Leaded Fuel and Valve Trouble:
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DuringRecent Months No Problem in Maintenance Has Aroused More Interest and Divergent Views Than This, for Thousands, of Vehicles Are Being Affected
REGARDING the article, "Keep the Engine Hot to Keep the Valves Cool," in your issue -dated October 15, the writer has made a simple phenomenon appear complicated. There is one statement that I would like to dispute, i.e., that valve trouble was not experienced with Ethyl petrol. It was my own experience and that of all those whom I questioned, that valve trouble. always occurred with Ethyl, the only difference was that, pre-war, only the private car used Ethyl, and a private' _ car engine is nbt subject to the sustained loading of the cOmnaercial-vehicle engine, thus the latter has mole valve trouble with Ethyl, as is the ca-se at the present . moment.
The explanation of the valve trouble is quite simple, . without far-fetched theories about corrosion. The exhaust valve 'sustains a very precarious existence onaccount of its permanent high temperature,' its chief difficulty being to dispose of its surplus heat, which it does via its contact with the valve seat. Anything that interferes with this good metallic contact greatly shortens its already feeble life.
Ethyl petrol deposits a layer of lead bromide—I • believe—on all the internal surfaces of the cOmbustion chamber. This forms a very good heat-insulating surface on the exhaust-valve seat, the valve cannot dispose of its heat so readily and pp goes the temperature of the valve head, with the familiar results. The obvious remedy is to reduce loading on the engine, so that the .valve has less heat to dispose of.
LeiceSter. T. G. SLATER, M.I.M.T., • For Messrs. Ford and Slater. /
AS a regular reader of ." The Commercial Motor I sawwith considerable ,interest the • article oft "
doped" fuel by Anthony High. Although his views • are somewhat different from previous writers they provide ample food. for thought.
I am a fitter engaged on the maintenance of a fleet of Fordsonsand one Bedford. Trouble has been experi
enced all round, but in different-ways. , The Bedford has burned-Out valves, one in particular getting to the stage shown in one of your illustrations, owing, of course, to keeping the vehicle on the road after the valve had started to burn out. After fitting new exhaust valves .they were givera rather more clearance than the makers advocate, 12 thous. instead of 8 thous., and .no trouble has been experienced since then. I might add that a small-percentage of ,oil was thoroughly•mixed with "the petrol, the ignition was also advanced on the micrometer setting. , • The Fordsons are another problem. One engine (V8) ,.was dismantled and the corrosive' action or burning was found to have taken place Mat on the exhaust valves —which were perfect—but on the top lip of the cylinder liner insert nearest the valve heads. Here there had been burnt a hole in the liner almost as big asthe one in the valve in your illustration. This hole corresponded with the firing point, as it is exactly opposite the plug. Yet on the Bedford engine the exhaust valves 'are nowhere near the firing point, or perhaps I should say flash point.
Considerable trouble has also been experienced (since the use -of this " doped " fuel) with cylinder-head gaskets blowing. • One goes nearly every week on one or other of the Fordsons.
It is the compressed-fibre type of gasket that goes, and these have been replaced by a metal-bonded type which stands up to the job—at least, so far. Incidentally, several cylinder heads have cracked, also on cylinder block. I am wondering if the " doped" fuel has anything to do with this, as no trouble of the kind has been ' experienced before. '
Some difficulty has also been experienced in starting 'the early war-time -Thames, Models V8 or 7V. This . difficulty has been partly overcome by taking the measures advocated in an ea.rlier issue of " The Commercial Motor," but it is not yeteliminated. A. F. WARD.
Dunrnow, READ with interest the article by Anthony High ou that much-debated 'subject, leaded petrol, and give my observations, for what they are worth, with due regard to my lack of knowledge of chemistry.
Because of failures amongst the: fleet I control, I sought the best technical' advice, as in all cases corrosion was.
obvious.
Briefly, present-day leaded petrol, .dr 80 octane, as it •
is known, is leaded to suit 'military .requirements. Tetraethyl is adversely affected by heat, so a corrective is blended with it. This corrective, in turn, is affected by heat, for a rise of temperature above normal neutralizes it—hence the corrosion. • So it. would seem to me, in fact proved to me, that the more arduous the
nature 'of the work-the more this corrosion occurs. • I have tried all known so-called remedies, but so far without success. I am still trying, and should -I be successfulwill at once notify " The Commercial Motor." I would also welcome any advice operators may be able to give me.
• Finally, I think if a more generous response had been made to Mr: Quick •Smith's query on this subject in The Commercial Motor" some months ago, the question of a petrol more suitable for civilian consumption might have been accelerated. • G. 0. NEIL, Charlestown Manager, for The HeaVy Transport Co., Ltd.
St. Austell.
THE article by Anthony High on present-day valve troubles was-read by me with interest. Whilst certain people seem to hold opposite views there may be reason to suppose that the author is on the right track. My company operates Albions and Commers, and from my observations I am convinced that the former, which used to give a lot of valve trouble, are functioning better than in previous years, whilst the latter are giving more trouble under present conditions.
It would be interesting to learn of other operators' experiences with various makes of machine.
Newcastle-on-Tyne, 2. J. M. RIDLEY, Manager, for John Forman, Ltd.
[On this vexed question of high-valve mortality caused by petrol rich in anti-knock compound, opinion seems to be unanimous that the ethylene dibromide in the fuel is ultiMately responsible for-the damage. If this bromine compound were replaced by an organic fluorine compound, destruction of any residual tetraethyl lead in the exhaust 'could be equally assured, whilst, in all probability, a resistant film of fluoride would be formed on the valves, protecting them from progressive corrosive destruction and even from straightforward oxidation.—ED.]