Norfolk Garage
Three 300Tdi engines; three different causes – no two days are ever the same for Richard Hall
ONE OF the advantages of being a specialist is that you get to know the common faults and quirks of the vehicles in which you choose to specialise. This saves a huge amount of time in diagnosing faults and in many cases I can be reasonably sure I know what is wrong with the vehicle before the customer has got halfway through describing the symptoms over the telephone.
Only yesterday I had a good example of this when a Defender 90 turned up on the back of a recovery truck. The owner had noticed what he described as a rattling, squealing and vibration which rapidly got worse. He was absolutely convinced that the transfer box had disintegrated internally and rang me to ask whether I had any spare ones available.
As it happened I was just about to remove a good 1.410 transfer box from another Ninety to fit a Discovery high ratio box, but I had a feeling it would not be needed. What my customer had described sounded to me like a failed propshaft joint.
The vehicle arrived and I set about finding out what was actually wrong. I jacked the vehicle up at both ends and turned both propshafts by hand. I could not feel any roughness or unusual movement coming from within the transfer box casing. There was a certain amount of backlash in the differentials and halfshafts, but no more than I would expect from a 25-year-old vehicle with plenty of hard-working miles behind it. There seemed to be no play in any of the propshaft joints. I checked the oil level in the transfer box – clean oil and up to the mark.
Time for a road test so that I could hear the noise for myself. I turned out of the workshop entrance onto the road, accelerated away and by the time I had selected third gear I was absolutely certain that a front propshaft joint had failed, with the characteristic high-pitched squealing and vibration under load that most owners of older Land Rovers will have experienced at some point.
Back at the workshop I unbolted the front propshaft and found that the joint at the transfer box end had seized almost solid. There was no free play in it, but precious little movement of any kind. A new propshaft joint fixed the problem and the owner was soon on his way with a bill around a tenth of what he had been bracing himself to pay.
The danger with this kind of experiencebased diagnosis is that you can fall into the trap of jumping to conclusions, assuming that because a fault has similar symptoms to something you have seen recently, it must be the same fault.
I have been looking after this particular Ninety for a few years now – it first came to me breathing heavily and only running on three cylinders. I had just had a run of head gasket replacements on 200 and 300Tdi engines, and all had failed in the same place (between number four cylinder and number eight pushrod tube) resulting in the engine being down a cylinder and blowing fumes all over the place. So I told this customer not to worry and that it was only the head gasket, so not an expensive job. Unfortunately when I lifted the head I found that two of the cylinder bores were outrageously worn, so bad in fact that I ended up having to re-sleeve the block. So I try these days to be a little more cautious in my initial diagnosis, at least until I have actually got my hands on the vehicle.
I also learned a while ago that it is possible to have several different faults producing the same (or at least very similar) symptoms. Over the last few months I have had three 300Tdi engines in with what appeared to be the same fault: a light tapping noise from the top end, seemingly not load-related but directly proportional to engine speed. The first one I wrote about a few months ago – a Range Rover Classic which had so much metal skimmed off the head that the valves were contacting the pistons. In the last few weeks I have then had two more with similar symptoms and very different causes.
The first was an old One Ten which had been fitted with a Discovery 300Tdi engine in place of the original 19J. On this one the tapping noise manifested itself above 2000 rpm or so, and only appeared when the engine got hot. If you stopped to refuel the noise disappeared, only to return after a few minutes. My initial guess was that it was another example of an overskimmed head, with the clearance between valves and pistons being so tight that when the pistons got hot they expanded just enough to gently kiss the faces of the valves.
I was half-right or thereabouts: piston expansion was the immediate cause of the problem. The engine had been given what I would call a mid-life makeover as opposed to a full rebuild, with new (pattern part) pistons in very lightly honed bores. Nothing wrong with that provided the bore measurements are still within factory tolerances, although the piston to bore clearances on these engines are fairly generous even on a brand-new engine, and one with the bores at the upper end of the wear limit will be a rattly old thing when first started from cold, until the pistons have the chance to warm and expand a little.
There were no valve-shaped contact marks on the tops of the pistons which ruled out my initial diagnosis: but close inspection revealed a lightly-polished area of piston crown on the edge of number one piston, and a corresponding mark on the underside of the cylinder head. That explained the tapping noise anyway, but why was there so little clearance? To allow for variations in the dimensions of the pistons, Land Rover offered four different thicknesses of head gasket, denoted by the number of holes punched in the edge. The correct procedure is to measure the distance that the piston crowns protrude above the face of the block at top dead centre, then select the correct head gasket with reference to the
piston which has the greatest protrusion. This engine had been fitted with a two hole (1.4 mm thick) head gasket, but when I measured the pistons, number three was right at the upper end of the range for a 1.5 mm three-hole gasket, and number one was a bit taller than that.
