We did not check it, we didn't even pull the flywheel off. All we did was tighten the flywheel nut.

 

Did you take a look at your drive shaft u joint how people mentioned before. My car doing the same thing I replaced motor mounts, transmission mount and trans mount bracenter bushing and I still had crazy vibration from my driveline I could feel it hard on the shifter. Then once I replaced the driveshaft with a new one it all went away. I checked the old driveshaft after I removed it and the front u joinst were all busted up. Check the drive shaft, remove your trans oil before you pull it out.

 

this is your issue, ignore all that mount shaft hog wash, your fly wheel is turned, trust me... pull the trans and clutch you will see.

 

With 350ft/lbs on the nut and the engine rotation tightens, a loose nut would be highly suspect.

What would be a likely cause of a turned flywheel? I would like to avoid.

 

well i had about 10k miles on my build, but when the woodriff key sheered it was because i had dropped the clutch from like 5k rpm on a gravel/sand road. hard to say load was a major factor, i mean it was sand and gravel.. but it was a 5k clutch dropp. soo...

 

Dumping the clutch... Drag racing. Not enough torque on the flywheel nut from the start. These kind of things.

 

Good to know. Metal fatigue (age) + stress.

 

Thanks and what size is the woodriff key?

 

I don't have a spare to measure, but here is a pic from the Mazda 85-85 parts catalog.
Flat on the outside, curved on the inside.

 

Keys may be available through Mazda, using the P/N in the above diagram. You can also probablly source one at a hardware store too. Woodruff Keys are sized by number, each number reflects a certain diameter and width of key. You should be able to measure the keyway with a pair of calipers. Basically, the key is just half of a diameter made to a specified thickness. The keyway is machined for a percise fit width wise, and to a depth of just slightly shy of half the diameter, so that the face of the key protrudes slightly, to provide a positive ancor to the pully, gear or in this case, flywheel to the shaft. A lot of times, the O.D. of the shaft is also tapered in the key'd area, to provide additional alignment and strength to the whole joint.

https://catalog.nordex.com/cc2273

 

I tried looking up the part number and I couldn't find anything

 

part number is 0820-11-705, its the same for every rotary engine