No worries on that count... I've got plans for this one!

The consensus seem to be 76-78 J-Spec 13b, with the possible holdout of the oil pressure sensor on the rear housing. I'm expecting to find some port work inside based on the idle pattern/tone I remember from when it was running, not to mention the power I remember!

I'll be updating this as I make progress and/or new discoveries. Thanks all for your knowledge!

Do we agree then that except for the pan and intake, I could use a 12a gasket set for the internals? Especially since it's (quoting Mazdatrix) $83 vs. $230 odd for the "early 13b" set?

Thanks again!
Dan

 

Steve, did your 13B have an oil pressure sender? If not, you got a nitrided 13B from the '80s. They had a high volume oil pump and electronic ignition (note the eyebrows at the spark plug holes).

gearhead-42, I bet your engine has an oil pressure sender hole in the usual place. I say this because I rebuilt an identical engine to yours a few months ago. It's where that tiny port intermediate plate came from. It said R5 on all plates and Automobiles mazDa on the rotor housings. The rear plate only had 18 tension bolts with an undrilled casting in the upper right (when viewed from the rear). This allows the use of GSL-SE rotor housings with the oil injectors and/or a Y intermediate plate which lacks a tension bolt hole in that position. As you can see in one of the pictures, the finished product got a Y intermediate plate.

kenn chan is correct in stating these engines came from the Luce. No Cosmo ever had an engine quite like these. The exhaust ports open late to allow more time for the expanding gasses to push the eccentric shaft. You can easily port these out to T2 spec by simply going down and wider. Of course this reduces low end torque. I'm keeping mine as is for a rotary baja project.

You're going to want to purchase a high volume oil pump (the 17.5mm gear type) because these engines came stock with a wimpy 12mm. It's your call whether to keep the chain tensioner. I did simply because I didn't get a new chain.

Oh, they also did not come with an adjustable rear oil pressure reg. Get one or smash the end of yours a few mm.

Hmm, it looks like the side inspection cover is from an '83-'85 1st gen (to fit the '83-'85 style flywheel). Obviously you have an aftermarket flywheel. Has the oil pan been to swapped to GSL-SE too?

 

That $230 set contains 12A and 13B gaskets. Kind of a dumb set if you ask me. (rather I suspect it was intended for dumb people not knowing what to buy) You could buy the '74-'75 13B gasket set. It's what I used while the price was $106. Now it's more.

Just get the 12A set and the 13B oil pan and intake gaskets if you want. Also you WILL need a '76-'78 exhaust gasket because along with a header flange, will block the thermal reactor ports. Or you could take steps to block them and use whatever exhaust gasket(s) you want.

Note the '74-'75 set comes with seperate exhaust gaskets and is compatible with 12A or 13B as long as there are no thermal reactor ports to deal with.

 

I pulled my 13B 4 port from a stock looking 4 door RX-4 in the local PNP.
It didnt have an oil pressure hole on the rear iron,and it still had the stock carb,points and thermonuclear reactor on it.There was an MSD sticker under the hood,but no signs of any mods.I used the Mazdatrix threaded banjo bolt to get my oil pressure gauge up and working.Im pretty sure it had rotor housings with 3 little rectangular tabs around the sparkplugs.It definately didnt say "automobile" on it,just Mazda and 13B.

Damn engine ran like a top,never smoked and had great,great power for being all stock.Pretty good considering it sat in the car for at least 2 months with the hood open and the air cleaner off.I dumped 4 cans of carb cleaner through it along with some ATF before firing it up.I figure it was probably a rebuild.....last I heard its still running strong in RS Devil's car,with my old Yaw Nikki on it.....

 

Steve, you had a nitrided R5. Those are very good engines. I've rebuilt several and they're usually pretty good on the inside since they're from the same era as 1st gen 12As. (ever lasting)

You can make the earlier non nitrided ones similar if you swap out the intermediate plate for a tallport and swap in rotor housings with the same port timing. Also don't forget to install a high volume oil pump like I did to this one.



Notice the full coat of paint and the oil pressure switch? It is identical to 42's engine other than the intermediate plate and the parts I mentioned above. Now it will perform like the excellent nitrided R5 13Bs from the '80s.

By the way, the rear plate had that crayon writing and green tipped tension bolts.

 

Huh,thats my old motor to a tee.....I even painted it the same colors.

 

Jeff, you're making me want to dig up a blown 12a somewhere for that intermediate...

 

Made some more progress over the weekend...

I count 18 tension bolts...




and it was definitely an -SE pan... look, you can see where they scratched it into the grunge with yellow crayon





Looks like a stock (type) oil pressure regulator... I'm not sure about the pump, I'll measure once I get the front cover off...

 

Yep, 18 tension bolts and one undrilled casting; non adjustable oil pressure reg; small oil pump etc.

I bet you can't wait to tear it down to see the wonderfully small intermediate ports.

Drop in a Y intermdiate plate, high volume (17.5mm) oil pump, lose the chain tensioner, or not (your choice), and crush the presure reg a few mm. Also port the exhaust ports either up or down depending on where they are from the factory. Or leave 'em if you want better low end (if they're the late opening, late closing like mine).

