Ld exhaust manifold nut - cast & brass

[rlpembridge]

I'd like to discuss the subject of brass manifold nuts on exhausts for Ld's.

I noticed and raise this subject here after having experienced the exhaust detaching itself from the cylinder whilst I was riding along.
Last summer (when I last rode my 1957 Ld b MkIII), I added a 'C' spanner to my tool kit. However, no matter how judiciously I tightened the brass manifold nut before riding out, when the engine got hotter, the nut undid itself. Thankfully my ear became attuned to the engine note as soon as it began to slacken-off and full detachments were avoided but this was a whole new pain-in-the-arse experience for my Lambrettering.

At the end of my last ride, before the scooter was packed away in the garage again, I ran the engine up to temperature, quickly stripped off the magneto-side cowling and tightened the exhaust manifold nut, using two 'C' spanners, whilst everything was still hot.

The benefits of that exercise are yet to be tested but I then checked the exhaust I had replaced and discovered that, as I thought, it had a cast iron manifold nut. I've had the scooter since 1982 and I'm pretty sure that all previous exhausts have had cast iron manifold nuts, too.

The cast iron ones never undid themselves and yes, I always use a gasket in the exhaust.

Perhaps I should seek out someone skilled in the art of flanging and see if they can retro-fit a cast nut. Either that or a good welder who can cut and replace the upper section of the down pipe.

I would be please to hear any observations from others who have experienced brass manifold nuts on exhausts.

[jbcollier]

A brass nut is going to have a different rate of thermal expansion, and be inherently more "slippery" compared to a cast nut. The slippery bit is usually viewed as a bonus as it won't seize, or fuse, with the cylinder after repeated heat cycles. I think you have done the right thing in tightening it up when it is hot. I would now lock wire it into position. I don't remember if my exhaust nut is cast or brass but I did have a problem with it loosening over time. Lock-wiring solved that.