Hi - I’m pulling apart a 4.2 from a 72 XJ6 that has a lot of miles on it and has definitely been rebuilt in the past judging by the aftermarket pistons and undersize bearings. Marked on all of the main bearing caps on the bolt head pad is ‘5 OFF’ - I haven’t seen this before but I’m thinking that it means that .005" was machined off the the caps mating surfaces to facilitate align boring the block. Has anyone else seen this notation and does it make sense that only .005" would be removed for an align boring procedure?
BTW they are actually marked vertically like this:
Is it the same location as these? So far as I am aware, the main caps on all XK 6 cylinder engines are stamped with a three letter + one number code XYZ 1, XYZ 2, XYZ 3, etc. The same three letter code plus the number is also stamped adjacent to the cap on the block skirt, The three letter code is also found on the side of the timing cover. The three letters identify them as parts of a specific block.
Thanks @Mike_S and @Robin_O_Connor - On this block there is only the number of the cap itself in the positions Mike’s pics show without the 3 letter prefix (1,2,3 etc…)
The ‘5OFF’ markings I’m questioning are the same on all the caps and are on the flat machined pad where the head of the bolt fits - not on the raw cast area. IIRC the last 7L block I did - which was also from a 72 Series 1 XJ6 - didn’t have 3 letter prefixes with the cap index numbers either.
It’s all still really dirty - gonna clean it up a little tomorrow and see if I can see ‘5OFF’ anywhere else.
That is an ATI damper with a GM Performance Parts part number that was homologated for NASCAR Chevrolet crankshafts with big block Chevrolet crank snouts. The BBC crank snout is really very similar a Jaguar, and ATI makes a hub for the Jaguar crankshaft. It does not use the cone. You used to be able to buy it separately from the complete damper assembly, but they still catalog the complete assembly. This cropped image is the best photo of it I have. BTW, that is the notorious silicone XJ6 seal right behind it.
The seal rides on the stock Jaguar distance piece and the ATI hub abuts it. The timing marks and belt alignment were absolutely perfect. You do need to use a big block Chevrolet 3 hole crank pulley. I found this sand cast Moroso was similar in appearance to a stock pulley.
