Hi Nick,
We had a very similar thing happen here.
A new GT40 owner who had recently purchased his car from the owner/builder, drove it a while and then brought it here to solve some cooling issues.
Initially I thought air cooling system, incorrect piping to the rad or header tank or a malfunctioning header tank / overflow tank.
There were corrections required in all those areas, some of it quite extensive. All said and done the car now was drivable without overheating.
On my short test drive the car (RCR GT40 with a Ford 347 stroker, G50 transaxle) it pulled really strong through the gears, however could barely pull itself up a drive way ramp. Made no sense at all but the cooling system worked fine.
About a hundred miles later the party was over, oil pressure dropped, the driver shut off the engine and called for a tow. The engine was not happy to restart.
To make a long story short: a) Engine and Transaxle out b) Engine sent to reputable engine builder for diagnosis and repair c) Problems: Crankshaft and rod bearings wiped out, crank thrust bearing wiped out, several rod and crank bearings spun d) Probable causes: 1) improper bearings for forged stoker crank 2) Excessive thrust on end of crankshaft. e) Solution: Complete rebuild required. There was less than 350 miles on the engine by the way.
Before reassembling the new engine to the transaxle checks were made to the condition of the clutch, flywheel, pressure plate, throwout bearing and slave cylinder and verified to be usable.
Also, I checked, rechecked and triple checked the distance between the pilot bearing in the new crankshaft against the input shaft on the transaxle.
The pilot bearing (or bushing) holds the input shaft concentric with the crank however it should never be end loaded, as would happen if the input shaft was too long, the bellhousing adaptor thickness was not accounted for correctly, the pilot bearing carrier or bushing was not fully seated in the crankshaft or otherwise too long.
The input shaft of the transaxle was about .035 longer than the space available to avoid end loading the pilot bearing (and therefore the crankshaft thrust bearing). A new, shorter aluminum pilot bearing carrier was spun up, installed, test assembled and measured to confirm there was no end loading of the crankshaft.
I suspect that was your problem. Hope this helps with the diagnosis regardless.
Cheers
Ian
Unless you're in the habit of leaving the car in gear while stopped at intersections or in the pits, meaning you are holding the clutch pedal down for long periods of time, I doubt there's enough pressure in the clutch pressure plate(s) to hurt the crankshaft bearings.