thick flanged barrels

[frankenstein]

hi...just a quick one for the forum....both my flash and my mates bike both have half inch flanged barrels instead of 3/8 inch ....i thought these barrels where just for the rocket models...please correct me if im wrong....cheers !

[bsa-bill]

No both my Flashes have thick flange, I might be wrong ( very possible ) but I thought they were introduced across all A7/A10 range, don't know just when though,

All the best - Bill

[trevinoz]

The Flash got the thick flange barrel in 1958.
 Trev.

[groily]

And everyone was better off for the change. Years ago, an engine with the thin-flange barrel was almost in the 'don't-touch-it' category, notwithstanding the fact that many thin barrels had done many miles without hassle and weren't at risk with 7:1 pistons and mild cams etc.
However, I got my first 'thick flanger' after my first thin flange parted company from the rest of the barrels and caused mayhem. Or did the fins leave the the flange? Bit of both actually. So I guess the BSA people knew what they were doing in 1958, when global warming hadn't been invented and carbon footprints were what you got when you held a pencil between your toes. They must have realised belatedly that people just would insist on stuffing 9:1 pistons and lumpy cams in bog standard motors and to hell with the fact that the vapour trail rivaled a Jumbo jet's. Who? Not me guv.
I am pretty sure though that you still don't want thin ones on anything with any pretensions of power of delusions of grandeur. Now, had BSA used through-studs from crankcase to head on the twins like on the singles, or like one or two other marques' twins, it probably wouldn't have mattered. But they didn't. So we have to find silly little spanners to get on to the nuts round the bottom, and pray that they stay done up, don't let oil out, etc. Mind you, at least they didn't adopt those very precious little 12-sided nuts found elsewhere. Luckily the head steady is quite sturdy, so if and when the bits let go, they stay in the general area of the frame.

[trevinoz]

Funny you should mention that, Groily. Back in the 60's I put 10:1 pistons and 357 cam in my '55 Flash.
First problem was getting the cam to revolve in the cases. A little work with a large round file fixed that.
Second problem was on the first time I rode it and found that the premium fuel available was not up to the job so I had to use high octane racing fuel at a 50% premium.
Third problem after only a few days was the parting of the barrel above the flange which became noticeable with the amount of oil dripping from my boots. The engine was still running but was very noisy with the increased tappet clearance and in fact the barrel was moving up and down. I jammed a lump of wood between the frame and head to get home, stopping regularly to bash the timber back in.
I still have that engine but it is now considerably detuned from that effort!
  Trev.

[Brian]

Fortunately I have not had the pleasure of a set of barrels coming apart.

I have heard of this happening but only ever on the early swing arm models so my question is, did it also happen on the plunger models. There must be heaps of owners of plungers that put higher compression pistons etc in.

Trev I love the idea of the lump of wood to hold it all together but may I suggest that some beer would have improved things. My theory is, if you had drunk some beer then you would have had to stop for a leak on the way home. We all know that when wood gets wet it swells.....................................

[LJ.]

My theory is, if you had drunk some beer then you would have had to stop for a leak on the way home. We all know that when wood gets wet it swells

Not when there is a high voltage Magneto in the vicinity!! 

[dpaddock]

I suggest that the engine steady brackets be part of the periodic tightening procedure as you maintain your bike. I use Nyloc nuts and robust torqueing of the bracket bolts. My 3/8" barrel has been used in drag (sprint) racing as well as road riding and has many miles on it.

[RichardL]

It's interesting that the head-steady brackets should be considered part of the system for keeping 3/8"-flange barrels on the crankcase. I have 1/2"-flange barrels and the original brackets were cracked at the elongated holes. Aftermarket replacements are of lighter material and, I would think, less likely to provide the added protection. I think if this is a real need, someone should come out with truly heavy head-steady brackets.

Richard L.

