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Thread: WTB: 13b 4-port motor from 74-75
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Jeff20B
Moderator
Posts: 661
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posted March 12, 2004 12:10 AM |
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Some trivia for you all. R5 had 17 tension bolts and no oil pressure sender hole below the oil filter. They were sorta odd-ball in that regard I guess. Stock REPU stuff had 19 tension bolts and an oil light sender under the oil filter.
Even more trivia. The '76 Cosmo supposedly has only 18 tension bolts (according to my FSM) with the updated mazda 'font' (raised letters) on the rotor housings, while the '76 REPU still had the old style all-caps '74-'75 style MAZDA raised letters that we are all so itchin' to aquire here. :)
I'm not sure what the '77 REPU had. They changed so much about the truck in '77, that your guess is better than mine. Actually, the front engine mount is smaller and less heavy-duty than the '74 unit (I compared them side by side today).
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'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
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Klaus43
Rotorhead
Posts: 1259
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posted March 12, 2004 10:37 AM |
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Brad:
Just emailed/forwarded emails to your '777' address...
I'll have to go check on further specifics of my disassembled motor...
Still curious: What were R-5 housings stock issue in?
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Jeff20B
Moderator
Posts: 661
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posted March 12, 2004 12:03 PM |
 Edited By: Jeff20B on 12 Mar 2004 12:05 |
I wish I knew. From the four that I've seen, three had the three little aluminum outcroppings around the spark plugs. The fourth had semi-circle shrouds just like RX-7 housings. These rotor housings don't have air injection holes for a thermal reactor, which tells me they were meant for catalytic convertors ('81+?). I could be wrong about that, but it seems most likely at this point. Also, the rear plate's heater core fitting is not pressed in like the later style engines. I'm not sure when Mazda started pressing them in. I sorta like the screw-in type because you can easily replace them with a plug from RB.
Hmm, The two I've torn down both had 17.5mm oil pumps (high volume), 13B-length stationary gears (5mm too long to work with 12A rotors), and non adjustable rear pressure regulators. The other two I've seen are the one in Elysian's blue REPU, and one sitting under a tarp in a local rotorhead's backyard. I might rebuild his engine for him (the local guy), so I'll know more if and when I do. As for Elysian's engine, he'd be able to measure the oil pump gear and tell us if it's 17.5mm (or just show us a pic of the housing because it's beefier than the 15mm or 12mm type).
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'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
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Klaus43
Rotorhead
Posts: 1259
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posted March 12, 2004 01:59 PM |
Edited By: klaus42 on 12 Mar 2004 14:09
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Went and checked...:
It appears that all my 'original '74' motors have the '3B' designation steels.
Where it gets interesting is comparing my buddy's 4-port that's living here right now, to my own that I thought to be a j-spec...: Both have 'R-5' designation end steels, and both have newer-style (lowercase mazda logo) rotor housings, no 'eyebrows'...but that's where the similarity ends. His motor has but 16 tension bolts, and no center steel exhaust-to-intake pre-heat rectangular riser port, and the steels are all nitrided. Mine uses 17 tension bolts--just like the '74 '3B' motors--and the steels are not nitrided, plus the center steel has rx-7-style 'tall port' primaries, and there is the rectangular heat riser port... but the rear steel says 'R5' on it... (!)
My 'driver' REPU has what I think to be a j-spec in it... no eyebrows, lower case logo script, nitrided steels... but I'd have to start taking things apart to quote stampings, or look at porting...
To complicate matters further, I used to own what I thought to be a j-spec 4-port... it had nitrided steels, and the obnoxious eyebrows around the plugs... but I never had it out of the rx-4 wagon it was in, so I don't know any more details... except that it had a 'mod-stock' exhaust setup with the air pump disabled, and the thermal reactor gutted... and it ran great. There's one I never should've let go of...
No wonder I had no idea about some aspects of which early engine is which--or what combinations of parts were used in a build... obviously, the only way to be 100%sure is to pull the motor and have a look at all the bits... no matter what some potentially misinformed PO sez... Guess none of my stuff is 'original REPU' after all.
Hey, Neal-- What do your steels say? And, how many tension bolts holding your engine together?
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Jeff20B
Moderator
Posts: 661
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posted March 13, 2004 03:41 AM |
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I was slightly mistaken earlier. It seems there was an R5 iron that had 19 tension bolts and five freeze plugs without nitriding. It is in my Cosmo FSM. By the way, my R5 end plate has four freeze plugs.
klaus, about your intermediate plate that's missing the rectangular exhaust port, does it have tall or short ports? Tall would indicate a Cosmo reversed runner manifold came stock on it (or possibly some 12A equivilant). Short with a freeze plug would be like the pathetic intermediate plate on my semistock REPU engine (non nitrided front and rear plates with '74-'75 rotor housings and a nitrided intermediate with no rectangular exhaust port, but with an EGR hole at the top and a freeze plug directly under the short ports). The intermediate ports are very small and can't be ported much because the casting is not ideal for porting.
