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Corroded SU Carbs
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Nick57



Joined: 09 Dec 2013
Posts: 35
Location: Leicestershire

PostPosted: Thu Jun 26, 2014 7:24 am    Post subject: Corroded SU Carbs Reply with quote

I have a pair of 1930s 7/8th bore SU carbs that are totally seized. Pistons, jet and butterfly all seized solid.

I have tried penertrating oil, leaving in a bath of diesel for several months without sucess.

Anybody have any ideas on getting them apart without causing damage to them as I think with care they could still be useable.

Nick
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Rick
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Joined: 27 Apr 2005
Posts: 22429
Location: UK

PostPosted: Thu Jun 26, 2014 7:54 am    Post subject: Reply with quote

Coca-Cola can work too but it has to be the real stuff, not own-brand supermarket fodder apparently. Although if diesel didn't work, maybe nothing will...

RJ
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Nick57



Joined: 09 Dec 2013
Posts: 35
Location: Leicestershire

PostPosted: Thu Jun 26, 2014 10:35 am    Post subject: Reply with quote

Thanks Rick.

I will give it a try and report back.

Nick
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Jim.Walker



Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield

PostPosted: Thu Jun 26, 2014 12:17 pm    Post subject: Reply with quote

In a working SU carb there is an inevitable air leakage past the piston. If there is anything such as pitting or corrosion on the cylinder walls or piston edges their operation will be unsatisfactory.
The test is to push the piston right into the cylinder, invert it and holding the piston,spin the cylinder until it falls off under gravity. From memory there should be no metallic noise and the "spin off" period should be about 3 to 4 seconds. I would not expect units which have been seized to pass the test though.
Any quicker and the unit will not work satisfactorily.
Of course that does not apply to the early "bellows" types which are closer in operating principle to Stromberg CDs. As they say "there is nothing new........................................."

Jim.
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aps



Joined: 15 Mar 2013
Posts: 37
Location: aberdeenshire

PostPosted: Fri Jun 27, 2014 9:49 pm    Post subject: Reply with quote

i may have a pair of reconditioned su,s im currently clearing out one of my workshops ,i know i have them when i come across them your more than welcome to them rather than dump them ,wayne
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baconsdozen



Joined: 03 Dec 2007
Posts: 1119
Location: Under the car.

PostPosted: Sat Jun 28, 2014 7:56 am    Post subject: Reply with quote

I seem to remember reading somewhere that vinegar will loosen corrosion on aluminium alloy. I might be wrong but trying a bit could be worth an experiment.
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Nick57



Joined: 09 Dec 2013
Posts: 35
Location: Leicestershire

PostPosted: Thu Jul 10, 2014 7:06 pm    Post subject: Reply with quote

10 days in Coca Cola did clean up some of body casing and the brass, but sadly still unable to dismantle carbs.

I will give the vinegar a try.

I know that heat usually works, prehaps 20 mins at gas mark 6 when Mrs N is out might do the job.

Nick
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Old Wrench



Joined: 23 Dec 2013
Posts: 226
Location: Essex and France

PostPosted: Fri Jul 11, 2014 9:42 am    Post subject: Reply with quote

The early 1930s SU carbs were mainly constructed from sand cast ally.

The verdigris will mainly be Corundum: sadly, one of the hardest substances known to man! Think Aluminium Oxide abrasives!

Corundum will dissolve in acid: I would probably try a 10% solution of Hydrochloric Acid, used as a warmish bath and keep checking to ensure not too much of the parent metal becomes eroded.

The jets and jet carriers are of course, brass and since brass is made from Copper and Zinc and as Zinc is the softer and most reactive metal, the process of "De-Zincification" means Zinc molecules sort of corrode out.

Judicious application of local heat should allow removal (since the relative rates of liner expansion means the ally housing expands faster than the brass) and thereafter use Phosphoric Acid, carefully, to clean (e.g. Jenolite simple liquid).

After cleaning brass using phosphoric acid the surface will "Pink Up", not a problem as it will soon go.

BTW: seems two carbs like this are worth quite a bit of cash!
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roverdriver



Joined: 18 Oct 2008
Posts: 1210
Location: 100 miles from Melbourne, Victoria, Australia

PostPosted: Fri Jul 11, 2014 11:39 am    Post subject: Reply with quote

The mix that I use for 'unsticking' rusted items like nuts, bolts studs etc., is a 50/50 mix of acetone and ATF. The acetone thins down the ATF so that it penetrates into the bonded area. I have used it on steel bolts into aluminium castings, but have never tried it aluminium to aluminium.

It does have the advantage of being a non corrosive lubricant rather than something that could etch away the surfaces.
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petermeachem



Joined: 23 Sep 2013
Posts: 358
Location: Chichester Sussex

PostPosted: Fri Jul 11, 2014 11:54 am    Post subject: Reply with quote

If Coca Cola worked a bit then stronger phosphoric acid might work better. I bought 5l of milkstone remover which is used in dairies: I used it for de-rusting purposes. It is much more concentrated than coke but not so much that it dissolves you. I'd dilute it somewhat and pull the carb out every hour to check nothing nasty was happening.
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Bitumen Boy



Joined: 26 Jan 2012
Posts: 1733
Location: Above the snow line in old Monmouthshire

PostPosted: Fri Jul 11, 2014 1:27 pm    Post subject: Reply with quote

petermeachem wrote:
I bought 5l of milkstone remover which is used in dairies: I used it for de-rusting purposes. It is much more concentrated than coke but not so much that it dissolves you.


Maybe not, but I find it still stings like mad if I get it on my hands - you'll find that rubber gauntlets are a sound investment Smile
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