Time sert kit is not that cheap. I ordered from USA
https://www.threaddoctor.com/ipod-nano?search=&description=true&category_id=20&sub_category=trueUpon this kit a number of inserts since the inserts included in the kit is not enough for a CB750's urgent repairs and coming ones.
https://www.threaddoctor.com/index.php?route=product/search&search=M6&category_id=18&description=trueMail them and ask about package price. I use mostly 8-9 mm carbon steel which is rather soft to file down if it will not go deep enough which happen all the time. Difficult to use the tool enough for the top to go deep enough. You will know what I mean.
20 inserts are not too many
Only the valve cover can consume 10. Cam holders 8 more + 4 for the studs.
Plus eventual stripped motor cover, chain tensioner housing etc.... My K6 has some inserts... My K2 build consumed 10-15 direct when I assembled the engine despite careful tightening by less than 8Nm on valve cover and a few other covers stripped threads with a good torque wrench.
I cheated with cheap heli coil on one exhaust M8 thread I secured extra with Loctite 272 (red hi temp) as I use on all time serts.
The thread doctor has also Big-Sert which is next step when a helicoiled thread is stripped or abused M6 time sert going up.
Check that you do not have rotten repairs in need of that set too. For that enough to have 10 inserts as what I see it. I have used a couple so far.
If the cam studs are going up off the alu (head has a curved surface upwards to stud). Time-sert, secured with Loctited 272, bolt sealed with
https://www.permatex.com/products/thread-compounds/thread-sealants/permatex-high-temperature-thread-sealant/I have also plugged the hole on the outside for those studs, Spark plug cavities. Head upside down, clean the holes with acetone and close them with JB Weld after you have repaired the stud threads and assembled them if bad. This to ensure no oil leaks that way.
Permatex under rubber pucks under the cam holders.
Clean first with acetone, smear the brown/black thing on the machined surface for pucks, not too much. Let dry for an hour, place plugs on. Assemble cam holders and tight them with half torque. Remove them and clean off the overfloaded permatex with acetone. Make sure you have all 4 o-rings under cam holders. They must be a little bit thicker then the indents for them so they can seal well.
One important thing before is to remove the 2 oil orifices, blow the holes clean and clean the small alu orifices too. Good idea to save them safe before leaving head at a chop. They will fly if you blow head clean without removing them.
I heard one bouncing around in my garage once. (I have been careful for weeks, finally forgot I had mounted them and blew one extra.... I could recall all bumps against walls and finally find it. This scared me enough to order a set direct I saw one for OK money so I have next time I make a mistake.
This reminded me that I have a fresh refurbished ported k1-k2 head in need of at least 10 inserts. All cam holders plus more. One cam holder thread is an old bolt drilled and threaded M5. Probably a fight to remove. I think I'll used the drill direct, hopefully Ok with std time sert. Probably big sert needed.
Be careful with the cam holder threads when repair. Do not drill too deep and go thru to the head causing future oil leaks. I drill alu M6 thread by hand, thread tap holder. Worst case a short drill not possible to drill too deep.
