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#878618 04/25/22 8:54 pm
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Hello. Has anybody tried ditching the O -rings when mounting carbs to the spacers on the cylinder head on a A65? .I am considering using 3bond1211 or Loctite 518 after warping my carb bodies. Cheers, Max.

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mdodds #878620 04/25/22 9:01 pm
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I hate to say this, but it isnt the "O" ring that is causing your problem. Not that difficult to straighten if you make up a proper tool to do it.

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mdodds #878633 04/25/22 10:38 pm
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Really? Very helpfull mate.

mdodds #878635 04/25/22 10:52 pm
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On both T'bolts and Lightnings, the o-ring is a good way to go BUT if you
use the triumph slightly thicker one it works a treat. Just don't tighten the
carb up too hard and either use nyloks or similar. You should be able to
rock the carb on the o-ring a little. It's excessive tightening that distorts
carbs. Getting a couple of 5/16 bsc nylok or clevlok nuts is now the harder
part.
You can use 518 and a gasket either side of the spacer but the o-ring way
is the better insulator of both heat and vibration.

mdodds #878644 04/26/22 1:51 am
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FWIW
I tossed the O rings decades ago
The trick is to use a soft gasket that when compressed between the manifold & carb flange will partially fill the the slot where the O ring used to go thus make a good seal and without the O ring to be a fulcrum point, no chance of warping the glang thus distorting the carb body and making the slide stick.

The O ring is a good idea except when a shaved gorilla is let loose on the bike.
The original carb nuts were 1/2 thickness like a proper lock nut and a very light split ring went underneath
So it was a ase of tighten till the split washer just flattened and all is good
Being 1/2 thickness they are easy to fit as well.
However just about every bike I have worked on the original nuts & washers were gone in favour of a full sized nut & regular split washer which is way too tight if done up till flat.
As previously mentioned when properly tightened you can twist the carb a little .

With old carbs there is a good chance that the flange will be worn thin
This happens because the "ix" for a warped flange was to rub it on a surface plate of some sort till it was flat again.
This of course removes metal and makes the O ring groove shallower so the flange will be more prone to bending over the O ring which wil sticj out further so be even more of a fulcrum point that it was to start with .

Way way back John posted the details of the tool he uses to straiten the flange and instruction haw to use it.
Should be one in every BSA owners tool kit and many thanks to John for doing it .


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Trevor
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NickL #878658 04/26/22 8:07 am
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Originally Posted by NickL
On both T'bolts and Lightnings, the o-ring is a good way to go BUT if you
use the triumph slightly thicker one it works a treat. Just don't tighten the
carb up too hard and either use nyloks or similar. You should be able to
rock the carb on the o-ring a little. It's excessive tightening that distorts
carbs. Getting a couple of 5/16 bsc nylok or clevlok nuts is now the harder
part.
You can use 518 and a gasket either side of the spacer but the o-ring way
is the better insulator of both heat and vibration.

To reduce heat transfer to the carbs (causing me bother), I fitted 9mm Tufnol spacers, stainless studs, fibre washers and nyloc nuts. Any bigger the air cleaners would foul the side panels.

As mentioned, the BSC ones are hard to get so I made the studs all BSF which is the thread for the cyl. head.

The nyloc nuts can be fine tuned easier, once set never move.

Last edited by semprini; 04/26/22 8:08 am.

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semprini #878660 04/26/22 8:24 am
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Originally Posted by semprini
Originally Posted by NickL
On both T'bolts and Lightnings, the o-ring is a good way to go BUT if you
use the triumph slightly thicker one it works a treat. Just don't tighten the
carb up too hard and either use nyloks or similar. You should be able to
rock the carb on the o-ring a little. It's excessive tightening that distorts
carbs. Getting a couple of 5/16 bsc nylok or clevlok nuts is now the harder
part.
You can use 518 and a gasket either side of the spacer but the o-ring way
is the better insulator of both heat and vibration.

To reduce heat transfer to the carbs (causing me bother), I fitted 9mm Tufnol spacers, stainless studs, fibre washers and nyloc nuts. Any bigger the air cleaners would foul the side panels.

As mentioned, the BSC ones are hard to get so I made the studs all BSF which is the thread for the cyl. head.

The nyloc nuts can be fine tuned easier, once set never move.

Motalia sell the correct BSF/Cycle studs at various lengths.

6mm is about the thinnest you can get away with and not suffer fuel boiling in the carbs(least not in the uk).

