Re-Rotorising RX-2 - Technical thread

[Martiny]

Hi All

Thanks to you all for the help on Saturday at the old school meet.

For those who dont know, my current setup is:

71 RX-2 sedan with Ford Pinto power.

I have, in the shed, a series 2 , 12A RX-7 Motor , Gearbox and prop shaft. One problem with fitting this engine is the question of engine mounts. Had a look at the Rx2s 3s and 4 on Saturday, and it seem the best thing to do is to modify my cross-member to make it into the 1973/4 style crossmember to take the RX-7 engine mount.

Now, I have toyed with the idea of using the RX-3 style mount which is an extra cross-member, fits under the anti-roll bar mounts if I remember correctly.

QUESTION  - If I used the RX-3 style setup, will I have to replace the sump, or turn it round?

[MikeLMR]

I reckon the only way to do it is to pull that pinto out and get your engine a box sat where you want it, then see what needs moving. Thats the plan for the 323 anyway, the variation on engines, X-members, gearboxes etc. seems to make nearly every swap slightly different.

[Martiny]

Mike,  I see you bought an RX-3 cross-member. Your car is obviously different to mine, but what was the thinking behind this?

For me, the possible advantage of doing this is the the gearlever might line up. If I use the standard 74 mounts, then I will have to either cut the tunnel and or modify the gear selector extender.

[MikeLMR]

I bought an rx3 crossmember as it bolts up onto my chassis rails as the 323 floorpan is basically a short rx3/818 floorpan

I don\'t think the rx3 X-member will bolt into an rx2, you probably be better making one out some 50mm box section and welding that in between the chassis rails.

am I right in thinking that the rx2 mounted on the side of the front cover and not from as per most of other oldschool rotors ?

[Martiny]

am I right in thinking that the rx2 mounted on the side of the front cover and not from as per most of other oldschool rotors ?

Mike the 2 was side mounted, on twin dizzy motors. The front housing had the engine mounts on it. Then 73/74 they changed it to single Dizzy and mounts on the front cover, RX-7 1st gens.

 
My options are:

1) drill and tap threads into the front housing to accomodate an RX-2 mounting.

2) Cut 71 RX-2 mountings off existing cross-member and fabricate mountings and weld to existing cross-member.

3) Fit cross member under anti-roll bar mounts.

My most likely option, I think, is No 2. I was just toying with the idea of 3) to try and save me cutting the floor. ( thats precious Mazda metal there, you know !)

[oldone]

you are right on all occasions Mike........It is easier to try and get a 2 crossmember,if that fails then remove all engine mount towers on existing crossmember and motor........mock install motor to required position,remanufacture crossmember mounts and front engine mount.This is the procedure we have followed for years and it is really quite easy to do. :guinness

[Martiny]

Ok, well prop shaft is out, gearbox is loose and coming out tonight.

Guess what, the floor has been cut towards the rear already, so that makes decisions easier, then, eh?

Well I might be able to now play with the gearbox and engine positioning to help the prop shaft.

The shaft that came out, has a bearing like the RX-2 shaft, but it seems ot be in a different place. The RX-7 doesnt have a bearing. So, next questions is..

What prop shaft should I use? Do RX-3 and 4 shafts have a bearing?
Does the 2 have a longer wheelbase than the 7? I suspect so.
Will the longer gearbox from the 7 remove the necessity to have the bearing?  I wouldnt have thought so, and I would be more comfortable drving it at 80 with a bearing, I think.

I will probably have to get a shaft modified one way or another anyway, so maybe the shaft that come out could me modified to fit somehow.

[OLSKOOLROTAR]

what sort of gear box are you running? I would\'ve thought a later model 7 box will be similar in length if not the same as the RX2 box.

I\'d say the prop shaft will have to be modified in some way or another.

Is your engine & box mated together? if so you could take your measurements before hand and that would give you a better idea of positioning.

Jase

[oldone]

Put the motor and gearbox in,measure prop and have a solid one made....you dont need the bearing bud......solid prop is good for the speeds you will do.had a solid prop on all the race cars and they survived Welcom main straight,8600rpm 5th gear !!!!!!!!!! Stop fussing around and just do It !!!!!!! :spank

[MikeLMR]

Martin, have you read this ? ... lots of ideas and photos.

http://www.rx7club.com/showthread.php?t=503695&page=1

[Martiny]

Jase, the RX-7 gearlever  sits further back than the 2 box, usually requires the floor to be cut, but i dont know if the actual box is longer/shorter.

Era, thanks for that, I guess the thing is to get it properly balanced.

Mike, yes I have been reading that thread, I will look again and see if I can find out about the shaft.

Had a look in the workshop manuals. RX-3 does not have a bearing, I wonder if the RX-4 has?

Era, if you say we dont need one, I wonder what made Mazda put one there, then?  Maybe it just makes things run smoother?

[Ray]

Hi Martin,

RX-4 does have a centre bearing, RX-3 does not, however we\'ve used both centre bearing and single piece props on the race RX-3 with no noticeable difference. The way I\'d go about it is to get the engine and box in first and see what gap is left, then tape measure in hand check other mazda\'s to see if one from a scrapyard might fit, possibly RWD 626. If that fails you can get one made up for not too much, if you supply both UJ ends of the propshaft and ask them to make to a particular length, it should be trivial for a specialist company. Thinking about it series 1 and 2 RX-7 should have the correct ends, but I\'m guessing it will be too short.

The RX-7 gearbox shifter can be mover forward about 3 to 4 inches by cutting the selector rod and remounting, difficult to describe in words, probably easier to give me a ring with a gearbox in front of you and I\'ll explain. Alternatively, I\'ve got a 4 speed RX-4 gearbox which would drop straight in, depends how much you want your overdrive.

Good luck  :3gears-rh

[Martiny]

Thanks a lot, Ray. With our fuel prices, I REALLY want that 5th gear!. I have the 7 prop in the shed, so, yes, I will look at the ends and U joints and see. I cant remember having heard that these were unreliable, so I doubt if they changed it for the 7.

[Martiny]

Here is....

Engine nearly ready to come out.

Exhaust - I couldnt get one of the nuts loose, so angle grinder came out!

Tunnel after prop shaft removal.

[travellinbob]

Cool get stuck in Martin. The underside of the car looks great!
 Ray, those rx4 boxes are real rare these day with the genuine bellhousings in oz getting really good money for. They are strong boxes too. I really love the way the old school section of the forum has come alove with all you guys. It is great.
 cheers, michael.