B31 valve timing

[neil1964]

Not sure if the old wives tale is true (sorry if that offends any old wives here😉) but I have understood not to leave these engines (or at least the Gold Star variants) ticking over too slowly for too long as there is insufficient oil flowing at these speeds and you risk overheating with a piston face picking up or big end getting 'dry'. 
Any knowledge of this out there?

[Derek996]

Not sure if the old wives tale is true (sorry if that offends any old wives here😉) but I have understood not to leave these engines (or at least the Gold Star variants) ticking over too slowly for too long as there is insufficient oil flowing at these speeds and you risk overheating with a piston face picking up or big end getting 'dry'. 
Any knowledge of this out there?

I'm not sure that that would be the case with a roller bearing big end. It would to be a very low flow indeed, but piston face overheating may be a possibility.
In Ducati circles I have certainly heard this mentioned but that was concerning the engines with plain bearing big ends which depend on a good oil pressure.

[Greenfield]

Looking at the back of the inlet timing sprocket/cam on my 1950 B33, there is a number stamped which could be 12-1 or possibly A2-1. Could anyone advise whether these are standard for this model or quieter cams that were fitted later?
Cheers

[neil1964]

Looking at the back of the inlet timing sprocket/cam on my 1950 B33, there is a number stamped which could be 12-1 or possibly A2-1. Could anyone advise whether these are standard for this model or quieter cams that were fitted later?
Cheers

The A2 is commonly seen on 65-2420 cams which are the standard type for B31/B33 and the B32/4 competition models post war until end in early 60s. These all had quietening ramps and 3 thou clearances. The Gold star type 65-134* and 65-243* (known as type A) pre 52 did not have ramps and need close tappets at 1 thou. Cams with 65-244* (type B) had ramps and wider clearances (6-8 thou).

[Greenfield]

Thanks Neil, any thoughts on a cam stamped 'D'?

[neil1964]

Thanks Neil, any thoughts on a cam stamped 'D'?

Sorry, I do not know. I've got a few Goldie standard cams across the era but just a D means nothing to me.
Can you do quick measurement of base circle and lift?
Otherwise you'll need to install and measure lift in situ and measure the opening times with degree disc on the crank.

[Derek996]

As Neil says, the standard 65-2420 is often marked A-2 but just as often have no markings or sometines some other letters. The biggest give away as to whether a cam is a gold star one or not is the base circle diameter, which is smaller on a Goldie cam effectively giving more lift.
The cam on the left in the attached picture is a standard cam and the one on the right is a 65-2446. Note the wider diameter at the bottom and the more pointed peak.

[V500]

is that base circle measurement dependent on the intended use for said Goldie cam? Fast road work maybe, but trials etc too?

[Derek996]

is that base circle measurement dependent on the intended use for said Goldie cam? Fast road work maybe, but trials etc too?

BSA produced cams for trials, scrambles, touring and clubmans and racing. Various combinations were used depending on the use, and whether 350 or 500. The ZB series used the same cams for tourers and racing yet had a different pair of cams for clubmans! The 1949 Scrambles used the same cams as the 350 tourer. It seems there was a constant development going on.
The trials Goldies used the standard 2420 cams. All the other Goldie cams have higher lift and reduced base circle diameter. I suspect that the base circle diameter may be different for different cams. I have a few that I could measure to get an idea.

[Derek996]

The measurement across the base circle of the standard 2420 cam is 25mm as near as damn. The Goldie cams that I had to hand measured 22.5mm, 22.5mm and 22.3mm.That's an increase in lift of 2.5mm and 2.7mm. The cam profile itself will set the timings and opening durations.

[Greenfield]

A couple of my bikes had a mix of 'A2' and 'D' stamped cams. Both are 25mm diam across the round and about 32mm at the cam peak, so doing the same job. One or both could well have been replaced over the years.