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#664211 - 08/17/16 6:56 am Warped Amal Concentrics - is there really no cure?  
Joined: Jul 2016
Posts: 17
Ruaridh Offline
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Ruaridh  Offline
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Joined: Jul 2016
Posts: 17
Argyll, Scotland. UK
As many of you will know, the AMAL Concentrics (mine are 930s) are very sensitive to over-tightening of the flange bolts, which causes the body to deform making the slide bind, especially in the upper section.

This has happened on my A65, not sure if by me or some previous owner. The thing is, the gasket set I got had thick carb gaskets which I fitted. But with these, even modest tightening seems to pull the "ears" of the flange in too much and cause said deformation (like I say the carbs could have been like this before I got them). The concentrics all seem to have an o-ring fitted to a groove in the flange, which in my experience often means a gasket is not used. The AMAL website says (Credit to Burlen Ltd.):

Quote:
Mark 1 carburetters are not designed to bolt tightly to the intake flange and may distort if overtightened. It is only necessary to compress the O ring seal to ensure air tightness. When correctly tightened the carburetter flange and engine manifold should be just touching. Nyloc nuts should always be used to mount Amal Mark 1 carburetters and should be tightened to no more than 4 ft lb.

This also suggests no gaskets should be used. But the A65 parts books show gaskets, and I've seen plenty of pictures of Lightnings etc. with the thick gaskets fitted.

So what gives? I assume that if the carbs had never been over-tightened on the thick gaskets all would have been well, but I'm curious. I've tried it with just the o-ring but the carbs seem to get very hot, and I still get air leaks when up to temp because of the warpage.

The AMAL site pretty much says to chuck them in the bin if this has happened, but I always like to see if there's a way to fix things. Actually, when I first bolted one direct to the head without a gasket it actually freed off the slide again! But I could get a feeler gauge past the o-ring, and with thicker O-rings the binding came back. I put them on with the original rings and some flange sealant but still no use when hot: sticking and air leaks.

I know the solution is new carbs, but I'd be interested to hear of other's experiences first:-
1) Thick gaskets or not? (twin-carb head)
2) Has anyone ever cured the binding on a deformed mk 1 Concentric?

Thanks, Ruaridh.

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#664219 - 08/17/16 8:13 am Re: Warped Amal Concentrics - is there really no cure? [Re: Ruaridh]  
Joined: May 2013
Posts: 4,533
Allan Gill Offline
Allan Gill  Offline



Joined: May 2013
Posts: 4,533
Rotherham - S. Yorkshire
The thick gaskets are Tufnol (furnol) insulating blocks, the original ones were about 3-5mm thick. I run 15mm blocks on my Lightning. They are cruical in keeping the carbs cool from the heat of the engine. Gasket between the head and the block, then o-rings between the carb and block


beerchug
#664221 - 08/17/16 8:27 am Re: Warped Amal Concentrics - is there really no cure? [Re: Ruaridh]  
Joined: Dec 2004
Posts: 8,896
kommando Online content
kommando  Online Content


Joined: Dec 2004
Posts: 8,896
Scotland
I use nyloc nuts, so just nip the carb up and no worries about the nuts coming loose so no temptation for that extra 1/2 turn just in case. Thicker spacers are the best to stop the heat soak you get 5 to 10 mins after stopping.

#664233 - 08/17/16 10:36 am Re: Warped Amal Concentrics - is there really no cure? [Re: Ruaridh]  
Joined: Aug 2001
Posts: 3,408
gavin eisler Online content
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gavin eisler  Online Content
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Posts: 3,408
argyll. scotland, uk

John healy has commented on this before , to paraphrase.

The distortion can be reversed, a round bar is turned to fit in the slide bore, a hole is drilled through this at 90 degrees Concentric with the venturi when fitted in place . The carb flange is bolted to a thick flat plate , it has a hole which corresponds to the hole in the centre bar, a bolt is passed through plate and round bar then tightened to straighten the body, thin washers may be needed between carb flange and plate if it springs back to give a slight overbend.
Easy project with a lathe and pillar drill.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
#664242 - 08/17/16 11:47 am Re: Warped Amal Concentrics - is there really no cure? [Re: gavin eisler]  
Joined: Sep 2004
Posts: 680
gunner Online content
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gunner  Online Content
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Posts: 680
Farnham, Surrey, UK
Its all explained in This Link which was posted a few years ago as a fix for Monobloc carbs, I believe the same process works for Concentrics as well.

I have never tried this myself but it looks like the procedure will work and hopefully you wont need re-sleeving as well.

Last edited by gunner; 08/17/16 11:52 am.

1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
#664246 - 08/17/16 12:09 pm Re: Warped Amal Concentrics - is there really no cure? [Re: Ruaridh]  
Joined: Mar 2005
Posts: 9,971
John Healy Online content
John Healy  Online Content


Joined: Mar 2005
Posts: 9,971
Boston, Massachusetts
A bike with carburetor slide that sticks should NEVER be ridden!! I am here to tell you there are things a lot worse than death.

