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Lighter = Faster (RX-7 Build #2)

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1984 RX7 GS
I joined this group after finding your excellent, extensive posting of your build. Terrific detail and great pictures. My after retirement gig is rebuilding all Mazda 5 speed RWD transmissions including turbo. Current projects are 79' RX7, 2-Spec 90s Miata rebuilds, and S5 turbo. I'd be happy to help sort out your trans noise issue. With a new rebuild noise issues tend to be gear or clearance related and not immediate bearing failure. Did you purchase an aftermarket bearing kit for your rebuild and do you remember what bearing you installed in the center C/S position? The picture of your assembled center bearing housing isn't clear enough to determine what bearing was installed. However, from the picture it doesn't appear to be the bearing that I would expect for a Miata gear set.
 
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'86 RX-7 Base, '79 RX-7 GS
I joined this group after finding your excellent, extensive posting of your build. Terrific detail and great pictures. My after retirement gig is rebuilding all Mazda 5 speed RWD transmissions including turbo. Current projects are 79' RX7, 2-Spec 90s Miata rebuilds, and S5 turbo. I'd be happy to help sort out your trans noise issue. With a new rebuild noise issues tend to be gear or clearance related and not immediate bearing failure. Did you purchase an aftermarket bearing kit for your rebuild and do you remember what bearing you installed in the center C/S position? The picture of your assembled center bearing housing isn't clear enough to determine what bearing was installed. However, from the picture it doesn't appear to be the bearing that I would expect for a Miata gear set.
Honestly, I can't remember what bearings I used. At the time I had two N/A RX-7 transmissions and the Miata transmissions in various states of disassembly. I want to say I used everything from the Miata transmission internally, and just used the RX-7 housings. I think my assumption was the Miata transmission was ~10 years newer so it had to be in better shape. I don't recall any rough spots in any of the bearings though. Idling with the clutch engaged (pedal out) I have noise but with the clutch disengaged (pedal in) it's silent. Everything I've read online points to the input bearing. It's entirely possible my 4th gear noise while driving is something completely different. I already have new OEM input and front countershaft bearings I plan on installing over the Winter. Getting to those is easy compared to tearing down the entire transmission so I figure I'll try them first. I also have a strange vibration in 5th gear that appears to always be there. It's just more noticeable at certain speeds due to resonance. Dropping into 4th or 3rd causes the vibration to go away. I haven't figured this one out yet and I'm not too concerned because I rarely use 5th gear.
 
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1984 RX7 GS
Yes, excellent thought on replacing bearings especially the front input drive. That could certainly be the source of your neutral and 4th gear noise. When the transmission is in neutral only the center and rear main bearings do not spin while the car is parked. When you have the gear set out of the housing you should consider replacing the rear main and C/S bearings. 5th gear puts direct pressure on both of those bearings. The bearings are not expensive and also relatively easy to replace. However, I would recommend picking up a new C/S lock nut. Maz part no.: M501-17-309. If you decide to pull the rear main bearing check the 5th gear thrust clearance between 5th gear and the thrust washer. It should be between 0.004" and 0.012" for the factory standard. The standard thrust washer is 0.252 in. If the clearance exceeds 0.012" you can obtain either a 0.256" or a 0.260" thrush washer from your local Mazda dealer to bring the clearance into compliance.
 
