LCJ Posted January 5, 2014 Share Posted January 5, 2014 My 300tdi had a new head in early December after the old one cracked and has done around 300 miles since then. Recently it developed a rapid tapping at high revs and under load. All gaskets (head and exhaust manifold) fine and the car drives very well, though slightly flat in fifth. Took the rocker cover off today and while the valve clearances are fine, rocker assembly good and valve stem caps all in place, but 3rd push rod is bent. I'm guessing this is cause of the tapping but would what have made the rod bend that I ought to check before reassembling? All thoughts appreciated! Quote Link to comment Share on other sites More sharing options...
Ash.Witty Posted January 5, 2014 Share Posted January 5, 2014 How bent is it, I have seen a few bent push rods occurring when the rocker shaft has been tightened down without slackening off the adjusters after the head has been skimmed and then barring the engine round to set the clearances, valve comes into contact with the piston and the push rod bends. Or if the pushrod wasn't correctly located in the follower, whilst tightening the rocker shaft it has been bent then relocated when barring to do the clearances and the valves were set correctly to look at you may possibly not notice until its running and making the tapping noise. Quote Link to comment Share on other sites More sharing options...
LCJ Posted January 5, 2014 Author Share Posted January 5, 2014 Thanks for response. It's pretty bent. And very obviously visible to the naked eye, maybe two - three degrees? Not sure where it is on the scale though? Can I get away with just replacing the bent rod or do I need to check for damage to the piston? Quote Link to comment Share on other sites More sharing options...
Ash.Witty Posted January 5, 2014 Share Posted January 5, 2014 Do you know anyone with a boroscope? Could have a look inside without lifting the head. When you checked the clearances did you bar the engine and check each individual one or just have a quick look and rattle? It might be possible to see the piston if you remove the glow plug and injector and shine through the holes and trying to peek in, although you might not see much. Quote Link to comment Share on other sites More sharing options...
western Posted January 5, 2014 Share Posted January 5, 2014 tdi valves & pistons sit square to each other, so piston shouldn't be damaged, maybe the rod wasn't fully seated in the follower or rocker ball 7& just got caught. Quote Link to comment Share on other sites More sharing options...
LCJ Posted January 6, 2014 Author Share Posted January 6, 2014 Thanks both. I'm going with the not seated properly theory as I checked the valves one by one properly. Anyway, have sourced a new push rod and will reassemble when the heavens close and report back. Thanks again Quote Link to comment Share on other sites More sharing options...
LCJ Posted January 15, 2014 Author Share Posted January 15, 2014 So, push rod fitted, valves adjusted properly and...the tapping is still there. The noise is a rapid metallic flutter/tapping occasionally at lower revs but mostly towards the top end of revs in higher gears. No noise audible when the vehicle is stationary. I had through about the vacuum pump, but then it would make the noise all the time if it's on the way out, no? Any ideas please? Slightly reluctant to drive the vehicle at the moment in case it's serious and goes from tapping to bang! Thanks Quote Link to comment Share on other sites More sharing options...
Eightpot Posted January 16, 2014 Share Posted January 16, 2014 I had a problem with similar noises in a 300TDi a while back - sounded like it was coming from the top end, would come an go with different revs, but could see nothing wrong. Ended up taking the head off, and found an old valve cap which had dropped down into the pushrod hole. Might be worth having a good peep down the holes to check theres nowt down there. Quote Link to comment Share on other sites More sharing options...
LCJ Posted January 16, 2014 Author Share Posted January 16, 2014 Thanks for the thought, but I don't think that's likely. Bought a complete new head a month or so ago, and all my valve caps (and other parts) are accounted for. Quote Link to comment Share on other sites More sharing options...
Tanuki Posted January 16, 2014 Share Posted January 16, 2014 Check the roller cam-followers: if the bolts that hold these in place work loose the follower can move about in extremely unhelpful ways. If it gets slack enough it can even rotate through 90 degrees [so the roller is running _sideways_ on the cam lobe] at which point something usually ends up getting expensively broken. Quote Link to comment Share on other sites More sharing options...
currymunster Posted January 16, 2014 Share Posted January 16, 2014 Could be the head is not sealed - I had a 300Tdi go on piston 4. That made a tapping noise till I fixed. Other options are Caps Lift pump Vacuum pump Exhaust manifold gasket Tappets need adjusting othersbut these are most prevelant. Quote Link to comment Share on other sites More sharing options...
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