Hi Everyone and Happy St. Patrick's day.

I've searched but was unable to find an accurate size for these fasteners. I want to make sure that I have the proper hex socket wrench before I begin the valve seal replacement job.

Thanks for your help in advance!

The head does not need to be removed to replace valve seals. There were two types of bolt heads, internal hex or triple square. You may be able to see a few bolts from outside the valve cover to tell which type your car used.

Good luck!!!

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thanks for the reply.

I of course will not be removing the head, rather I am looking for the hex size for the bolts that mount the rocker assemblies to the head.

8mm.

If you do not have a service manual,please read some threads on the topic (almost everything has been discussed) :

https://www.google.com/search?q=valve+stem+seals++site:https://www.peachparts.com/shopforum/diesel-discussion&safe=images&hl=en-US&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjHxLKC7-T9AhUej4kEHfgRAkQQ0pQJegQIAxAC&biw=1920&bih=955&dpr=1

https://www.google.com/search?q=rocker+tower++site%3Ahttps%3A%2F%2Fwww.peachparts.com%2Fshopforum%2Fdiesel-discussion&tbm=isch&ved=2ahUKEwjhg_GG7-T9AhV3KN4AHZyQCE4Q2-cCegQIABAA&oq=rocker+tower++site%3Ahttps%3A%2F%2Fwww.peachparts.com%2Fshopforum%2Fdiesel-discussion&gs_lcp=CgNpbWcQA1CHFFjeRWCESGgBcAB4AIABeogB2QeSAQQxMi4ymAEAoAEBqgELZ3dzLXdpei1pbWfAAQE&sclient=img&ei=YVwVZKHPFPfQ-LYPnKGi8AQ&bih=955&biw=1920&safe=images&hl=en-US

https://www.google.com/search?q=valve+adjustment++site%3Ahttps%3A%2F%2Fwww.peachparts.com%2Fshopforum%2Fdiesel-discussion&tbm=isch&ved=2ahUKEwjM89nM7-T9AhXEE94AHR5cAi0Q2-cCegQIABAA&oq=valve+adjustment++site%3Ahttps%3A%2F%2Fwww.peachparts.com%2Fshopforum%2Fdiesel-discussion&gs_lcp=CgNpbWcQA1DsIFijPGDRQmgAcAB4AIABRIgBiAiSAQIxN5gBAKABAaoBC2d3cy13aXotaW1nwAEB&sclient=img&ei=81wVZIyuLsSn-LYPnriJ6AI&bih=955&biw=1920&safe=images&hl=en-US

...and do not forget to remove the oil from the towers' bolt holes in the cylinder head before reassembly.

Thanks all! Sorry for the late reply too much on the brain.

I picked up an 8mm hex head socket and will be doing the job hopefully soon. Does anyone happen to have the specific torque for these bolts?

OM617 Torque Values Rocker Arm

Also make sure the rocker arms not stressed by the cam lobes on R&R :
https://www.youtube.com/watch?v=O2T82oEFQ2I

And make sure the centering sleeves for the towers are all present and in good condition.
OM617 rocker arm problem?

Good luck !