AMAL JETS/SMALL DIAMETER HOLES

[CHARLES lipscombeParticipant @charleslipscombe16059]

This thread could also be placed under motorcycles but I thought I might get more replies from engineers under this heading

Amal carburetters used to claim in their advertising that their jets were reamed to size for accuracy. However in the smaller carbs the jets are tiny, with very precise apertures around 19 thous. Does anyone know how Amal could have achieved this 60 or more years ago? The jets are made from brass.

What on earth would a 19thous reamer look like and where would one be obtained?

[CHARLES lipscombeParticipant @charleslipscombe16059]

[roy entwistleParticipant @royentwistle24699]

Watchmakers broaches or something similar ?

[julian atkinsParticipant @julianatkins58923]

For those of us who make small injectors for miniature locos this is not a problem.

Cheers,

Julian

[MWParticipant @mw27036]

drill service will do that size for you as a slot drill for £19 it seems..

**LINK**

Depends how much its worth to you I guess.

[Mark CParticipant @markc]

"For those of us who make small injectors for miniature locos this is not a problem"Thats a lot of help Julian…

For those of us with electron drilling machines it is not a problem either!

Mark

[julian atkinsParticipant @julianatkins58923]

Hi Mark,

You can make a reamer out of silver steel or HSS to any shape of size to ream very small holes. It need only be of 'D' bit half section type for brass.

The problem usually in injectors of small size for miniature locos is drilling the pilot hole accurately and true.

1. centering for the drill which is smaller than any centre drill will produce. I use some very small dental burrs or some very small clock makers spade drills or an old fashioned graver.

2. getting the lathe fettled up and altered to produce an accurate hole of very small size to some depth for the pilot hole. This requires accurate tailstock adjustment, a high speed for drilling, and a sensitive lever feed tailstock attachment.

Cheers,

julian

 

Edited By julian atkins on 15/01/2017 22:04:42

[Mark CParticipant @markc]

Thanks Julian.

I don't have any need of small holes currently but you never know what is around the corner.

I did need some aperture plates making for a confocal microscope some time back but that required extremely tight concentricity and size (and also a tapered cylindrical profile) which was done using photo etching on nickle foil.

Mark

[Michael GilliganParticipant @michaelgilligan61133]

As Roy said; Watchmaker's broaches are readily available in that sort of size … 'though they do produce a slightly tapered hole.

Julian, of course, knows all about making injectors.

That only leaves me to mention that good quality sewing needles can provide a very useful source of material for a small 'toolmaker's reamer' [a diamond hone or an Arkansas slip will soon produce the flat] … which I have found very suitable for enlarging Amal jets. 

The needle-making industry was alive and well long before the carburettor was invented.

MichaelG.

Edited By Michael Gilligan on 15/01/2017 22:44:00

[JAParticipant @ja]

Charles

I was told you opened up an Amal jet by taking a needle, or round broach, that was significantly smaller than the hole, and repeatedly passed it through the hole. I don't know when you decided to stop. The last thing you do is to use a drill.

JA

[Jeff DaymanParticipant @jeffdayman43397]

Not familiar with watchmakers' broaches but am familiar with old fashioned toolmakers' reamers. Just an accurately turned-to-size piece of drill rod, with one end ground with a flat about 20 degrees included angle across it. Harden and temper to straw colour if cutting steel, harden and temper not required for working brass or die cast alloys. Worked by hand or with slow speed these will cleanly open any hole to size and are easily made.

Used them for years for work on oddball carburetors and also on mould and die precision work.

(have not used them in injectors though – too much top secret info there)

[HopperParticipant @hopper]

I've always just drilled the jets on Amals when enlarging them to suit megaphone mufflers etc on classic Brit bikes. You can buy sets of jet drills made for the purpose, they come in a little holder like a pen, with a set of drills in the handle and a tiny chuck on the other.

Perhaps if you were jetting a TZ750 to run around Daytona without seizing you might ream the jet holes. But for the average bloody old Brit bike banging around the streets the drills do the job. Any Amal carb is going to be so worn anyway that it is never going to be a precision mixture metering device, so reamed holes is like waxing a dirt floor.

