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CORE PLUG REPAIR - Betson Bolt - CO-105B

This "solution" applies only to the MGB five main bearing engine and gearbox combination with the tall rear plate. If this engine blows the core plug at the rear of the engine block, the repair would ordinarily require removal of the engine and disassembly of the clutch and flywheel to remove the engine rear plate for access to this core plug. Ah, but the Betson Bolt may come to your rescue.

At 09:49 AM 6/8/05 +0100, Chris Betson of Octarine Services wrote:
>"Yes, I originally came up with the solution to the blown rear plug without having to remove the engine. The BBS fraternity dubbed this the "Betson Bolt"!! Although I am sure that others may have also developed this solution since it is fairly obvious if you sit and contemplate the amount of work it saves!
>
Betson bolt for core plug repair >Simply take one of the thick washers used to clamp the inlet & exhaust manifolds to the head and tap it out to 3/8 UNF or a suitable metric equivalent. You also need a matching screw (thread all the way to the head) about 1 inch long. Take the washer with the coned side facing the rear engine plate and slide it in till it locates over the hole in the back plate and insert the screw. Tightening the screw will force the washer against the back plate and the core plug into its recess.
>
>I improve the design slightly by turning a flange into the washer so it locates positively in the hole in the back plate, but this is not essential."

On 6/27/2016, David Adams wrote:
"Chris Betson kindly advised that:
  • The new core plug should be edge coated with a Loctite permanent sealant, not silicone.
  • Place the core in a clean and dry recess in the block
  • Put the bolt in the backing plate and tighten to just touch the plug
  • Tighten the bolt at least another full turn, depending on the pitch of the thread, so the center of the plug is depressed level with the outer edge
  • The bolt can be secured with Loctite.


  • "I did not have a spare manifold washer so I made a backing plate from a scrap of 30 x 5mm flat bar with a tail 70mm long from the bolt center so I could fix it in situ while I fiddled to get the bolt in, it's tight in there. The backing plate has a 25mm OD washer riveted to it to locate the backing plate in the back of the access hole, as shown in the first picture.
    "I used a 3/8" x 24 UNF thread and first tried a 1" bolt which was too short so ended up with a 1-1/2" bolt and clamped the tail of the backing plate with vice grip pliers, as shown in the second picture. I gave the bolt 3 turns to get 1/8" depression on the plug with another half turn for luck.
    Betson bolt for core plug repair Betson bolt for core plug repair
    "Whilst the engine was stripped for removal I gave the 3 other plugs a good clout, using a failed core plug with a 3/4" hole drilled through it to guide and centralize the 5/8" drift I used. The black item in the first picture is the alternator bottom fixing bolt with a locating washer welded to the head so that fan belt adjustment is a one-handed spanner job".

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