Head gasket replacement..... finally at the installation point

Take it to your machine shop and ask them to tap out the threads or retap to a larger size. Maybe they have a parts cleaning vat as well to clear the internal carbon.

If that fails you could shop eBay with the part number below. It’s an expensive stainless steel part so new it’s maybe $300 up. Used but clear is fine.

 

You don’t need thread inserts, just a tap that makes threads in the hole. Maybe it can be retapped to the original threads or tapped to a slightly larger thread. Tap and die set- but you probably don’t need to buy just for this. It’s five minutes at the shop.

 

I you ignore the #18, the only one to take a washer and a 10 mm socket, there are two kinds you're left with:

1. the thick ones (14 mm socket, 51 Nm of torque, 4 short and 3 long), and
2. the thin ones (12 mm socket, 26 Nm of torque, 18 short and 2 long)

This is how I memorized the order:

1. The thick, short ones go on first, and you need to memorize their locations. The holes are also larger here.
   
2. Then the thin ones go in in a clockwise pattern around the periphery starting from the top right edge. Two of these (#7-8) hold the water pump to the cover and are the long ones. You have to leave out the 4 holes that hold the oil filter housing to the cover—you'll get to these later. The two that go in at the top right and top left (#5, #17) will need a line of threadlocker.
   
3. #18, the unique one, is next.
4. The thick, long ones hold the engine mounting bracket to the cover.
5. Finally, you use the 4 remaining thin, short bolts to fasten the oil filter housing to the cover.

 

Thanks for the tips! I just got the cylinder head off mine today, gonna try to measure the flatness to see if it needs resurfacing. My brother, the Nissan master tech, told me he has never found a car this new with a blown HG that the head was actually out of spec. The machine shop in town is booked 3 weeks out too. But better safe than sorry, so I'll take it down to the machine shop tomorrow. If I don't have to wait 3 weeks then I can start reassembling next weekend.

 

Obviously your brother hasn't seen many Prius.
Doesn't he have a straightedge at the shop?
If you clean off the matting surface, and bring it to the machine shop, they will probably
check it for you, for free. It only takes a minute or two.
Maybe autozone or napa has a straight edge you can check it with.
No reason to wait 3 weeks...

 

...

 

Yes, he says he has rarely seen newer cars out of spec, even after the head gasket has blown.