My Focus just saw the sunny side of 70,000, Chilton says inspect at 60,000, if needed replace. Ford says the same thing, my local mechanic says inspect and replace if you see cracks, otherwise it should last 100,000 miles. This is a zero tolerance engine, if the belt goes, valves punch through the pistons, the heads, and the connecting rods break. If your lucky, you get a block and a crank out of the deal. So with that much riding on my belt, what do you think?
Also, should I leave the timing belt plastic cover on, it seems a cooler running belt would last longer. I did read in a Fiat manual that the cover prevents microscopic dust from being trapped in the teeth and punching through the belt weakening the belt. On the other hand, V-belts and serpentine belts are left to the spinning exposure of dust in the air their entire lives and seem to go as long as a timing belt, your thoughts?
If the engine is an interference engine which I am not certain it is, I would change the timing belt at least by 75K miles and also change the water pump while I had it off, because if the bearing in the water pump ever goes out it will probably cause it to strip teeth off of the timing belt. That just happened to me about a month ago on my '88 Escort Pony, but I just replaced the water pump, lined up the timing marks, put a new timing belt on and fired it up. This is the second timing belt I've had to break on that car over the 16 year that I've owned it and no damage either time. Most publications say that the engines in the Ford Escort are interference engines, but in reality they are non interference engines. Even the DOHC engines in the Escort ZX-2 are non interference. I would suggest you find a good Focus forum on the Internet and research whether or not your engine is truly an interference engine or not. If you find out it's not I would go ahead and try running the belt to 100K and it will most like make it provided the water pump doesn't go out. I've ran several belts 100K on my '88 Escort Pony and the one that just broke the other day, because of the water pump had been on it for about 95K miles. I'm not familiar with the Focus, but if it is a SOHC engine the timing belt and water pump are a pretty simple change if you'll buy a repair manual like Chilton's or Haynes to help guide you through it. If you are mechanically inclined don't pay someone several hundred dollars to do this for you. On my '88 Pony I can do it start to finish in about 4-5 hours if I don't run into any unexpected problems. As for the timing belt cover I've seen people run without the cover, but I always keep mine on to help protect from mud or water splashes. I guess it's up to you to make that call. If you have an interference engine I wouldn't trust running the belt more than about 75K miles covered or uncovered.
Engines idling still turn the belt regardless of the distance the car is driven. High revs wear a belt faster than conservative driving. Also temperature extremes and the time a belt sits without moving can play a part.
Distance is one factor but not the only one.
Personally I would renew the belt since if / when it fails it won't be a cheap or convenient fix as it will be if you do it at you choosing in your garage or wherever.
Refit the cover. Car companies built car with a very close eye on costs and if they fitted it you can be sure it is meant to be there.
Serpentine and cam drive belts are not the same although they are similar.
It is the "lugs" on a cam drive belt which do all the work and a build up of dust can act like sandpaper and cause the lug to come adrift from the rest of the belt with the inevitable result the rest are about to go the same way.
Another reason to fit the cover.
Yup, cam belt needs to hold time, serpentine doesn't, also serpentines are made with more "give" hence sprung tensioners.
Cover = good, don't be a moron and leave it off, just twiggy bits of leaf or maple keys blowing in there could throw the belt off. Slush and ice might do it too. As will squirrels storing walnuts in there. (Every fall, start finding nuts in all sorts of wierd places in my engine bays)
I think the ford 4cyls are what you might term "light" interference. On a sub 3000 rpm breakage you'll likely not have issues, on a high rpm breakage, you could get anything from a light ding to full on bent valves. The valves are very close to the piston at TDC. Hot engines might hit harder too.
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I hate to be an advocate for something that is less safe, but if your cover is a huge pain in the butt to install and remove like every cover I have ever had to deal with, you can probably get away with leaving it off. I've never replaced any of the covers that I have removed and never had any trouble with belt failures.
The likelyhood of anything getting in there and damaging the belt or engine is scant compared to the risk of body parts, clothing etc., if they should end up caught by the moving belt however. The up side is that every time you open the hood, you have the opportunity to give it a cursory look-see and can probably push the replacement interval out more safely - but that doesn't mean it can't just snap either.