If you ride a bike and have the throttle stick for what ever reason, and cannot reach the kill switch in time, pull in the clutch. A bent valve is a lot less of a catastrophe than what can happen to you in a crash.

A long time a go IMI AMAL increased the slide clearance to a point where even what they considered a "heavy hand" couldn't cause the slide to stick. They didn't realize just how determined some people are at wanting to bend the carburetor.

With the difference in heat between England and a lot of the US these days. I just talked to a dealer in southern New Jersey where the air temperature was over 100F. The patio brick around his pool were 135 and the plastic fence around the pool was 175. Point being a solid phenolic heat insulating block, rather than the the thick paper gaskets people just can't get enough of, might just what is needed to keep the fuel from boiling in the float bowl. It is obvious that the good fellow who wrote that bit for Burlen hasn't ridden a Bonneville in Dallas on an August day. In Boston where we have been having near 90F days for a couple of weeks.

Tool I use to straighten carburetors:

Mike Gaylord was one of the first guys over hear sleeving carbs. As he notes because of how thin the original body is he straightens the body before he bores it. As I found out when I started straightening carbs it was often all that was needed to put the carb back in service.




#664248 - 08/17/16 12:32 pm Re: Warped Amal Concentrics - is there really no cure? [Re: Ruaridh]  
Joined: Nov 2011
Posts: 3,984
Magnetoman Online content
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Magnetoman  Online Content

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Joined: Nov 2011
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U.S.
My version of the straightening tool is shown here and here, along with a description of how I used it on a carburetor. Although the tool I made applies the force by tightening from the flange end rather than from the intake end, the principle is identical.

The links are to a restoration thread that I really want to get back to. "Unfortunately," things keep getting in the way. Like acquiring a Catalina in June that filled my spare time since then getting it ready. Too many projects, too little time.

#664249 - 08/17/16 12:39 pm Re: Warped Amal Concentrics - is there really no cure? [Re: Ruaridh]  
Joined: May 2013
Posts: 4,533
Allan Gill Offline
Allan Gill  Offline



Joined: May 2013
Posts: 4,533
Rotherham - S. Yorkshire
John, To add to Mike Gaylords quote, and on contary to it.

I have found cast iron bantam barrels and numerious A65 cylinder heads to be warped at the mounting face. I do stone these flat on every one I work on. I first noticed it when I modified my first cylinder head and ran a sharpening stone over the face.

The worst case was on a bantam. Not only was the 626 body bent (which shamefully I did flatten off as the slide ran with no issues up the bore) but the barrel was seriously out of shape and between the two melted a piston. At the time it was fitted with a thick Fibre gasket/block - not the Phernolic spacer. I blame that for its reason of miss-shape.

I have had float bowls bow too, in one case it matches the carb body and so i have left these as a pair, the carbs function fine with them, but when mated (high flow bowls) with a new carb the out of shape is more than noticable.


beerchug
#664266 - 08/17/16 3:57 pm Re: Warped Amal Concentrics - is there really no cure? [Re: Ruaridh]  
Joined: Sep 2004
Posts: 680
gunner Online content
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gunner  Online Content
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Joined: Sep 2004
Posts: 680
Farnham, Surrey, UK
One of the main issues with AMAL carbs is that they were never built to withstand years of service, and being built of cheap of pot metal all kinds of problems can occur after a few years.

In my opinion AMAL carbs should be treated as disposable items with a life expectancy of 15k miles or so and although it may be possible to recover a carb with a distorted flange, you have to consider the other issues such as slide wear, bent float bowls etc. In other words, it may be more economcal in the long run to buy new carbs, preferably the AMAL Premier types.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
#664280 - 08/17/16 4:41 pm Re: Warped Amal Concentrics - is there really no cure? [Re: Ruaridh]  
Joined: Mar 2005
Posts: 9,971
John Healy Online content
John Healy  Online Content


Joined: Mar 2005
Posts: 9,971
Boston, Massachusetts
While the AMAL Premier is a good bit of kit, being a Yankee (read thrift to a fault), and the son of one of those poor immigrants who gave me a dollar when I went into business, I learned the value of a "Buck" ("Quid").

A 15,000 mile AMAL, where the mechanical wizard who owned it before I found it at a flea market, had warped it, but didn't sand, scrape, file or otherwise get his unskilled hands on it, would find a home on my motorcycle any day.

It would require a new MEASURED needle jet (It's the needle jet "stuuppid""), the pilot jet cleaned, a twirl in my tool, a small swim in the ultra sonic cleaner then throw some gaskets its way and for a few "bucks" I would have an instrument that would give another 15,000 miles service a couple times over.

Lucky for Burlen, and me too if you know what I do for a living, people seem to have, and not in a nice way, their turn with AMAL's.


#664282 - 08/17/16 4:51 pm Re: Warped Amal Concentrics - is there really no cure? [Re: Ruaridh]  
Joined: Aug 2001
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triton thrasher Online content
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triton thrasher  Online Content
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scotland
Buy a Premier if you're going to enjoy having something "nicer."

Don't expect to ever get the price difference back in mpg, performance or resale.