You can get cycle thread nyloc nuts from Middleton stainless.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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mdodds #878805 04/27/22 8:23 pm
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One way to avoid the O-ring and warping problem is to cut micarta insulators (or buy stock ones) and laser cut a silicone gaskets to put over it. That way the whole carburettor face is supported by the silicone. Peek washers under the nuts will reduce heat transfer through them.

mdodds #878818 04/27/22 11:11 pm
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I had to google peek washers, great idea. I got fed up with the whole lot , fitted spigots, and rubber mounted the carbs, solved some problems and introduced entirely new ones, if I stuck with the originals id go fat insulator and triumph Oring.I use this to mount my carbs to the spigot adaptor, with nylocs and wobble on the O ring.
Rubber mounts split regularly and carb rubbers dont line up for filters easily.
I recently came across a Tbolt with a sticking slide , when I backed off the flange nut DS and heard the slide drop I was shocked at how little it took to distort the body, it wasnt really overtight. The AMAL flange is made with butter. or something close to it.

As Trevor mentions above, its tempting to file/sand warped flanges flat, this is not a good idea, the John Healey tool which bends the flange straight is a much much better fix.

Last edited by gavin eisler; 04/27/22 11:15 pm.

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56 Norbsa 68 Longstroke A65
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mdodds #878847 04/28/22 8:23 am
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Gavin: “recently came across a Tbolt with a sticking slide , when I backed off the flange nut DS and heard the slide drop I was shocked at how little it took to distort the body, it wasnt really overtight. The AMAL flange is made with butter. or something close to it.”

I think a lot has to do with what insulator your using in between. The tufnol ones don’t seem to give me any problems, I find even fairly tight I don’t
Get any distortion. There’s some which seem more fibrous like lots of gasket paper stacked together. These devils caused me no end of problems on one bike as they soften and crush, even generated an air leak after a period of time which then holed a piston. Should have known the bike (bantam) went like the clappers for about 20 miles before that. Luckily the engine died at the same spot where my Lightning lost a chainguard bolt (cycle thread, reduced hex and domed head… can’t be too many folk with one of those about)

I’ve also seen rubber ones… definitely avoid these.

If you can flex it or squish it…. It’s no good for a carb insulator.

Peek! Fantastic material, appearances not too dissimilar to nylon. Very easy to machine yet really durable and tough material. Also very flexible if bought as a rod length.
If you put a 1/4 diameter length of it into a drill chuck and used it like a drill bit against a lump of stainless, the stainless would wear before the peek does.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

mdodds #878876 04/28/22 2:13 pm
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To insulate the carburettor studs what is really needed are top hat shaped washers like what is used to insulate the points from the base plate. The mounting holes on a 930 AMAL are 0.340" so it would need a stud stepped down to 1/4". 5/16" is overkill for holding a carburettor. Besides, with 0.028" difference be tween the hole and stud can leave a big match between the carburettor and port.

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mdodds #878895 04/28/22 5:32 pm
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Been reading and can’t understand what the fuss is?
If tightening the stud nuts to the point off flange contact, that’s all wrong. Think of the O-Ring in terms of a fluid HydraStatic lock, as example: a brake system. If the O-RING captured in the groove has nowhere to escape, it acts as a solid and the flange bends around it, and distort the slide fit. ANSWER: don’t tighten the nuts any more than good O-Ring contact. Don’t know where I saw this mentioned years ago, but have been doing this for years. In fact, if proper contact/seal is made, the carb will still shift on the studs if twisted back and forth. Need I mention self locking nuts? I can even see a sliver of space between flange and head. Works fine, seals, and may even help with the mentioned heat transfer. My 2c

Last edited by KC in S.B.; 04/28/22 5:52 pm.

Down to 1 BSA, 2 Triumphs, 1 '56 Chevy
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mdodds #878915 04/29/22 12:46 am
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I tend to agree KC, i've been using o-rings (triumph ones) for years but
each to his own eh?
Dave's suggestion is a better engineering answer but i've never found it
necessary to go to that length.
I have made up spacers from 'type x' busbar support material in the past though
as some of the spacers around are like blotting paper (if anyone remembers what
that is!)

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gavin eisler #879060 04/30/22 7:13 am
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Originally Posted by gavin eisler
The amal flange is made with butter. or something close to it.
The same metal used to make the oil pumps on your beloved BSA. laughing


It's not a bug, it's 'character.'

