Q After fitting new piston rings to a heavy
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diesel engine some time ago, oil consumption was excessive and has only improved slightly since then. I have been advised that I should have used a glazebuster machine to treat the bores of the cylinders before fitting new rings. What is your view? And how much bore wear can be allowed before reboring and what ring side clearance can be permitted?
AIt is essential to remove the glaze on the
cylinder-bore surfaces before fitting new pistons rings, otherwise bedding-in of the rings is delayed indefinitely and oil consumption is excessive. Removing the glaze roughens the surface and although the rings and bores initially wear at a high rate this allows the rings to bed-in over a short period and thus provide a good oil seal.
Applying a fine wet-and-dry emery paper to the bores manually can be just aseffective as using a glaze-buster if performed with care. Normally, fitting new piston rings is satisfactory if the bore wear does not exceed about 0.010/0.012in. Side clearance should not exceed about 0,0015/0.002in. if the clearance is greater than this the grooves should be machined out to take oversize-width rings or standard rings with inserts.
The clearance of the pistons and the width of the ring gaps should accord with the maker's recommendations as measured in an unworn section of the bores.