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'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
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Klaus43
Rotorhead
Posts: 1259
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posted March 13, 2004 12:56 PM |
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Well...
...your description of 'pathetic' fits that center steel to a 'T'... perhaps it's fortunate for me that one's in my buddy's motor, not one of mine...? Definitely, the 1st-gen seven center steels ('Y' stamped on the front one)have taller ports than that...(to the point that it's obvious where the too-small ports on the gasket restricted their flow)!
What has me baffled, however, is the number of tension bolts on my buddy's motor... it's like there's an un-drilled location for the 17th one thru the intake area... as viewed from the rear steel, anyhow. All his steels are nitrided, too...
I'm now very curious to pin down the ID of my R-5 plated core... with it's non-nitrided steels, tall center ports, 17 tension bolts, and newer-style 'lowercase' mazda scripting on the housings... I pulled it, running, from a '76 rx-4 coupe, assuming at the time that it was not the original engine...
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Jeff20B
Moderator
Posts: 661
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posted March 13, 2004 01:26 PM |
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'76 you say? It may infact be stock. I've never had the engine out of my '76 Cosmo, but I've had the intake manifold off. All of this is so fascinating. :)
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'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
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Klaus43
Rotorhead
Posts: 1259
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posted March 13, 2004 01:45 PM |
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Indeed...
...add to that, that the car it was in had apparently been an automatic that was converted to 5-speed... apparently...
There 'must' be a way to ID these kinds of things...!
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rotarydave
Hauling
Posts: 108
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posted March 15, 2004 09:29 PM |
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Ok ok ok the confusion is too much for me. After as many engines as i have pulled from different chassis and year combos i am totally screwed up, therefore i turned to my best source of information and i still have no totally definative answers, but here is what i was told, from Dave Atkins
REPU should be 3B cast irons with 74-5 (big mazda) rotor housings for all 4 years 74-77 (this would make sense as all 4 77s i have owned originally had these rotor housings)
The R-5 cast irons came in Cosmos (may have come in Rx4??) but they also were found in several versions of the J-spec motors into the 80s exactly what they were used in and from is anybodies guess. Also Dave did say that he has seen some R5 castings in Rx7 engines that appeared to be factory installed as 12as (not 13b) again I have no answer and no idea if this is right or wrong.
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Jeff20B
Moderator
Posts: 661
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posted March 16, 2004 03:11 AM |
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I'd have to agree with Dave Atkins. The R5 castings don't have an oil pressure guage hole, like the '79-'80 RX-7. The rotor housings found on R5 13Bs are catalyst-type. The intermediate ports found on R5 13Bs are tall like the later FB 12As. The front covers have a fat timing pin and a stud for the distributor ('74-'78 style), instead of a thin timing pin and a bolt for the dizzy. R5 13Bs have high volume oil pumps (17.5mm gears) and non adjustable rear oil pressure regulators.
I pretty much thought they were retrofitted 12As with '74-'78 rotating assemblies. Then when I was able to compare two R5s side by side, I became even more interested. One came out of a '77 REPU, and the other had a GSL-SE oil pan and an RX-7 front cover mount on it. Then I saw Elysian's R5, and also the local rotorhead's R5, I had to step back and say wait a minute. There is a missing link somewhere.
Both my R5 engines have tan colored main drive pullies. One was missing its waterpump, but the other has a tan waterpump pulley. The LT split is 15º.
When I pull the engine in my Cosmo for a seal freshen-up and possibly a tranny swap at the same time (auto to manual), I'll definetly see if it's got R5 plates. Hmm, maybe if I removed the upper inspection cover, I'd be able to see between the flex plate and the back of the engine.
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'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
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Klaus43
Rotorhead
Posts: 1259
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posted March 16, 2004 10:33 AM |
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No argument here!
Just curious to learn what there is to know... and to know all I need to learn, before (eventual) reassembly of proper or desirable part combinations. Thanks for the enlightening conversation!
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Jeff20B
Moderator
Posts: 661
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posted March 16, 2004 11:32 AM |
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The info I listed above should help find the missing link. If we can narrow down the newest part(s) on these engines, we'll be able to figure out when they were built. I suspect the newest part is the 17.5mm oil pump. I'm not sure when they came out, but I think they are '83-'85 (for the 12A turbo, regular 12A at least from '84-'85 and the GSL-SE).
I tore down a dead '84-'85 12A a while back and it had a 17.5mm oil pump, and tall intermediate ports. Those are the only things it shares with the R5 13B. I've also not seen R5 on the intermediate plate, so it;s anybody's guess I think. Hmm, I think I've seen an R near the oil filler tube.