[groily]

I agree with dp that regular checks on the fasteners up there should be part of the general maintenance routine. I tend to stick a spanner on everything I can get at whenever I have the tank and seat off.
But I don't think there's a really big risk of a properly-screwed together 3/8th flange engine flying apart (with apologies to Trevinoz if his was well screwed together as well as well screwed on the road!). I have a feeling youthful indiscretion and throttle-happy enthusiasm coupled with hit and miss maintenance, non-existent finances and the usual sense of juvenile immortality were what made mine blow up.
All the same, the word on the block in those days was that you didn't want the thin flange barrels, just as you 'didn't want' an 8 stud Triumph. People didn't want dynamos either, as I recall, with the mag/alternator of the 60s Triumphs being quite the thing. (Mike hadn't made the DVR2 then, however!) And of course you 'didn't want' an A50 or A65 either, let alone, when they came out, an early Commando with the High Explosive Combat engine. Nor an early 750 Bonnie, because 'they all run their mains mate, usually just after the warranty runs out'. Above all else you 'didn't want' anything with more than one cylinder from AMC. Well, I've been breaking that bar-room rule for 35 years and have been very happy.
Such a fine line between myth and reality.
Apart from the one about 'japanese-crap' being fit for nothing, when it was a lot fitter for nearly everything than most of what it had to compete with. No fine line there.
And through it all the entire BMW range ticked along very nicely for them as could afford them. How perverse was it that when I eventually got my hands on a big Boxer, I promptly blew it up far more expensively than any British bike I had ever had . . . was that a case of reality flying in the face of a very positive myth? Don't know, but bought a K series instead, where myth and reality came together in harmony for well over 100,000 entirely hassle free miles.
Must get out more.

[trevinoz]

Just a couple of points.
Groily, I have cracked two sets of thick flange barrels above the flange. The first was .060 oversize and the other was a re sleeved item. If you have a look at a set after being bored for re sleeve you will see that there is not much thickness of metal left so we have been brazing the new sleeves top and bottom to the barrel and so far so good.
The thin flange barrel I destroyed way back as described was also a re sleeved one and when it let go the sleeves actually pulled out of the bottom section of the barrel.

Richard L, I would not consider the head steady as having any effect whatsoever on the security of the barrel. it is too flimsy. The original pressed ones were shockers and commonly cracked as you have found. I have made my own straps from thicker steel, 12 x 3 mm from memory. I also made my own brackets from 3mm steel after buying a pattern set of dubious quality.

Brian, I can't remember seeing any cracked off plunger barrels but I have seen plenty with skirts smashed off after, usually, the left rod seized.
Your beer theory sounds good to me but on that occasion I was on my way home from a weekend away with a heap of mates and we had put away plenty beforehand. I couldn't have looked at another one!
    Trev.

[beezalex]

If they keep breaking at the barrel above the flange, it seems to me it isn't the flange thickness that's the problem.  My plunger A10 has 8.5:1 pistons in it and I spank it hard from time to time.  It's got the original thin-flange barrel and it's been sleeved .  5000 miles since I've bought it so far so good.

[frankenstein]

my a10 has been running with out any  head steady bracket for years....long before i owned it as well...looks like i should buy one a.s.a.p !

[dpaddock]

I dare say BSA made the two engine steady braces adequately for the task. I made one brace for my 'thin' flanger from 1/4" x 3/4" steel; I sized and spaced the holes very precisely and attached it to the right side.

It should go without saying that elongated holes and the like are to remedied asap - such neglected wear is not acceptable if we're to maintain the marque.

[olev]

Gday Trev,
I posted a pic of some stuffed a7 barrels a couple of days ago.
The main problem is the damage in the top of the sleeves.
your thoughts on the following would be appreciated - don't be gentle if its crap.
1. grind the brazing off the sleeve and skirt
2. heat the barrels in the oven
3. fill the cylinders with dry ice
4. press the sleeves up about 4mm
5. braze the sleeves top & bottom
6. machine the protruding sleeves level with the face
7. rebore

That should get rid of the damage at the top of the bore.
How do you braze the sleeves at the top?? do you take a slice off the cylinder to give the braze a bit of purchase ?
cheers