I've always understood, to determine "length of bolt," the measurement is of actual shaft length; taking measurment from under the head. (not including bolt head thickness.) This is how i have always measured bolt lengths. Generally, the shank is considered the "working distance" of a bolt and length of bolt is determined by shank length.
On another note, just last week, Chris and i were discussing concern for losing the thought processing how we induce, deduce, come up with conclusions for what we believe most accurate about sandcast details; simple case in point, pillion bolt length.
I can't remember where the 146/148mm measurements came from i listed in this thread from "Prod.Models."
I know in the past, when i was restoring 232, i measured early and late bolts, i wrote it down "somehwere" and now the only place i can find the measurement is in the website.
I know Chris and i had conversations about these lengths. I know Chris has measured these bolts. The parts books acknowledge different pn's ending at 1221 and beginning at 1222. When the data listed in "Prod.Models was loaded, i loaded engine info, Chris loaded chassis info. So, as far as length, without puling a bolt from 232 and puling a bolt from 4363, i think that's about all i can offer. I am guessing i took the 146/148 meaurements from the Prod.Models when i was putting "88 Distinctions" together.
If i took those 146/148 measurements, they were taken starting under the bolt head, NOT including bolt head.
I guess the bottom line here is that topics such as length of pillion bolt has been discussed and we've lost the info which created confusion or having to "reinvent the wheel."
What concerns me is losing this info, Chris says it best in his email ato me a few days ago, "Between us all, I am sure we have pondered in great detail so many of these anomalies – I still worry that our reasoning’s may gradually be lost over time. I suspect it ALL needs to be recorded somehow, and web sites are not necessarily the best way to do that given that if enthusiasm to maintain such resources wanes, or without others prepared to continue the work, they can simply be switched off and lost at some point."
I've not seen seen a center drill mark in a pilion bolt, other than Mark's and i've seen a fair number of pillion bolts.
Bo, it's probably just as difficult to explain your first hand observation of why 1462 has short bolts as it is my very distinct memory 4779 having a smooth round oil cover. Maybe some of these differences were not as "hard and fast" as parts books say.
I just measured the bolts i am using for 2157, which i believe to be late bolts. The shank length, measured under bolt head is 142mm. The total length, including (7mm) thickness of bolt head is 149mm. I took these measurements three times.
I can't remember how thick an early bolt head is. I can't remember how long an early shank is. Nor can i remember the difference in length between early and late bolts...... 2mm ? 3mm ? I went through all this a few years ago, and now it's seemingly lost to the ages. (should have started that old fashioned notebook i thought of starting several years ago.)