Since no one reads my forum… an update.
Thanks for all the suggestions regarding what might be causing the gears to grind when the car is warmed up. The throw at the throwout bearing lever was measured when the car was cold and again when it was hot… exactly the same… nuts. That means the problem is not in the activation of the lever but is something inside the bellhousing. After thinking it through the problem became simple: the reason the gears are spinning can only be due to the clutch or pilot bushing dragging.
The drivetrain is being prepared for removal and should be out by Sunday or Monday. The best I can hope for is that there’s something obviously wrong with the pilot bushing because I can deal with that here. If it’s not that then it’s “probably” the clutch, which will be removed and shipped off to the manufacturer. That’ll side-line the car for a couple weeks but there’s plenty to do in the meantime. The design of the lower bushing in the rear uprights will be improved (and noted in the book), and a thermal switch will be added to the radiator. Also, new front uprights will have the steering arms bent (to fix bumpsteer) and so that stock Miata steering tie-rods can be used. As it is, the combination of big brakes and large aftermarket rod-ends (used with the bumpsteer kit) don’t live well together. The rod-ends had to be ground down to clear the rotors to such an extent that I don’t trust them (being front steering it means that under braking, the tie-rods are put under tension – toward the weak grounded side.) That task will take a while as bumpsteer will have to be rechecked, though it’s easier to do now since the radiator has to be removed anyway for the welding above. If all this doesn’t get boring then there’s this book I keep hearing about that has to be finished…
This is the start of a two-week “man-cation”, staying at home while the wife’s away, morning walks with the dog, making points on yard projects, and all the above car stuff; no lounging about. Also, there’ll soon be a Ford F-150 truck in the picture, something more suitable for towing a car :).