Rotarded MG project.
03-05-06, 04:50 PM
#1
Rotarded MG project.
I had been meaning to do this for a while, but a recent post by buzz2 inspired me (kicked me out of my complacency 
) to post it today.
An RX-2 top mounted starter (twin dizzy) 12A and 4 speed tranny were installed back in '88. I swapped them out in favor of a 13B in '00. The RX-2 engine was locked up when I got it in '96, so I don't know how it drove, but from what I can remember back in the day, it was difficult to start and didn't idle smoothly. It was as fast as a stock 1st gen RX-7, and could go fast enough to be scary on the stock (tired) suspension, according to the previous owner.
I installed the 13B and 4 speed from my REPU for test fitting purposes, and the previous owner's stories of easy burnouts were not exagerated. A stock heavy (30 lbs) flywheel in a small light car with narrow tires tends to allow for such things. He destroyed two or three stock rearends, finally settling on one from '79 with its tall 3.7 ratio, which helped a little. Of course having a 13B's iron seals and increased torque at my disposal allowed for some interesting low RPM burnouts, though.
More recently, I swapped flywheels to a Racing Beat light steel flywheel and noticed a major improvement in acceleration with only a minor drawback in launching ability. Over all, an improvement, which will find its way onto the new engine I'm building specifically for the MG.
Some old pics of the car and the REPU engine.
) to post it today.An RX-2 top mounted starter (twin dizzy) 12A and 4 speed tranny were installed back in '88. I swapped them out in favor of a 13B in '00. The RX-2 engine was locked up when I got it in '96, so I don't know how it drove, but from what I can remember back in the day, it was difficult to start and didn't idle smoothly. It was as fast as a stock 1st gen RX-7, and could go fast enough to be scary on the stock (tired) suspension, according to the previous owner.
I installed the 13B and 4 speed from my REPU for test fitting purposes, and the previous owner's stories of easy burnouts were not exagerated.
A stock heavy (30 lbs) flywheel in a small light car with narrow tires tends to allow for such things. He destroyed two or three stock rearends, finally settling on one from '79 with its tall 3.7 ratio, which helped a little. Of course having a 13B's iron seals and increased torque at my disposal allowed for some interesting low RPM burnouts, though. More recently, I swapped flywheels to a Racing Beat light steel flywheel and noticed a major improvement in acceleration with only a minor drawback in launching ability. Over all, an improvement, which will find its way onto the new engine I'm building specifically for the MG.
Some old pics of the car and the REPU engine.
03-06-06, 07:14 PM
#2
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Jeff- I have always loved your projects. What is the progress on the 20bGLC?? I have not seen an update since www.vintagerotaries.com days.
03-09-06, 12:24 PM
#3
I haven't seen that forum in a while, hence no updates.
It turns out the spare 4 speed I had kicking around is incompatible with the car. I was going to combine that gearbox and my tail housing but Mazda changed some things. What's worse is that as I was removing the tail housing from the spare, the reverse shift rod lifted up and would not go back down. The REPU tranny did not have this problem, nor have any others I've ever worked on. I tried tapping it back down and it eventually went back to where it was supposed to be, but now it and the 3rd/4th rod are stuck. Only 1st and 2nd works. Crud.
I don't know much about transmissions, so you'll have to forgive me. I'm left with two options. Either throw the old REPU tranny back in as is (along with its bent input shaft, grindable 2nd, and noisy 3rd and 4th), or take both trannies to a competant transmission shop and have them swap the good bits from the spare over to the REPU case. Money is keeping me from doing option number two right now.
You guys may enjoy reading about my projects, but they're always done on a shoestring budget after careful consideration. I could get this MG running for very little cost, and it would be fast and scary, but the tranny would constantly remind me that it's not very comfortable. What's more, the only way to remove the tranny is by first removing the engine since the frame rails are very close together. It's a tough decision.
The reverse gears and their setup were entirely different from each other. What if the other gears are different as well? Perhaps the only interchangeable part is the shaft itself? What if it's different too?
