exhaust manifold bolt size

[izzy_Britton]

I hate starting new threads for what should be seemingly easy info to locate, however, for more than an hour i have googled and searched this forum and i am unable to find the specifics i am looking for. any help would be greatly appreciated.

So i have been working on my wifes truck, I have the heads off the engine doing lifters and head gaskets. upon cleaning up the heads to get all the gunk and buildup off of them i noticed that the PO had an issue with a busted exhaust manifold bolt or bolts. after removing two busted bolts on the right side head, i noticed that one of the left side (the left rear) bolts had previously been extracted. apparently the person doing the extrication had difficulties because he missed the mark and drilled the hole oblong. the bolt is out, but the hole was oversized. I figured i could drill it out and do a heli-coil in it.

well i stopped off at NAPA (140 miles from home and shop) and after a short argument about the size of the exhaust bolts, the counter guy looked it up and sure enough i was wrong and the bolts are 10x1.5 mm. I bought the heli-coil kit and when i got to the shop i drilled, tapped and heli-coiled the new hole....

as you may have guessed i was RIGHT and the darn bolt was 8x1.25 not 10x1.5...

so now i have ONE oversized exhaust bolt hole.

NOW i am trying to locate the specific size of the stock or standard bolts, specifically the length of the part under the head, so that i can locate a 10mm bolt to fit the new hole wilst using as much thread as possible in the hole but without the need for extra washers.

see my pickle? anyone got a clue here? i would really like to buy a bolt asap so i can slam this biotch back together before the weekend arrives.

thanks in advance.

_izzy

[mongocanfly]

Mine are 8x1.25....25mm underhead length..since you've already drilled tapped and helicoiled the hole there's no need for your bolt to be any longer than the helicoil length and manifold and gasket thickness combined...make sure your bolt doesnt bottom out in the drilled hole....we were taught rule of thumb is a minimum of 3/4 of bolt diameter is all the thread you need...more is always better..

[DjS71]

According to ARP's website, the replacements they sell are 25mm (.984") UHL for a 1/4" flange and 30mm (1.181") UHL for a 3/8" flange

[izzy_Britton]

25mm (.984") UHL for a 1/4" flange

exactly the info i was looking for. i kept seeing the UHL note but it was not hitting home that this is what i needed to know. i couldnt for the life ofme figure out what UHL meant even tho i knew i was looking for under head length...

thanks for the info. I needed to buy ONE bolt to mend the issue... but i could only find a 25 pc minimum... extras.. so that equates to one bolt needed, equals $30. and a drawer full of stuff. either way its ordered, i can thread that bolt when it gets here and in the mean time i can get the rest of the truck assembled around it.

-Izzy