Amateur Loctite enthusiast.
#664300 - 08/17/16 7:31 pm Re: Warped Amal Concentrics - is there really no cure? [Re: Ruaridh]  
Joined: Jul 2016
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Ruaridh Offline
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Ruaridh  Offline
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Posts: 17
Argyll, Scotland. UK
Brilliant, many thanks to all.
Slightly embarrassed I didn't search for how to straighten these before posting!
Unfortunately I lapped a tiny bit off one of my faces before I realised the folly of what I was doing. Maybe it will be saveable, perhaps lapping a tiny bit more off after straightening (if that's a success sticking-wise) will bring it back.

#664325 - 08/18/16 2:22 am Re: Warped Amal Concentrics - is there really no cure? [Re: triton thrasher]  
Joined: May 2013
Posts: 4,533
Allan Gill Offline
Allan Gill  Offline



Joined: May 2013
Posts: 4,533
Rotherham - S. Yorkshire
Originally Posted By triton thrasher


Don't expect to ever get the price difference back in mpg, performance or resale.



Same can be said for any aspect of restoration or repair to any vehicle.


The mk1 is a very inexpensive, tuneable carb. I've always ran chromed (and recently anodised) slides in my 10 year old 930s it will be a cold day when I switch to something different because I no longer have the skills to tune them properly. The race bike will have Mk2's for the simple reason that I require carb sizes at 34 and 36 mm, which are not available in mk1 or GP carbs.


beerchug
#664327 - 08/18/16 2:52 am Re: Warped Amal Concentrics - is there really no cure? [Re: Ruaridh]  
Joined: Sep 2008
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jaycee Online content
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jaycee  Online Content
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angeles city, rp
way before i knew about this forum i managed to warp the carb bodies on my norton, around 1978 i beleve. i lapped the flanges at the time and went about my business to 30k miles without further incident. im not known as "ham fisted" and as ive seen the same issue with lots of other white metal parts but most notably numerous small engine carbs and lots of others with the same problem. as a result ive gotten to be quite "anti gasket" in these applications. several years ago i rebuilt those carbs again. this time i filled in the o ring groove with jb weld and faced it off on a lapping plate fitted chrome plated brass slides used the original phenolic heat barriers and sealed them with a smear of 515 loctite. it still runs great. if i bought new amals for it i would do the same thing. but still i dont see the need to "crank em down" im not completely certain that they wont warp from their own weight! i dont pretend to be in the same league as some of you folks but this did work for me.

#664330 - 08/18/16 4:10 am Re: Warped Amal Concentrics - is there really no cure? [Re: Ruaridh]  
Joined: Jun 2002
Posts: 195
wbabojo Offline
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wbabojo  Offline
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Ipswich England
I have bought new slides (Albeit in a different cutaway) to rectify this. The seller informed me original AMAL replacements were manufactured slightly oversize and needed to be rubbed down to fit. Start with engineers blue etc to find high spots. Casting and heat effects will take their toll on this soft alloy. Metal fatigue is a phenomenon not limited to AMAL carbs. You will find a much improved throttle response.


Gavin
You can't make a silk purse from a sow's ear.
#664336 - 08/18/16 5:54 am Re: Warped Amal Concentrics - is there really no cure? [Re: gunner]  
Joined: May 2004
Posts: 3,548
BSA_WM20 Online content
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BSA_WM20  Online Content
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Sydney Australia
Originally Posted By gunner
One of the main issues with AMAL carbs is that they were never built to withstand years of service, and being built of cheap of pot metal all kinds of problems can occur after a few years.

In my opinion Amal carbs should be treated as disposable items with a life expectancy of 15k miles or so and although it may be possible to recover a carb with a distorted flange, you have to consider the other issues such as slide wear, bent float bowls etc. In other words, it may be more economcal in the long run to buy new carbs, preferably the Amal Premier types.


Nothing wrong with the mythical non existant material called "pot metal"

It is actually a very complicated zinc based die casting alloy and is still in use today for lots of critical applications where very tight casting dimensional stability is required to reduce machining to a minimum.
A perfect choice of materials for the application.
A tad thicker would have been a bit better, however these were designed in the days of slide rules and not computers that can do modeling in micron incriments in wall thickness.

The trouble is idiot morons incapable of reading an instruction book who war used to doing up carbs tight enough to hold the Queen Mary in a hurricane.

I for one gave up on the O ring 30 years ago.
Enfield used a soft gasket between the carb and the tuffnol spacer.
Their carbs do not have the O ring groove.

If you fit a thick klingerit gasket under the carb when you tighten it will self extrude into the O ring hole and make a very good seal which is a way of using a carb body that has been straitened one time too many on a sheet of emery paper.


Bike Beesa
Trevor
#666225 - 09/02/16 2:11 pm Re: Warped Amal Concentrics - is there really no cure? [Re: Ruaridh]  
Joined: Aug 2016
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Jimbo Yokel Offline
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Jimbo Yokel  Offline
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NE Ohio
After having a stuck slide on my 930 and reading a couple of threads on the subject, I asked my father-in-law to machine me a straightening tool using John's picture and explanation as a guide. I'm happy to report it works like a charm!


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