wrong sprocket

i have fond out why my 550 had no acceleration, the previous owner swaped the back rim to a 16 inch rim and the sproket on the rim is a 41 tooth and i need to get a 45 or 46 for it, but the only problem is i don't know what the rim is off of so i don't know what kind of bike to order the sproket for, the rim is a 16 inch but they are not maxim rims, they are still straight spoked just like the front rim, would anybody have a clue as to what it came off of so i have a starting point in my search

 

Post a pic.

 

GACK. Straight spoked? And a 16" to boot? DAMN. Somebody was resourceful. The 550 Seca was the ONLY (US market) XJ to use the straight-spoked wheels until the later bikes with the "box" spokes.

Boy, I'm drawing a blank on what bike of the era would have those wheels, especially in a 16. It's gotta be EARLIER, like maybe from an altogether smaller bike like an RD400. A lot of the early Yamaha mags (going back to '78 or so) were similar to the wheels on the 550 Secas, the "swirly" wheels came later.

I have a concern with this, and here's why: The stock 550 Seca sprocket is held on with 6 bolts; the smaller bikes, like the 400 twins which shared the same brake assembly only had 4. In addition to the size of the hub and strength of the sprocket attachment points itself, there is a "cush drive" inside your rear hub. The cush drive from a smaller bike was probably never intended to handle the power and torque put out by the 550 four-cylinder. I would be very concerned about a component failure in this area, especially in light of your apparent high-performance leanings...

Speaking as someone who knows and loves the 550 Seca, I STRONGLY RECOMMEND you track down the correct 18" rear wheel assembly. NO, a 120 won't fit anymore, but the bike handles FINE with the stock wheels and good tires (suspension upgrades help.) No, it won't look as sexy maybe but it WILL BE A LOT SAFER.

 

the bike is in my buddies garadge so i cant get a picture, but i do know that it is a six bolt pattern holding the sprocket on, so now it gets real complicated...

 

ok so i did a little bit of quick research i was looking through a denis kirk catalog and in the back it had a reference of all the bike make and models with OEM sprocket sizes tire sizes sparkplugs yada yada yada, and the ony other bikes to come stock with a 41 tooth are 1967 YR1 grand prix 350... 68 YR2 350... 68 YR2/c 350... and 86/87 FJ1200

all the 67/68 bikes have wire spoke wheels, and the FJ doesnt have expanding brakes they have disk (thanks to google images)

so mow im even more lost that before, does anyone know what the measurment is on the bolt circle for an 81 550?

all this thinkin is makin my head hurt

 

dude, I don't quite know how to say this but I wouldn't use a Dennis Kirk catalog as a definitive reference on '70s and '80s Yamahas.

I've got spare sprockets laying around, I can measure one for you but it will be later on I don't have access right now it'll have to wait 'til I get home this evening.

I still recommend jumping on eBay and getting the correct wheel. There are TWO 550 Secas being parted out right now on eBay plus I'm sure you might even find one on our board...

 

OK; the 550 sprocket ('81-'83 were all the same, 45T although the '81 was SUPPOSED to have a 46T I haven't found an original one yet.)

ANYWAY: the hole in the middle is 74mm; the bolt holes are on a 92mm circle (approx 3.5".)

I still recommend fitting the correct wheel.