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MG MGB Technical - bonnet

hi all,
posted a question on the mgc board and its very quite over there so wondered if anyone here can answer. all i want to know is did all mgcs have alloy bonnets.
thanks bob.
bob taylor

Answer NO. I think the change came sometime 1969 ish. Probably BL influenced!
Allan Reeling

Sorry that's B's changed from Aluminium to see 1979 ish. Whether C's shared the same time scale it doesn't seem clear and Clausager seems vague on that too. Looks like some C's had steel bonnets right at the end of their production in 1969.
But you know the BL organisation, a lot of what you got was whether they had one on the shelf when your chassis came past!
Allan Reeling

"Sorry that's B's changed from Aluminium to see 1979 ish."

Late 1969.
paulh4

Yes Paul got the year and decade right, up to the point when finger hit key, similarly "steel" which came out as see!!?? Bad typo day!! Came out right on my first post though!
Allan Reeling

Indeed. I read back before I click Submit ... and still get things wrong :o)
paulh4

So Paul
Did any MGC's have steel bonnets
I've only ever seen aluminium here
There again there would be lucky to be four or five of them on our little island at the most
willy
William Revit

Willy, That's still a probably possibly! The material change was "somewhere" around the time C production ended. Depends what the stock of Aluminium bonnets was before the plug was pulled I suppose. There doesn't seem to be a definite cut off point for the B either, could possibly be because both types were stacked on the same racks and aly and steel bonneted B's and C's were emerging together from Cowley.
Allan Reeling

Clausager does say 'possibly', although personally I think it unlikely. Bonnets would have been made in batches, and as the MGC was a 'special', and because of planning lead times for modifications and also the demise of the MGC, I can't really see them making steel bonnets for the last few MGCs. Would they have been made on the same presses? It doesn't seem likely given the forces required, aluminium might come out like Bacofoil from a steel press :o)

He goes on to say that there is only one part number for the MGC bonnet, and other records indicate that the MGB got them during the 1970 model year after the stock of aluminium were used up. So the other way round is more likely, i.e. some 1970 MGBs may have had ally when in theory they should have had steel.

In the words of Patrick Moore: "We. Just. Don't. Know".
paulh4

Hmm interesting
I had, years ago a early C auto 68 model-- it had an aluminium bonnet
On the subject of alloy/steel B bonnets--
The steel one has more of a curl in it crosswise compared to the flatter alloy one - I found this when doing V8 conversions
There would be roughly 1/2" difference in height in the centre above the engine which is handy for carb. choice on a V8
willy
William Revit

According to Clausager (I seem to remember, but can't find it now) the bonnet for the V8 needed a slightly more pronounced curve to clear the carbs - compared to the steel 4-cylinder bonnet, subsequently adopted for all MGBS (as indicated in the Parts Catalogue). And since the carbs are very near the back one would expect it to be higher crosswise there as you say. But it then wouldn't line up with the panel at the base of the screen, so I wondered if the profile remained flat as it came forwards, before dipping down. The V8 still needed cut-outs in the under-bonnet insulation for the carbs, and you can see where mine have rubbed the paint. But whether it's an original V8 bonnet or a replacement to the 'flatter' design I don't know, the cut-outs were a subsequent modification.
paulh4

I was told that all MGCs had an alloy bonnet originally but if it got damaged in house or away from the factory it was replaced with the steel version.
steve
s p brown

According to Geoff Allen the bonnet for the V8 needed a slightly more pronounced curve to clear the radiator, mounted further forward than in the preceeding 1800s.

That would agree with Pauls's thought about alignment with the panel at the base of the screen

My V8 experience bears Geoff's comments out, I have an aluminium bonnet and angled the top of the radiator forwards a little by using spacers ( those for the seat rails are the standard practice ). My bonnet is only just clear of the radiator, and in fact has developed a very small dimple where it seems to just touch occasionally - despite the cutout in the forward insulation piece.

The cut-outs in the rearward under-bonnet insulation apparently gave enough clearance for the carburettors.
J N Gibson

This thread was discussed between 11/07/2016 and 29/07/2016

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