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'86 RX-7 Base, '79 RX-7 GS
Yes, excellent thought on replacing bearings especially the front input drive. That could certainly be the source of your neutral and 4th gear noise. When the transmission is in neutral only the center and rear main bearings do not spin while the car is parked. When you have the gear set out of the housing you should consider replacing the rear main and C/S bearings. 5th gear puts direct pressure on both of those bearings. The bearings are not expensive and also relatively easy to replace. However, I would recommend picking up a new C/S lock nut. Maz part no.: M501-17-309. If you decide to pull the rear main bearing check the 5th gear thrust clearance between 5th gear and the thrust washer. It should be between 0.004" and 0.012" for the factory standard. The standard thrust washer is 0.252 in. If the clearance exceeds 0.012" you can obtain either a 0.256" or a 0.260" thrush washer from your local Mazda dealer to bring the clearance into compliance.
In hindsight I should have replaced all the bearings while I was in there. I was using the factory service manual as reference during the rebuild and it's not always the most detailed in explaining what needs to be done. The inspection of the clearances on the output shaft is one area that could have used more detail. I was never sure I was measuring the correct clearances. In the end I reused all the original Miata internals under the assumption the clearances. This is another reason I kept the original bearings. Perhaps this is why I'm getting 5th gear vibrations, who knows. A quick internet search hasn't turned up anything for vibration in 5th gear only. Fortunately these transmissions are literally a dime-a-dozen. Provided the shafts, gears, and housings are still okay everything else can be replaced fairly cheaply. They're not known for their strength so I imagine I'm looking at a rebuild down the line anyway pushing 200+ HP through it.
 
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'86 RX-7 Base, '79 RX-7 GS
Dead forum is dead. Up to 1500 miles. Finally replaced the water pump and almost had to pull the engine due to a mistake I made in the process. Transmission still makes noise. Still needs an alignment. Got the engine harness cleaned up so I don't have wires spiraling around anymore. Picture:

 

Lewis7789

Evan aka "Lady Hands"
Contributor
:
1995 MX-5, 2006 MZ5, 2001 Yamaha R1
Sorry to hear about the minor issues. But I LOOOOVE seeing updated in here. That picture totally made my morning.
 

chuyler1

goes to eleven
Moderator
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2013 CX-9
Looking good, still one of my favorite looking engine bays. Clean and simple. Wish I could see it in person.
 
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'86 RX-7 Base, '79 RX-7 GS
I finally dropped the car off to get an alignment at a performance shop up in the city. Oddly, that was probably the most highway miles I've put on the car to date and I'm rethinking my decision to drive it to so shows/events in the near future. I'm seriously curious just how bad the current alignment is. I told 'em to go with -3/-2 for front/rear camber and 0 toe all around. Their "track guy" is also going to take a look and offer his suggestions. I also asked them to throw it on their scales as well. I'm not going to have it corner-balanced unless it's horrendously off but I do want to know its weight for towing purposes.

I finally broke down and purchased a passenger's seat and harness. Decided to get an OMP WRC-R and another G-Force 5-point harness. I would have preferred to get a seat with lower side bolsters to make it easier on passengers (e.g. OMP ARS) but, oddly, most were narrower than the WRC. If OMP offered an ARS-R XL that would have been perfect. I suppose I could have gone with a Sparco EVO II or something but the OMP/Sparco mismatch would have bothered me to no end. I'm already annoyed OMP redesigned their seat designs in 2014 so the new WRC-R is going to be slightly different from my current WRC. The plan is to switch the current, expired WRC and 5-point harness I'm currently using to the passenger's side and use the new, non-expired stuff for me. I'll finally switch over to the new brackets as well to hopefully gain a little more headroom.

I still need to get the headlights aimed. I can do it myself if I can find a straight, vertical wall on a flat surface with ~30 ft of space. Otherwise, I'm going to have to find a shop with the optical aiming equipment. I still need to replace the front bearings in the transmission but I've been putting that off due to the effort involved. I noticed a small leak in one of the rear CV boots a while back. I didn't see any tears but there's a small amount of grease splattered on the underside of the car. Then there's still the act of finishing break in (around 1600 miles now) and finishing the tune.

All this has to be addressed before I can start tracking the car again.
 

Lewis7789

Evan aka "Lady Hands"
Contributor
:
1995 MX-5, 2006 MZ5, 2001 Yamaha R1
Well, you're getting there! Think she'll be on track this season? I just can't wait to watch the GoPro footage.
 
