Can I fit 2" drain pipe into this vent stack?

[chud13]

I have a washing machine that I need to tie into the main stack. It is not up to code right now, as the 2" washing machine drain pipe ties into 1 1/2 inch sink drain pipe, then drains in the main stack. Is there a simple fix of removing the 1 1/2 pipe from the fitting and replacing with a 2" fitting at the main stack. When I eyeball the "y" at the main stack, it looks much bigger than the 1 1/2 pipe entering. Whaddya think?

 

[CountryBumkin]

I'm not a plumber - but it looks to me like the Wye at the stack necks down to 1-1/2 (?) right behind the coupler flange. Would replacing the existing 1-1/2 copper with 2" get you any more flow?

 

[Sponsor]

 

[Terry]

That's a 2" hub.
Remove the fitting that is leaded into the cast, pick up a 2" rubber sleeve and a 2" pipe will fit in there.

However, you said vent stack..............Waste doesn't go into a vent.
Are you sure it's not a waste stack?

 

[chud13]

Yes, Terry it is a waste stack. Thank you for taking the time to respond.