M900 rear swingarm - any offset to the center line?

[phantomaz]

I'm doing rear wheel swap. The donor is Aprilia RSV 1000 - 6" rear wheel vs 5.5" on monster. A lot of modifications needed ,many of them already done! But now I was thinking if there is any offset of the monster's rear swingarm. Is it enough just to put the wheel to an equal distance from the swingarm walls ,to be sure that it is in one line with the front wheel?



I think that the left swingarm "leg?" is a little more bent than the right?! Anyone of you guys can measure if it is the same distance between both sides of the wheel and the swingarm? I can't measure it because already machined the swingarm holes - the "new" wheel has 25mm rear axle.

Since we are talking about rear wheel ,I want to ask if the monster can accommodate 190 tire on 6" wheel - do you know if Pirelli Diablo 190 is 20 or 21cm wide? Thanks!

[carbmon]

happen to have my nearly bare frame on racks so took a look at this ('01 M750 w/M900 swingarm tentatively aligned; Marchesini 5.5" mag wheel) ....

Bottom line: seems that the dimensions you seek vary a bit side-to-side depending on where the wheel is in the adjustment slot due to the assymetry of the swingarm.  I don't think there's a 'meaningful' measurement there to help you due to the angle of the arms.

It would seem you need to go to the trouble of mounting & shimming the arm and setting up a jig to ensure the rear wheel centerline exactly matches the front wheel centerline.  Then of course you've got the matter of ensuring the rear sprocket aligns correctly with the counterhsaft sprocket.  I'm assuming the Aprilia wheel may have different relationships between the wheel centerline and the faces of the hub, which is part of why this is such a sporting proposition for you  .

Good luck and have fun!

[phantomaz]

Bottom line: seems that the dimensions you seek vary a bit side-to-side depending on where the wheel is in the adjustment slot due to the assymetry of the swingarm.  I don't think there's a 'meaningful' measurement there to help you due to the angle of the arms.

Yes ,I know it depends where the wheel is in the slot. What I need is not an exact number but ,if both left and right dimensions /wheel to swingarm wall/ are equal. The sprockets are another problem ,which I think is solved ,but when everything is mounted will see.

[BastrdHK]

I think the 190/6 incher will work.  I am running a 5.75 BST with 180 and it is tight, but there is room for a little more if your setup i spot on.  The wheel I am running is for an R6, and the hubs are wider than the OEM M900 wheel.  I had to take about a .5in off the rear brake holder and drop  the spacer on the left side of the bike b/c the BST/R6 has a bearing on the left that acts as the spacer.  The wheel definitely is closer to the right side of the swingarm by nearly an inch.  The bike tracks straight with no hands on the bars, it does not misbehave/fight turn in on either side and the sprockets/chain are aligned with even wear on both sides.  Either it is pretty damn close to centerline, or I am a very adaptable rider with limited perception  

I have not done this myself, but a rolling the bike over a long, metal straight edge (or simply marking a straight line on the ground) aligned with the center line of the front should get you as close as needed in the rear.  

I ran into issues while fitting things up:

- Hubs on the new rim were wider than OEM so I machined the rear brake holder and had to reverse it to get the caliper to line up with the rotor.

- I have the 17mm rear axle and machined a piece of aluminum tubing to serve as a spacer for the BST with 25mm axle and 17mm OEM axle.  This kept me from machining the swingarm in case i needed to reverse things in the future.

- Had to drop the spacer on the left side, but the bearing on the BST accomodates that.

Good luck with your project, I hope you get everything sorted!

[phantomaz]

I think the 190/6 incher will work.  I am running a 5.75 BST with 180 and it is tight, but there is room for a little more if your setup i spot on.  The wheel I am running is for an R6, and the hubs are wider than the OEM M900 wheel.  I had to take about a .5in off the rear brake holder and drop  the spacer on the left side of the bike b/c the BST/R6 has a bearing on the left that acts as the spacer.  The wheel definitely is closer to the right side of the swingarm by nearly an inch.  The bike tracks straight with no hands on the bars, it does not misbehave/fight turn in on either side and the sprockets/chain are aligned with even wear on both sides.  Either it is pretty damn close to centerline, or I am a very adaptable rider with limited perception  

I have not done this myself, but a rolling the bike over a long, metal straight edge (or simply marking a straight line on the ground) aligned with the center line of the front should get you as close as needed in the rear.  

I ran into issues while fitting things up:

- Hubs on the new rim were wider than OEM so I machined the rear brake holder and had to reverse it to get the caliper to line up with the rotor.

- I have the 17mm rear axle and machined a piece of aluminum tubing to serve as a spacer for the BST with 25mm axle and 17mm OEM axle.  This kept me from machining the swingarm in case i needed to reverse things in the future.

- Had to drop the spacer on the left side, but the bearing on the BST accomodates that.

Good luck with your project, I hope you get everything sorted!

Thank you very much for sharing your experience. I decided to bore the swingarm holes straight to 25mm. A lot of machine work ,somebody will say is it worth the money and the work, but nothing is comparable to the satisfaction you get when you do the things wright.

So you are saying about an inch closer to the right side ... this is too much. You mean the center of the wheel / the hole with the bearings ,where the axle is / or not? I am talking about the wheel edge /the distance marked in red on the picture/,where the tire begins ,or even the tire edge will work. For example : is the tire 1cm from both sides of the swingarm or is 1.5cm to the left ,and 0.5 to the right?

[Speeddog]

Should be equal distance on each side, from the edge of the rim to the inside of the swingarm.

I've checked an M900 with an aluminum swingarm and a couple M750's with steel swingarms.

[BastrdHK]

Thank you very much for sharing your experience. I decided to bore the swingarm holes straight to 25mm. A lot of machine work ,somebody will say is it worth the money and the work, but nothing is comparable to the satisfaction you get when you do the things wright.

So you are saying about an inch closer to the right side ... this is too much. You mean the center of the wheel / the hole with the bearings ,where the axle is / or not? I am talking about the wheel edge /the distance marked in red on the picture/,where the tire begins ,or even the tire edge will work. For example : is the tire 1cm from both sides of the swingarm or is 1.5cm to the left ,and 0.5 to the right?

Again, my current wheel is not a good reference because the R6 wheel is, obviously, different.  I was measuring from the edge of the 180 Michelin 2ct.  It is approx 1.25in from the left (chain) side of the swingarm, measured where the tire is closest to the engine, top of the swingarm and 0.25in from the right.  The right/left hubs are very close to equidistant from both sides of the swingarm at the axle, but I did not measure while I was out there.  I can say I have put 3,000mi on the bike and current set up with no issues including several "spirited" runs through the Appalachians and maybe one or two top speed runs 

I don't have a clear picture, and never measured the OEM wheel/tire.  I want to say it was still closer to the swingarm on the right side measured from the edge of the tire.   

[greenmonster]

"Should be equal distance on each side, from the edge of the rim to the inside of the swingarm."

+1.
I have a standard R6 rim on mine.
Made mods so it has equal distance rim-swing on both sides.
Sprockets & wheels align as before & behaves steadily.
Maybe the above bst example are aligned but a bit offset?
Some bikes have that from factory.

[phantomaz]

Thank you all for the help. Now I can continue my work ,thanks!

[BastrdHK]

Confirmed the OEM wheel swingarm setup on M900/750 this weekend.  The tire is equidistant from both sides of the swingarm.  Good luck!