Hmm... What if I just throw the REPU tranny back in for now and break in the new engine with it, so at least I know the tranny is 'good'.
It turns out the spare 4 speed I had kicking around is incompatible with the car. I was going to combine that gearbox and my tail housing but Mazda changed some things. What's worse is that as I was removing the tail housing from the spare, the reverse shift rod lifted up and would not go back down. The REPU tranny did not have this problem, nor have any others I've ever worked on. I tried tapping it back down and it eventually went back to where it was supposed to be, but now it and the 3rd/4th rod are stuck. Only 1st and 2nd works. Crud.
I don't know much about transmissions, so you'll have to forgive me. I'm left with two options. Either throw the old REPU tranny back in as is (along with its bent input shaft, grindable 2nd, and noisy 3rd and 4th), or take both trannies to a competant transmission shop and have them swap the good bits from the spare over to the REPU case. Money is keeping me from doing option number two right now.
You guys may enjoy reading about my projects, but they're always done on a shoestring budget after careful consideration. I could get this MG running for very little cost, and it would be fast and scary, but the tranny would constantly remind me that it's not very comfortable. What's more, the only way to remove the tranny is by first removing the engine since the frame rails are very close together. It's a tough decision.
The reverse gears and their setup were entirely different from each other. What if the other gears are different as well? Perhaps the only interchangeable part is the shaft itself? What if it's different too?
Hmm... What if I just throw the REPU tranny back in for now and break in the new engine with it, so at least I know the tranny is 'good'.
03-09-06, 01:21 PM
#4
Here are the specs. If it was my only car, I'd put this list in my sig.
1977 Rotary MG Midget:
13B '74 spec port
Hitachi 13B carb with RB 105 primary jets (matched to ports)
DLIDFIS
Yoohoo belt
RB light steel flywheel, stock 215mm disc and pressure plate
short header, Rotary Engineering 24" glasspack, dual Monza tip
As you can see, I'm not anxious to get bogged down by a tranny problem. It was to be a quick tailhousing and bellhousing swap and then I could shift my attention to replacing the REPU engine with a custom built one specifically for this car.
The new engine would consist of:
Y casting (1st gen RX-7) side plates which are lighter than 3B or R5 plates, and of course are nitrided. '74 spec ports and matched Hitachi carb because a Holley will not fit the car (without mods), and the better low RPM torque is nice and noticeable/useable. Better gas mileage than street ports as well. Besides, my Holley is water damaged and may not be rebuildable (I got it free from a friend).
'76 Cosmo intake manifold with its reversed runner manifold is no longer required now that a different engine with a decent intermediate plate will be going in, but it fits better than my '74 style manifolds, so it's staying. There is very little room to work with unless you like cutting sheet metal.
The doner engine was a nitrided R5 13B (my favorite of the 4 port 13Bs) complete with a high volume oil pump as original equipment. Still debating about oil pressure since it means swapping in an adjustable ROPR. The side plates were water damaged and the rotor housings had some missing chrome, but the rotors themselves appear ok.
Along with different side plates, I've got a set of well seasoned, but ok 13B rotor housings from an RX-4, and some new Atkins apex seals. They should break in fairly quickly.
Speaking of well seasoned, I have an adequately broken in yoohoo belt which shouldn't stress the bearnings too much upon startup. Hmm, I may leave it out of the loop until after the engine has had a chance to get comfy in its new home.
The stock duty clutch disc and pressure plate were on the RX-2 engine that was in this car when I got it. They're in good shape so I decided to use them with a light steel flywheel. The car itself was originally modded to fit the RX-2's short top mounted starter tranny. To fit the REPU tranny, I had to have the driveshaft shortened. The extra length of the later trannies wasn't really an issue, nor was the length of the 13B. It's the rotation of the gearbox that is causing all the grief. It contacts the car in several places. I'm dealing with those areas now to prevent noises and vibrations. Who knows... maybe after the tranny tunnel mods are done, the tranny noises won't be as annoying? It was actually fairly quiet in the REPU.