72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
92 BMW K100rs "Gustav"
mdodds #879063 04/30/22 8:26 am
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How about putting the carb in a lathe and turning off the flange?
The carb could then be mounted using a "plate manifold" see below. It would remove the chance of distortion, isolate the carb from heat and vibration
https://www.allensperformance.co.uk...ber-manifold-dimension-information-page/


BSA B31 500 "Stargazer"
Greeves 200 "Blue Meanie"
Greeves 350
Greeves 360
GM500 sprint bike "Deofol"
Rickman Jawa 500 "Llareggub"
'35 & '36 OK Supreme
Kawasaki ZZR1400 "Kuro No Senshi"
Kawasaki Ninja H2 "Fujin"
Andy Higham #879071 04/30/22 8:55 am
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Originally Posted by Andy Higham
How about putting the carb in a lathe and turning off the flange?
The carb could then be mounted using a "plate manifold" see below. It would remove the chance of distortion, isolate the carb from heat and vibration
https://www.allensperformance.co.uk...ber-manifold-dimension-information-page/

Much like the Mk1.5. You would probably want to machine the groove into the carb to match that of the rubber mount (plate manifold). Never machined one so I don’t know what wall thickness you would have left but you might have to sleeve the outer to give you enough support.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

mdodds #879072 04/30/22 9:10 am
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It is worth thinking about


BSA B31 500 "Stargazer"
Greeves 200 "Blue Meanie"
Greeves 350
Greeves 360
GM500 sprint bike "Deofol"
Rickman Jawa 500 "Llareggub"
'35 & '36 OK Supreme
Kawasaki ZZR1400 "Kuro No Senshi"
Kawasaki Ninja H2 "Fujin"
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Andy Higham #879081 04/30/22 11:58 am
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Originally Posted by Andy Higham
It is worth thinking about

I agree. Just need an old Concentric to play about with. Most of mine are quite new and G.W.O


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

mdodds #879091 04/30/22 1:12 pm
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This might be of interest;

This morning I did a 30 mile run on the A65. 5 mins after I got back I checked the temperature (laser gun) of the head adjacent to the carb stud, the carb flange, and top part of the float chamber.

L.H. was 89c, 54, 38. R.H. 86c, 60, 38. Ambient temp. was 20c.


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semprini #879093 04/30/22 1:51 pm
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Originally Posted by semprini
This might be of interest;

This morning I did a 30 mile run on the A65. 5 mins after I got back I checked the temperature (laser gun) of the head adjacent to the carb stud, the carb flange, and top part of the float chamber.

L.H. was 89c, 54, 38. R.H. 86c, 60, 38. Ambient temp. was 20c.

Petrol can start to boil about 38 C. The 5 minute delay would cool the head from a partial throttle position to idle, right? I'm thinking an aluminum heat shield made up of say 16 gauge as large as would fit without offending aesthetic sensibilities would be worth a retest of the temps. The shield should be held directly against the head and with the same orifice dimensions as the carb. No question the temps will drop, but only by empirical observation can it be determined how useful the drop is. Near WOT on a warm day would be a good test.

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Semprini ......"Ambient temp. was 20c" .......... in Sheffield???!!!!

Check your thermometer! it was one year living in Sheffield that precipitated my permanent move to the tropics ....... Petrol boiling in the carb was the least of my worries, freezing solid perhaps, hypothermia was never far off.
Polar bears foraging in the street were a serious threat in the 1990s.

More seriously ....... this overheating of the float bowl thing ....... if it wasn't a problem 40 / 50 / 60 years ago why is it now? for surely if it was a problem then, BSA would have fixed it?? They did make bikes for quite a long time. Than being said I have tuffnol spacers on my bikes, but also I didn't have a problem before I fitted them.

Dave Martin #879129 04/30/22 6:26 pm
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Yes, 20c on my outdoor thermometer at 12pm, working outside in shirt sleeves.

My first A65 back in 1967 had a remote matchbox float chamber so it wasn't an issue. This one has Concentrics. When I first bought it, it would develop a misfire after a few miles (same symptoms as a blocked pilot jet but never found it blocked). I identified it as overheating float bowls, so fitted the thick tufnol spacers and this fixed the misfire; the existing ones were around 2-3mm thick.

How previous owners of the bike coped I don't know, mine came from Germany and have been unable to contact. No idea why others have not had the problem, but it appears many have.

Temp. will vary somewhat around hilly Sheffield and position of thermometer- https://www.sheffieldweather.co.uk/live_weather.htm


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Boiling fuel in Concentric carbs has been a constant problem with my '72 500cc Daytona.

That's why I have always had to tickle the carbs before starting it, even when the engine is hot.
Once it;s running it is O.K.

I always assumed it's because the carbs are located too close to the cylinder head.
The stock insulating blocks have always been between the carbs and the manifold.

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I've never had a problem with my B44R. I agree with Dave Martin, if there's a problem with boiling there must be something else wrong.

Last edited by LarryLebel; 04/30/22 10:02 pm.
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Well, if petrol can boil at 38 degs c it would be boiling in my
bike about 4 months of the year.
My old t'bolt will happily sit in traffic and tick over no problem,
it's me that cooks. My old heap of a triumph t120 was the same,
that just used to give it more reason to leak from pushrod tube seals.
But then, they all do that eh?
How's that lovely clutch on your triple DavidP? Work of art eh? So
easy to get to etc.

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