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'86 RX-7 Base, '79 RX-7 GS
Well, you're getting there! Think she'll be on track this season? I just can't wait to watch the GoPro footage.
Man, I thought I replied to this. If I do get on track it'll likely be later in the season. There's still a few things I need to take care of. The transmission and tune are the biggest things. I'll hopefully have the front and rear transmission bearings replaced in the next couple of weeks if my parts ever arrive and once the car is broken in, likely the end of April, we can finally tune for power. Even then I'm really anxious about getting back on track. I might just stick with a couple hyperdrives this year to verify the car can handle 20 minutes at racing speeds. I still don't have a trailer either so the car will have to handle track time and 2.5 hour return trips.

I got the car back from the shop on Tuesday. Final camber is something like -2.9/-1.9 degrees front/rear. Oddly, that's with the front camber plates maxxed out. I figured we'd be able to get more. Now the fun part. The car's weight? 2325 lbs with about a half tank of gas. That's more than 300 lb less than the weight of the '86 base model (the lightest FC) and 500 lb less than my old '89 GXL. I was shooting for 2500 lb but it now looks like that's the weight WITH ME IN IT. No wonder this things seems to scoot when it's probably only putting down like 150 hp to the wheels. My '79, which is about the same weight, now seems so slow...

I did notice the car seemed to want to pull to the right more after the alignment even with 0 toe front and back. I don't think their machine is wrong so I'm looking elsewhere. The tire pressures checked out find. I checked the front wheel bearings and found them out-of-spec; both play and pre-load. The passenger's side was especially bad. I pulled everything apart and cleaned them. The bearings and races look good so I opted not to replace them and just repacked them and reset the pre-load. I haven't had a chance for a road test yet, but it shouldn't be any worse.

I got my new seat and harness in and everything is installed. I'll get some pictures up later. Unfortunately the seating position didn't change much. I was hoping for a slightly lower position. At least the interior is "complete" until I decide to replace the carpet and adjust the position of the display. I'm also thinking about getting a different steering wheel. Something slightly larger in diameter with a little less dish, if possible.
 
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'86 RX-7 Base, '79 RX-7 GS
Changed the steering wheel so the shift lights are no longer being obstructed from view.



This one is larger in diameter and has less "dish." Overall it puts the wheel in a more comfortable position and makes turning at low speeds a little easier.

The next two tasks are aiming the headlights so I can finally drive at night and changing some bearings in the transmission. Once that's done all that's left is to finish the break-in cycle. I'm over 1700 miles and counting and hitting 8000 RPM regularly...
 

chuyler1

goes to eleven
Moderator
:
2013 CX-9
Once that's done all that's left is to finish the break-in cycle. I'm over 1700 miles and counting and hitting 8000 RPM regularly...
You do know that people build motors in the morning and race them hard on the track in the afternoon, right? You are well past break in period. Change the oil and let her rip.
 
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'86 RX-7 Base, '79 RX-7 GS
You do know that people build motors in the morning and race them hard on the track in the afternoon, right? You are well past break in period. Change the oil and let her rip.
My understanding is the more new stuff you use the more break-in time is needed. For example, had I only replaced the soft seals the break-in cycle would be near non-existent since everything is already "bedded" together. Just run the engine for a couple hours, change the oil and filter, and go. Add new hard seals and break-in increases to ~500 miles. New/resurfaced housings: ~1000 miles. Since I had a new eccentric shaft and all new bearings I was advised to double the normal break-in duration. So, with "new" (i.e. ported, re-surfaced and re-nitrided) housings and all new hard seals ~1000 miles became ~2000 miles. I changed the oil and filter after the first few hours of running (20W50 -> 10W40) and then again at 1000 miles (10W40 -> 10W30). I'm going to do it again at 2000 miles and might drop the viscosity to 5W-20 like the RX8 calls for since I have a RX8 e-shaft and stationary gears. I'll probably switch over to synthetic oil as well. But to your point, if the engine was going to fail it likely would have done so by now.
 
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'86 RX-7 Base, '79 RX-7 GS
Dyno fun!

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