Most people who stuff a 12A into a Midget bolt a 1st gen RX-7 tranny to the stock crossmember, with maybe a rubber mat in between. The people that modified mine cut and welded in something to allow the stock Mazda rubberized tranny mount to be used for a quieter end result. I may someday redo it all under there to fit a 1st gen tranny, but for now, I'm going to grind and ballpien my way to a quiet setup with the REPU ribcase tranny. Its rotated gearbox, to make room for a bottom mounted starter, causes it to hit the upper endge of the tranny tunnel; which was not even a concern with the earlier RX-2 ribcase and its straight gearbox.
1977 Rotary MG Midget:
13B '74 spec port
Hitachi 13B carb with RB 105 primary jets (matched to ports)
DLIDFIS
Yoohoo belt
RB light steel flywheel, stock 215mm disc and pressure plate
short header, Rotary Engineering 24" glasspack, dual Monza tip
As you can see, I'm not anxious to get bogged down by a tranny problem. It was to be a quick tailhousing and bellhousing swap and then I could shift my attention to replacing the REPU engine with a custom built one specifically for this car.
The new engine would consist of:
Y casting (1st gen RX-7) side plates which are lighter than 3B or R5 plates, and of course are nitrided. '74 spec ports and matched Hitachi carb because a Holley will not fit the car (without mods), and the better low RPM torque is nice and noticeable/useable. Better gas mileage than street ports as well. Besides, my Holley is water damaged and may not be rebuildable (I got it free from a friend).
'76 Cosmo intake manifold with its reversed runner manifold is no longer required now that a different engine with a decent intermediate plate will be going in, but it fits better than my '74 style manifolds, so it's staying. There is very little room to work with unless you like cutting sheet metal.
The doner engine was a nitrided R5 13B (my favorite of the 4 port 13Bs) complete with a high volume oil pump as original equipment. Still debating about oil pressure since it means swapping in an adjustable ROPR. The side plates were water damaged and the rotor housings had some missing chrome, but the rotors themselves appear ok.
Along with different side plates, I've got a set of well seasoned, but ok 13B rotor housings from an RX-4, and some new Atkins apex seals. They should break in fairly quickly.
Speaking of well seasoned, I have an adequately broken in yoohoo belt which shouldn't stress the bearnings too much upon startup. Hmm, I may leave it out of the loop until after the engine has had a chance to get comfy in its new home.
The stock duty clutch disc and pressure plate were on the RX-2 engine that was in this car when I got it. They're in good shape so I decided to use them with a light steel flywheel. The car itself was originally modded to fit the RX-2's short top mounted starter tranny. To fit the REPU tranny, I had to have the driveshaft shortened. The extra length of the later trannies wasn't really an issue, nor was the length of the 13B. It's the rotation of the gearbox that is causing all the grief. It contacts the car in several places. I'm dealing with those areas now to prevent noises and vibrations. Who knows... maybe after the tranny tunnel mods are done, the tranny noises won't be as annoying? It was actually fairly quiet in the REPU.
Most people who stuff a 12A into a Midget bolt a 1st gen RX-7 tranny to the stock crossmember, with maybe a rubber mat in between. The people that modified mine cut and welded in something to allow the stock Mazda rubberized tranny mount to be used for a quieter end result. I may someday redo it all under there to fit a 1st gen tranny, but for now, I'm going to grind and ballpien my way to a quiet setup with the REPU ribcase tranny. Its rotated gearbox, to make room for a bottom mounted starter, causes it to hit the upper endge of the tranny tunnel; which was not even a concern with the earlier RX-2 ribcase and its straight gearbox.
03-10-06, 02:38 PM
#7
People always comment on the bungee cords. I think I'll leave them.
Ok, it looks like I'll just have to put the REPU tranny back together and throw it back in. No other option at this point. I have like five engines to rebuild in the coming weeks, so I can't spend forever on this.
I'll put some pictures up of the progress soon.
