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THREADS And FITTINGS For External Ports, - CF-155
and Other Threads which are Not Unified Threads

The MGA and MGB 4-cylinder engines were Austin B-series engines. Austin may not have been so vigorous as MG about post-war adoption of the Unified thread standards. Most of the fasteners (screws, bolts and studs) would be Unified threads, while many of the threaded ports in the MG/Austin engines retained some pre-war design using Whitworth threads, or BSF threads (based on Whitworth thread form). This article endeavors to detail all of the threads in the B-series engine that are NOT Unified thread standards.

Part No's Description Where Used thread Ref.
... Plug w/ Cu washer LR above oil pressure port ... ...
... Plug w/ two fiber washers LR oil pressure relief cap ... Can sub. one Cu washer
... Special Adapter, oil outlet, w/Cu washer RR side of block ... ...
... Thread for tube coupling Outlet end of Special Adapter ... ...
... Adapter w/ Cu washer, oil inlet Into filter mount or adapter Same thread as port 7 ...
... Plug, dipstick port (standard engine) Right center lower block near sump flange ... ...
... Plug, dipstick port (Magnette engine) RF lower block near sump flange ... ...
... Plug, dipstick port (Twin Cam engine) LR lower block near sump flange ... Machined for Twin Cam only
2F4249
2A380
88G257
Plug, sump drain (except Twin Cam) Right, low on sump 1/4-BSP or G1/4 Same thread as port 2
2F4249X Plug, sump drain, magnetic (except Twin Cam) Right, low on sump 1/4-BSP or G1/4 Same thread as port 2
2H4685 Plug, sump drain (Twin Cam only) Right, low on sump 3/4-14-ADM Larger thread than std. eng.
... Coolant drain petcock Right block, aft of dist. ... Same thread as port 2
... Coolant drain petcock Bottom of radiator ... Same thread as port 2
... Crank dog nut w/ locktab Front end of crankshaft ... ...
... Bolt, square head, and Square Nut distributor clamp plate ... ...
... Thermostat cover studs Bottom end into head ... May be BSF threads in head
... Flare nut for temperature sender RF of cylinder head 5/8-18-UNF DT-102D
DT-102H
Moss Mot's 361-065 Flare nut Adapter for temp. sender RF of cylinder head 5/8-18-UNF DT-102D
DT-102H
... Manifold Studs Left side in cyl. head 5/16-24-UNF Inboard 4 of 6 need sealant
... Water Pump bolts Front of block 5/16-24-UNF 3 of 4 may need sealant

Separate Care page for all double threaded studs in the car.

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