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Technical Information for Gunsmiths and for Classic Car Enthusiasts

MG Restoration

MGB 18V Engine Bolt Sizes


Les Bengtson


(MAY APPLY TO OTHER VERSIONS OF THE “B” SERIES ENGINES, BUT I HAVE NOT CHECKED.)


Note: See other article (Bolt Sizes) for notes on how to use taps and dies and how to determine sizes of studs and bolts.


BLOCK—Bottom

  • Main bearing bolts and holes on the three large caps ½-20
  • Oil Pan (sump) bolts ¼-28
  • Oil pump studs 5/15-18


BLOCK—rear

  • Rear engine plate 3/8-24
  • Rear main oil seal  5/16-24


BLOCK—top

  • Cylinder head studs  3/8-16


BLOCK—right side (as you sit in the car—side with distributor)

  • Distributor hold down clamp  ¼-28
  • Alternator bracket 5/16-24
  • Oil Pressure sending unit (18GF engine, two holes not used behind alt bracket on 18V) 5/16-24
  • Distributor drive hold down plate (the one with the screw) ¼-28
  • Oil pressure take off (rear of block—non standard)   .513”-20
  • Line to oil cooler/filter (rear of block—non standard) .822-14 non-tapered (not pipe thread)
  • Oil filter adapter (main bolt holding to block) ½-13
  • Motor mount 3/8-24
  • Plug below oil pressure take off (non standard) .508-18


BLOCK—left side (as you sit in car—side with carbs/manifolds)

  • Tappet covers  5/16-24
  • Fuel pump blanking plate (lower left front—looks like a shield shape) 5/16-24
  • Left motor mount 3/8-24


BLOCK—front

  • Water pump and front plate—all holes are either ¼-28 or 5/16-24


CYLINDER HEAD

  • Rocker arm studs    5/16-18  (top end of stud is 5/16-24)
  • Water temp sending unit   5/8-18
  • Water choke studs ¼-28
  • Thermostat housing studs 5/16-18
  • Manifold studs 5/16-24
  • Air injector rail 7/16-20


(Inside the head, there are four air injectors which may be removed from the head as desired. They can be cleaned using a 1/8” drill bit for the main body and a number 43 drill bit for the smaller hole on the end near the valve.)


OIL GALLEY PLUGS—BLOCK ENDS

There are five brass plugs that go into the oil galley on the front and rear of the block. These can be removed and the holes threaded ¼” pipe thread (this is a tapered tap). I removed them by drilling and tapping them ¼-20, then using a socket head cap screw and a socket to remove them. The holes were then tapped ¼” tapered pipe thread and hex headed plug screws inserted, with sealer, to cap them off after cleaning of the oil passages. The right rear must have the plug shortened very slightly to prevent its interfering with the oil line take off at the right rear of the block. The oil passages may also be re-sealed using the factory style plugs.


This monograph may be reproduced only for non-commercial use without other permission of the author. Reproduction for commercial use only by written permission.


Copyright © 2001 by Les Bengtson