Ok, it looks like I'll just have to put the REPU tranny back together and throw it back in. No other option at this point. I have like five engines to rebuild in the coming weeks, so I can't spend forever on this.
I'll put some pictures up of the progress soon.
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03-12-06, 01:12 AM
#9
I got it today and swapped the parts over. They are identical other than a bit more wear of the gears and a noisy idler gear (I think). There was some evidence of internal water damage that seemed minor. The sound produced while spinning the input shaft has changed from an unhealthy rasp to something not too disimilar to my other one. In other words, encouraging. I think I'll use this one.
I think I'll use this one.
03-12-06, 03:30 AM
#12
Here you can see the mod they did to fit the RX-2 tranny with a stock rubber tranny mount to the MG. This is why I opted for the REPU tranny when going 13B because it had two sets of mounting holes and an unobtrusive tailhousing.
Here you can see the differences in tailhousings. The one with the longer stud and smaller mounting perch is incompatible with the setup in the MG.
Thankfully I was able to locate a tranny with identical features to my REPU tranny so as to be compatible with the MG. (that Wayne Dyer person knows what he's talking about) Here they are side by side right after I finished swapping tail and bellhousings.
The '74 carb, front cover mount, FC NA starter and FB alt.
Here you can see the differences in tailhousings. The one with the longer stud and smaller mounting perch is incompatible with the setup in the MG.
Thankfully I was able to locate a tranny with identical features to my REPU tranny so as to be compatible with the MG. (that Wayne Dyer person knows what he's talking about) Here they are side by side right after I finished swapping tail and bellhousings.
The '74 carb, front cover mount, FC NA starter and FB alt.
03-12-06, 02:53 PM
#14
You should get an RX-3 or something from Arizona. I'd like to get a Subaru 360 and put a single rotor 13B in it. That would be cool.
Here's a better angle so you can sorta see what the '74 carb looks like.
The rear plate is a Y casting with a threaded heater hole. Racing Beat sells a bolt of the correct size and thread pitch to block it. I figured this was smarter than using a short length of hose with something stuffed into the end and two hose clamps.
A couple used 13B rotor housings.
A couple used 13B rotors.
The Y intermediate plate I picked up yesterday.
I'd like to get a Subaru 360 and put a single rotor 13B in it. That would be cool.Here's a better angle so you can sorta see what the '74 carb looks like.
The rear plate is a Y casting with a threaded heater hole. Racing Beat sells a bolt of the correct size and thread pitch to block it. I figured this was smarter than using a short length of hose with something stuffed into the end and two hose clamps.
A couple used 13B rotor housings.
A couple used 13B rotors.
The Y intermediate plate I picked up yesterday.
03-17-06, 01:30 AM
#17
I got the tranny in on Monday. It was a little more difficult than I remembered. I realized I forgot to swap one small (6mmx1.00) stud for a short bolt of which I filed the head down some to clear the edge of the tranny tunnel. With the tranny hanging down a little, I removed the stud and bolt from the old gearbox and swapped them. It then went up into the correct position with millimeters to spare.
Dear reader, you must be made aware that I literally only have millimeters in places and metal to metal in others. I modded a few areas that were obviously rubbing, last week. in hopes of quieting this beast down. I'll take millimeters over metal to metal any day.
It'll be interesting to discover what, if anything, still rubs after all of this. I'd like to build a torque brace, rubberised in some way, to limit engine movement without transfering much noise. At least the obvious metal to metal contact has been corrected. The next step is to try it without the brace first. Then proceed logically.
I ultimately decided against painting the engine. The side plates and rotor housings don't need paint. Neither do the carb, manifold, alt etc. I figured the natural look won't stick out like a sore thumb in such a rough looking engine bay. The only things that were painted are the front cover mount and rear inspection covers. Those covers are either rusty or dirty, and if dirty, once cleaned, they usually don't look all that great. Mine were rusty and dirty.