I believe my R5 with the GSL-SE oil pan was a retrofit into a formaerly 12A 1st gen. That means the oil pan was installed anytime after '84 (geez, that doesn't narrow it down much). The banjo bolt was drilled and a brass fitting was installed for an oil pressure guage. It was definetly in an RX-7, as evidenced by the front cover motor mount. I'm not sure if it's the RB one, or a stock one. The RB one is shaped differently to allow a 13B to fit in a 12A chassis. The GSL-SE has a different subframe thus it's able to use the 12A front cover mount.
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'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
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jfaplanet
Redlining
Posts: 356
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posted April 30, 2004 07:51 AM |
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Confused!!!
OK, so now I'm confused. I've been poking around on various threads and find a lot of talk about R3 and R5 plates. I pulled my old REPU motor out 2 yrs ago when I got it and have just started getting ready to rebuild. What is my best option for plates. I have the R3 plates but if they are not any better (port wise) I have several nitrated plates that I could port and use. Whats the difference between the R5 and R3 (port wise). Any help is is greatly appreciated.
Thanks, C
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Jeff20B
Moderator
Posts: 661
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posted April 30, 2004 09:51 AM |
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That's 3B and nitrided. The 3B end plates have large ports but are not nitrided. The R5 plates are nitrided but have smaller ports which means more time with a porting tool. The R5 rear plate also does not have an oil pressure fitting.
The 3B intermediate has small plate-to-manifold (outside) ports while the R5 intermediate has tall outside ports. I think the 3B is also lighter because the wall thickness (or whatever it is) is thinner. I think Mazda beefed them up in later engines.
I have Y, 3B, and R5 plates sitting right here to look at. :)
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'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
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jfaplanet
Redlining
Posts: 356
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posted April 30, 2004 12:24 PM |
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Thanks for the infor
Thanks, Jeff. Looks like I have 2 sets of 3B plates, 1 set 6 port plates, and about 5 12A nitrated sets. I may build 2 engines. 1 3B and 1 ported nitrated, Just time and money..
Thanks again for making it all clear..
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rotormunky
Redlining
Orlando, Florida
Posts: 424
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posted April 30, 2004 02:55 PM |
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Has anyone thought about trying to find a shop that could re-coat housings? Preferably with a newer, harder technique that would produce less friction?
Is it even possible?
I've not seen a lot of discussion on it.
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-Martin
Orlando, Florida
http://www.themonkeyhouse.org/REPU
'77 REPU (Some assembly required :)
'91 Cabrio (Battered and bruised, but she's still my baby.)
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jfaplanet
Redlining
Posts: 356
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posted April 30, 2004 09:51 PM |
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Ceramic
There was a company, I believe in TX, that was experiementing with ceramic coatings for the rotor housings. Not sure if they had any success. It sure would be nice to have the old ruined one redone. If anyone finds out anything please keep us informed...
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brad
Rotorhead
Posts: 1672
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posted May 02, 2004 10:55 AM |
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quote:
There was a company, I believe in TX, that was experiementing with ceramic coatings for the rotor housings. Not sure if they had any success. It sure would be nice to have the old ruined one redone. If anyone finds out anything please keep us informed...
the guy that was experimenting with that...ended up costing $350 to get a rotorhousing chrome surface re-coated with a high tech compound. and resurfaced properly. when a new rotorhousing costs $400, it defeats the purpose. plus the shop that actually sprayed the stuff, sprayed inconsistantly. too thick...too thin...etc...no good
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-brad-
74 REPU Lawn Green
81 Rx-7 racecar. 12a J-
Bridge
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jfaplanet
Redlining
Posts: 356
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posted May 02, 2004 11:30 AM |
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Update
Thanks, Brad for the update. When I found the link 2 yrs ago I wasn't ready to even begin to look into engine work. Now the time is nearing and I have gotten some GSL-SE housings. But it sure would be nice to be able to get the old MAZDA 13B housings redone since they are no longer available. But $350 is a little steep when you can find replacement ones for a pair for that. If anyone finds something keep us all informed. Thanks, C
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rotormunky
Redlining
Orlando, Florida
Posts: 424
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posted May 02, 2004 09:40 PM |
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$350 for what they were offering sounds a little steep but I was thinking more along the lines of something that significatly improved over the stock coating.
Something that was harder and more durable and also produced less friction which would generate more power and less heat. I'd pay $400/each gladly if there was a proven process. ESPECIALLY if it meant being able to get more life and reuse housings.
Judge Ito says he's used some experimental coatings on the end housings which have let him cut down on friction and heat and produce a little more power but no word on durability or feasibility as a rotorhousing coating.
Its interesting to think about. Probably I'm just jealous of the really nice sleaved LT-1 I saw this weekend. Course for what that thing was going for $350/rotorhousing is cheap cheap cheap.
Big (reliable) HP seems to cost money no matter what sort of engine your using.
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-Martin
Orlando, Florida
http://www.themonkeyhouse.org/REPU
'77 REPU (Some assembly required :)
'91 Cabrio (Battered and bruised, but she's still my baby.)
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