ive got 530 "o"ring on my 500 and it clears ok,
Please define "ok".
I haven't measured the clearance on a 500. But, I certainly have on the 550. It's right around 1/8 inch clearance between cases and the STANDARD chain. An Oring chain is not quite 1/8 inch closer to the engine case.
First: If you just lay the Oring chain on the sprocket at rest, it may appear not to touch the case. There are more factors for proper clearance than this initial observance.
Second: The sprocket may not fit tightly on the spline shaft, allowing it to "wobble" while operating the bike. The wobble can get worse with wear. Wobble allows the chain to move toward the cases/seal.
Third: Wear the of the sprocket hold-on plate and the shaft groove that it engages can allow the sprocket to move laterally on the spline shaft.
This is another wear dimension that must be subtracted from the observed "at rest" clearance between case and chain.
Fourth: The sprocket tooth width positions the chain in relation to the cases. Sprocket tooth side wear allows the chain to move closer to the engine case. Meaning a worn sprocket becomes more likely to allow chain contact with the engine case.
Fifth: The chain side plates engage the sprocket tooth sides during operation. These can also wear over time and allow the chain to creep closer to the engine case.
When you add the width, wobble, wander, and wear factors (Ahh, the 4 Ws
) that occur with the bike under road conditions, you can easily get case grinding, if not now, sometime down the road.
Perhaps someone with a 500 will make comparative measurements of clearance between chain and engine case?