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[Datsun 1200 encyclopedia]

Welch Plugs

From Datsun 1200 Club

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Categories: Engine Mechanical | Cooling System | Transmission

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.



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".


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

Nissan A14 core plugs
PLUG-WELCH A10/A12/A13/A12A/A14/A15 (see Block_&_Pan_Part_Numbers)
11019-32200 44  CAM bore, rear
00933-15000 50  CORE block, rear
00933-13500 35  CORE block, side (3)
* NOTE: M2 Block reportedly uses 25mm plugs
Some sets include:
11021-13200 PLUG-taper (12.7) (fixing [cam] oil gallery) (2)

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

REPCO 058-4030 Expansion Plugs for A12, A13, A14
28765.jpgAlbum click to view

DORMAN 557-031 A12 & A13 engines
28767.jpgAlbum click to view

MAFCO 437 120Y 1969-1972 ( MAFCO have got the name and years wrong, and one plug appears to be the wrong size

Cylinder Head

One Welch Plug:
15003.jpgAlbum click to view

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

Engine Block


Five Welch Plugs (including three on side of block)
15004.jpgAlbum click to view

Two on REAR: Large core plug + smaller cam bore plug
28768.jpgAlbum click to view

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

Three 35mm core-plugs on manifold side
6107.jpgAlbum click to view 6109.jpgAlbum click to view

* 00933-13500 PLUG-WELCH 35  CORE HOLE (3) block, right side


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


Three Welch Plugs
1668.jpgAlbum click to view

  • 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.


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 

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