Fletch1971

While acquiring parts to build a new 13B engine for my 1990 RX-7, I have been forced to acquire substitute parts, as specific FC S5 parts have become unavailable. One of these parts is the eccentric shaft. I have spent the past month inquiring from rotary experts what I can and cannot use in my build if I want to avoid having the rotating assembly dynamically balanced. At long last, I have a plan, and want to share what these experts have advised me to do. I am going to utilize an FD eccentric shaft, but I am also going to use the hardened RX-8 front stationary gear to match the FD e-shaft. After viewing Dan Atkins' video on comparing the different e-shafts through the generations, and asking the people at Mazdatrix and Racing Beat, I can use the RX-8 front stationary gear as a substitute for the FD front stationary gear, since the latter is outrageously expensive. I had already purchased a S5 front gear from Atkins prior to viewing the video, but soon realized that the oil holes in the bearing and the gear unit do not line up correctly with that on the main bearing journal of the FD e-shaft. The RX-8 front stationary gear, (N3H3-10-E0YC), does line up perfectly, however.

In addition to using the RX-8 front stationary gear, I was advised to use FD/RX-8 needle bearings, thrust plate, thrust washer, end play spacer, and bearing plate, (front stack parts?). On the other hand, I am still stuck on the issue of whether or not to use the FD front counterweight. I had already purchased this counterweight, being advised that it will work for all S5 and FD engines, as long as it is not an RX-8 front counterweight. In contrast, the expert at Racing Beat indicated that this FD front counterweight would necessitate having the rotating assembly balanced. I will be using a FC S5 REAR counterweight, since I am going with an aftermarket lightweight steel flywheel. This new engine won't be used for racing, and therefore will not see anything in excess of 6,500 rpm.

rxtasy3

iTrader: (2)

why start a thread here when u already have a similar thread in another section?

https://www.rx7club.com/new-member-r...ution-1167138/

peejay

FD and S5 rotors are the same weight, use either one as long as it matches the rest of your thrust bearing setup.

The eccentric shaft is so close to the axis of rotation that a little weight difference there doesn't matter. I have an S3 eccentric shaft with S4 rotors and I spin that engine past 10k with no bearing issues, which is where an imbalance will show.

I also use S3 stationary gears because that is what I had with good bearings. You only really need hardened gears if you are spinning the engine hard with pre-1986 rotors, which are very hard on the gears due to the 9 roll pin rotor gears.

Fletch1971

Speaking of hardened stationary gears...I noticed that there are two different front gears for the RX-8: The low power version and the high power version. Is the low power version similar in hardness to the front stationary gear of the FC S4? Alternatively, is the high power RX-8 front stationary gear similar in hardness to that of the FC S5? Since I already have a new S5 rear stationary gear,(That is supposedly hardened), I would prefer to run with the RX-8 front stationary gear which matches the hardness of the front S5,(Remember that I need to run the RX-8 gear to match the front main bearing journal of my new FD e-shaft).

TeamRX8

iTrader: (2)

high power is hardened and recommended, low power isn’t.

Not sure what you mean in the reply above, but would think that you want the hardened one regardless given it’s not really that expensive. If it was multiple hundreds of $$$ more maybe.
.

peejay

I think the low power ones also come with lower bearing clearances, since they had a much lower redline.

If the difference in price is small, then there's no sense even thinking about it, just get it. It won't affect anything if it's different from the rear or different than the rotor gears.

Fletch1971

Yes. I do want to run with the hardened RX-8 front stationary gear since that would be the same quality as the S5 front stationary gear. I simply wanted to verify which of the two RX-8 front stationary gears were hardened. My impression was that all front and rear stationary gears from S5 and later were all hardened.

j9fd3s

iTrader: (3)

the FD and High Power also get the multi window bearing, while the Rx8 low power has the FC bearing.
i believe everything after the S5 is hardened. oh and FD onwards gets the larger thrust bearings.

TeamRX8

iTrader: (2)

except for the Renesis 4-port / low power version

not really sure what somebody at Mazda was thinking to have done that with different part numbers, part tracking, etc. rather than one part for all. 🤔
.

j9fd3s

iTrader: (3)

i don't get it either, they actually list THREE different gears too. one would think you could just condense it to one number by now, but they haven't.
there is the A/T Low Power version (4 Port), FC bearing, if i'm reading you right non hardened
then the High Power, Marking O. FD style bearing
and the High Power, Marking Y, also FD style bearing

the really odd part is that there is a big price difference between the O and the Y, for what?
i'm obviously rusty about the Rx8, its all new fangled! the kids these days!

peejay

There's probably more oil pressure at low RPM with the low power bearing, which would be important with an automatic transmission.

Fletch1971

Since I decided to adopt a new FD eccentric shaft for my FC S5 engine build, I came to discover that I really should not be using a S5 front stationary gear with this part. Reason being that the oil hole on the front main bearing journal of the FD shaft is located 2.13 mm farther forward than that of the FC e-shaft, and the oil hole in stationary gear bearing does not line up correctly. So, I am planning on purchasing a new RX-8 high power front stationary gear to use with this FD shaft. I then started to question whether or not my new FC S5 REAR stationary gear would work on the rear main bearing journal of the FD e-shaft. So, I removed the new FD shaft from the box and lined it up side-by-side with a used, 151,000 mile FC eccentric shaft that I pulled from a 1991 RX-7 in a wrecking yard back in 2013. Upon observing the two oil holes in the rear main bearing journals of both shafts, I then noticed the difference. The oil hole in the rear main bearing journal of the FD shaft is about 1.5 mm,(As it appeared using my stainless steel ruler), farther back than the hole on the old FC e-shaft. It was apparent that the oil hole in the bearing of the FC S5 rear stationary gear would also not align correctly with that in the rear main bearing journal of the FD shaft. Now, to make things right, I now have to go out and purchase a new RX-8 high power rear stationary gear as well.

Since new FD rear stationary gears, (N3G1-10-E1Y), are no longer available from Mazda, the alternative is the RX-8 rear stat gear, (N3H3-10-E1YC), which does not have the groove machined for the o-ring. Now, I can use this part since it is cheaper, and simply use some hylomar sealant applied in the area where the o-ring would go, or I can purchase a modified gear from Mazdatrix, (SKU 10018), which has the groove for the o-ring machined in for about $70 more. Either way, I am getting a stationary gear with a multi-hole bearing for improved oiling, which is obviously superior to that of the FC S5 gear, and hardened as well. The same would apply to the RX-8 front Stat gear. The cheaper unmodified RX-8 high power rear stationary gear is tempting, but I am not sure how effective in using hylomar sealant in lieu of a machined groove and o-ring is in preventing oil leaks.

TeamRX8

iTrader: (2)

you are way overthinking this

use an anaerobic sealant, a very thin coat and it will cure in about an hour or so.

if it’s a race motor and you might be tearing it down on a regular basis, then the cost of machining a groove and using an o-ring might be justified.

but then at the same time wanting to cheap out on a less durable major engine part, it’s a bit nonsensical …
.

peejay

Wait a minute. If the difference is only 2.13mm.... that isn't going to make any significant difference. The oil passages will still line up just fine, and everything will work okay.

So, use whatever you want. Or fret endlessly about non-issues and never finish your engine.

fidelity101

iTrader: (11)

youre really overthinking this