throttle body.

People think they are cleaning carbon but the darker colour is a chemically resistant dry lubricant/sealant.

Tomei in Japan makes a paste called Tomei Throttle Coat which you can apply to the back edge of the throttle plates and the edges of the shaft to lubricate and seal. I know this is available in Australia but possibly not the US but other alternatives have been suggested on this forum.