Combating Leaded -fuel Trouble in Bedford Engines
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Adjustments and Modifications Which Will Assist Operators in Securing Mote Satisfactory Service with frirT80 Leaded Petrol AS is now generally known, the leaded fuel which is at present being sold for use in all classes of road vehicle has been responsible for serious valve trouble. The pros and cons of the subject have been dealt with at some length in these columns, but no finality would appear to have been reached as to how the trouble can be avoided.
Vauxhall Motors, Ltd., has been carrying out its own• research in this connection, and its findings have resulted in the issue of a service bulletin which has been sent to all Bedford distributors and dealers.
It deals with only the 28 h.p. (3i ins, bore) engine. and we understand that a separate bulletin is to be issued at a later date to cover the 27 h.p. (3* ins, bore) unit.
Valve clearances are first dealt with, the recommended setting for exhaust valves being .018 in. and for the inlets .010 in. It is interesting to note that the normal figures are .013 in. and .006 in, respectively. It is important that the engine be brought to normal running temperature and that the holding-down bolts of the cylinder head be checked for tightness before adjustments are attempted.
The engine under review has
exhaust-valve guides which project into the exhaust port to the extent of
beyond the boss. This lowojecting portion, which is counter-bored-to clear the valve stem, should be removed when the cylinder head is being reconditioned. This operation can be carried out with the aid of a pilot cutter. If new guides are being fitted they should first be cut down to an overall length of 2* ins, by removing the counter-bored portion ; the edge of the guide bore should be left sharp.
Discarding Exhaust valve Washer
The next feature concerns the felt washer and cup on the exhaust-valve , stems. The washer should be discarded and the flange of the cup cut off, the cup being replaced under the valve spring. If omitted, valve-spring pressure will be decreased, which is not desirable. It is emphasized that the felts and cups on the inlet valves should not be disturbed, In the case of engines having single valve springs, replacement springs should check up to 73-61 lb. at a loaded spring height of 1.829 ins. and 137-125 lb. at a height of 1.519 ins.
Some points in connection with valves are concerned with head thick ness and valve-seat angle. Respecting the first, if the thickness of the parallel portion above the seating has beconie less than 1/32 in. as the result of refacing, it should he discarded. Valve-seat angle should be exactly 20 degrees, this applying troth to inlet and exhaust Beatings.
The width of the exhaust-port seat
ing should be kept between in. and 5/64 in., and that of the inlet port between 1/32 in. and )16in A valveseat width in excess of these figures can be corrected by using a 20-degree cutter or grinding stone. Another way is to use a 70-degree cutter or stone in the throat of the port, but this method needs some skill and care if cutting metal away from the port itself is to be avoided.
From the miscellaneous items mentioned in the bulletin we quote the following :—Advance ignition-distributor timing by 5 degrees beyond the normal basic advance, which is also 5 degrees. This can most easily be done by giving the micrometer .adjustmerit on the distributor three 'full turns in a clockwise direction.
• The sparking plug-recommended is the AC K9V, the gap of which should be get between .038 in. and .040 in.