Friday 13 October 2023

Castings Galore

A few days ago the foundry phoned to tell me my castings were ready. This is what I collected:

There is now a lot of fettling and machining to turn these into usable parts. The material is AB2 Ni-Al Bronze and in my experience this can be quite a tough material to machine - I have used it in the past to make various small parts, however it does have the strength that I need for various critical components such as girder fork links.

For reference, the patterns for the various different parts are detailed here.

Incidentally, the 3 rockers at the bottom of the picture are not for any of my bikes but are destined for a 1930s bronze-head Ariel that had suffered a broken rocker. Apparently this is a common problem with this particular engine as a result of poor design of the rocker geometry,



Thursday 5 October 2023

A bit of work on the V-Twin

While I was waiting for the castings to come back from the foundry there were a couple of jobs that I needed to do on the V-Twin. The last road test had revealed that I had still not entirely solved the problem of oil escaping from the inlet side of the cambox on the rear cylinder where the rocker exits and that the oil was getting quite a bit hotter than I would have liked. The oil tank that I had made for the bike – whilst fitted into the available space quite neatly, was not of great capacity.

There are 3 possible solutions to the cambox oiling problem:

1)    Reduce the oil flow rate to the cambox

2)    Prevent the oil from escaping the end of the cambox beneath the rocker

3)    Prevent the oil from being transported from the cam chamber to the end of the cambox – the direction of camshaft rotation does not help in the respect of “flinging” oil towards the inlet side.

 #1: I had already reduced the oil flow rate to the cambox by putting flow restrictors in the feed line and did not want to reduce the flow rate any further for fear of damage.

#2: I had fixed multiple pieces of felt to the outside of the cambox to try and block the gap between the rocker and the cambox but this was only partially successful in preventing oil escaping because of the oscillatory motion of the rocker and the consequential opening/closing gap between the underside of the rocker and the slot in the cambox.

That leaves #3 – but how to stop oil getting from the cam chamber to the end of the cambox?

The only way that oil can leave the cam chamber (apart from its “proper” path through the large bearing on the drive end of the camshaft and into the timing case) is via the small hole in the casting where the rocker skid enters the cam chamber. And so, my latest attempt at solving this problem is to insert a 1mm thick piece of viton sheet, cut to an appropriate shape

and then fixed to the outer surface of the cam chamber inside the cambox using viton adhesive (it goes under the number PC 1473). The picture below shows the viton strip attached and with the rocker removed.

A piece of felt was also fixed to the underside of the cambox cover to hold the 2 viton strips vertical when assembled.

Hopefully this will restrict the amount of oil reaching the end of the cambox but still provide sufficient lubrication for the rocker spindle. We will see what happens with the next road test.

The 2nd modification was to insert an oil cooler into the oil return line and positioned under the seat.

I am hoping that the splayed riders’ legs will provide some kind of crude ducting to ensure a reasonable airflow to the front face of the heat exchanger and it has the added advantage of doubling up as a seat warmer in the winter.

I’ll report on how well these modifications worked when I have had the opportunity to road test.