more on tapping aluminum
more on tapping aluminum
(OP)
I read a recent thread on tapping aluminum with interest, but have some questions on the subject regarding a current project. I have an aluminum intake manifold from a Dodge Stratus which bolts to an aluminum lower intake manifold. One of the 6 bolts was broken off in the hole, and the owner's attempt to drill out the bolt and retap the hole were not successful. In addition, one of the other holes is stripped, and will not hold a bolt. I am considering drilling out both holes for a larger diameter bolt. The existing holes were originally treaded for a #8 x 1.25 metric bolt, but the hole that is stripped now allows the bolt to slide through without even threading; the attempt to drill and retap the other hole left it a bit wallowed out and slightly out of round. In order to avoid purchasing a metric tap, I am considering using a 3/8" SAE tap, but would like to know if, in the opinion of those with more experience tapping aluminum, that size hole would be sufficiently large to provide enough threading given the existing #8 metric hole size. If so, I would also appreciate recomendations as to which would work better in aluminum; a coarse (20tpi) thread or a finer (28tpi) thread? Finally, what size hole would you recommend I drill for tapping a 3/8"x 20 or 28 tpi hole in aluminium. The hole I will be drilling will be approximately 7/16" deep; one hole being a through hole, and the other a bottomed hole. The threads will need to be strong enough to stand up to the manifold being torqued to the recommended 160 inch pounds.
In reading the previous post on tapping aluminum, several people recommended using helicoils or keyserts. I am not sure if these would be a better option in this case, but when I looked up the instructions for installing keyserts on line, I was not clear how they would be an improvement, since they still require tapping a new hole in the aluminum.
Thanks in advance for your suggestions
carpenterson
In reading the previous post on tapping aluminum, several people recommended using helicoils or keyserts. I am not sure if these would be a better option in this case, but when I looked up the instructions for installing keyserts on line, I was not clear how they would be an improvement, since they still require tapping a new hole in the aluminum.
Thanks in advance for your suggestions
carpenterson





RE: more on tapping aluminum
KENAT, probably the least qualified checker you'll ever meet...
RE: more on tapping aluminum
3/8 fine is 24tpi -recommended drill dia. is .332"
You're probably already too big for coarse, fine thread would be better anyway.
i don't know off hand about the torque values, but if the 8mm was good for 160 in/lbs you should be fine.
RE: more on tapping aluminum
SECOND do you have to tap the hole - can you use a bolt and nut?
THIRD If it were mine I would keep all fasteners the same ie metric. I do enough of that metric versus SAE at work (carry full set of tools for each) and get tired of that fiasco.
FOURTH Get a good tap and pilot drill chart.
FIFTH Heli coil and other type inserts are a LAST option. They are a good option when NOTHING else can be done. They are not foolproof and like anything else break or wear out. When that happens you often end up scrapping unless you are able to build up by welding.
Dan Bentler
RE: more on tapping aluminum
So if you are going to use a UN thread, I would suggest a 3/8"-16 UNC.
Taking the science out of rocket science...One step at a time.
RE: more on tapping aluminum
Another option would be to just buy a used lower manifold. You didn't mention what year or engine size your car was but I looked on www.car-part.com and they have used lower manifolds for Dodge Stratuses starting at $30. Throw in another $20-30 for gaskets and you're done, no worrying about having enough meat around the new threads, cracking the boss on the upper intake manifold when you tighten the bolt down because drilling out the clearance hole to accomodate the larger bolt weakened the boss too much, or opening up the hole in the gasket to accomodate the larger bolt decreased the sealing surface enought to create a leak path (doubtful, but you never know).
Bob
RE: more on tapping aluminum
-Derek
RE: more on tapping aluminum
KENAT, probably the least qualified checker you'll ever meet...
RE: more on tapping aluminum
There are thick walled thread repair inserts that are useful when attempts to remove seized bolts go bad, or when you make something for Northropp Grumman or the US Navy, who pretty much demand fasteners not be threaded directly into aluminum.
h
I'd try to repair it back to metric.
Those used manifolds might be the best solution.