Friday 10 November 2023

More work on the V-Twin….

The most recent modification to the V-Twin to prevent oil exiting the cambox, described here, did not work. Apart from the obvious – oil dripping continuously from the rear of the cambox on the rear cylinder, I found that the piece of Viton that I had so carefully attached to the inside of the cambox had simply disintegrated from being battered by the rocker.

One thing that I had not done – and should have done many months ago – was to try and measure how much oil was coming out of each internal collection chamber in the cambox and so I made up 3 short lengths of copper pipe and attached these to the outlets, shown below.

At the same time, I fabricated a small pot and attached that to the side of the timing case to where I had plumbed in the oil drain back into the engine. The purpose of this was to determine if oil would drain as expected.

There were a number of outcomes to this exercise: firstly, no oil came out of any of the copper pipes attached to the cambox when the engine was running – only when the engine stopped! It was also observed that the cyclic pressure variation being transmitted from the crankcase to the cambox (via the timing case) was noticeable in the “suck” and very strong “blow” being felt at the end of the copper tubes. Furthermore, the oil that had been squirted into the small pot and that should run into the timing case did not go into the timing case as expected - the level didn't change. So, a rather unfortunate combination of factors, all of which contribute to poor (zero!) scavenging of the cambox.

The one-way check valve was still in place and this was removed so that the pot was connected directly to the timing case and the exercise was repeated. The oil in the pot now drained and so the simple solution for this part of the problem would be to remove the check valve.

However, the “suck-blow” problem in the cambox could not be so easily solved and I surmised that the “blow” part of this cycle was transporting (= blowing) oil towards the slot where the tappet exits. The only way to prevent this would be to eliminate the oscillating pressure and the only simple way of doing this would be to replace the open bearing supporting the camshaft with a sealed bearing – at least, sealed at one end as it would still need lubricating. This is not a 5-minute job as it requires removal of the camboxes and the timing case. At least it allowed a look inside to make sure everything was OK.

A couple of new bearings were ordered (an original on the left, new one on the right)

One seal was removed (leaving the seal on the timing case side in place) and dropped into the housing

before reassembling the camboxes, checking the valve timing and replacing the outer timing case cover.

Although a running check will be made with the 3 copper pipes, new oil collection systems were made for both front and rear cylinders, shown below.

As with the single cylinder AJcette, I have incorporated a collection volume into the oil drain line – a short length of exhaust pipe with a couple of machined end caps.

While I had the bike up on the hydraulic bench I made one more modification. During road testing, I had found that the bike could easily accept higher gearing and so I decided that I would increase the number of teeth on the engine sprocket from 18 to 20.

I new triplex sprocket was purchased – shown below alongside the existing engine sprocket

and set up in the lathe for machining.

After removing 2 rows of teeth, the sprocket was turned round to machine the 40 taper and checked using my reference male taper to position the sprocket correctly on the crankshaft.

After chemical blacking

and increasing the length of the primary chain by 1 link the new sprocket was fitted on the bike.

Last, but by no means least, I could have removed the camboxes without removing the whole timing case (and oil pump and exhaust) if I had been able to remove the Vernier pin washers on the end of the camshafts through the inspection plates. However, the pins are a good fit in the sprocket and hub holes, they are difficult to access and are nearly impossible to grip using long nose pliers. I have therefore put 2x 2BA threads into each Vernier pin washer so that they can be removed easily through the inspection cover in future.

I am now waiting for a break in the succession of low-pressure weather systems coming across the Atlantic and the rain to stop long enough before testing these latest modifications.

There has been progress on the wheels for the Velocettes – I now have 6 rims for the 3 bikes and all the rims and hubs have been black powder coated.

I’m now waiting for the spokes.

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