head bolt help
 

Been working on a project to add Vintage Air to my 61. At least on days the garage gets warm enough to inspire ambition. Anyway, my approach to this project uses an original 61/62 AC compressor mount. That requires changing two head bolts to longer bolts. My front corner head bolt came out but I can't get the new bolt to thread in. Just won't engage the first thread and pull itself in. Like maybe a small piece to gasket is stopping it. I have tried three different bolts, one old, some new. Nothing gets them to start in the thread. I have blown out the hole several times with air. I have reinserted the original bolt several times and it will go in and torque down. All bolts thread nicely on a tall 1/2-13 nut I used for testing. All will allow a die to go on full thread length. I have a tap but it is so short I am about to loose it in the hole. I can get long taps but McMaster Carr wants $50-80 per tap. There may be cheaper ones around but I haven't done a search yet.

Anyone have an idea that will save me from pulling a head. Dang those 3x2 manifolds are heavy while leaning out over a fender.

Just an idea....
Maybe cut threads 1/2 - 13 threads on a long rod so you can check thread engagement. When it bottoms you can then mark the length needed for the longer bolts you need or cut that to length and cut threads for a nut and use it as a stud?

I have run into a few situations like that. Those long gun taps are very expensive as you mentioned. For a 1/2"-13 tap, I would consider buying a regular tap and and buying a cheap 6" long 1/4" drive extension and welding them together. I have a drawer full of weird homemade tools. No 1/2" long tap unfortunately.

If the old one will still go in .... I'd make a real close comparison between the one that will thread in, and the ones that won't ... has to be some difference there.

If you removed both old bolts ... will the one from the other hole screw into the problem hole?

Might not be your issue ...but when I've had that happen it was usually the threads on the very end of the bolt rolled over a bit. The "class" fit of the head bolt and hole is probably a tighter spec than the nut you are using, that's why the nut will screw on all the bolts.

I would go with the welded extension to tap deal.

I know what you mean about heavy Manifolds and such, the few times I had to lift the 671 blower off of my car by myself I had to pull the hood off and stand on top of the firewall and rear of the motor!

The market is ripe for someone to design an engine component lift. Like a hydraulic engine lift except of course much less robust. Capacity of maybe 300 lbs. Something folds up and rolls into a corner. With the lower weights it could use a small electric winch or a simple hand crank boat winch instead of hydraulics.

I'll build one for $1000 if anyone wants one :)

New bolts factory bolts or hardware store?

On non factory bolts the threads and shank could be a hair bigger than factory bolts. If it is...check to see if the front exhaust manifold bolt is sticking out in the head bolt hole.

That make sense?
Clay

Hey Quick-Silver - you the man. I had forgotten that that front exhaust bolt went into the head bold hole. I think I once knew that but had forgotten. Of course my original generator mount had a plate mounted on the two front exhaust bolts. After taking that mount off the bolt went into the head bolt hole just far enough to be an interference. I'll just get a shorter bolt. I know I have one here in my stash of old left over parts.

The simplest damn things that can get over looked. I sure didn't want to pull that head. And it wouldn't have shown me anything anyway. Thanks.

i would thnk about the tap deal plenty before going that route,, regular taps are for cutting and removing metal,, once u do that cant put it back !!!! they do make real chasing taps, that just clean out the hole with no metal removal..these longer bolts u have grade 5 or 8?? asian made hardware store crap?

Not a regular taper tap, but a bottom tap!
Such will not remove any meat until the getting to the bottom of the hole, and since the head bolt holes and main holes ARE bottom taped from the factory all will be fine!

Bottoming taps
 

bottoming taps dont remove metal till they hit the bottom of hole ???? BULL,, i have been a machinist since 1979 and in all my experience they DO remove metal gettin to the bottom of a hole.,the cutting flutes on a bottoming tap are NOT reduced in size,from the 2 or 3 flutes at the bottom of tap,and will do some cutting on the way down to the bottom of hole,,bottoming taps are rarley used and will be sharper than a used but good cond tap,and so thats why they cut some getting to bottom of hole..and u say ALL head bolt and main holes are bottom tapped..really ,,just how do u know this ??? u worked in a pontiac engine plant back in the day and examined these taps your self ?? ever section a broken block up and verified this "fact" for your self ?? u get a big flashight and look in a hole an think u see threads at the bottom of hole ?? i dont know either way,but i have never heard about it on this board, and have not seen pics to verify it either,,not that it matters,,i doubt Generous Motors would use bottoming taps,would cost more,would require another secondary machining step on the engine block machining line,and is not really required at least on the head bolts,,they just add more material in the casting and use regular taper taps which dont require a lot of torque to get the tap started which a bottoming tap would if the hole was just drilled and then u try to put the bottoming tap in.. thats why bottoming taps require threads already in a hole, is the torque requirments are too high to start hole threads and continue cutting till bottom of hole is reached,but then u cant tell when that has happened because of the exxessive torque and u wind up breaking the bottoming tap..hence this is why bottoming taps are only used in most materials as a secondary operation to put more threads at the bottom of a hole ,and only when needed, manufactures are not going to do anything not needed..