-% I recently had to strip a relatively new I
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diesel engine in the 2.5 1 category ?cause of a premature bearing faililre, and !though the piston rings appeared to be in 2od condition I was advised to renew them. tested the gap of the rings in the unworn dinder bore and it was only a "thou or two" wirer than the recommended gap. Since ?assembling the engine with new rings oil msumption is considerably greater titan it as before. What is the explanation for this ad what is the test of a ring to deckle whether ! is suitable for further use?
k Assuming that the vehicle has covered S. a sufficient mileage for the piston .ngs to bed in and fitting was expertly one, there is no ready explanation for the igher oil consumption since the engine /as reassembled.
It should be remembered that bedding is a slow process when a modern etergent oil is employed. In an older engine igh oil consumption could be explained y glazing of the cylinder bores which an be removed with the use of a glaze buster. L glazed surface is a very hard one and roper bedding in is virtually impossible. 'his is an unlikely possibility in your case.
If the gap and side clearances of a ring re within acceptable tolerances, it may e unacceptable for further use because s resistance to compression has been reduc d and the lower radial pressure on the bore urface results in excessive blow-by and envy oil consumption. An appropriate !.st of a ring's elastic properties can e made by placing it on a polished and kricated flat surface and applying a prestire at right angles to the plane of the gap rith the help of a new ring in contact rith it.
The old ring is held in position on one side y means of a block of wood or other laterial and the new ring is located with .s gap in the same position. Pressure is pplied progressively to the outer edge f the new ring; if the gap of the old ring s closed by the pressure exerted and the gap I the new ring has closed a relatively mall amount this indicates that the elastic properties of the old ring have seriously leteriorated and it is unfit for further use.
In general, the advice to renew piston ings when an engine is stripped after a chicle has covered a relatively small aileage is normally good advice. After 11 the cost is small compared with that of he stripping operation. In your case it would eem likely that something went wrong in the fitting of the rings.
It is assumed that there was no measurable wear of the bores. Wear is highest at the top of the bore at the point of maximum -travel of the top piston ring. If wear had produced ridges in this area and they had not been removed before fitting new rings, one or more rings may have been broken by contact with the ridge. And this would have resulted in heavier oil consumption as well as blow-by.