Wiseco Ring End Gap

[2T]

Wiseco recommended ring end gap for my WR500/YZ490 is .35mm (.0137 inch).

I am about to install new rings and the gap is .485mm (.019 inch).

The bore is 1st oversize (87.5mm), as are the new rings, and a measurement of the bore shows it bang on 87.5mm.

Can anyone suggest why the gap would be so big and also if this ring gap is acceptable?

[John Orchard]

I would guess a few more bore measurements taken at various points? I've only ever used my 'eyecrometer' for a guestimate.:-)

[2T]

I would guess a few more bore measurements taken at various points? I've only ever used my 'eyecrometer' for a guestimate.:-)

I measured in two spots, one which looked like it would be the most worn.

Will do some more measuring and get back to you.

[2T]

Multiple measurements around the bore are showing up 87.5mm.

The end gap reading is taken about an inch down the bore.

My verniers are pretty old but they've never given me reason to doubt.......until now.

[Wasp]

I would say the gap should be MINIMUM  .35  . Yours is only .13 more than minimum =4 hairs..... I wouldn't worry, especially on a big piston that expands a lot. Better too much than not enough.

[2T]

I would say the gap should be MINIMUM  .35  . Yours is only .13 more than minimum =4 hairs..... I wouldn't worry, especially on a big piston that expands a lot. Better too much than not enough.

Thanks for your help.

[pokey]

 Wasp is correct  and the gap should be fine.  My calcs are not too far off your actuals and bearing in mind a higher compression means more heat thus more expansion.
 

[2T]

As Wasp mentioned, 'minimum' looks like the key word, which I overlooked when reading the destructions.

The workshop manual lists standard gap as .35 - .50mm, with .8mm as the limit and, although Wiseco may have different specs, it wouldn't have hurt me to read that a little earlier than just now.