Lighter = Faster (RX-7 Build #2)

Thanks Jon!

The rotary engine is pretty fascinating the more I see and read. What goes on the middle smaller lobe(s) in the pictures above?

The large lobe with the 4 holes is for the rear rotor. The middle section rides in the hole of the center iron; it's not a bearing surface. The other visible bearing surface is the smaller diameter just behind the rear lobe and that rides inside the rear stationary gear. I didn't take a picture of the engine with the center iron installed because my hands were pretty oily by that point. I also have the rear rotor housing, rear iron, and flywheel sitting on top of everything to keep it all compressed. I'm pretty sure the engine assembly process is intended to be carried out in one session so I wanted to keep everything compressed as if that were the case.
 
I made a lot more progress last night than I expected. I guess that's what happens when you can work 5-10 PM without any interruptions. I also managed to take more pictures this time around; maybe too many.

Setting up for the rear rotor:

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No pictures of the rear rotor installed. My hands were pretty oily at that point. Here's a shot with the rear iron installed and all the tension studs and bolts torqued down:

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That's 18 nuts/bolts that have to be incrementally tightened down in a specific order. This is where things got fun:

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The flywheel is held on by a 2-1/8 in. nut that's torqued to something like 290-350 ft-lb. Since I have neither a 2-1/8 in. socket or a torque wrench capable of 300+ lb I got creative. I bought this giant wrench to remove the nut years ago. My body weight applied at 24 in. from the nut center should put the torque within the specified range. Yay, Physics! After that I threw together the front stack to check eccentric shaft end play. I finally got to use my fancy dial indicator and base:

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The end play is a little high at somewhere between .0025 and .0030 in. but it's still in spec. It's adjusted by using spacers of known width and I'm currently using the second-smallest. The smallest would buy my about .0008 in. less play but I didn't want to have to wait for another part. Another option was to try to "modify" my spacer to make it thinner. I decided to leave it as is. I then installed the oil pump and chain and then front cover and main pulley:

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Even though I'm no longer using the crank angle sensor I still have use its drive gear in the front stack. I called it a night before installing the oil pan to give all the other sealant time to dry.

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I'll install the pan, water pump assembly, and clutch tonight, which means I should be able to bolt on the transmission and drop everything in the car tomorrow or Thursday.
 
I've also been following this thread and I must say I'm really impressed with your progress...Big thanks for sharing your build with us and for including lots of juicy details! (2thumbs)

Seeing you rebuild your own rotary engine makes me wonder if I could do such a thing myself someday (with a lot of help)...Especially when considering how much a rotary rebuild costs in Japan. I could buy a brand new kei (small) car for the amount it would take to rebuild the 20B. :(

On a related note, what's your take on running premix vs the factory oil metering pump? Apologies if you mentioned it already but what are you going to run? I'm still running the factory electronic metering pump which I've heard can be problematic and my tuner (TCP Magic) says it's functioning now but it could fail at some point and to replace it (if possible) would cost a fortune...Another option I believe would be to run an older mechanical metering pump but I'm not sure that would work on the 20B. I'm also not keen on premixing and I'm not sure if that's possible with a street car in Japan...Anyway, your thoughts would be very much appreciated and keep up the awesome posts!


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I've also been following this thread and I must say I'm really impressed with your progress...Big thanks for sharing your build with us and for including lots of juicy details! (2thumbs)

Seeing you rebuild your own rotary engine makes me wonder if I could do such a thing myself someday (with a lot of help)...Especially when considering how much a rotary rebuild costs in Japan. I could buy a brand new kei (small) car for the amount it would take to rebuild the 20B. :(

On a related note, what's your take on running premix vs the factory oil metering pump? Apologies if you mentioned it already but what are you going to run? I'm still running the factory electronic metering pump which I've heard can be problematic and my tuner (TCP Magic) says it's functioning now but it could fail at some point and to replace it (if possible) would cost a fortune...Another option I believe would be to run an older mechanical metering pump but I'm not sure that would work on the 20B. I'm also not keen on premixing and I'm not sure if that's possible with a street car in Japan...Anyway, your thoughts would be very much appreciated and keep up the awesome posts!


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Im going to throw in my 2 cents on this.

Premix is the way to go unless you are doing emissions testing.

I suggest, and have been suggested to run premix even if u have the omp.

It will fail eventually.
 
On a related note, what's your take on running premix vs the factory oil metering pump? Apologies if you mentioned it already but what are you going to run? I'm still running the factory electronic metering pump which I've heard can be problematic and my tuner (TCP Magic) says it's functioning now but it could fail at some point and to replace it (if possible) would cost a fortune...Another option I believe would be to run an older mechanical metering pump but I'm not sure that would work on the 20B. I'm also not keen on premixing and I'm not sure if that's possible with a street car in Japan...Anyway, your thoughts would be very much appreciated and keep up the awesome posts!

I'll be premixing. The original ECU I was going to run couldn't control the electronic OMP so I junked everything. The one I have now can control it but I'm not sure of the durability of the electronic units. Someday I'd like to add a mechanical OMP with a dedicated reservoir. That will require some some significant changes but I like the idea of having the oil injection system separate from the fuel injection system. Even then I'll still probably premix but to a much lesser extent.

