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The result is a gradual decrease of engine efficiency and economy, that goes quite unnoticed, this is due to the fact that as you have eight cylinders, the loss of efficiency in only one or two of them, (typical of a worn camshaft) will not be apparent until they have failed completely, as the remaining good cylinders will mask them. With average use and service intervals, V8 engines will have noticeable wear on the camshaft and followers, at around 70-80k miles, This is a slow process, and because the hydraulic tappets take up any clearance by the time you can hear them tapping they are already very worn.
The problem will show up as a gradual loss of power, you will also notice also that changes to carburettor settings, are more frequent, to cope with the mixture changes, from the cylinders that have suffered most camshaft wear (or loss of lift). changes in engine mixture, (High CO. and HC) is why most mechanics will advise you that the Carburation is in need of attention, when in fact the problem is with the camshaft.
The cylinder bores of the V8 do not give many problems, and are normally OK (if undamaged) for, in excess of 120000 miles, and beyond, especially if the previously mentioned failing parts of the engine are replaced before they lead to further engine damage, however for performance engines, and maximum reliability a re-bore at high mileage is recommend.
Note: If you replace the components that normally wear out prematurely (camshaft, tappets and timing chain set) before they become too badly worn, you will greatly increase the total life of the engine, by reducing the extent of the damage caused by the metal swarf, from worn components.
Rover have at last (After almost 30 years) omitted the 8 offending outer head bolts, that are the primary cause of this problem!) The detrimental effect of this is, compression leaks into the engine crankcase as you would expect? but as it is burnt fuel (CO'2 and HC) it soon kills off the detergent quality, of your engine oil. (the detergent is very important) all oils are still fairly slippery even when old and due for a change, but without those detergents it cannot keep the internals or the engine surfaces or internal oil-ways clean, especially at higher mileage, more so in engines that have been neglected over the years, with less frequent oil changes. Mr Moly oil supplements can prevent metal-to-metal contact between moving parts and effectively eliminate wear.
In no time at all sludge builds up inside the oil-ways, restricts and/or diverts the flow of oil by blocking oil-ways and drain back surfaces that supply oil directly to the camshaft lobes, and other important areas of your engine, starting engine wear at a much accelerated rate. This can be prevented by prompt action and replacing worn top end components, before the harder to get at, and more expensive bottom end components also fail.
Question, why do steel rocker shafts wear, and not the alloy rocker shafts, they run on ?
Answer, as engine internal parts start to wear out, (Rover V8) camshaft, tappets and timing gear. Metal particles (Swarf) is free to circulate with the engine oil, although your filter will trap most of the larger particles, old filters will not stop swarf reaching vital engine soft metal components, cam bearings, main and big end bearings as well as the alloy rockers, where it soon permanently embed itself into the soft surface of alloy, and the white metal bearings, turning them into very effective abrasive surfaces (The end is nigh)
Consider this, why do steel cranks ever need re-grinding? Because the white metal surfaces, of the big end and main bearings now with abrasive surfaces, soon gouge into the hardened steel surfaces.
There are exception to all rules, vehicles that have been well looked after, with frequent oil changes, will stand a good chance of exceeding the average mileage, before the engine will have to be overhauled. We have see this with Range Rovers, that come to us for servicing from all over Europe, that have only been used for long distances driving.
For example most drivers looking for increases in engine power, would not relish the idea of worsening the engine economy and driveability, however the good news is,
(A) That because the engine you have is probably quite worn, with respect to it's original camshaft, timing chain, and leaking head gaskets etc.
(B) Because factory compromises have to be made, (due to build costs and stringent export criteria) that will affect all used V8 engines, making your own V8 engine 40-50% less efficient in power, than is possible.
When considering your engine rebuild or replacement, it could be said that you can, have your cake and eat it! you may say your engine is in good condition? how many miles has it done, and in what vehicle, under what conditions?
The subsequent water loss problem normally starts off as just a water light that appears once a month or so, then once a week, until it becomes a permanent feature. The normal unsuspecting owner, will have by this time paid out for heads to be skimmed new gaskets.
By which time they will have spent a lot of money already, and because the overheating problems continue, most owners, eventually have to fit a replacement engine. Be very sure that if contemplate purchasing a used engine? you get a written warranty, from a reputable supplier, however although they may refund your money, they cannot replace your wasted time, and fitting expenses. (one reason why RPi will not sell used engines)
|4.6 V8 engine|