Welch Plug

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Original submission by T Apr 6th 2007:

A 202 Engine. The welch plugs are the 5 round shapes running from front to back along the block between the head and the sump in the middle of the engine. Click to Enlargen. Photo by Brad Canniz.

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Welch Plug:

A Welch Plug, named after the inventors (and otherwise known as a core plug), is a round hammer-in device that is tapped into the  Engine Block or Cylinder Head to fill a casting hole that was left from where the core was supported. The core is a mixture of sand and binding agent which is placed inside the casting mould to form the water jackets etc.  After casting the core is destroyed during removal and the supporting holes are left. These holes are fitted with core plugs. During the metal pouring process air and excess metal are expelled through "risers". These risers appear on the top of the casting as columns of metal and are ground off. "Why are sewer covers round? So they won't fall down in." ... Professor Julius Sumner Miller. The Romans made sewer covers round for that very reason. By the same reasoning, Welch Plugs are round. 
Brass Welch plug. Some Welch Plugs are made out of Metal that corrodes. Click to Enlargen. Photo by Nobody123.

Welch Plug Replacment:

Welch Plugs can rust out and need replacing. They tap out with a screwdriver and hammer taking care that they don't fall into the block. Nobody123's Shed and Welch Plug Replacement

Welch Plug History:

Welch plug history.

Welch Plug Testimonial:

Welch plug. Click to Enlargen. Photo by Nobody123.
Info provided by 76HXMonaro Apr 6th 2007. Brief History of the Welch Plug by Nevin Hubbard of www.hubbardspring.com A brief bit of totally obscure history that I am one of the few living persons who knows. My family business, established in Pontiac, Michigan in 1905, is the original manufacturer of the "Welch" plug. The Welch brothers had a motor car company at the turn of the century that was later bought by General Motors - the Welch Motor Car company. They would run the cars around Pontiac to "break them in." At that time core holes in the engine blocks were fitted with pipe plugs. During one of these run-ins a pipe plug backed out. In order to get back on the road one of the brothers drove a quarter or half dollar into the hole. From this they developed the Welch plug, some with the help of my Great Grandfather Martin Hubbard. They then patented the plug and the M.D. Hubbard Spring Company become the sole manufacturer of the Welch plug for the life of the patent. To this day we have the largest range of sizes available anywhere. So the Welch plug in origin is an American innovation and name. Best Regards, Nevin Hubbard M.D. Hubbard Spring Company www.hubbardspring.com
Cylinder Head Steel type Welch Plug in a stage 2 Red Motor Cylinder Head. Click to Enlargen. Photo by HQ_SS.

Blown Welch Plugs:

If proper Coolant isn't used in the Engine, the Welch Plugs will be the first to fail. They will rust through from their centres outwards. The result appears in the attached image. One responsibility of Coolant is to prevent rusting inside the Engine Block Water Jackets. Straight Water will make the Welch Plugs rust. 
Blown Welch Plug in a 202 Engine. The position is near the Starter. Click to Enlargen. Photo by Dusty Dirt Roads.
Blown Welch Plug in a 202 Engine. The position is between the Alternator and Starter. Click to Enlargen. Photo by Dusty Dirt Roads.
Cylinder Head Welch Plugs in a 202 Engine. Click to Enlargen. Photo by Juzzy.
Blown Welch Plug in a 186 Engine. Click to Enlargen. Photo by FulySicHT.
Blown Welch Plug in a 186 Engine. Click to Enlargen. Photo by FulySicHT.
Blown Welch Plug in a 186 Engine. Click to Enlargen. Photo by FulySicHT.
Rear view of a 202 Engine. The lower right hand Welch Plug is for the Camshaft. Image by Brad Canniz. Click to Enlargen.
Rear of 186 Engine from HT Holden. The device in the upper left is a Heatstamp which will change colour if the Engine is overheated. The Engine Builder will know that the Warranty has been voided. Photo by Davequey. Click to Enlargen.

Red, Blue and Black Six Cylinder Engines Welch Plugs:

  2 X 1 7/32" and 3 X 1 5/8" for the side of the block 2 X 2" for the rear of the block 3 X 3/4" for Red heads and 1 X 3/8" for the front oil gallery. 


Welch Plug Removal Thread



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