I would probably have got away with giving the piston crowns a thorough clean and fitting a 1.6 mm head gasket, but number one piston had clearly taken a hammering and was outside the usual dimensional tolerances, while number three had small bits of shrapnel in the crown where a foreign object had been ingested into the cylinder. So I replaced those two pistons along with the big-end shells, re-measured the piston crown protrusions and put everything back together with a three-hole gasket (which is the most common size on these engines). The vehicle needed a long road test to get the engine up to the temperature where the fault had previously manifested itself, so I used it to go and fetch some parts I had bought 30 miles away and it was good as gold.
No sooner had that one departed than another came in – a late Defender 300Tdi Station Wagon. It had been in a couple of months previously for some gearbox work, and the sound of the engine drew my neighbour Lee out of his workshop to see what was wrong. “Sounds like an accident in a castanet factory” was his assessment. So I had arranged for the owner to drop the vehicle off at a convenient time, warning him that the head would have to come off and we would see what we found and go from there. The engine was allegedly a recent reconditioned unit fitted after the previous one had dumped all its coolant and seized solid. I say allegedly because it quickly became clear that most of the materials bill for the rebuild was taken up with shiny paint, with little if anything having been spent on the engine internals.
This engine sounded slightly different to the other two, being more of a busy tapping sound like an unlubricated sewing machine. No too long ago I had a set of new tappet rollers fail on a rebuilt engine due to defective manufacture, and my first thought was that this engine might have been fitted with components from the same batch. The tappet slides and rollers on these engines do not usually give much trouble being generously dimensioned and well lubricated, but when problems arise the only way to get to them is to remove the cylinder head. This revealed four original, standard-sized pistons with valve-shaped marks in them.
I very quickly discounted the valve marks as a possible cause of the noise. They were an old injury, partly filled with soot and probably caused by a broken timing belt at an earlier stage in this engine’s life. In support of this theory, three of the pushrods were bent. This is not the kind of thing you expect to find on an engine described as reconditioned, but the bores looked fine with the original factory cross-hatch honing marks still visible all the way up. Whether the pistons had been fitted with new rings I could not say, but in any case the engine had not been breathing heavily, so I carried on digging into the engine internals in search of the elusive tapping noise.
The tappet assemblies come in three parts: outer steel guide, yellow metal tappet slide and steel roller. With the retaining screws removed, the slides and rollers can normally be lifted out in a single operation, with the oil film between the two components holding them together. Not this time: as soon as I started to pull the tappets upward, the rollers dropped back down into the guides. The slides are asymmetric and marked with a large letter F on one face, this face should be towards the front of the engine. Six of the eight slides had been fitted the wrong way round. The slides themselves were quite badly worn, with the rollers a very slack fit, which explained why the two components had separated so easily. And to cap it all, when I pulled the guides out of the block one of them had a large piece of metal swarf completely blocking the oil way.
All in all I had found enough defects to make me think I had probably got to the bottom of the problem, so I sent the cylinder head off for the usual light reface and pressure test, and started preparing the bottom end for reassembly. The pistons had a few carbon deposits on the crowns which needed to be cleaned up so that I could measure the piston protrusion and select the correct head gasket, so I turned the engine by hand until pistons one and four were at top dead centre, at which point I discovered that the crown of number one piston was flush with the block rather than protruding 0.6 mm like number four. I have seen this before and the usual cause is a bent connecting rod, caused by the engine ingesting water due to over-ambitious deep wading. I could not just ignore this, so I dropped the sump, knocked the piston and conrod upwards out of the bore, and immediately found the cause of the rattling noise. The little end bearing had disintegrated, allowing the gudgeon pin (which connects the piston to the conrod) to move up and down by around half a millimetre.
These bearings can be replaced, although they have to be pressed in and reamed to exact size which is normally a job for a machine shop. I had a spare 300Tdi conrod in good condition, but before fitting it I needed to establish why the old conrod had failed. On the Tdi engines the little end bearings are lubricated by spray from an oil jet, which is located at the bottom of the cylinder bore and fed from an oil gallery via a hollow bolt which contains a tiny pressure valve. On badly neglected (or badly assembled) engines the oil jet can become blocked, starving the little end of oil. I removed the jet assembly and found that the jet itself was clear of blockages, but the pressure valve had seized solid which explained everything. It was not jammed with debris: it had simply ceased to function.
It is a basic principle of vehicle repair, too often neglected, that if a component fails, the cause of the failure should be established before replacing the failed component. If I had simply fitted another conrod, the little end would have failed again within a short time. As it was I could reassemble the engine (with new tappet slides fitted the right way round, and unbent pushrods) and be confident that the problem would not recur.
Three 300Tdi engines, three top-end rattles, three different causes. This is one of the reasons I love what I do: no two days are ever the same.