Learning everyday about these old 4 port 13b engines. My car has one in it. Took off my Dellorto to remove the block off plate on the int plate. Clearance problem with the RB air cleaner. Thought it was for EGR but it is a coolant passage. Used a 28mm freeze plug to gain more room. Anyone have more info on this block? Good or just OK? Has italic Mazda on rotor housings.. See pic.....

 

THese are 3B irons and housings. Dated from 74-75. Small exhasut ports. 74 spec intake ports close at 50 degrees (typical 12A irons close at 40 degrees). Not nitrided so you probably have smoke at startup. Also a medium sized oil pump at 15mm. Lousy thrust assembly which is prone to wearing out. Small stationary gear teeth prone to failing with high RPM and/or high power, but I don't know the limits. Heavy 30 pound flywheel with a 215mm clutch disc. Or if you have the REPU setup, it's still 30 pounds but has 9 pressure plate bolts and an odd step on the 225mm disc. Only old school with a 225mm disc and it's incompatible with everything else. Otherwise nice score!

Oh and the 28mm freeze plug is a neat idea. Be careful of possibly one threaded hole up there being all the way through to the water jacket. Not sure about that. Check it before you throw the manifold back on.

 

The knowledge on this forum amazes me!!

 

found the threaded hole thanks for the info...

 

I noticed you have a beehive. That's cool. They get a bad rap but I like them.

I installed a beehive on a fresh rebuilt 12A with nitrided R5 irons the other day - just test cranked with oil about an hour ago - no leaks. IT needed a threaded-in coolant T fitting.

Also installed a beehive on an S4 NA / R5 13B hybrid a couple months ago. Added a plastic T fitting for coolant.

Then had to stretch another beehive to fit an R5 / Y hybrid 13B (will add a plastic or metal inline T fitting later as the rear Y iron is from '82).

You have to get the long steel tube to fit without any angle to it so it points accurately at the fitting in the front cover. That's how Mazda does it for the 12A. Otherwise you can get leaks. But I'm sure you knew that.

By the way, how is your coolant routed? The stock 3B rear iron used a short threaded in fitting.

 

Jeff.. Not a big fan of the water cooled oil coolers. caught my interest, will check. Thanks for your info...

 

I hope this little 'info' thread keeps going.

I have a 1976 4 port 13B in my Cosmo. As far as I know, it is stock, and was rebuilt in 1988 by a Mazda dealer in Knoxville, TN.

It already had a header, and the REAPS system was removed. I have stripped all the remaining emission off of it, and am about to pull the motor and see what's what internally.

Couple questions:
-if I do a stripped rebuild of the Hitachi Carb, will there be any gains?
-How big of a port should I do? Intake? Exhaust? Both?
-Will the Hitachi keep up with a port job? I have read that the jets are replaceable, where can I find some?

Lets keep this going. My Cosmo is going to need some more oomph before DGRR.

 

If it still runs ok, it's probably going to look like mine inside. My 76 Cosmo engine was a runner with just a bit of smoke at startup and decel and if you have to sit idling for a while. High vacuum pulled oil past the oil seals.

Ahem.

Stat gears are the longer style so they're ok to keep using if they look fine. The oil pump is the stupid small type so look for any 83-85 12A or 13B pump with 17mm gears. If you have access to a beehive 12A, use its oil pump. The old oil seals will need to be changed because all early rotaries with non nitried side plates wear out their oil seals, so get a set out of later nitrided engine (check the FSM for wear spec). Also get some competition outer springs and new o-rings. The inner springs are probably reusable. Change all the other rotor springs. Get RX-8 corner springs or the more expensive and stiffer (higher drag) NF01 (20B and FD) springs. It's up to you. Avoid the early wire type as they like to collapse. My apex seals were good enough to reuse, as were my rotor housings so I just changed out the springs.

The biggest improvement you can make to a 76 Cosmo engine are the side plates. I swapped in a set of Y irons. No porting so it's still the 76 & 12A spec. It went into my baja so I needed to retain low end torque. I thought about porting out to 74 spec, but the later the closing of an intake port, the greater reduction of low end torque you get, while the midrange and high end is improved. Not needed in a baja. You might consider 74 ports.

Keep the reverse runner manifold. They're pretty cool. As for the carb mods, no there is not a lot you can do. You can change the jets and air bleeds but you need a wideband to know where the carb is at and whether it needs to be adjusted leaner or richer at any given RPM.

The early accel pump is leather. If it still works, that's great! If it doesn't , I don't know where to get new ones. Later ones are rubber and they seem to work ok, but are different in some ways such as length of stroke, cc volume, stopper height under the plunger etc. Just use it as is.

 

Oh to answer more of your questions, even though I didn't do any intake porting, I did smooth the rough parts and casting flash. I also ported the exhaust ports up 2mm untuil the stock bevel was gone, then recreated it. This just lets it breath better than a stock US-spec tiny exhaust port. They open at T2 spec but close way earlier, so I just delayed the closing a little. You could potentially port all the way up to T2 spec but I wouldn't unless the intake ports were enlarged the right (matching) amount as well (note T2 intake secondaries are 74 spec!) ansd you needed to drive a turbo, and even then it's not totally necessary to go that big.

Do not port the exhausts downward unless you know what you're doing.

 

Ok, so the plan is to rebuild it, using an Atkins kit with FD corner seals and springs. Not going to port it, just smooth everything out. I am rebuilding the Hitachi, and am also going to pick up a 45 DCOE.

Already have plans to use an electronic dizzy, which incidentally I bought from you years ago. FC coil for direct fire, and an S4 alternator. The oil pumps we have lying around so that isn't a problem either.

Should be fun!

 

You can't use FD corner seals. They're for 2mm apex seals. You have 3mm apex seals. You also shouldn't use FD corner springs because they are too stiff for non nitrided side plates. It will make a deep step wear in a kind of figure 8 pattern around the irons. The strongest springs you might get away with are RX-8 springs but even then I'd still look for a set of Y irons just to be safe. Or just get another set of wire type springs and rest easy.

The electronic dizzy should have been swapped in years ago. :tongue: Who uses points anymore? Ahem the FC coil isn't really that great to use with a 1st gen dizzy because you can only power it from one ignitor. If the stock J-109, it will live a short life. It's better to go with DLIDFIS and two Diamond coils from a 1st gen for leading and one Diamond coil for trailing along with a total of three J-109s (two for leading direct fired and one for trailing through the cap and rotor). My Cosmo had that setup and it worked flawlessly. Of course GM HEI ignitors are another option which works well. You can also use better coils because the HEIs can handle higher loads.

 

I'll have to check the Atkins kit. I swear it said FD corners. No biggie.

If its any use, I also have a GSL-SE engine as well I van harvest.

This engine has been pickled since 1999. It isn't a current runner, but was when taken off the road.

Good to know about the coils. I have a shitload of diamond coils at work.

 

Must have been FD corner springs. But Atkins doesn't sell the FD/20B NF01 part number, which is very stiff. They sell the RX-8 springs and call them FD springs. These are a little less stiff and don't produce as much parasitic drag on the engine.