During dissassembly. Loosen the screw at the top first, while it's still in the engine. Makes your life easier.


It's good to have a container for parts.


How I keep it protected in a vice. Cushioned jaws and a paper towel tube.


There's the 115 shaft. Upper screw is loosened beforehand but the grease will hold it in so I leave it there during the work. This shaft is ready to come out.


Welded shaft slot in the process of filing. You need to be careful here. Not too wide or too narrow, or too long. Looking for just 10 degrees on this one.


The above is just a comparison shot. Any 115 shaft can swap into any other dizzy with a 115 shaft. That would be all N201 and N231 part numbers or '81-'82 and '83 respectively. The later N249 ('84-'85) has a different shaft with a different number, and a slightly longer straight slot. Sorry, no pics.

 

Getting there.


Reassembly in reverse order. Grease the moving parts and make sure the shaft advances properly, then springs back easily.


Here's that one I removed earlier, set up for welding.


Gotta do both sides to build up enough steel.


And you gotta grind it flat and remove any slag or "weld *****" as my welder likes to make, which stick to any exposed metal.


Sorry about the focus. Not much detal to see. The slot now needs some lovin' with a file.

 

I did some math and determined what it would take to get to 15 degrees on this one. Why? Because just limiting myself to 10 degrees might be a little conservative. Especially when I add an intercooler. Or I might just plunk this one in the engine that's getting a Camden. Either way, I already have one that's at around 12 degrees while all the rest are at 10 degrees. Why not try 15? It took a little more effort (more time spent filing the slot to get it to the right length) but it should work out ok. The measurements make sense in any case.


And now for a previous owner's fully locked job. I took this out of a dizzy and just had to get a picture. Pretty funny. The dizzy now has the 15 degree shaft in it.


And there's six completed semi-locked dizzies for blow through turbo applications.

 

So then what about the math? Kind of important if you are debating whether to fully lock or semi lock. I know this info can be helpful. Heck I didn't even start from scratch. I got a semi-locked or rather "limited advance" dizzy in a pile of parts, which was the inspiration for this thread.

Measure one of the stock length slots. If it's a 115 shaft, I've seen 9.9mm to 9.8mm. Let's use 9.8 as seen in this thread.

Next we measure the advance weight's pin that slides in the slot. I saw 5.00mm.

Then we do some math.

9.8 - 5.0 = 4.8

That's just 4.8mm of total travel for a stock dizzy which translates to 20 degrees of eccentric shaft advance as seen with a timing light on the main drive pulley.

To get 10 degrees, you cut 4.8 in half to get 2.4mm.

7.4 - 5.0 = 2.4

So I would fill the slot with weld and file until it got to 7.4mm

2.4mm translates to 10 degrees of eccentric shaft advance as seen with a timing light on the main drive pulley.

By the way, feel free to double check my math, ok? I mean heck it's your dizzy and you probably only have one so you don't want to ruin it. Of course you can always weld more steel in and try again.

Now that we know the formula, I calculated 15 degrees would need a slot length exactly between stock and my 10 degree mod. So I arrived at 3.6mm. It's really basic math here. This meant the slot needed to be 8.6mm long.

8.6 - 5.0 = 3.6

So I filed on the slot until I got to 8.6mm.

And now that the dizzy is back together and I can rotate the upper shaft while holding the lower drive gear steady, it does move noticeably more than the 10 degree jobs but not quite as far as a stocker. So I think I did ok.

Anyone else going to attempt a semi locked dizzy? It really is the best choice. Easier starts, better idle quality, better driveability and it's no more or less reliable than a stock dizzy, assuming you did the mod correctly. And it needs a lube job after all these years anyway. Go for it!

 

nicely done, thanks for taking the time and posting

 

Nice job! Now, would you like to sell me one?

 

FWIW, Jeff, the '80 no-ignitors dizzy also uses the 115 shaft... which makes it likely the 79 points units did, too, since one was developed from the other.

Possibly useful to know for replacement parts sourcing, if nothing else.

 

i locked the distributor in the P port, and during testing found that it really does want an advance curve. i've been wanting to do this for a long time. maybe we'll try it on Fungus mungus's engine first.

 

i have been doing the regraph semi lock for years, recently put up a refreshed post to restore the pics here-


AusRotary.com ? View topic - how to lock a dizzy

PS
if you pull ( or push ) on the spring post you can alter the rate of mech advance V rpm

over here our late dizzy is marked with 155 , and relates to 31 degrees of total mech advance at the crank
the vac pots are also marked 17 T and 10 L [ double the numbers for crank degrees ]

while earlier s2 dizzy pots are usually 7.5 L and 12.5 T and have 14 ( 28 crank ) marked on the mech advance

and the book i have is for the initial rx7, and shows the advance as 12.5 mech ( 25 at crank ) and the leading is 7.5 ( 15 at crank ) and 15L ( 30 at crank )

 

Perfect timing (no pun intended) I'm just at this point in my little project, and I'd almost decided to go full locked.

 

just to add, the distributor advance curves are in the appropriate FSM, Foxed.ca - Mazda RX-7 Manuals

the distributors are all stamped with a 4 digit part number, that tells you what it came in. the part number directly references the parts catalogs, so you can look them up in the parts catalog

the GSL-SE is an N304. the 12A's have an N2xx number, N201 is like an 81, and N249 is a late one. an 88xx or 89xx is probably a 79-80 part.

 

N306 is RE-SI
N304 is GSL-SE
N249 is 84-85 12A
N231 is 83
N201 is 81-82

N306 backwards curved slot
N304 curved slot
N249 long straight slot
N231 short straight slot
N201 short straight slot

 

you the man Jeff thanks for posting helped clear up how I was gonna do the timing after rebuild and break-in.

I have devised such a cleaver turbo set up I must put it on paper

 

just to add, the parts catalog says

N225 is the 12A 6 port (others ball without!)

and N245 is the 12A turbo (others bo)

 

Ah, I should have included the N225. I have one of those 6 port 12As and the part number was stamped on the waterpump too.

Ever notice the 83-85 rotors share the N225 part number? Yep, those rotors began life in the 6 port 12A. The front CW has a 45 degree bevel to clear the lump in the aux port casting on the front iron. It shoudl also be forwards compatible with GSL-SE and RE-SI front irons. Or an S4 NA if you're brave.

 

I have a 12at distributor stamped N246 and N236 also.

 

It's good to have a container for parts.


How I keep it protected in a vice. Cushioned jaws and a paper towel tube.


There's the 115 shaft. Upper screw is loosened beforehand but the grease will hold it in so I leave it there during the work. This shaft is ready to come out.


Welded shaft slot in the process of filing. You need to be careful here. Not too wide or too narrow, or too long. Looking for just 10 degrees on this one.


The above is just a comparison shot. Any 115 shaft can swap into any other dizzy with a 115 shaft. That would be all N201 and N231 part numbers or '81-'82 and '83 respectively. The later N249 ('84-'85) has a different shaft with a different number, and a slightly longer straight slot. Sorry, no pics.[/QUOTE]