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Title: 78mm crank ? Post by: glassback kid on December 12, 2016, 11:18:56 am just want to run this past people, getting my head confused at the moment, i was originally planning/massing parts for building a 1914cc type1, so i currently have new mahle 94mm normal stroke barrels and pistons, However a new 78mm crank has come my way and it would be the first time building a stroker motor, so if i was to use the above B&Ps i guess these will need around a 4.5mm shimming to accommodate the stroke increase ? am i best stepping the case a few mm when machined and use a smaller shim ? would the use of shorter rods be better, obviously everything has to be mocked up numerous times to get all clearences/figures spot on just trying to get it all together in my head
Title: Re: 78mm crank ? Post by: Zach Gomulka on December 12, 2016, 18:15:54 pm It can be done but if this is your first engine I would skip it. 74mm plays nicely with standard pin height pistons (especially with short rods), after that you will run into more issues than it is worth. Skirts interfere with the crank at BDC, engine grows wider, tins won't fit, etc. However, if it is a good quality crank (not cast) then it may be worth looking into swapping your pistons for strokers and building it up the right way.
Title: Re: 78mm crank ? Post by: Neil Davies on December 12, 2016, 23:22:18 pm I'd get rid of the 69mm stroke pistons and barrels and get the right ones for the 78mm crank. Modified stock rods (Rimco, etc), 40x35.5 heads, Engle 130 and a pair of decent sized carbs. Old school but proven.
Title: Re: 78mm crank ? Post by: Jim Ratto on December 13, 2016, 23:56:47 pm If you have the ability to swap the stock-stroke 94mm for the stroker type, you will see how easy building a 78mm stroke engine is. The bottom end doesn't need much in clearance-grinding of case (regardless of using A or B type pistons), especially with some kind of aftermarket rod. If you use the B type piston, designed for stroker, then the top end goes together almost like stock stroke motor. If you use the stock stroke 94 (for 1914 etc), you get to juggle cylinder spacers, pushrods, rocker pads ,and then slot cylinder covers and trim deflectors to get everything together.
Stroker 94's are lighter too. Title: Re: 78mm crank ? Post by: glassback kid on December 17, 2016, 12:32:12 pm thanks for the input guys, thought i would be causing problems trying to build with the 78mm and A pistons, i think i will stay with original plan of using 69mm crank as i have already put time and work into match weighting the pistons so dont fancy buying another set at this moment in time, the 78mm crank can get shelved or sold on for now.
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