I've used the jet drills for drilling holes in virgin material in the lathe. Put the jet drill in its holder and put the other end of the holder in the tailstock chuck. Run lathe flat out. Feed very cautiously and take your time.

Jet drills can be purchased from bike parts dealers and sometimes from welding shops, used for cleaning jets in acetylene torches etc.

Edited By Hopper on 16/01/2017 05:07:52

[Chris Evans 6Participant @chrisevans6]

Hopper, I also use drills. Amal jets go up in 10s for sizes Mikunis go up in 5s. I am now tasked with replicating Mikuni sizes in Amal jets in the quest to get good carburation using this dreadful excuse for petrol we now have with ethanol added.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Jeff Dayman on 16/01/2017 05:05:05:

Not familiar with watchmakers' broaches

.

Jeff,

For info. they are pentagonal in section, and slightly tapered.

The negative rake angle works beautifully on brass.

MichaelG.

.

https://www.cousinsuk.com/category/broaches-cutting

Edited By Michael Gilligan on 16/01/2017 08:40:38

[duncan webster 1Participant @duncanwebster1]

Posted by Hopper on 16/01/2017 05:07:22:

Perhaps if you were jetting a TZ750 to run around Daytona without seizing you might ream the jet holes. But for the average bloody old Brit bike banging around the streets the drills do the job. Any Amal carb is going to be so worn anyway that it is never going to be a precision mixture metering device, so reamed holes is like waxing a dirt floor.

Edited By Hopper on 16/01/2017 05:07:52

They were never precision mixture metering devices when new. I've seen pictures of Triumph twins with SU carbs, seems a much better bet to me

[JAParticipant @ja]

Posted by Hopper on 16/01/2017 05:07:22:

Perhaps if you were jetting a TZ750 to run around Daytona without seizing you might ream the jet holes. But for the average bloody old Brit bike banging around the streets the drills do the job. Any Amal carb is going to be so worn anyway that it is never going to be a precision mixture metering device, so reamed holes is like waxing a dirt floor.

You can buy new Amal Monoblocks and Concentrics. They make a considerable improvement in the running of a bike from a worn out carb. However the improvement is nothing compared to using a Mikuni.

The Mikunis are far better designed and made. For a start proper aluminium is used instead of metal rejected by Dinky.

JA

[roy entwistleParticipant @royentwistle24699]

Just a thought, but aren't carburetor jets tapered anyway ? ( I could be wrong )

Roy

[thaiguzziParticipant @thaiguzzi]

Amal now is not what Amal once was back in the day. Far, far superior today than back then. Chalk and cheese. Different alloy used, up to date machinery, better fits and tolerances, high quality components internally. Same co. owns SU too.

I presume because there is no current British motorcycle manufacturer left that uses Amal on a production machine, they don't have to be built DOWN to a price like back in the old days…

[Jeff DaymanParticipant @jeffdayman43397]

"Jeff,

For info. they are pentagonal in section, and slightly tapered.

The negative rake angle works beautifully on brass.

MichaelG."

Thanks for the info on the watchmaker broaches. JD

.

[CHARLES lipscombeParticipant @charleslipscombe16059]

Thanks to everyone who replied to this thread, it has been a major help in understanding the whole business of making small diameter holes.

The background to my request is that I am the Vintage Motorcycle Clubs(UK)marque specialist for New Imperial motorcycles (although I live in Australia) and I am trying to sort out why some of our members are having difficulties with the special, small Amal carbs fitted to pre-war lightweight New Imps.

These carbs use main jets of the order of 24 thous with only 1 thous steps between different jet sizes. These jets are no longer available, even from the current makers of Amal carbs because they are a completely different style to the jets fitted to the usual size of Amal carb.

These replies have reminded me that jet reamers were once to be found in any veteran motorcyclists toolkit but dropped out of use circa 1910, presumably when jet manufacturing techniques improved

Whilst I more-or-less agree with Hopper about the need for precision, it seems that these tiny carburetters are very sensitive to jet size variation

Julian: what size drill would you use to make the pilot hole, in brass, prior to feeding in the D-bit?

