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Quote from: JonC on July 29, 2020, 03:45:02 PMHi Steamer, I agree it doesn't give much engagement but working back from the cam pulley size restriction it's the biggest I can get on the crank.The bouland engine below is 1/3rd scale and looks like its using a 12.7mm single belt driving both cam shafts from a similar small crank pulley.JonMike and Jon, What size is the crank shaft pulley?.....
Hi Steamer, I agree it doesn't give much engagement but working back from the cam pulley size restriction it's the biggest I can get on the crank.The bouland engine below is 1/3rd scale and looks like its using a 12.7mm single belt driving both cam shafts from a similar small crank pulley.Jon
My usual starting point for actual designs (when I am not winging it) is: https://sdp-si.com/D820/PDFS/Technical-Section.pdf 6 teeth seems to be minimum wrap. Belts that are wider than diameter of pulley give tracking issues. Short belts also give tracking issues. Roundinsh profiles have less cogging action and don't tend to ride up the pulley as much. But their profiles are generally proprietary although the sdp-si manual conveniently gives the related patent numbers for further educaation. They can apparently be approximated using ball nose end mills and cnc. :-)One suggestion might be to gear drive from crank to the large central pulley, then single belt from there around al the cams. Outside idlers are preferred over ones riding on teeth.
Hmm, problem.I need to keep the top centre pulley running at half crank speed. It drives the auxiliary pullies for the water and oil pumps as well as the distributor.Lucky old Mr Duckworth didn't have this problem before the invention of toothed belts.
I think having two belts running next to each other may cause problems if they don't track perfectly and there's no room for a central flange to separate them.Jon
Mike, yes that would work or maybe just slice them to bits
Hello Jon,That looks to be a very practical solution to the staggered cylinders and belts. I assume the crankshaft pulley has the two belts running side by side.I am impressed with your idea of building a plastic mock-up to tease out all the tolerance and clearance issues before you commit to the castings. You cannot afford to find problems, once the die is cast, as they say.MikeMike,the block moulds are printed in six different parts, hence the elastic bands holding it together, it's the only way to produce the waxes. I have splits the "machined" print in the same way in order to try and maintain accuracies (less support area etc)because this produces a much better quality print of a complex shape, I'm also applying it to the "true" DFV model (geared etc) meaning that it should be easier for people to print themselves. Also there's less likelihood of scrapping a print because one area failed.Maybe your cheap Chinese printer might still be able to produce a decent model?Jon
An interesting development. As I recall the Cosworth developments were first the FVA (four valve Anglia based on the Ford engine) then came the BDA (belt drive Anglia, heavily developed for rallying) and the DFV (double four valve Formula 1 engine). There was also a development of the Ford V6 with belt driven four valve heads.