Bicycle Mechanics - Chainring switching

Anyone know how to tell exactly what Shimano chainring they have. (part #)? This is an ultegra crankset bike, 8spd.

I want to swap the chainring on to a 9spd dura-ace bike.

Will 8spd ring work with a 9spd chain?

Thanks.

The chainring should be marked something like 39-B if the chainring you want to put it with has the "B"(52-B,53-B) designation it will work. Generally the 8 and nine stuff is very slightly different, the biggy is the chain which has (if I remember right) a .4mm width difference. It has been a while since I checked but I think the 9-speed small ring is machined to sit a little closer to the big ring.
For the price of a ring I would just get a new one.

Find the part number and you will see what speed it is. Or sometimes you will find a bike with it and figure it out from there.

Chainrings are pretty much universal. As long as the bolt circle diameter is the same - 130mm, 110mm, 94mm - and you can bolt it on it will work. The only difference between an 8sp crank (not chainring) and a 9sp crank is pretty much the distance between the chainrings not the thickness of the chainrings. Consider that the inside width of all multi-speed chains from 5sp through 9sp is 3/32". Only the outer width varies. You do need to use a 9sp chain, for instance, on a 9sp cassette. I have run a 6sp crankset with generic Engagement Ring chainrings with 9sp Dura Ace shifters and front der with no trouble at all. There may be some times when chainring brand/model may be important, but I have not found it.
FWIW,
Raymond

The spacing of the chainrings is machined into the chainrings themselves. If you run a 8spd small ring39/42 with a nine speed chain it can drop between the two rings. I have both 8 and 9 rings laying here and they are very different in their built in spacing. The chains measures .6mm different.