Thanks everyone, Chas

[vintagengineerParticipant @vintagengineer]

You can remove the ethanol by getting a 25 liter can with a tap at the bottom ( Camping water carrier). put 20 litres of petrol in it then add 2 litres of water. Give it a good shake up and leave to settle overnight, then drai n the water off the bottom and you will have ethanol free petrol. Ethanol being an alcohol mixes with water.

Posted by Chris Evans 6 on 16/01/2017 07:40:36:

Hopper, I also use drills. Amal jets go up in 10s for sizes Mikunis go up in 5s. I am now tasked with replicating Mikuni sizes in Amal jets in the quest to get good carburation using this dreadful excuse for petrol we now have with ethanol added.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by vintagengineer on 16/01/2017 23:00:10:

Ethanol being an alcohol mixes with water.

.

… and what you drain off might mix nicely with Tonic Water

MichaelG.

[vintagengineerParticipant @vintagengineer]

I would not try it.

As a central nervous system depressant, ethanol is one of the most commonly consumed psychoactive drugs.^[26]

The amount of ethanol in the body is typically quantified by blood alcohol content (BAC), which is here taken as weight of ethanol per unit volume of blood. Small doses of ethanol, in general, produce euphoria and relaxation; people experiencing these symptoms tend to become talkative and less inhibited, and may exhibit poor judgment. At higher dosages (BAC > 1 g/L), ethanol acts as a central nervous system depressant, producing at progressively higher dosages, impaired sensory and motor function, slowed cognition, stupefaction, unconsciousness, and possible death. Ethanol is commonly consumed as a recreational drug, especially while socializing, due to its psychoactive effects.

Posted by Michael Gilligan on 16/01/2017 23:21:03:

Posted by vintagengineer on 16/01/2017 23:00:10:

Ethanol being an alcohol mixes with water.

.

… and what you drain off might mix nicely with Tonic Water

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by vintagengineer on 16/01/2017 23:26:49:

I would not try it.

.

Nor would I

[hence my use of the devilish smiley thing]

… But, neither would I pour petrol into a water container.

MichaelG.

.

https://m.youtube.com/watch?v=0vxukHgmKQ4

https://www.norfolkfireservice.gov.uk/nfrs/images/files/EPUK%20Storing%20Petrol%20at%20Home%20leaflet.pdf

Edited By Michael Gilligan on 16/01/2017 23:41:01

Edited By Michael Gilligan on 16/01/2017 23:57:02

[HopperParticipant @hopper]

Posted by CHARLES lipscombe on 16/01/2017 22:05:17:

 

Whilst I more-or-less agree with Hopper about the need for precision, it seems that these tiny carburetters are very sensitive to jet size variation

Thanks everyone, Chas

Bear in mind too that most carbutator problems are electrical. I'd bet two rabbit traps to the old black billy that if you get your New Imperials' magnetos professionally rebuilt so you have a good strong, reliable spark, you will find the old bangers will run much better on any jet that is close enough.

I've seen it happen over and over again on vintage Harleys and various Brit bikes over the years. Weak spark will appear for all the world like fueling problems. You stop on the side of the road, change jets and presto, it runs better — because the maggie or the spark coil and the sparkplugs have cooled down. Then down the road it starts playing up again as the maggie or coil heats up so, hey, a bigger jet helped earlier, so lets stop and put the next bigger one in, and hey presto the bike runs better again — because the maggie or coil has cooled off again. Then next time they roll the bike out of the shed and start it up from cold — guess what, the jets are too big! Must be super sensitive to jet size! So down in jet size they go and all is good, until they get on the road and the maggie heats up … repeat, repeat, repeat etc.

New coil (if used) plug leads, caps and plugs are essential too. Seen many vintage riders come to grief trying to run the original equipment for authenticity but as the insulation breaks down, inevitably, over time dramas ensue. Most of those guys thought it was fueling problems too and spent massive time tinkering with carbs, cleaning gunge out of tanks, sealing manifolds etc etc only to find it all cleared up with a good ignition system. It took one old guy I know , a lifelong Harley expert, engineer, former beach racer etc,  about 10 years to give up on the fuel system of his WLA  and fit a new coil and leads. Guess what happened to his carb problems instantly?

Edited By Hopper on 16/01/2017 23:47:38

Edited By Hopper on 16/01/2017 23:54:59

[Author]

Posts