Packard Forum Index » Post-War (1946-54)

Hello everyone,

After putting the head back on my 359 one of the headstuds gave it up and began te come loose... did not make it to 60-62 ft... so i need to repair the threads in the block. Now my question is what is the size of the bolt/treads for what i could find it is 7/16 and 20 someting? The 20 stands for the threadwind? Course or fine? And is 7/16 20 correct ? There are a lot of helicoil sets with diffrent sizes.
Thanks👌🏻

You have an extra post with this question so I would suggest you delete the other one so answers don't get posted on both and something pertinent be lost as one or the other posts sort of get buried on the site.

7/16-20 is the correct designation and the 20 stands for 20 threads per inch or the US standard for fine threads in a 7/16 diameter fastener. Coarse thread spec would be 7/16-14. There is a wrinkle in the thread going into the block though and I really don't know for sure what anyone else has done.

In late 47 and in all engines thru 54 Packard went to what is called a rolled thread on the end of the stud going into the block in order to cut down on water seepage around the threads. From what they say in their article announcing the change, the rolled thread is incompatible with a typical cut thread hole. I do know in an older block trying to install a rolled thread into a cut thread hole causes a problem and sometimes the stud starts binding so tightly you think it will break. In 48 Packard made available a special rolled thread tap but I don't know if there is or ever was a rolled thread helicoil type repair. I suspect there might be enough give in the ordinary helicoil that it can overcome the difference since it has been mentioned as being used before but that is the big question.

Hopefully you will get Ross or one of the other good engine guys to see your post and have an answer as to what they have done for the repairs. I am sure being in the Netherlands may make the situation worse in quickly trying to find something that will work.

I'm just here to say that I so appreciate HH56's replies! Thorough and factual!