CYLINDER-HEAD JOINTS

Evening Post, Volume CVIII, Issue 102, 26 October 1929, Page 28

CYLINDER-HEAD JOINTS

USING OF SHELLAC

One often hears it suggested that if a cylinder-head gasket be given a eoat of shellac or varnish on both sides before it is used or refitted the likelihood of a water or compression leak is reduced.' That is.so; but—and tho qualification is important—tho probability is that the gasket will be worthless when next the cylinder-head is remov ed; a new gasket will be needed, whereas if the shellac had not been applied to the old one it might well have served again and again. What happens is that the shellac adheres not only to the gasket, but also to the block below and the cylinder-head above, and forms a hard film between the units as it dries. When the cylin-der-head is next removed and the gasket lifted off some of the shellac is left on one unit and some on the other, resulting in very uneven surfaces to be brought together again subsequently, It is almost impossible to clean off all the film from tho surfaces,' and rarely does a fresh coating enable a good joint to bo remade with tho same gasket. Thoro is really no need for shellac tc be used to mako a good joint, providing tlio surfaces to come iuto contact arc scrupulously clean and tho gasket is in good condition; if a gasket is defectivo r.v will require something fur more effective than shellac to make it'worth reinstating.