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[simon]

I've spent the last few days working in the shed on a very tired 389 body. I bored it oversized on a jig I made to drive it centrally on the lathe and then turned a bronze sleeve to fit. most satisfying task and I now have a really precise fitting slide rather than one that flops around like a cock in a sock. I let you know how it performs once it get a chance to fit it to the bike but I'm hoping it will cure the lean spot just off idle.

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[Alan R]

Hello SIMON -----------Well, just when you think it can't be done-------someone proves you wrong !!! EXCELLENT piece of turning old son---well done !! How much interference fit did you use ??>>> As a machinist myself in a former life (Self-employed contractor on the Severn Valley Railway) I particularly admired the close use of the fixed steady. You had me baffled on one point though---- I had a look in my various Engineering Reference books on Limits of Fits etc and can't find any mention of ---"Cock-in-a-Sock"--.Is this another piece of Brussels Euro-Babble or maybe an early Anglo-Saxon, pre-Whitworth nomenclature that has been lost in the mists of time and pub-crawls ?? If the slide had that much clearance I would have thought the WHOLE CARB was a lean spot LoL ?? Yes please--do keep us informed on the performance but don't let Burslem (AMAL) Carbs. find out--- they may try for a hostile take-over !!

[simon]

The cock/sock index is well known in these southern climes Alan, standard Imperial sock and ah yes nuff said. The worn throat sadly doesn't provide even leanness as the slide will move to a different position once it is lifted off its seat. I fitted the sleeve at as close as I could get to the exact size of the bored out body around 1.48" and chilled the sleeve and boiled the carb body (raised wifely eyebrows)even still it took a few taps with a copper hammer to get it to seat home. I turned a steel collar to run in the fixed steady which had the dual effect of preventing the top from splitting when I drifted in the bronze sleeve. The biggest issue was getting it to bore to size without making the tool sing and ruin the finish. A very negative rake on the tool and a relatively slow speed seemed to be the answer. I'd speed it up and all would be sine until all of a sudden Maria Callas! The cross holes were achieved with a die grinder with a tungsten carbide burr and a set of fine files helped size up the various other holes. The proof of the whole thing will of course be in its operation which I shall report on at a later time.

[Alan R]

Thanks matey--much chuckling, as have been there and heard Maria at her best !! My own similar experiences were at the Army Engineering Workshops here in Telford when the turner had a mounting ring for one of the MBT's ( Main Battle Tank--- Challenger Mk2) being finish-bored in the big lathe. Due to the local tool post situation there wasn't much he could do once our operatic friend got going. He did try hanging some heavy weights off the end of the boring tool ----- those rings are about 6ft in diam.---- which just changed the pitch but not the tune !!! In my younger days at home I was a keen grass-track racer and on the one occasion used mum's gas oven to heat up some crankcases to fit new main bearings. Trouble was it was an ex-speedway JAP engine with magnesium cases !! The house is still standing --no thanks to me though. Take care----

[Dennis C]

Hi Simon

Looks like a good job well done, definitely a different way of addressing the problem, the usual way is to true up the carb body then turn down the slide and fit a sleeve to the slide, your way is probably better long term, if the slide is standard size as in the future a new slide should cure any wear.

[Mark M]

Simon, I don't have a fraction of your turning abilities but have, like you, always thought that the boring and sleeving of the carb body is the best solution for a worn carb. I have been fortunate to get this done several times now by skilled engineers, originally because new Amals weren't available and also sometimes to preserve the originality of the bikes. I've been very happy with the results. Sometimes you get a slight tight spot due I suppose to the improved clearances showing up discrepancies on the slides but these are easily lapped out with Autosol or fine grinding paste. Ensuring clearance for the throttle stop and other holes needs particular attention as you say. The finished job is well worth it!
REgards, Mark

[simon]

Thanks for the positive comments chaps. I've not done a vast amount of turning having recently purchased the lathe but I had some excellent advise from a friend that is a very skilled engineer so that helped a lot. The carb appears to work nicely after a very limited test. It idles ok and responds to the mixture screw which I have found is not the case with worn carbs especially where the jet block isn't making good contact with the body. I might have a crack at the 276 on the 51 next which should be a bit easier as the body doesn't bottom out the way the 3 series does, mind you I think the main reason for the success of this job is that I constantly expected to cock it up and have to throw it all away so I adopted the measure nine times cut once policy, Too much confidence will likely result in a stuff up!