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MG MGA - Dizzy clamp

Can someone remind me of the orientation of the dizzy clamp ring? It is not flat, so do you assemble it so there is a gap below the bolt holes or is it supposed to contact the block at that point ? Also, which side of the dizzy does the pinch bolt go, block side or outside?
Art Pearse


The stamped out center section of the mounting plate needs to stand proud of the engine block. In other words there should be a small gap.

All of my cars have had the pinch bolt on the block side.

jjb Backman

Thanks John.
Art Pearse

Further to this, can anyone advise what size bolts secure the dizzy clamp to the block, noting that I have a Marina 1800 engine block? Per Moss manual, code for the MBG engine bolt is GHF117. This is where confusion starts as a MGB BBS describes GHF117 as "UNF 1/4", but elsewhere it is described as "BSF 1/4". I understand UNF is 28tpi whereas BSF is 26tpi. The threads of the bolts I have are really worse for wear but appear 26tpi. I want to re-tap the block threads and replace the bolts.

Assistance will be appreciated.
Joe Gates

1/4 UNF
Colin Parkinson

I think they are all UNF, same as NF, 28 tpi. If you are unsure, take a new bolt of UNF and BSF and try them in the hole. The difference is enough to prevent entry very far. Don't retap until you are sure!!
Art Pearse

This thread was discussed between 21/11/2009 and 29/11/2009

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.