 

Jeff, slightly OT but I was searching some old threads, and saw you were contemplating grafting the FC waterpump to an early 13b... did that work out for you? I was thinking of picking up a tired 89-92 motor for the hi-comp rotors, figured that could be some free "added lightness"

 

what version of the 13b came in the rotary pickup ? (hits one deep into left feild)

 

You thought that was an easy question, didn't you?

Short version, it's a 4-port 13b... alot like the one pictured in this thread... but for a much more involved explanation of differences, start here...

https://www.rx7club.com/1st-generation-specific-1979-1985-18/fighting-reversion-591879/

Highly edumacashunal!

 

Looks identical to my old RX5 (Australian) 13B 4 port before it was BPed and installed in my RX3. Of course I'm going from a memory that is 12 years old....Oh and it had a oil pressure switch on the rear..

 

the s4 waterpump housing bolts up with minor mods, the s5 however hits the main pulley. if thats what your refering to.

 

Hmmm... guess I got some experimentin' to do. Plan is to run a set of aftermarket "multi-rib" serpentine pulleys and a Pineapple alt relocation kit, so it _may_ not be an issue

 

It's not that hard to fit an S4 waterpump on an early engine. I've done it a few times.

Tap some 10mm x 1.5 threads in the extra hole. Fill it full of RTV. Get yourself a bolt about 1.5 to 2 inches long and drill out the alt bracket a little so the bolt slips through it. Install it with the rest of the bolts and nuts while installing the waterpump. Tighten them evenly in a pattern. Don't forget the metal spacers on the two outer studs.

 

Well, its been almost a month but I finally made some progress!

The rear housing and port...


Rotor finally exposed... is it common for there to be NO rubber inserts left in the corner seals?


The exhaust port... there is no visible flaking, and no scoring that is deep enough to "feel" with a fingernail...


The intermediate plate... sad little port, isn't it? I'm in the market for a 12a Y plate if anyone is selling!


Hard seals are all in excellent shape. I'll replace the o-rings, corner seals and apex springs, but keep everything else after a thorough cleaning...


In a perfect world, I'd stumble across a 12a to steal the intermediate plate, and an S4 T2 for the housings and water pump... save me a lot of time porting! Oh yeah, and that 17mm oil pump as well, mine is the skinny one as predicted earlier...

 

You can't use S4 housings because the coolant seals are in the wrong place.

Your rotor housings look like mine in chrome wear except mine had cleaner coolant passages. Those exhaust ports are the late opening, late closing type like mine. If you want a good torque monster, leave them alone (they're still taller than US-spec 13Bs from the '70s and also taller than 1st gen 12A ports). If you want to port them out to T2 spec, all it takes is to go down a few mm, wider by 2mm on each side, but leave the top alone as it already closes at T2 spec. Of course like a T2 port, you can go a few mm higher for a more peaky, higher HP and higher RPM powerband. Your low end would suck though. Probably ok in a small light car with a turbo or SC. It depends on what you want to do with it. Mine will stay the way they are for better torque.

Yes, find yourself a Y intermediate plate. The weak flow of those stock ports just can't be justified regardless of outside port height, as far as I'm concerned. They're the short style compared to the tall style of Y plates. I wouldn't bother trying to port them either. The casting looks unfriendly inside and out, if you know what I mean. Heavier than Y plates, too.

Definitely get an S4 waterpump and I've found the $17 genuine Mazda 1st gen 82°C/180ºF thermostat (at Mazdatrix) works great. Don't bother getting the 2nd gen one (it gave me trouble and doesn't look as well made). The 1st gen style is working better than expected in my bro's SC RX-4 with NA S4 waterpump on a 55° streetported set of non-nitrided '78 R5 side plates and GSL-SE rotor housings ported out to T2 spec (intermediate plate fortunately had tall ports, woohoo!). It always runs cool (170-180) in ambiant temps ranging from 32F to around 65-70F measured from directly below the thermostat before the hot coolant enters the radiator. We completed the swap in late summer, early fall so there was no way to check the temps in hot summer driving.

 

That makes a whole lot of sense, thanks. I do like torque, and as this is meant to be an autocross motor, more torque is a good thing. I think I may widen the exhaust a bit, keeping the timing the same, and just "polish" the intakes. Definitely will leave surface rough for wetting, just take down any nasty casting lines...

Off to the classifieds for some 12a parts!

 

LOL that is a really small port.

 

yea it is rare for the rubber inserts to still be there in on a higher mileage motor.
the 74 repu motor i tore down had solid corner seals.
whats up with that?

 

That engine came from a 76-78 jspec delivery van that had a 5 speed ribcase tranny with a torque converter. Here are some pictures of the torque converter/clutch combo that was used with the ribcase 5 speed tranny. It was a pretty interesting setup.

 

Only the late 74 and all of the 75 13-B's came with the Solid Corner seald from the Factory...

Dan

 

Take a look at his corner seals. They aren't solid. They are the 76 and later "springy" style with the hole in the middle.

 

Sorry Dan,
I thought you were referring to the seals in the picture..my bad!