Wednesday 18 November 2020

The Timing Case Patterns

Having previously made the patterns for the single cylinder AJcette, detailed here and here and which worked out pretty well, I planned to use the same approach for the V-Twin.

The first step was to make a number of resin copies from the K7 timing case moulds and to then cut-and-shut these to assemble new inner and outer V-Twin timing case structures.

The picture below shows the first 2 pieces that were amputated from resins and stuck together with JB Weld at an angle of 500 ….you have to start somewhere.


The plan was to make most of the inner timing case and to then match the outer timing case to the profile of the inner. It is a slow and laborious process making the patterns using bits of resin to get detail close to the original plus pieces of wood and metal, held together with JB Weld and Araldite and finished with P38 body filler.

The inner timing case was made by first constructing the lower section that could be clamped to the timing-side crankcase and then adding the upper portions according to the chain run. The whole assembly was then positioned approximately in the correct location in the frame to determine the length of the magneto chain section of the timing case. 

This process takes time – it took me about 6 weeks to make both patterns, because it is only possible to do a bit at a time before waiting until one or other of the adhesives has hardened sufficiently to handle the pattern and  attach the next bits.

On the outer timing case on the right of the above picture, I have machined the main flat part of the pattern from a piece of aluminium plate to give it structural strength. The circular section in the centre is formed from a pair of stainless steel Korean rice bowls bought on ebay for very few ££ and spaced apart for thickness of the casting. The main oil pump is screwed onto this face and a reasonably thick section is therefore required for the threads.

I found it useful to use tailored strips of wood for the sides and these can be clearly seen on the inner case pattern on the left. The wooden strips were made to order by AA Woodcrafts for a reasonable price and delivered very quickly.  I also found a local company, Finecut, that would make more sophisticated shapes in wood, in this case semi-circular sections. These, together with machined aluminium sections, were used at the extremities of the chaincases.

I wanted the castings to be as flat as possible at their mating surfaces as I do not have and do not have access to any machine tools on which these surfaces could be machined in one operation. The plan for ensuring  the patterns were as flat as possible was to first eliminate any bowing by weighing down the patterns in the appropriate places, as shown below, and to eliminate high spots by carefully rotating the patterns on a flat sheet of plywood to which multiple sheets of coarse emery cloth had been stuck. The flatness was checked using a thick sheet of glass.

The picture above is taken prior to attaching the Korean rice bows. Additional thickness to surfaces that will eventually be machined has been added in the form of thick cork gaskets cut to shape; these can be seen at the holes at the end of each chaincase section.

Eventually the patterns were finished and ready for the foundry.


As the patterns are fairly fragile – they would definitely be damaged if dropped, a bespoke box was made to store and transport them. The surfaces to be machined have been painted red to assist the foundry in positioning the sprues and risers in the mould.

….and there were plenty of offcuts of resin timing cases left over for scrap.



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