Set Screw Holes Stripped in Aluminum Head, Need Adice!

Perhaps rather than worrying about going to a larger thread size, just drill and tap for 7mm helicoils, and use the original stud. There are 7mm kits out there, here's one on ebay: Helicoil 5546 7 Thread Repair Kit 7mm x 1 00 | eBay but you may want a longer insert for better pullout resistance in the head. I'd be tempted to use a high-heat threadlocker when installing the inserts and studs, then use a good anti-seize on the nuts when reassembling.

Getting M9 studs is not easy, M8 will be easily avalible. All depends on how deep you can go, drill the M7 out to 6.8mm which is std tapping size will still leave some thread but don't sweat it, if the final tapped hole can end up at least 2 diameters deep chances are it will hold just fine. Ruff rule of thumb, in steel with a std 8.8 grade bolt 1.25-1.5 diameters deep is sufficient thread to shear the bolt before the thread will fail and thats at only typical tapping drill % of engagement. Allow abit more depth for a larger tap drill and things should be fine.

how would the hole left behind the m7 thread be 8 mm? you will have 7 mm instead of 6.8 mm, which is not too bad.

When this happens at my shop, it gets the next best fitting size be it standard or metric.

The engine wont know it has one different size bolt or stud in it.

dont overthink it, if u run into a water jacket put thread sealer on it and continue on.

is this on a modular ford (4.6,5.4)v8?

Look at Timeserts. It's a solid insert and it uses the Helicoil thread on the OD

Yes if you are going up one size, you should drill with the proper tap drill, But, going up just one size
will leave some of the old thread. Perhaps not much as you say they are stripped. It would probably work, but if possible a better repair would be using inserts. That way you jump to several sizes larger and will have a steel thread instead of the aluminum so it will last much longer.

I am not over thinking it like roll-a-leblond suggested, I just wanted an answer to 1 question, and was corious about a few other things, since I just learned everything I was talking about. The one question was, " if you want the best strength out of your threads, should you always remove all old threads before tapping, or will the .75mm or .125mm of threads left behind completely not mess with the new threads strength. The only part I'm over thinking is; with this much room,
View attachment 136716
I should just go with the M10, and not have to worry. But, I want to take the least amount of material, not do what you guys do. (I couldn't think of a nicer way to say that) I just need the answer to the question about the threads. I wrote all of that, because on forums, people seem to want more info than the actual question. Everything else I asked, was just curiosity, since my knowledge in this is new.

Milland said:

Perhaps rather than worrying about going to a larger thread size, just drill and tap for 7mm helicoils, and use the original stud. There are 7mm kits out there, here's one on ebay: Helicoil 5546 7 Thread Repair Kit 7mm x 1 00 | eBay but you may want a longer insert for better pullout resistance in the head. I'd be tempted to use a high-heat threadlocker when installing the inserts and studs, then use a good anti-seize on the nuts when reassembling.

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If I was tapping for a thermostat bracket, or something of that sort, I would use these, but I do not want to use "something" for this, I want to make it "original" so to say. Plus, the coils only cover 10.5 mm, I need at least 25-28mm long.

adama said:

Getting M9 studs is not easy, M8 will be easily avalible. All depends on how deep you can go, drill the M7 out to 6.8mm which is std tapping size will still leave some thread but don't sweat it, if the final tapped hole can end up at least 2 diameters deep chances are it will hold just fine. Ruff rule of thumb, in steel with a std 8.8 grade bolt 1.25-1.5 diameters deep is sufficient thread to shear the bolt before the thread will fail and thats at only typical tapping drill % of engagement. Allow abit more depth for a larger tap drill and things should be fine.

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I'm not looking for a don't sweat it situation, I want to do it to the point, when I screw in these exhaust studs, know that the old threads left behind, because of pitch difference, are not going right through the new threads that I want to be as strong as they can. This is also aluminum, if this was steel, I would just tap up to next size and not even worry about the threads in the hole, I'd be worried about the threads on the bolt, the hole it's steel.

dian said:

how would the hole left behind the m7 thread be 8 mm? you will have 7 mm instead of 6.8 mm, which is not too bad.

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I explained it in the OP, but this will help.
View attachment 136719
When you buy a M7 (7mm) bolt, The 7mm is the (Pitch Diameter), the (Major Diameter) will be 8mm. 6mm dill bit + 1mm pitch on EACH SIDE of the bolt = 8mm (Major Diameter) The M8 requires a 6.75mm drill bit. 8mm hole - 6.75mm = 1.25mm of threads left behind. 1.25mm divided by 2 (EACH SIDE OF HOLE/BOLT) (actually my math was wrong in OP) it's not .75mm of threads left on each side, 1.25 divide by 2 = .625. if I go M9, it requires a 7.75mm drill bit, leaving .25 of threads behind. .25mm devided by 2 =.125, but M9x1.25x39 set crews are kind of hard to come by. That's where my question comes in, will .625mm's of 1mm pitch threads, get in the way of the new threads that are 1.25mm pitch. Will the groove for the 1mm threads and the 1.25 threads cross at some point, in a 25-28mm hole. If they do cross, where the tap & die sets made to the point were the cross wont matter, or is there some rule of thumb that says, always remove all old threads, leaving me to use the M10.

roll-a-leblond said:

When this happens at my shop, it gets the next best fitting size be it standard or metric.

