crusader

Anyone ever seen this before or know what caused/cures it? BACKGROUND--One very cold morning this past winter I jumped into my rover and (without much warm-up) began driving home. After a quarter mile the 2.5 NA diesel began tapping pretty loudly (taps in phase with engine RPM). No change in performance, just a loud tapping. I stopped to investigate, couldn't find anything obvious and limped 2 miles home. Noise cleared up after another 1/4 mile. Timing belt was changed 10,000 miles ago. I figure it's time for an engine overhaul anyway, so that's what I did. This engine had been overhauled at some point by the MoD and had all cylinders sleeved. I just got the head back from the machine shop. New valves, guides, seals and the mating surface machined flat. Waiting for the cylinders to be bored +.020" and new pistons & cam bearings to be fitted. While waiting for the block to get back from the shop, I've finally had time to closely examine the old pistons and I've discovered that the exhaust valves have interfered with the pistons (or the other way round), as shown in the photos. Other than limping home I hadn't driven the truck since. Looking at the second photo of the uncleaned piston with all the soot under the valve strike area, as well as the circumference of the valve in the first photo, it would seem that this was not an ongoing issue, but rather something very recent, so I suspect that was the cause of the noise. So... back to my question...Anyone ever seen this before or know what caused/cures it? Having discovered this, I'm now worried that machining the head mating surface flat will exacerbate this problem. Thanks, --Mark [EDIT:] Just remembered that when I replaced the timing belt 5,000 miles ago that somehow I ended up 1 tooth off on the cam wheel. Cranked it--wouldn't start, disassembled and corrected. Ran as good as it did prior after that. Could this camage have been caused 5,000 miles ago by being only 7.5 degrees off on the cam? [END EDIT]

Hello All, First post on this board--I usually post on the US boards, but there is much more 2.5 NA diesel knowledge on this board, due to the relative rarity of this engine across the Atlantic. A little backgound: I have my 2.5 NAD torn apart for a rebuild. All 4 cylinders have been sleeved (lined) to bring them back to standard specifications in a previous rebuild. I want to have the cylinders bored to fit +.020" pistons. My concern: Somebody mentioned on another board that lined cylinders can only be bored .010" oversize, and this sounded familiar to me, for some reason; However, I can't find anything in the Workshop Manual that says this. Can anyone help confirm or disprove this? Also, Anyone know which manufacturer of aftermarket parts Famous Four uses? I want to order my pistons and rings from them, but am trying to avoid a particular manufacturer of aftermarket Rover parts because I have NEVER had anything from this particular manufacturer last more than a year. Thanks!