Dear reader, you must be made aware that I literally only have millimeters in places and metal to metal in others. I modded a few areas that were obviously rubbing, last week. in hopes of quieting this beast down. I'll take millimeters over metal to metal any day.
It'll be interesting to discover what, if anything, still rubs after all of this. I'd like to build a torque brace, rubberised in some way, to limit engine movement without transfering much noise. At least the obvious metal to metal contact has been corrected. The next step is to try it without the brace first. Then proceed logically.
I ultimately decided against painting the engine. The side plates and rotor housings don't need paint. Neither do the carb, manifold, alt etc. I figured the natural look won't stick out like a sore thumb in such a rough looking engine bay. The only things that were painted are the front cover mount and rear inspection covers. Those covers are either rusty or dirty, and if dirty, once cleaned, they usually don't look all that great. Mine were rusty and dirty.
05-01-07, 01:00 PM
#19
It's been a while. The oil pan, tranny and rear oil line were dripping and I had a ton of other stuff to take care of so I put this project on the back burner.
I recently had a chance to get back into it so I did what any self respecting rotor head would have done. I pulled everything back out and rebuilt the engine. Not because the pan leaked, but because I wanted to use the old school MAZDA rotor housings like the old engine had, and I needed the other rotor housings for a different project.
I took it all apart, resealed the bellhousing (this time with The Right Stuff) and carefully rebuilt the engine with better parts. It actually feels tighter this time around (higher compression). All it cost me was a waterpump gasket, front cover gasket and a set of black coolant seals, since the old ones grew (technically I could have used them but I didn't want to take chances) and about two weeks of hobby time spent dinking around in the garage.
Enjoy.
I recently had a chance to get back into it so I did what any self respecting rotor head would have done. I pulled everything back out and rebuilt the engine.
Not because the pan leaked, but because I wanted to use the old school MAZDA rotor housings like the old engine had, and I needed the other rotor housings for a different project.I took it all apart, resealed the bellhousing (this time with The Right Stuff) and carefully rebuilt the engine with better parts. It actually feels tighter this time around (higher compression). All it cost me was a waterpump gasket, front cover gasket and a set of black coolant seals, since the old ones grew (technically I could have used them but I didn't want to take chances) and about two weeks of hobby time spent dinking around in the garage.
Enjoy.
05-01-07, 08:15 PM
#20
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12-18-07, 02:14 PM
#21
I just got an old school 215mm-only super light steel flywheel. This weighs less than the RB light steel flywheel I mentioned earlier in this thread. The clutch disc is a stock OEM 215mm as is the pressure plate, so they'll work great with this (and the RB flywheel can go to a different project requiring 225mm stuff). There is no need for anything bigger or grippier in this car. 
Freshly resurfaced (now it's even lighter lol).
I almost can't wait to pull the engine to swap the flywheel. Yep, I gotta pull the engine because the bellhousing is too wide to drop the tranny between the frame rails. Oh the joys.
Freshly resurfaced (now it's even lighter lol).
I almost can't wait to pull the engine to swap the flywheel. Yep, I gotta pull the engine because the bellhousing is too wide to drop the tranny between the frame rails. Oh the joys.
12-19-07, 09:10 PM
#24
That's pretty cool. Does it have a rotary in it?
I pulled the engine and swapped flywheels. I had to reseal part of thr oil pan because it sprung a small leak. Looks like I didn't schmutz enough Right Stuff on the rear corner. I wiped off all the oil, cleaned the area with brake cleaner and gooped it all up on the outside. It was a slow leak, and the right stuff works great so I bet this quick fix will work.
I got a picture of the super light steel flywheel installed. I'll post it later.
I pulled the engine and swapped flywheels. I had to reseal part of thr oil pan because it sprung a small leak. Looks like I didn't schmutz enough Right Stuff on the rear corner. I wiped off all the oil, cleaned the area with brake cleaner and gooped it all up on the outside. It was a slow leak, and the right stuff works great so I bet this quick fix will work.
I got a picture of the super light steel flywheel installed. I'll post it later.