U.M.R. Engines

BLOCK - BENT / MISALIGNED / WARPED

Two places on an O.H.C. block to be checked for straightness and misalignment are the block face and the Main bearing tunnels. If the block has camshaft or balance shaft tunnels, these areas also require close inspection. Line boring of a block camshaft bearing tunnels will depend upon the availablity of o/sized backed Cam bearings being available.

The face of the block requires a surface grind when the finish or flatness becomes unacceptable to provide a secure sealing surface for the head gasket. Another position on the block face that requires close inspection is around the threaded head stud area. This area quite often becomes raised due to the clamping force required to seal the head gasket.

The main tunnel has to be straight. The main bearing tunnel inside diameters have to be within tolerances. If these problems exist the block will require a tunnel bore. This is a considerably complex machining procedure but is essential to the performance of the main bearings. The misalignment occurs when the block shifts. This may come about from normal use but again is accelerated by engines operating outside their ideal maximum temperatures and loads.

Large diesel engines suffer this problem the most and line boring is considered a standard machining process during reconditioning. Most times a tunnel line hone will correct minor misalignment. A good quality straight edge and inside micrometers are used to determine the integrity of the main tunnels.

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