edwardbahaw Posted December 8, 2010 Share Posted December 8, 2010 This is a video of a 300tdi block with new standard pistons and liners fitted It shows that the pistons can move up/down and left/right in the bores! Would this lead to problems? These are the specs The bore diameter is 90.47mm The piston diameter is 90.395mm The ring gap clearance is 0.4mm Quote Link to comment Share on other sites More sharing options...
Range Rover Blues Posted December 8, 2010 Share Posted December 8, 2010 Pistons are actually ground slightly oval towards the bottom of the skirt because of how they expand and how the gudgeon pin effects their expansion. Aluminum expands almost twice as much as iron or steel by the way, then there should be room for some oil. I'll admit that looks like a lot more than 0.075mm of play though. Quote Link to comment Share on other sites More sharing options...
leon_81 Posted December 9, 2010 Share Posted December 9, 2010 oddly enough we had the head of my friends 200tdi last night and noticed the same sort of amount of movement, also found there is a lip in no4 bore about 10mm down from the block face - you can see it and feel it with your finger we're thinking its been like it a while, so will stick a new head gasket on and chuck it back together and see what happens! worst case scenario he'll buy a new engine from a breaker Quote Link to comment Share on other sites More sharing options...
cackshifter Posted December 9, 2010 Share Posted December 9, 2010 The lip is very likely the wear ridge where the top ring gets to - worn bore below, original bore above. Nigel Quote Link to comment Share on other sites More sharing options...
Range Rover Blues Posted December 9, 2010 Share Posted December 9, 2010 It's a wear ridge alright, normaly when I find them in just one cylinder it's because one of the rings has broken But if it was running fine there's no reason to imagine it won't do so again. Quote Link to comment Share on other sites More sharing options...
edwardbahaw Posted December 10, 2010 Author Share Posted December 10, 2010 We should complete the reassembly soon and should be able to start her up over the weekend. Would be reporting back on the outcome then! Quote Link to comment Share on other sites More sharing options...
monkeyb0y Posted December 10, 2010 Share Posted December 10, 2010 with regards the excessive play....i also beleive this is normal under worktop conditons..as there must be some CTE properties allowed for in the piston design. http://en.wikipedia.org/wiki/Thermal_expansion theres a bit at the bottom which specifies poor performance of cold engines. boring but plausable.. Rich Quote Link to comment Share on other sites More sharing options...
leon_81 Posted December 10, 2010 Share Posted December 10, 2010 sorry for the thread hijack - but my friends 200 went back together yesterday and still runs like a bag of carp! so i'd say the misfire and awful smoke must have been the dodgy cylinder rather than just the head gasket! new engine time for him anyway - hope yours goes back together and runs properly! good luck Quote Link to comment Share on other sites More sharing options...
edwardbahaw Posted December 10, 2010 Author Share Posted December 10, 2010 Leon I would be able to report back the outcome by Sunday. Ed Quote Link to comment Share on other sites More sharing options...
Range Rover Blues Posted December 10, 2010 Share Posted December 10, 2010 with regards the excessive play....i also beleive this is normal under worktop conditons..as there must be some CTE properties allowed for in the piston design. http://en.wikipedia.org/wiki/Thermal_expansion theres a bit at the bottom which specifies poor performance of cold engines. boring but plausable.. Rich Couldn't see the link you mentioned but you are right in what you say. Aluminum expands almost twice as much as steel and iron (as I said above) the figures are about 11x10-6 for iron and 23x10-6 for aluminium, that's per degrees celcius. Also the piston runs hotter than the block, the block obviously is cooled by water at around 100 degrees, the piston is cooled only by oil at around 130degrees or more. In operation the piston face is exposed to temperatures approaching the melting point of aluminium and is only protected by the thermal boundary layer (that's why pinking causes so much damage in a petrol). Anyway, pistons are ground so that they become fully cylindrical when hot, when cold they can be tapered and oval because of how the gudgeon pin effects expansion. Quote Link to comment Share on other sites More sharing options...
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