Unless you clean out all the old oil and the carbon build up off all the parts the oil is going to change rather quickly. If you’ve changed diff parts and are getting a howling sound you might need to change the shims as the backlash may need to be adjusted.
Do you have pics of the engine? The process is straight forward, remove the perimeter bolts, pry valve cover off, clean off both mating surfaces, insert gasket into grove, reinstall valve cover and tighten bolts in stages in a criss-cross pattern .
Has the phone been dropped, liquid damaged, damaged? How do you know the phone is still working, is it giving you notification sounds/vibes? I have been seeing an increased number of iPhone 6 Plus' this week that have burnt out backlights, hold a flashlight up to the screen and see if you can still see an image, otherwise the LCD might have burnt out.
Most likely the phone is set to charge only mode, if you pull down your notification panel while it's connected you should see a notification saying it's in charge mode click on that and you can change it to MTP (media transfer protocol).
If you are trying to get past the initial setup and it's asking for your Google password, there is no way around that. The device is recovery locked to that account and won't allow you to use it until that password is entered.