I'm trying to wrap up my new cylinder head installation, and it hit me that I never found the infamous long allen head bolt that runs through the lower intake. It's one of several things I've found wrong or missing from when the previous owner had the engine rebuilt. I read in a past thread to replace the allen head bolt with a hex head, but I have nothing to copy the specs from since the bolt was never reused. I'm guessing it's the same 8mm thread as the rest of the intake bolts, but don't know the length. Also, does anybody know the inside diameter of the o-ring used in the connection of the lower intake and coolant tube? Thanks for the help.

 

I'm confused about the allen bolt. Is it missing, or did the previous rebuilder replace it?

I have one. It is 6.8MM in diameter and 95MM long from the end of the threads to the bottom of the allen head, 100MM overall length. It has the same diameter and is threaded like all the other bolts holding the manifold, I can not remember what metric screw pitch it is.

On o rings, they are cheap. Take the tube with you or guess the size and get an extra couple of them smaller and larger from an auto parts store. One will fit.

 

The previous re-builder never replaced it. I never came across the bolt when I disassembled the top end and finally realized it when the time came to put everything back together.

The bolt is metric 8x1.25, the same as the other intake to head bolts. The big box hardware stores near me only carried up to 70mm length in that bolt spec.
Luckily, I had an old quill stem bolt (bicycle) that happened to have the same threads and was plenty long...too long, the threads stopped short of simply cutting it to length. I could have cut new threads, but I didn't have that size dye. All I did was use a tube spacer to make up for the missing threads and cut it to length. It actually worked pretty well, the bolt head was now 1" away from the intake and could be accessed easily. All of that may be hard to picture without a visual, sorry about that.

I was trying to avoid buying several o-rings to find the right one. I've already nickel-and-dimed like crazy over the past week and the parts store is tired of seeing me and my returns. But that's what I had to do in the end...16mm is the correct size for anyone wondering.

 

i just had to remove my intake and when i put it back on to connect that pipe up i just scrounged up an o ring that had a little bit smaller diameter than the pipe itself and i just slipped it ove r and put some rtv sealant on it. doesnt seem to leak though