I didn't take any pictures last night because it was a short night. I got the oil pan and clutch bolted up but in the process of installing the water pump assembly the water pump gasket ripped. Fortunately, they're cheap but it's cost-prohibitive to purchase online due to shipping costs, so I'm trying to see if a local dealership can get one in. This doesn't affect the ability to install the engine but it'll make installing the water pump assembly a little more difficult. Plan tonight is to get the transmission bolted to the engine and get everything ready to drop into the car.
 
I've been premixing for over 10 years on my rx7 with a 12a, I completely eliminated the OMP. I use synthetic 2cycle oil from Royal Purple , it doesn't smoke much except when the car is cold. I can not address if it would pass emissions testing since the car is old enough to have Historical plates and doesn't need to be tested.
 
I got the transmission and most of the peripherals bolts onto the engine last night.

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A local dealership should have the water pump gasket today so tonight I plan on installing the pump assembly. I need to find a M10x1.5 bolt for the starter, which shouldn't be much of a problem. I also think I need to find a 1/8 in. BSPP plug for the stock coolant temperature sensor location on the block. I have a 1/8 in. BSPT plug but it threads in pretty far before getting tight. BSPP fittings have straight threads and seal with a washer whereas BSPT are tapered and seal with pipe sealant. Mazda switched from BSPP to BSPT somewhere in production and I guess I have an earlier rear iron. None of this should prevent me from dropping the engine and transmission in the car tomorrow or over the weekend.
 
I will say it's significantly easier to bolt the transmission to the engine when it's out of the car.

I guess I will find out later this winter, I am doing a refresh of the 79 rx7. Mostly seals and bearings in the drive line.
 
I guess I will find out later this winter, I am doing a refresh of the 79 rx7. Mostly seals and bearings in the drive line.

I was referencing the time it took us all afternoon and early evening to swap that transmission into my old '89.

A local dealership was actually useful! I had them order a part on Wednesday and they had it by noon on Thursday. I'll gladly pay the extra $2 through the dealership than wait a week for something like a gasket to arrive. With that, the water pump assembly was installed:

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I don't think the engine was intended to be installed with the transmission bolted to it:

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Doing this by myself with the hood and fenders still on was interesting. Lots of pushing and pulling involved with little collateral damage. Since I got the engine in ahead of schedule I started bolting other things on that won't get in the way later. Here's how it looked when I called it a night:

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I may have an issue with the oil cooler lines interfering with the side-mounted alternator. The front line is a little long, which causes the fitting to angle upward at the front cover. While I haven't confirmed, this could be an issue with the belts. Worst case is I'll need to remove about 4 inches from that line and perhaps change the fitting angle. Nothing is bolted down so maybe it won't be an issue. The rear line could also be shortened by an inch or two.
 
Well there's not much time left to work on this. After this week I have to focus on the move and we'll be living in an apartment for <6 months. During that time the RX7 will be in storage and I'll only be checking up on it to turn the engine over a couple times per week. I dunno, maybe my wife will let me work on some wiring in the house...

It was a pretty productive weekend. Saturday I got just about everything I have bolted onto the car. I'll have to remove some of this again in the future but it's safer to move everything with the car than risk losing a small box with a critical (and expensive) piece. The intake, exhaust, and drivetrain are completely installed and the transmission is full of fluid. All that's left on the engine side is the radiator and cooling fan. Here's the engine as it sits now:

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On Sunday I took advantage of the nice weather and painted the new pieces of the roll bar. Fortunately the VHT "roll bar and chassis" satin black paint is pretty close to the powdercoating on the main hoop. One day I'll get everything re-done in the same color. I also got the driver's seat bolted in with the Wedge Engineering bracket. The seat is still a little tall in my opinion but I think I have a way to modify (i.e. cut up) the side brackets and mounting bracket to get it lower.
 
I found a good way to figure out the oil cooler line routing and length was to cut up a garden hose an insert it into the fittings to see if would interfere with any thing and then measure the hose and make a copy of it out areoquip line. That car is looking dangerously close to running. loving the color
 
I found a good way to figure out the oil cooler line routing and length was to cut up a garden hose an insert it into the fittings to see if would interfere with any thing and then measure the hose and make a copy of it out areoquip line. That car is looking dangerously close to running. loving the color

I found a way to make the lines work. I had to get a little creative like running the rear line underneath the swaybar and putting an "S" bend in the front line. I'll have to keep an eye on them to make sure none of the fittings are stressed to the point of leaking.
 
Quick chime in here to say thanks to everyone for the thoughts on premixing...I'm assuming I can't with a street car in Japan but I will double check...Thanks again!

Awesome progress by the way, I'm going to miss your build updates after the 7 goes in storage!



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That last bay shot was the money shot. Great progress, Jon.
 
I'm happy to say the car has safely made its way to Richmond and is now hibernating in a storage unit. The move has been very nerve-wracking so a little break will be worth while. That being said I can't wait to get it back in a garage sometime in the Summer and resume work.
 
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