Things are being confused by the terms being used; let me restate.
I have no "original" bolts. The earliest ones in my possession are the "suspect" ones from the 2007 rebuild and all four breakages were from this batch.
Wilkins s/h bolts were taken out of customer engines when he fitted new bolts in them, and they were just lying around. The first pair are different to the 2007 bolts and are nicely tapered at the shank step and have rolled threads; the second pair, provided this year, are of similar design and marked GKN. I don't have the original pair though but earlier photo shows they broke where the turning starts.
I have cleaned the threads in the block with a "plug" or No 2 tap (cost me ?1) and kept a rough note of the depth it went each time, between 3 and 5 threads from the top. Combined with the variation in bolt lengths and compared to the head thickness (see below) it is possible that one or more might have "bottomed", we are talking just a few millimeters clearance in all cases and I will, tomorrow, formally measure the depth available in each hole using a single bolt. The tap has a taper at the end of the thread so who knows what stops it.
I have, at last, received new QED bolts and washers and, as SteveH described on 27 Feb, they have small fillets under the head and also tapered shank changes but are turned threads (I believe; there is a hole in the end of the shank to support this operation). As Steve notes, the washers still have sharp edges and I believe that the underside of the bolt head is slightly tapered and also has a serious chamfer to the sides, so there isn't a huge amount of bearing surface.
- s/h GKN, s/h not known, 2007 failure batch, 2017 QED
- Difference between rolled threads (left two) and turned?
Some of the bolt length difference is an illusion as they are levelled at the top of the head flange, which varies in its thickness. There
is a similar difference between individual bolts, in the 2007 set at least.
The head thickness, measured by vernier caliper as close to the corner bolt holes as possible, is 116.5 mm ? 0.1 mm. (?, whatever it comes up as on your screen is the maximum deviation). What is the original thickness of a head? Also does anyone know how much a bolt stretches after 65 ft-lb tightening?
I have just purchased a two foot rule to check out all the flatness and twist features of head and block which I will attempt soon.
Any comments on observations will be gratefully received, and any answers. I will investigate the ARP type and might have to discuss matters with QED, who only do studs.