Welch Plugs

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Welch plugs (core plugs) are circular discs that fit into, and seal the casting and machining holes in the Engine block, Cylinder Head and Transmission.

Terminology

The Welch plug was originally designed circa 1910 by the Welch brothers at the Welch Motor Car Company of Pontiac, Michigan. You may hear them called "welsh plugs". See Patent No 1058210

They are often called "freeze plugs" because if the engine coolant freezes they'll be pushed out of the casting. However, the purpose is not necessarily to solve freezing problems but rather to seal the holes left by the casting or machining process (core plugs). Those that are designed for freezing safety may be called "expansion plugs".

Set

Sets are for the engine block only (does not include the Cylinder Head plugs).

PLUG-WELCH A10/A12/A13/A12A/A14/A15
44Ø CAM bore, rear
50Ø CORE block, rear
35Ø CORE block, side (3)
* M2 Block reported uses 25mm plugs

Pioneer PE-130 (PE-130B contains four brass plugs for the water-contact plugs + one steel)
Album 26530
Pioneer includes front & rear oil gallery blind plugs

11021-13200 PLUG-taper (12.7ø) (fixing [cam] oil gallery) (2)

DORMAN 557-031 A12 & A13 engines

MAFCO 437 120Y 1969-1972 (http://www.mafcobell.co.uk). MAFCO have got the name and years wrong, and one plug appears to be the wrong size

Cylinder Head

One Welch Plug:
Album 15003

• 00933-14000 PLUG-WELCH (1) head, rear [40 mm]

Engine Block

B110

Five Welch Plugs
Album 15004

* 11019-32200 PLUG-WELCH 44Ø CAM BEARING (1) block, rear (44.425 Ø) [1-3/4 inch]
* 00933-15000 PLUG-WELCH 50Ø CORE HOLE (1) block, rear prev. 01648-00084

* 00933-13500 PLUG-WELCH 35Ø CORE HOLE (3) block, right side 
Album 6107 Album 6109
* 35mm brass core-plugs

B120

35 mm Expansion Plug 00933-13500/11021-E3000/00933-1351A
Nominal Dia.: 35.21mm
Steel
Height: 0.380"

プラグ (35mm - 3 required)
7510-8506 00933-13500
8506-8706 11021-E3000 [11021E]
8706-     00933-1351A

Cam bore plug
11019-32200 44 mm -8506
01648-00191       8506-

Transmission

Three Welch Plugs
Album 1668

• 00933-11400 PLUG-WELCH TRANSMISSION CASE (2) inside bell, northwest of mainshaft

  14mm diameter, all 56-series and 60-series

• 32102-18000 PLUG-WELCH TRANSMISSION CASE (1) inside bell, below mainshaft

The two small plugs can be seen in this photo, to the left of the spring:

Removal and installation

Removal: tap one edge with a punch or chisel, then grab it with vice-grips and wiggle it out.

To install, fit squarely into bore, and tap gently and evenly into place. No sealer is used.

Others

MAFCO 438 1972-1980

MAFCO 441 Sunny 140Y 1980-1982

above looks to be for L14 engine
PB210 (140Y in South Africa) - L14 engine
11021-21000 PLUG-welch [6 total, 40 mm]
* (3) right side
* (2) left side
* (1) rear
cylinder head
* 00933-13500 PLUG-welch, 35 -7410
* 00322-13000 PLUG-welch, 30 -7410
* 11048-73403 PLUG-blind (2) 7411