I have a 1934 633cc big 4 with a cast iron head,,I am trying to buy a new exhaust pipe ,my one has a "straight" into the head held in by a grub screw,the supplier says it should be an ally head with the flared end on the pipe and a back nut ,,,is he right and I have the wrong head (original?) and it should be ally? surely cast heads were before the ally ones and he is wrong?
No pre-war Norton side-val…
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Previously richard_payne w…
Previously richard_payne wrote:
No pre-war Norton side-valves had ally heads. They were first seen with the 1948 re-design.
I'm not sure about your grub screw being an original fitment. Normally they were simply a push fit (but then clamped securely lower down).
Although the Big 4 cylinder is taller than the 16H, it has a longer exhaust stub and both models use the same pipe.
I can't confirm that the pre-'35 models were the same as those after the 1935 changes, but I suspect that your best bet would be to look at what's listed for WD16Hs. These don't always seem to follow the correct line which can cause problems with the lower clamp but they do seem to be able to connect cylinder to silencer.
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I think the theory is that…
I think the theory is that the (steel) pipe gets so much hotter than the (iron) head, that it quickly expands and stays stuck fast as soon as the engine starts, after simply being pushed in.
As Richard has said, there's no other fixing supplied or needed.
The WD 16H etc had another bracket part way down the front, but the earlier bikes (like yours) didn't seem to have it. Maybe the army wanted it to be more robust?
About 3 years ago I bought new pipes for my 16H from Armours and they were well made, well finished and fitted well. And the only support near the front is the same bottom bracket as in your picture. It's not escaped yet.
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No pre-war Norton side-valves had ally heads. They were first seen with the 1948 re-design.
I'm not sure about your grub screw being an original fitment. Normally they were simply a push fit (but then clamped securely lower down).
Although the Big 4 cylinder is taller than the 16H, it has a longer exhaust stub and both models use the same pipe.
I can't confirm that the pre-'35 models were the same as those after the 1935 changes, but I suspect that your best bet would be to look at what's listed for WD16Hs. These don't always seem to follow the correct line which can cause problems with the lower clamp but they do seem to be able to connect cylinder to silencer.