Auto Parts: 8mm allen hex bolt, 8mm hex, hex bolt

Question
Hello, Mike I have a 1990 Lexus LS400 I doing a timing belt job on it (first time not easy) anyhow I'm having trouble putting back the #1 idler pulley the 8mm bolt wont go back in so I'm thinking when I gave it a hammer to take the bolt out of the old one that i might of messed up the threads but to me they don't look messed up but I tried just putting the bolt by it self and it still doesn't go in. would you know what pitch this 8mm hex bolt would be?

Answer
    No, I don't, but I am sure you messed up the threads.  If you clean the bolt well and look at it real closely you should be able to see where they aren't straight.  A very small file, like a nail file, is perfect for dressing these threads up.  If you really can't find the problem by eye, just file the first thread and half of the second one until they are bright new metal.  A little oil and that should thread in fine.  Toyota is know for their tight tolerances, and this is a case where it's slowing you down to have such a good engine.  If you had to hit it really hard, then you might have to remove the whole first thread to get it start in the hole.  But we know it'll go in, 'cause it came out.