penno350 Posted February 25, 2013 Report Share Posted February 25, 2013 Planning to rebuild a C15 to trials spec. Is there any value in pushing the engine out over 250cc which I believe you can do with a Triumph piston or is it best to use normal oversize. Quote Link to comment Share on other sites More sharing options...
woody Posted February 26, 2013 Report Share Posted February 26, 2013 C15 is 67mm and 500 Triumph is 69mm so it's only an extension of the max oversize and just needs boring to suit. It takes it to 262cc so you're not really going to notice much, if any difference. The 650 Triumph piston is 71mm and takes it to about 277cc which gives it a bit more torque and pull. I can't remember whether you have to widen the head to go with the 71mm piston or not and it might need a thicker liner, again can't remember. You also have to make sure you get a piston with the correct shaped crown in order to keep the correct compression ratio. In truth, the standard bore size has more than enough for any classic trial. 1 Quote Link to comment Share on other sites More sharing options...
penno350 Posted February 26, 2013 Author Report Share Posted February 26, 2013 Thanks Woody, standard it is then. Quote Link to comment Share on other sites More sharing options...
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