Head Bolt Sizes

[topfuel83]

I'm getting ready to do some top end work (replacing some cracked pistons). I bought new Fel-pro head bolts. Last night i went to see if my deep 1/2" 12pt socket worked with the studs on the new head bolts and discovered something interesting. A 1/2" 12 pt socket did not fit on the new head bolts (socket too small), though a 13mm 12 pt fit great. The threads appear to be 1/2"-13 SAE. Fel-Pro lists the bolt heads as 1/2" 12 pt. for a socket size. Most people talk about the head bolts needing a 1/2" 12 pt socket, but I have seen some information on using a 13mm 12 point that fits better. Anyone ever pay any attention to what's going on here? Seems very strange to have a metric socket head on a SAE bolt.

 

[Apparition]

I'm ge

Hi ge

 

[topfuel83]

Hi ge

Stupid fat fingers on my phone!

 

[macleanflood]

I didn't pay any attention to those details when I replaced the head gasket and head bolts on my friends 04 WJ 4.0.

I did pay attention to which ones need sealant, the order and torque values.

I did add copper coat to the Felpro head gasket to make up for my lack of getting the head and block decked. The FSM doesn't call for that.

-Mac

 

[topfuel83]

Well, I guess I'll find out if they sent the correct head bolts (part number is correct) tomorrow when I remove the head.

 

[topfuel83]

Got the head off today. The factory head bolts were definitely 1/2" 12 point. 13mm fit a little loose. Fel-Pro did something funny with their head bolts as 1/2" 100% doesn't work, but 13mm fits perfect. I'll have to double verify the threads are SAE 1/2"-13 and not metric. Don't want to mess up the block.

 

[macleanflood]

Pictures!

-Mac

 

[topfuel83]

I'll start a new thread and get some pictures up later. Replacing pistons, rings, and rod bearings due to piston noise that was getting worse.

 

[topfuel83]

So just an update on the Fel-Pro head bolt kit for the 4.0. So strange enough, the socket head is 12 point 13mm, despite Fel-Pro saying it's 1/2" just like the factory head bolts. To install these heads bolts you will need a 12 point 13mm deep socket that is wide enough to allow a 7/16" stud to pass through on the inside (as a 1/2" socket won't fit).

Thankfully, despite the bolt head being metric, the threads are all correct SAE (1/2-13 for the block).

I did end up having to buy a 2nd head bolt set, as my 1st one was factory defective with messed up threads on some of the bolts. So watch out for that if the bolt is not threading in easily.