[Home | Mail Archive | Join the mail archive | Photo Gallery ]

Mazda Rotary Pickup Forum
you are logged in as
profile | register | faq | search (active threads) | memberlist
Sponsored by:
Index > Non REPU Rotary Trucks > Thread: Rotary conversion Tech
Thread: Rotary conversion Tech

Revvin Up
Posts: 55
posted December 04, 2006 05:47 AM

Rotary conversion Tech

I am currently pursuing conversions to Rotary power on two different rides - an 1985 Jeep Cherokee, and a pre-1986 B2000. I am sure that there are others out there who have done similar, and am thinking that some general tech would be usefull.

For starters,

Engines: comon available rotary engines are the RX-7 Engines, 12A (1147 cc) (Carbureted), 1984+ 13B (1308 cc) (Fuel Injected) All year front covers are interchangeable between 1974-199x, as are the distributors (until 1985)/crank angle sensors (from 1985) 12A Front Covers have two oil lines, 13B (Injected) have four oil lines. 1984 & 1985 13B are front mount engines, 1986+ are mid or rear mount engines. Block Seal o'ring grooves are located on the rotor housings, pre-1986, and on the end & intermediate housing (post-1985). Builable engine combos (pre-1986) from stock parts are 4 port 12A (stock), 4 port 12A w/ injectors, 6 port 12A w/o injectors, 6 port 12a w/ injectors, 4 port 13b w/o injectors (stock 70's), 4 port 13b w/injectors, 6 port 13b w/injectors (stock GSLSE)

Transmission/engine bolt pattern is identical for all years. Pay attention to balance when building hybrid engines, as there are different weights of rotors, flywheels, and counterweights.


Mazda Ribcase Transmission: Found in stock 70's RX-x Series, Cosmo, and 929. These are available in 4 and 5 speed manual, and have a removable bell housing, with integrated front bearing cover, clutch throw-out assembly, and starter mounting bracket. two types exist, a side mount starter (drivers side, under centerline) and an early top-mount type. The bell-housings from these can be used to start & run rotaries out of the vehicle, or to adapt to non-mazda transmissions with removable bell-housings via a bell-housing adapter. Bell-housing to transmission bolt pattern is an 8 hole octagonal pattern, with diferent lenghts between adjacent holes.

Mazda Type M "smooth case": Found in 1979+ Naturally Aspirated RX-7's, other mazda cars, and pre 1985 B-2000 pick-up trucks. Bellhousing is integral with transmission case, however these transmissions can be hyubridized by either case swap, or tail-housing swap.

Mazda RX-7 Turbo & 1986+ B2600 Transmission: Updated ribcase-style, with removable bell housing. Same bolt pattern for transnmission to bellhousing, with different "twist" Larger Bell for larger turbo fywheel, and different starter than N.A. rotary.

Ford Transmission Toyo-Koyo: Found in early to mid 80's Ford Rangers, Aerostars, and Bronco II's. Available in 2wd & 4wd. Manufactured for Ford by Mazda, known different internals, suspected diferent input shaft length. Transmission case is nearly identical to mazda ribcase tranny, so should allow for ribcase-style bell housing swap to transmission with spacer and front bearing cover, and tail-housing swap.

If anyone has any experience with any of the above, or updated or more accurate information, please reply.

View IP (Administrators only)

Posts: 1877
posted December 04, 2006 09:51 AM


This is excellent to have all on the same page; thank you!

View IP (Administrators only)

Revvin Up
Posts: 55
posted December 05, 2006 05:42 AM

Displacement & Engine Block Length

Engine block length: The main difference in dimensions with the 12a & 13b is the block length. Block width & height are the same. (not counting intake manifild set-up) The 13b generating dimensions is 105 mm radius, 15 mm eccentricity (main bearing to rotor bearing centerline distance), and 80 mm depth. The 12a dimensions is 105 mm radius, 15 mm eccentricity, and 70 mm depth. Displacement can be calculated by the formula D = N* 5.2 * (R*E*H), where D is the single Rotor face displacement, N is the number of Rotors, R is the Radius, E is the eccentricity, and H is the Rotor depth. One can correct this, as this will give a single chamber displacement only, and does not take into account the other two faces of the rotor, which would be counted in a comparable piston. A correction of 3 will give total chamber size at bdc, (equivalent to counting full bdc volume of a multi-cylinder engine, even though all cylinders are not at bdc at the same time) by 3 faces per rotor, or 2 via swept volume per complete cycle.

