Yes, the rod is shortened by HALF of the Total change of crankshaft stroke increase. I posted that way earlier.
I just wanted to be sure I understood it properly.
6mm of rod pin relocation = 12mm of total stroke increase, I doubt if that is even possible with this engine. Do you think that there is even enough clearance around the crankshaft?
I canít really tell. It looks tight, but there is no crankshaft to look at so I donít know how much room is actually available. Iím not saying you are wrong, Iím just saying I canít tell from the picture. Maybe I can find one on eBay to look at.
This entire project would be a lot easier if EMís kit was available. Or if his numbers were available, but Iíve been unable to find any to date. So just kind of guessing.
I did find a reference - donít know if itís true - that the 672c. Stroker was based on the same bore as the 685cc piston. Using that as a base figure - 102.5 mm so I rounded it up to 103- I calculated the stroke at 92mm. That provided a 767.57cc. Just playing a bit with the numbers to get close. What I got out of it was the stoke stroke of 83mm changed by 11-12mm.
If I bump - just plugged in the numbers - the piston bore up to 105mm - same as the 719cc BBK - then the stroke drops to 88mm with a change of 5 mm. With the 105mm piston and 88mm stroke that is 762cc. Based on that, itís more likely a 5mm stroke change would be used and the pivot pin would only need to be relocated by 2.5mm. Using a shortened connecting rod - someone posted a reference of 139mm, but later posted an EM measurement of 138mm - of 135.5 to 136.5 would appear to be correct.
Going with a lengthened rod and relocating the pivot pin inward by the same 2.5mm might be a safer/better choice.
Unless my numbers are completely wrong. If so, some experienced advice would be appreciated.
Why would any company build a bolt together rod to fit this engine? Wouldn't that increase rotational rod weight and weight is already your enemy. Wouldn't the rotational weight Increase the vibration of your engine?
I get what you are saying and it might be better to have a one piece connecting rod. Itís a trade off between ease of use - no need to split the crank - and a bit of extra weight. Honestly enough, I just planned to ask Crank Works Inc. about it and follow their advice.
As for why a company would build it, well itís not difficult. I was planning on purchasing a custom connecting rod anyway as Iím just not that much of a fan of cutting & welding or smooshing/stretching the connecting rod.
While weight might increase, I doubt it is a major issue as if I have Crank Works Inc. do the work theyíll be balancing the entire assembly anyway. I also planned to follow their advice on choosing the type of connecting rod so it could be a moot point.
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