Replaced the timing belt yesterday as I didn't know when it had last been done. Turned out to have the old-style crank pulley; the belt had run misaligned and was quite badly worn, so I was glad to have caught it in time.
I'd normally just mark the gears and belt and fit the new belt where the old one went. Sure, in theory that's bad, because the old belt might already have been out of position, but in reality that's never actually going to happen, right? This time, I actually set it all properly for once. It wasn't easy for all sorts of reasons, one of the main ones being that I couldn't get the injector pump locking pin in without advancing the pump quite a bit...
Well... the smoke on acceleration that I thought was down to over-enthusiastic fuel pump adjustment by the previous owner has gone entirely. The vehicle runs much better generally too. Clearly the pump timing was way out, probably having jumped a tooth or two at some point. I'm now a definite convert to doing it the "proper" way!
There are plenty of good how-to guides out there, but here are a few points, either things I picked up or places where I've found other advice to be inaccurate.
- You don't have to take the sump off the 300tdi, either to change the timing belt or to change the crank seal behind it. This one might seem obvious but nonetheless I've seen posts where it's been asserted that the sump has to come out - definitely not on a 300tdi Discovery at least!
- You don't have to disconnect the radiator hoses, drain the cooling system or remove the radiator. Sometimes the extra access might be helpful but it's not necessary. You will have to remove the fan (just buy the spanner and the job becomes a non-issue) but the fan shroud can stay. The crank pulley just / almost squeezes past it.
- If the crank pulley won't come off after you've taken the 27mm bolt out of the crank, there are four blind M8 holes in the front face. They're on a 75mm PCD. I used some 8mm thick aluminium flat (about 100mm long by 50mm wide) and some 8mm threaded rod in two of the holes to make up a puller, then used this to press against the 27mm socket and pull the pulley off. Clean the inner bore of the pulley with some emery cloth / wire wool to stop it sticking next time. It's also worth cleaning up the 8mm holes with a tap and greasing them while you've got access.
- To ensure the cam is properly positioned, use a mirror to look at the front face front-on and make sure the timing mark is properly aligned with the static marker.
- To align the crank, I took the wading plug out of the rear of the engine and rotated the crank until I could see a timing mark on the flywheel. It more or less coincided with the keyway in the front of the crank being at top dead centre, and was pretty obvious once visible - a groove running the full width of the flywheel, a couple of millimetres wide and deep. I didn't bother locking it in place with anything.
- I locked the pump with the butt end of a 9.5mm drill (like everyone else). It was in the wrong place to begin with, so the drill would go in but I had about 15 degrees of adjustment either way! This became obvious once I took the pulley off (undo the three bolts but NOT the single big nut).
Like I say, there are plenty of good how-to guides, so I won't attempt another - but I hope the above is useful.
I'd normally just mark the gears and belt and fit the new belt where the old one went. Sure, in theory that's bad, because the old belt might already have been out of position, but in reality that's never actually going to happen, right? This time, I actually set it all properly for once. It wasn't easy for all sorts of reasons, one of the main ones being that I couldn't get the injector pump locking pin in without advancing the pump quite a bit...
Well... the smoke on acceleration that I thought was down to over-enthusiastic fuel pump adjustment by the previous owner has gone entirely. The vehicle runs much better generally too. Clearly the pump timing was way out, probably having jumped a tooth or two at some point. I'm now a definite convert to doing it the "proper" way!
There are plenty of good how-to guides out there, but here are a few points, either things I picked up or places where I've found other advice to be inaccurate.
- You don't have to take the sump off the 300tdi, either to change the timing belt or to change the crank seal behind it. This one might seem obvious but nonetheless I've seen posts where it's been asserted that the sump has to come out - definitely not on a 300tdi Discovery at least!
- You don't have to disconnect the radiator hoses, drain the cooling system or remove the radiator. Sometimes the extra access might be helpful but it's not necessary. You will have to remove the fan (just buy the spanner and the job becomes a non-issue) but the fan shroud can stay. The crank pulley just / almost squeezes past it.
- If the crank pulley won't come off after you've taken the 27mm bolt out of the crank, there are four blind M8 holes in the front face. They're on a 75mm PCD. I used some 8mm thick aluminium flat (about 100mm long by 50mm wide) and some 8mm threaded rod in two of the holes to make up a puller, then used this to press against the 27mm socket and pull the pulley off. Clean the inner bore of the pulley with some emery cloth / wire wool to stop it sticking next time. It's also worth cleaning up the 8mm holes with a tap and greasing them while you've got access.
- To ensure the cam is properly positioned, use a mirror to look at the front face front-on and make sure the timing mark is properly aligned with the static marker.
- To align the crank, I took the wading plug out of the rear of the engine and rotated the crank until I could see a timing mark on the flywheel. It more or less coincided with the keyway in the front of the crank being at top dead centre, and was pretty obvious once visible - a groove running the full width of the flywheel, a couple of millimetres wide and deep. I didn't bother locking it in place with anything.
- I locked the pump with the butt end of a 9.5mm drill (like everyone else). It was in the wrong place to begin with, so the drill would go in but I had about 15 degrees of adjustment either way! This became obvious once I took the pulley off (undo the three bolts but NOT the single big nut).
Like I say, there are plenty of good how-to guides, so I won't attempt another - but I hope the above is useful.