Thus, times the two rotors, the 13b is 20 mm longer than the 12a. So, if you want to plan for future upgrades to a front-mount 13b, and all you have is a 12a, get 20mm longer front bolts, 20 mm spacers, and place the front mounts accordingly. If going from a 13b to 12a, no modifications are necessary except for the spacers and 4 longer bolts. Otherwise, plan on using a custom front bracket, or drilling a new set of holes.

View IP (Administrators only)

Revvin Up
Posts: 55
posted December 08, 2006 05:04 AM

Clutch Disk sizes, Splines, & Related

Mazda has a fairly standard transmission spline, pilot bearing, and clutch disc layout for the rotary manual transmissions. The 1983+ NA engines have a slightly larger clutch disk diameter of 8.875", with a 22 tooth spline and a 15/16" input shaft diameter. Earlier clutch disks have a 22 tooth spline, with a 13/16" input shaft diameter, and a ~1/4" smaller diameter clutch disk. The pilot bearing is a needle-type bearing, with an id of 0.595" (transmission input shaft) and a pilot bearing od of 0.789" (Ecentric Shaft). Pilot beaing depth is 0.625"

The stock mazda clutch disk is an off-set type, with the off-set towards the transmission, away from the flywheel.

These dimensions for most makes & models can be found in clutch catalogs, and, in some cases, a rotary engine can be linked with a non-rotary transmission (shaft coupling) merely by obtaining the clutch disk for the transmission with a suitable diameter, replacing the pilot bearing with one of matched id & od, and assembling the clutch assembly with the mazda flywheel & pressure plate. Engine block to transmission case, starter mounting, and clutch release mechanism are not taken into account here.

Incidently, the AMC 2.5 L 4 cylinder, AX-5 Transmission shares pilot bearing id with the mazda RX-7, and has a 9.125" clutch disk that will just barely fit in the 1983+ mazda oem flywheel. This clutch disk will not fit in earlier 12A flywheels, however. There may be other transmissions with the same input shaft pilot bearing id, but that will require some reasearch.

View IP (Administrators only)

Revvin Up
Posts: 55
posted December 17, 2006 08:03 AM

replies and tech

I am seeing some veiws, but not too many replies. Does anyone have hands-on experience with rotary conversions into non-rotary trucks, cars, etc?

Also, is anyone looking for specific information related to various makes, models, etc?

If so, please post related info, or requests.


Some possibly usefull information I am considering:

Stock Transmission gear ratios
Stock Tire & Wheel Sizes
Stock Rear Axle Ratios

Engine HP & Torque figures, stock and modified
Fuel Options & conversions

Best & worst Methods for engine & transmission mounting
Available Methods for engine oil cooling

Vehicle weights.

This information would allow someone to do a conversion with good results, and avoid the dis-satisfaction of, say,

putting an early 10A rotary into a 1980's GMC Crew-Cab, Long-Bed, 4WD, Dual-Wheel Full-size, 1-Ton P.U., with high gear ratios, a lift kit, and over-size wheels, resulting in a 99 second quarter mile at 40 mph top speed.

View IP (Administrators only)

Posts: 117
posted December 17, 2006 09:17 AM

Check out www.mazdatruckin.com
KansasCityREPU on RX-7Club.com
85 GSL
77 REPU (1/1/2004)
75 REPU (7/10/2004)

View IP (Administrators only)
All times are PST (US)
Post New Topic    Post New Reply
Rate Topic:
Powerd By: BlazeBoard

[Home | Mail Archive | Join the mail archive | Photo Gallery ]
0.013475179672241 seconds processing time