| Author | Message | ||
     Dooley |
What is the difference in the 9 and 12 motors? I know I know its been talked about here before and I new what the answer was but I forgot and thought that asking here would be easier than looking it up..please forgive me...is it rod length or just different pistons or both......thanks | ||
| Ft_bstrd |
The bore is the same between the two bikes. The 9 has a shorter stroke. I believe the 9 also has domed pistons and a different head, but I could be wrong about that. | ||
| Old_man |
Yes, the 9 has domed pistons and also longer con. rods. I think the heads are the same. | ||
| Hogs |
Old_MAn, I Think your right in sense that the 9 has a longer throw in the jugs , I think its made possible by the location of the whole in the wheels for the rods (Same Rods 9 or 12 ) , since giving more throw... | ||
| Hogs |
Don`t think the Rods are longer themselves Just the Position ( hole drilled ) in the Wheels To give more throw.. Sure you know that.. | ||
| Andymnelson |
I don't have any knowledge of the internals of our motors, but the geometry does not make any sense if only the wrist pin on the pistons is moved- that would still give you the same displacement (as would different length connecting rods). The only piece in the rotating mass that could increase displacement would be a crank with a longer throw to it. The wrist pin placement, connecting rod length and piston dome would all affect compression ratio, as well as head displacement. Cylinder displacement is measured as the volume between TDC and BDC, I believe (correct me if I'm wrong!), and changing wrist pin position, rod length and piston dome do not change that since you affect the difference the same at TDC as BDC. (Message edited by andymnelson on February 10, 2009) | ||
| Hogs |
Wrist pin location does not chance in the 9 or 12 pistons that I am aware of??? The Position of the RODS Big end is Drilled in a different location with the crank pin in the Wheels which changes the Stroke/Throw... | ||
| Old_man |
The 9s con rod connection on the crankshaft is nearer the center, giving a shorter stroke. The barrel is the same length as the 12s and heads are the same, necessitating a longer connecting rod so that the piston can rise to reach the head. A domed piston is needed to raise compression to match the 12. | ||
| Skinstains |
The increased rod length should be 1/2 of the stroke increase. | ||
| Old_man |
Exactly, The 9s con. rod is LONGER than the 12s. It should be 1/2 the stroke DIFFERENCE longer than the 12s con. rod. This gives the same space in the combustion chamber as the 12, but because of the shorter stroke results in a lower compression RATIO than the 12, if using the same piston as the 12. Thus, requiring a domed piston to give the desired compression ratio. | ||
| Hogs |
Sorry Old_man, I had thought it was just the location of the Rods not Being Longer as well, Thanks for that bit of Info... | ||
| Dooley |
thank guys I new the pistons were different I wasn't sure about the rods though...... | ||
| Skinstains |
Stock 9 pistons in a 12 will give you a nice little bump in compression. A very good 'bang for your buck' mod. | ||
| Hogs |
Skinstains, Yeah it sounds like it....JUst wonder though with using the aftermarket can, and say race ECM wd. that handle it, or "Have to" get into tuning etc etc... | ||
| 2dflyer |
So has anyone tried a 9 to 12 conversion? The 883 to 1200 conversion was an easy task, conceptually anyway. So the skeptic in me wonders if part of the reason behind the 9's cylinder dimensions was to make a conversion more difficult. | ||
| Old_man |
The 9s cylinder dimensions are exactly the same as the 12. The heads are the same. The 9 would need the crank and rods of the 12 to make the change. You could use the 9s pistons (same bore size) but because of the dome you would have higher compression. | ||
| 2dflyer |
Lousy choice of words on my part. Shoulda just said bore x stroke. What I meant is the 883 to 1200 conversion was basically top end work. The 9 to 12 conversion takes you a lot deeper in motor, making it less likely that someone would consider a conversion and protects 12 sales. | ||
| Old_man |
I don't think they considered that when they designed the 9. A shorter stroke design allows for higher revs (less piston speed per rev.) The only new parts needed are con rods, pistons and different con rod connection on the crank. | ||
| B00stzx3 |
2d, I looked at either convert or 12 swap, because the 12 has a lot more potential with the power packages and big bore kits. In the end though, might be worth it just to get an 1125R  | ||
| Skinstains |
As far as I know you needn't get into tuning with the 9 pistons in a 12. This mod goes back to the days when ECM-Spy wasn't available and everyone had the race ecm, K&N, and a less restrictive exhaust and the mod worked well. I will be putting 9 pistons in my Uly as soon as I can afford it. | ||
| Hogs |
Thanks Skinstains... GooD Point |
