Yes, if you have the part to take measurements from, that is an option, but sometimes you don't have a part, just a photo. Most of these sled engines are built oversea's and use mm vs inches. One web site said (4) 8mm bolts, one has said (4) 10mm bolts, but that doesn't give me the bolt pattern used. I know all the heads use 8mm 1.25 bolts.
I'm mainly interested in just getting the different Bolt Patterns. Like most Sled Heads, use a (4, or 5, or 6) Bolt Pattern. For now, I'm mainly interested in Skidoo/Rotax engine bolt patterns. The Skidoo/Rotax std. Cylinder Bores used are 62mm, 67.5mm, 69.5mm, 72mm, 76mm, 78mm, 82mm. Most Skidoo/Rotax thread depths are std. about 10-12mm. Most Single Cylinder, Air Cooled engines all use the same (4) Bolt Pattern, so does the dual cylinder 503(72mm). The smaller Dual Cylinder Air Cooled engines, 377/380/440/447, and the water cooled 440, 470, all use a smaller (4) Bolt Pattern, which I think is the same pattern. A good example is here:
The Seadoo 580/587/650/657, and the Skidoo 521, 536, 537, 580, 582, 583, 617, 670, and the Rotax 532UL, 582UL, 618UL, all use the same Head Bolt pattern, same Head OD Size, same spark plug location, except the Rotax UL Heads are Dual Angle Plug. All use 8mm 1.25 Head Bolts. So, if you have just that info, Head Bolt Pattern, Bore, you can design a Custom Billet RACE HEAD with Inserts, or just a Cast Head. The 82mm Bore is a 670 Big Bore. Engines Bigger than a 670 made 2000+ used another (6) Bolt, Head Bolt Pattern. Close, but different. For the thread per inch, lenght, you can look at a parts manul for that info. It's the Bolt Patterns that you need to figure out.
I would like to make some Templates, of the basic 4-5-6 Hole Bolt Patterns, printed on clear transparency paper also. Some times, you can adapt a head off another engine. Go to a swap meet with a few 6" x 6" Templates to lay over another head/part to see if the bolt patterns matchs up. Say a Big Crosshair, with the different Circle Bores Centered, with what ever Bolt Pattern your looking for. Maybe some measurements on the Crosshair. Bolt holes could have crosshairs also, so it could be printed and just glued to a piece of stock, that locates all the holes for drilling, machining.
Like here is an Aermacchi Harley Davision Motor Cycle, Dual Plug Head, adapted to a Skidoo/Rotax 277(72mm x 66mm) single cylinder engine. With a Clear Info Template, you could lay it over the head to see if it would work at the swap meet. $30 off ebay shipped.
I found a Skidoo/Rotax 503 head to actually measure. The (4) Head Bolt Holes measured 9mm OD. The engine ues 8mm Bolts. From inside edge of one hole across to the other hole inside edge, is 61mm. It's the same the oposite way. So if I figured right, the Rotax 503 Head Bolt Pattern is 70mm x 70mm, for 8mm bolts.
Attachments503_HEAD_BOLT_PATTERN_70mm_x_70mm_-_8mm.pdf, 59.8 KB
Nice job thanks for the info. Much appreciated.