Over the winter of 2007/8 I completely rebuilt the bottom end of the 2 litre "silver-top" engine in the Westfield. I'm not going to attempt to rewrite the Haynes manual, but I thought it might be useful to include some photos and comments/tips on some of the more interesting bits.
The first topic is why and when should the bottom end be rebuilt. I had previously taken the head off this engine and knew the bores to be fine (with regular maintenance the Zetec bores are good for 200,000 miles, but note that they do have a very special micro-honing process on them, reboring is not really an option. If you do need a rebore it's better to look for a good secondhand engine, but that's the subject of another article someday). The Zetec, running on the correct 5W30 oil should run at 4 bar oil pressure at 3000 rpm when warm, which mine did, but should also show a minimum of 1 bar, more normally around 1.5, at idle. When hot mine was around 0.5 bar at idle and also was taking a second or two to build up oil pressure when started. So, not really bad enough signs to be doing much damage but definitely a hint that not all was well. So, over the winter of '07/'08 the engine was taken out for a spot of bottom end inspection.
Here was the first evidence of wear and tear. Side by side here are a new main bearing shell and one removed from the engine. You can see the bearing surface almost worn away, it's also starting to show grooves and score marks rather than even wear, which were reflected in the mating crank surface also. So, there was no doubt that this needed rebuilding, and the plan was to do enough to not have to worry about the bottom end "ever" again. To my mind there's no point messing about doing half a job when the engine is out, so the tasks were: new/reground crank, new main and rod end bearings, new oil pump, ARP rod end bolts, new crank spigot bearing, new seals and gaskets and new oil jets. I had previously fitted a Dunnell lightened flywheel and heavy duty clutch, Dunnell sump, and a new cambelt kit, otherwise I would have replaced all of these as well. It was my plan to leave the head, cams, etc., intact for this rebuild as they had been checked out only a few thousand miles ago.
With so many Zetec engines in circulation my preference was to seek a good crankshaft rather than go for a regrind. Ford's somewhat bizarre engine nomenclature actually comes to the rescue here as whilst they name their current, and more recent, engines Duratec, Ecotec, etc, the Focus ST170 and the Focus RS are still Zetec engines under the rebadged cam covers and the bottom end is unchanged from the early 90's. I managed to find a low mileage crankshaft from a ST170. Visually it looked fine with no score marks or scratches.
The final check was the Plastigage test.
This is a small sliver of precisely moulded plastic which is put in the bearing gap. The bearing is then tightened up to the specified torque and the plastic compressed. The bearing caps are then removed again and the plastic sliver inspected. It should show no signs of taper or unevenness, which would indicate uneven bearing wear, but should be nice and parallel from side to side, as demonstrated by the example in this photo. The size is then compared to a scale on the packing, and this converts into the bearing clearance, which can then be checked against the manufacturers specification. Needless to say, if it's within limits carry on, if not the crankshaft or bearings will need replacement. Fortunately the replacement ST170 crank and the new bearings were all mid-range against the specification.
This picture shows the oil spray jets that are fitted to the 2 litre Zetec engine (not the 1800 other than the "RS" version). Firstly, it's worth fitting them even if they're not fitted to the engine as standard. If they are standard it's always worth replacing them when the opportunity presents itself. They serve to keep the bores lubricated and the piston crowns cool. Bear in mind that we can take the standard 2 litre Zetec at around 125 bhp to comfortably over 200, so a little bit of extra lubrication and cooling will not go unappreciated.
What you can also see here is half the new bearing shells fitted. It's really important that everything is scrupulously clean and that, as they are fitted, they are smothered in new oil to the correct specification, which for the Zetec is usually 5W30. Personally, I use Castrol Magnatec fully-synthetic oil.
The weak point in the Zetec bottom end is the rod end bearing bolts which, as standard limit the safe rpm to around 7000. Prolonged use above that is definitely to be avoided. So, whilst the engine was out I fitted a set of ARP rod end bolts, which are safe at a steady 7400 rpm. Incidentally, whilst I'm sure there are other makes, Dunnell Engines can supply rod end bolts that will go even higher.
It's important the instructions supplied with these high load bolts are followed to the letter. ARP specify tightening the bolts to the specified torque and removing them three times. Depending on the precise origins of the engine it is possible the shoulder radius on the ARP bolts may foul on the rod end cap. It's important to check for this off the engine and if necessary relieve the cap to give clearance for the bolts.
This photo shows the crank installed together with the ARP rod end bolts.
Even though all the bearing clearances have been checked with Plastigage it's also important to rotate the crank by hand to check there's not tight spots or any foul conditions.
As standard the Zetec engine is installed transversely. In the Westfield the engine is turned through 90 degrees and linked to a rear wheel drive gearbox, usually Type 9 or MT75. In my Westie it's a Ford Type 9. This means the crankshaft may require a spigot bearing installed at the flywheel end to locate the gearbox input shaft. If there is one fitted, as there was in the replacement ST170 crank I was using it's still worth changing it, which is what I did, and the picture shows the new one installed. Having written that it should be replaced, removing the old one is a real pain as it's located in a blind hole. I removed the old one with a hook attachment on a slide hammer but I appreciate that's a piece of kit that not everyone will have so it may need a spot of engineering initiative.
Centering the rear oil seal is very important. The oil (5W30) is really thin when hot and needs every chance to seal properly. Given any excuse, in my experience, the front and rear seals will leak. What you see here is the rear seal holder just nipped into place and I'm checking the clearance between the crankshaft and the seal housing and adjusting it until it's completely consistent all the way round. It's also important that the small step between the bottom face of the block and the rear seal carrier is the same on the left and right sides. It's all a bit fiddly but can certainly be done.
The next step is to fit the rear seal. The lip is very delicate so it's important that a shield is made to guide the seal over the crankshaft. I made a shield from a sheet of thin clear plastic as can be seen.
I thought I'd just include this one to show what a nice piece of engineering (although it's picked up a tiny spot of surface rust in my garage) the Dunnell lightened flywheel is, and if you can imagine a standard 1800, or especially 2000, flywheel you can readily imagine how much lighter this is. Just as an aside, a lighter flywheel doesn't add any horsepower, that's all done in the combustion chamber. What it does is reduce the moment of inertia of the crank allowing it to speed up and slow down more rapidly, which speeds up the transitional phases like gear shifting, throttle blip, and so on.
At the front of the engine there's exactly the same job to be done centering the seal holder, except this time the seal is located within the oil pump. This picture shows me checking the diametral clearance around the crankshaft nose. As for the rear seal I would suggest making up a shield over which to slide it over the crankshaft, although it is a smaller diameter and a bit more robust than the rear seal.
The final photo shows me checking the step between the bottom of the crankcase and the oil pump to ensure the left and right hand sides are equal.
And that's basically all there is to rebuilding the Zetec bottom end
I would suggest when you start the engine for the first time removing the spark plugs and if you can disabling the fuel pump. This reduces the load on the crank and bearings purely to the rotational friction. Turn the engine over on the starter until the oil pressure builds up. It will feel like an age but should usually be 5-10 seconds only. Only after you have oil pressure in this minimal load condition should you refit the spark plugs, re-activate the fuel pump, and start the engine. In general the crank bearings, oil pump, and other bottom end bits don't need running in. Perhaps a little caution for a couple of hundred miles wouldn't do any harm. After all this work you should see 1-2 bar oil pressure at hot idle and a steady 4 bar at 3000 rpm, again hot.