Posts Tagged ‘restore’

Aluminium welding and repair

Thursday, March 18th, 2010
Damaged 1903 Renault crankcases in for repair

Damaged 1903 Renault crankcases in for repair

At Stotfold Engineering we do weld aluminium on a regular basis and often have customers come in to have their crankcases repaired on their classic motorcycle or car. However not all aluminium is easily repaired. Firstly lets have a look at it in more detail.

WHAT IS ALUMINIUM?; Aluminiumis the most common of the metal elements on the  earth. It is used in almost all industries now, but its major use has been in the aircraft industry. Aluminium can be amalgamated with several other elements such as magnesium, sodium and zinc. These minerals give the aluminium a variety of different characteristics, changing the strength and corrosion resistance of pure aluminium.

WHY WOULD WE NEED TO WELD ALUMINIUM?; All metals used throughout industry have their weak points. Aluminium is no different. It cannot resist prolonged exposure to alkali’s and this causes the oxidised outer surface, which is acting as a protective layer from the elements to break down. Once the component starts to break down you have two choices; scrap or repair. In these days of recession repair is often the most cost effective course. Obviously, for example, to have a new crankcase cast and machined would be very expensive. However with the advent of modern materials and techniques you could end up with something better than the original. Straight replacement of parts with new is extensively employed in the aviation and MOD sector. In classic motorcycle and car restoration one tends to repair and restore due to maintaining the originality of as many parts as possible.

The finished repair on a engine mounting lug of a 1903 Renault

1. The finished repair on a engine mounting lug of a 1903 Renault

 

1903 Renault fully restored engine mounting lug

2. 1903 Renault fully restored engine mounting lug

 

 

 

 

 

 

HOW DO WE WELD ALUMINIUM? ;

TIG welding and gas welding are the most common types of aluminium welding in the restoration business. We use TIG welding for such things as crankcases or structural components and gas welding for body panels.  

  • Gas welding uses oxygen and hydrogen mixed from two separte gas bottles feed a nozzle that mixes the two together. This produces a flame ideal for welding aluminium sheet. 
  • TIG welding stands for Tungsten-arc Inert Gas. Firstly when aluminium castings are welded, like crankcases, it is important to first heat them in an oven to bring them nearer to the welding temperature. Then the TIG welding torch is applied with some aluminium filler rod to repair the damaged cases. Photos 1 & 2 show a repair to a 1903 Renault crankcase done by us. TIG welding is a mixture of electricity and gas. Electricity is passed through a tungsten tip shrouded by a ceramic tube.  An inert gas called argon is fed into the tube from a bottle. This gas acts as a flux so that the oxides produced when heating aluminium are kept to a minium, so keeping the weld clean and flowing easily.

HOW DO WE PREPARE ALUMINIUM PARTS FOR WELDING?; Preparation is critical, with the main goal being to cut out all the rotten parts. Think of the oxidisation as a metallurgical cancer that needs to be cut out, so only good clean metal is showing. Removal of the oxidised aluminium can be achieved with a grinder, file or burr, or even a drill, as long as one cuts out all the rot to shinny clean aluminium. When this is achieved we can put a piece of aluminium plate, cut to the shape of the hole that is left, or simplify fill it with aluminium filler rod.

Safety Note: You should always where a mask when doing this, as aluminium dust is very bad for your body. Colin here at the workshop uses an army resparator which provides protection for the lungs, face and eyes.
 
HOW WE DO IT IN PRACTICAL TERMS; Once we have received your damaged crankcases, for welding at our workshop, the first thing is to assess what needs cutting out and what needs filling with plate or solid welding rod. Any filler plates are made at this stage to fill larger holes or voids. The crankcase or part is then heated in an oven before employing the TIG welding process. Even bearing surfaces can be made up with rod.
After welding and filling holes, the crankcase or parts is fettled to create a smooth invisible finish. Any bearing housings are machined to their original sizes. The parts are then aqua-blasted if required.
 
WHAT ARE THE EFFECTS OF WELDING ALUMINIUM?; As long as the aluminium has been prepared correctly, pre-heated, and the correct rod has been selected for the grade of aluminium, there should be no adverse affects.
 
WHAT ARE THE COMMON FAULTS IN ALUMINIUM WELDING?; Aluminium is fairly easy to weld provided the preheating and preparation process is followed. If you do try to weld a casting that has not been cut back to clean metal you will find the surrounding material next to the weld is peppered with small holes and the weld will be brittle at the join with the original material. The key to strength lies in penetration of the material, particularly on things like engine mounting bosses. If there is shallow penetration the part that has been welded will break of at the edge of the weld.  
By Terry Ives

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TRIUMPH T100 CONRODS – scrap or not to scrap!

Friday, September 25th, 2009
Triumph Tiger 100 crankshaft & conrods

Triumph Tiger 100 crankshaft & con-rods

I have inherited from my father, Terry Ives, a 1954 Triumph Tiger 100, the first of the swinging arm models. The crankshaft and rods had gone missing some years ago, as they do, so I endeavoured to source a replacement.

The original one would have been what they called a one piece crank, but I knew the crank from this particular Tiger was swapped for a three piece one. The previous owner used it for sprinting in the seventies. The one piece cranks were a lot tougher under extreme loads. I looked on Ebay and found a crank for sale in Chile, South America. I purchased it and found it had very large big end journals, but according to my Triumph manual this was the right size. The whole of the crank was very grotty and had had modifications done to it to keep it running through the years, so I looked for a second one. I managed to pick up another Tiger crank, and this one came with rods, which I also needed.

The con-rods had white metaled steel caps and the rods themselves were made from duraluminium. The big end journals were a lot smaller and the crank was stamped 6T. The stroke was 82mm as was the Tiger 100. I measured the big ends of the rods and found they were worn out of tolerance. I asked several companies about reconditioning them on the off change that there were other engineering companies who had experience with salvaging con-rods, but nobody could help me. I fact several companies said it could not be done.

Have owned and run Stotfold Engineering for the past 40 odd years I thought I would put my restoration skills to the test and solve the worn out con-rod dilemma, and besides, nobody says it can’t be done to me. I machined the steel cap and the dualumimiun con-rod down by .015″ which caused the eye of the rod to be elliptical. I then secured the cap onto the rod with the correct torque settings to the stretch bolts. The con rod was then turned on the lathe to within .002″ under-size and then finish honed to restore the correct running clearances. The thickness of white metal on the cap was ample enough to have it machined out and leave plenty for years of service.

I was told in the past that if you have one of these type of con-rod , you should throw it away and get a new one. It seemed like a waste of a perfectly usable con rod and it has always been the policy here at Stotfold Engineering to repair, recondition or restore an item rather than just bin it. Our motorcycle repair and restoration workshop always look at the problems from this perspective to overcome engineering problems, not give other companies standard response of “you need to buy a new mate”.

by Terry Ives

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Posted in Advice | 28 Comments »