ROAD AND WORKSHOP by HANDYMAN

7th May 1965, Page 79

7th May 1965

Page 79

Page 79, 7th May 1965 — ROAD AND WORKSHOP by HANDYMAN

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"Things about Rings"

A T some time during the middle-life n. of an oil engine action has to be aken that at times eventually does not vork out according to plan. With fully iden vehicles running to tight schedules fri fixed routes, any falling off in perormance, oil or fuel m.p.g. variation, r tendency to emit smoke, can call for ome quick attention to return the engine 3 an acceptable and fully effective conition. The engine may be just a little if tune, but it can mean a series of rivers' complaints, arguments over fuel r oil consumption, or a GV9.

A compression check will indicate loss t either valves or rings—not difficult for engineer to decide which. If it is

valve trouble only, there is no problem, but it the rings are at fault—indicated by " wheezing" noises from the oil filler, together with sump fumes—the next move may not be so simple as it may appear. With heads removed, an inside micrometer reading may indicate no more than 0.003 to 0004 in. of wear in the higher region of the liner, and therefore no apparent reason why new rings should not re-establiih full power and tune.

Pistons, when removed, can show up quite well, nicely within the maker's limits diametrically and with no undue ring groove wear. So no problem should exist. Therefore, clean out grooves, oil holes. remove all carbon, lightly chamfer the uppe;-most edge of the new top ring —if not already relieved by the maker— and re-assemble. From long past practice this should prove satisfactory. However, on a now increasing number of occasions, this is not so and, on starting up, the engine emits blue smoke; this steadily worsens the longer the engine is running, until a point can he reached where black oil is seen at manifold joints and can actually drip from the exhaust pipe. A good deal of midnight oil has been consumed recently over this situation. from which ha,: enforced the answer—in two parts. First: the fault lies in already glazed bores, which do not permit the new rings to bed in. In fact, the rings will slide over the glassy surface and, if anything, further polish themselves and the liner. This will result in the rings becoming almost a set of displacement oil pumps, accepting and passing on all oil deposited on the lower part of the liner until unburnt oil is actually leaving the exhaust side of the engine. Idling, or running the engine lightly for some time after assembly, is the cause of this worsened state.

RE-RINGING With any re-ring job in used liners it is not the small amount of wear that is critical, but the glazed surface. Therefore, secondly: either check the bore surface and use a Glaze-buster to break up the surface polish beforehand, or ensure that on no account is the engine left to idle on starting up. Other than a quick check for any severe oil leak, make the engine work from the start. This is the only way to break down the glaze, bed the new rings, and ensure a good seal between piston and liner. The main supplier of the Glaze-buster is Wellworthy Ltd. and the price is 46s. 6d. It is a little awkward to operate, and would benefit from a bottom steady: nevertheless, it is the only sure answer

when excessive glazing is in evidence. :

ROAD AND WORKSHOP by HANDYMAN

Page 79

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