Interrupted fins on A10 barrels

[Sakura]

Hi, anybody got any info or ideas on the interrupted fins on the late, thick flange  barrels?

[muskrat]

G'day Sakura.
  Please explain. Look here https://tinyurl.com/4zdraw7e
Cheers

[Sakura]

Hi Musky, late A10 barrels had a different fin layout at the front. Every other fin is stopped short, as it didn't go all the way through like the earlier barrels. I'm not sure if that's a very good explanation? Obviously a photo would be better but I'm not sure it would show up well. It leaves more of a gap through to the pushrod tunnel, perhaps for better cooling? Possibly to reduce mud collection on the Spitfire Scrambler and common to the late range?  I haven't seen enough late engines to tell whether it applied to all engines. I did a search and nothing definitive came up except one post that mentioned "fancy finning" which I suspect is a late barrel. I won't be the only person who has spotted this so someone will no doubt make comment.

[muskrat]

G'day Sakura.
I'll have a look at the TF barrels on the Cafe compared to the LF A7 barrels on the plunger when I venture outside (starting to cool off here 5C).
Hold my beer!
Cheers

[Sakura]

TF /LF? Your turn!

[trevinoz]

This has been discussed previously.
It seems that these barrels were fitted to the 1963 models.
Some have said that they were for the RGS but that is unlikely.
I have only seen one and it had been blown and cracked around the base.

[muskrat]

G'day Sakura.
If Trevor's description is correct and it would be. I have late model barrels on my Cafe where the top two fins are joined then every second is joined the others are separated. Does that make sense?
TF = thick flange, LF = large fin.
Cheers

[Sakura]

Hi Musky, that's it! My question is- why? My bike is late '62 despatch and I doubt it was RGS only, why would it be? A10's are not known for fin "ringing" so I don't think it's that.

[muskrat]

G'day Sakura.
It could have had replacement barrels at some stage. My Cafe started life as a 56/57 A7SS, it's now a A10 RR/SR of mixed years.
Cheers

[Sakura]

Finally found trvinoz's post showing the interrupted fins barrel. I think my barrels are original, I first had the bike in 1970, so I doubt they had been changed, although it was in an accident in 1966, which required a frame change. My RGS was despatched very late 1962 and sold about May 1963. I think A65's might have had the same fin arrangement? Which brings me back to why the change? It obviously required a new pattern and so late in A10 production it must have been thought necessary.

[muskrat]

G'day Sakura.
The A565 barrels are different again.
There were quite a few changes through the A7/10 run.
Cheers

[Sakura]

Hi Musky, got the interrupted fins but I don't remember those bore cut outs?  Ventilation for piston skirts

[RDfella]

Bore cut-outs are common for conrod clearance. Those 'holes' in Musky's pic have either been accomplished with a hammer or are the result of mechanical mischief.

[Sakura]

Bore cut outs.
Hmmmm, my facetious comments were obviously misplaced there!