Sleeving Vintage Amal carburator

**Moby Duck** · Jun 19, 2018, 07:51 PM

Not sure if they still do it, but brake repair companies used to sleeve brake and clutch cylinders to reclaim them and actually make them better than they originally were. It might be worth talking to one locally to see if they still do it now. My experience with several of those Amal carbs was that the threads holding the top cap on often unscrewed or just popped off. e.g. 1960 Norton only 3 years old, straight off ferry at Calais, never driven on the right of a road before, opened throttle, cap popped off and bike accelerated to near full speed up the main street, through intersections, red lights etc etc and no idea where I was going. Key was in chest pocket of and anorak I was wearing, so only option was to turn fuel off while dodging cars with one hand on handlebars. Bike eventually used up the fuel in the bowl and stopped outside a bakers shop. It was surprising how much distance it travelled on a bowl and hose full of fuel. Sat down in the gutter for about an hour after that with fresh baking and coffee to calm my nerves.

**lanceks1** · Dec 22, 2018, 09:26 AM

Ive had a BSA for 40 years, always fooling with that carb. The problem was when the carb heated up the body would swell up, and grab the slide. Since I have isolated the carb from engine heat, I have not had any problems. works awesome!! Ask me how?

**thirdbike** · Dec 22, 2018, 10:00 AM

At the moment I am not sure of the BSA OEM carburetor gasket thickness. The problem is compounded with many aftermarket gaskets being paper thin and poor quality. In the case of the Triumph twins, the heat transfer is even worse as they called for the use of an O ring. The carbs being made of a soft pot material and is easily distorted especially with heat. The cure I have found is the installation of the extra thick gaskets used on the Nortons. The material is hard rather than the more common compressable gasket material. As such, the carbs could be bolted up securely without the fear of distorting the flange. Keep in mind that as the flange distorted so did the slide bore go out of round. A lot of slide sticking issues were attributable to this warping. Many users simply sanded the flange flat again resulting in the removal of material from the mounting ears. This only served to weaken the ears leading to even further warping. If you have another solution, please do fire away.

**thirdbike** · Jun 19, 2018, 09:06 PM

Andres, the carbs are Amal Mk1 930 concentrics. They are for a couple of 650 and 750 triumphs. So if I understand you correctly, you simply made up a new slide from aluminum. That would resolve the dissimilar metal issue for certain.
Moby Duck, I haven't seen or heard of a brake repair business in decades. There are still lots of brake shops around mind you but today, if a brake cylinder needs attention, it is simply replaced. Labor costs and liability issues killed the rebuilds years ago. I like your Norton tale.
Still hoping someone will address the issue of reaming versus boring. With my lathe I simply wouldn't be able to get the needed finish without sanding etc which throws out the hope of exact tolerances.

**NeiljohnUK** · Jun 20, 2018, 02:49 AM

Proper resleeving is possible with care IF the original mazak like 'monkey-metal' hasn't started to crumble. Though these days I'd be looking to rebuild with one of the Belzona (or JBWeld) products first then honing out to original size, even if the parent metal is doubtful.

**Frank S** · Jun 20, 2018, 07:34 AM

Originally Posted by NeiljohnUK

Proper resleeving is possible with care IF the original mazak like 'monkey-metal' hasn't started to crumble. Though these days I'd be looking to rebuild with one of the Belzona (or JBWeld) products first then honing out to original size, even if the parent metal is doubtful.

While Belzona or JBWeld or similar products have a great range of uses and might even be a viable solution in this instance.
The bore would still have to be bored out then the product applied then bored and honed.
My concern would be life expectancy and wear factor or the possibility of fuel causing deterioration the Slide would still need to be remade.

thirdbike has also asked about the possibility of using a reamer in the bore.
If one had a fixed size reamer say .002" oversize to the bore this would probably be 1 of the better ideas but after the bore was reamed to round and clean an internal lapping or burnishing tool would be required to polish bore and a new oversized slide could be made
If the epoxy like products were used the bore would still require lapping

**NeiljohnUK** · Jun 20, 2018, 09:36 AM

Originally Posted by Frank S

While Belzona or JBWeld or similar products have a great range of uses and might even be a viable solution in this instance.
The bore would still have to be bored out then the product applied then bored and honed.
My concern would be life expectancy and wear factor or the possibility of fuel causing deterioration the Slide would still need to be remade.

thirdbike has also asked about the possibility of using a reamer in the bore.
If one had a fixed size reamer say .002" oversize to the bore this would probably be 1 of the better ideas but after the bore was reamed to round and clean an internal lapping or burnishing tool would be required to polish bore and a new oversized slide could be made
If the epoxy like products were used the bore would still require lapping

Indeed the epoxy would require boring to size, with finishing to suit. I've been using Belzona for years and never had an issue with fuel, the Weber DCOE's I repaired with it in 1978 are still leak free, and industrial use has proven just how good a wear material it can be, a brass sleeved slide in a body lined with it would last for years. JBWeld is pretty good too, and a lot more affordable, my recent motorcycle repairs to a 10 year old BMW 'F's oil/water heat exchanger were done with it to keep costs down, fuel resistance should be ok but I've not used it in that way so I can't confirm what the manufacturer claims.

**thirdbike** · Jun 20, 2018, 12:51 PM

What the "original" carb rebuilders did was to clean up the carb bore to oversize and put a brass sleeve on the slide. In other words the bore is left oversized.
An epoxy product might be a option for application to the slide. I am wondering how well an epoxy product will adhere to the the pot metal especially as the slide needs to get shaved down to size. It might take a trial and error session to see how well that works out and then let it soak in the new ethanol blended gasoline.

**thirdbike** · Jun 21, 2018, 07:42 AM

I do appreciate the sentiments but would like to keep this thread focused on carb sleeving. Any tips and ideas are welcome.

**olderdan** · Jun 21, 2018, 10:57 AM

Originally Posted by thirdbike

I do appreciate the sentiments but would like to keep this thread focused on carb sleeving. Any tips and ideas are welcome.

Hi thirdbike,
A few thoughts on Amals, these are the carbs I have most experience with and have always found them to easy to tune and are perfectly reliable for a road bike. I have not found a worn slide or bore to be the main cause of lack of performance but more to do with worn jets and needles, the needle is free to find its own centre in the jet which leads to fairly rapid wear ( I used to replace mine at about 30K).
Obviously galling is not good but can be smoothed out, the slide needs to be a loose fit as it is only closed by a fairly light spring and any foreign matter can cause a sticking open throttle (nuf said). The later types of carbs with a cable opening /closing feature is much safer but sadly not on Amals.
The main concern seems to persieved air leaks past the slide but this only affects tickover settings which are easy to compensate.