The engine wont know it has one different size bolt or stud in it.

dont overthink it, if u run into a water jacket put thread sealer on it and continue on.

is this on a modular ford (4.6,5.4)v8?

Click to expand...

That's what I want to do, I want to use the M8, but the threads (like i explained before your quote) have to cross at some point; The pitch is different, and with an aluminum head, I'm not cool with that. I see where if I was to just go to the next size, like you have done, it will hold for a while, but I don't want to put my faith in that, until someone says for sure, the old threads will not matter; not that they shouldn't matter, or don't sweat it.

Also, it's an 02 BMW 325i.

Larry Dickman said:

Look at Timeserts. It's a solid insert and it uses the Helicoil thread on the OD

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A bunch of people on BimmerForum, suggested time-serts, but didn't know how much material can be removed before it's to much. So I watched a video, of someone using a time-sert on a BMW head bolt hole. The first thing I noticed was the amount of material that has to be removed to get the time-sert in. Granted it was a 10mm hole, but whether it's 7mm or 10mm, it will be proportionate to the size, there will be a decent amount of material removed. Another thing I noticed was, like heli-coils, the time-serts are short, and I need/want at least 25-28mm of good and/or new threads. I just went to Time-Serts website, and seen they have many time-serts in many lengths; That honestly seems perfect for what I want, but to completely remove all threads left behind by the 7mm, I would have to tap all the way up to M10, The Major Diameter will be 11.5mm. If I can use a 7mm time-sert, and it takes less than the M10-11.5mm of material, then I will probably use them. So I need to find out what the Major diameter of an m7 time-sert is. I just sent Time-sert a messgae asking them.





Thanks for the replies!

Go somewhere and learn thread terminology since you're totally clueless at this point. You've gotten some good responses but you're too ignorant of the details to realize it.

In the meantime, measure the major diameter of the next thousand M7 bolts or studs you encounter, and report back on how many of them are 8mm.

If your objective is to repair stripped M7 threads in an aluminum head, install M7 inserts. Time-Serts look like a very good option and have been recommended above. Many other insert types are available.

If your objective is to install M8 studs, and you can get 1.5D thread engagement without breaking into a water jacket (or worse), you will probably be OK with the imperfect thread form. I suppose that you'll have to drill the mating manifold to clear the larger studs and there's always plenty of clearance for the larger nuts too. Right?

AND there is a vast difference between a "setscrew" and a stud.

tdmidget said:

AND there is a vast difference between a "setscrew" and a stud.

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If you put a slot into the end of a stud, does it become a set screw??? If its threaded full length?
Or is a stud only threaded on the ends? But what about short studs that are threaded full length?


A few years back I needed some grade 5 or 8, 5/8" studs and I needed them yesterday..
Nobody had them, then somebody clued me in that the first place I had called
carried grade 5 threaded rod... So I called and asked for a grade 5 3 foot long stud,
they didn't have it, so I asked if they had grade 5 threaded rod... "we have that"...
... 2 hours of my life I'll never get back, and it was a place that
sold nothing but fasteners..

When you buy a M7 (7mm) bolt, The 7mm is the (Pitch Diameter), the (Major Diameter) will be 8mm.

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I think you need to brush up on thread terminology... A 7mm external thread has a major diameter of 6.974-6.794mm and pitch diameter of 6.324-6.212mm.

My take.... I'd rather have an insert of any kind in aluminum.. You then have steel to steel on your fastener, so you stand
a chance of getting it out somewhere in the future.. Leave all that galvanic corrosion crap in place between the insert and
head so you don't have to deal with it.. You also get the added benefit of a stronger (bigger) thread in the aluminum (weak half).

As for helicoils not being long enough, you can stack them.. Wind your first one in, break the tang or not depending on how long
your set screw/stud/threaded rod/cut off bolt is. Then wind in another one, and break the tang, then another if you need to..
You can shorten the helicoils also with a pair of dykes (good ones) or a cut off wheel. Then your threaded fastener of choice just
threads right on in...

m7 x 1mm?
never seen that one on a european car

exhaust studs are mostly m8

m9?
never seen that either as a standard in use

First of all, I'm not tapping my head anymore. I Figured out that the time-serts are not as big as I thought for 7mm. So, I'm just going to buy 16, and do it to all of them, buy new STUDS and nuts and be done. BUT

I would like to say, you guys are use to people coming on here and thinking they know what they are talking about, and their wrong. I said in my original post, if something I said was wrong, please tell me; so, you don't have to be condescending a-holes. I said I may be wrong, but (like religious people) if you do not provide evidence that I'm wrong, and/or how you are right, you could be just as wrong as I am. I had all this math and all this ""knowledge"" (that I thought was right) in my OP, I would obviously need math and knowledge, to be proven wrong. None of your answers were explaining why I'm wrong, just that I was. Then, I get on here a second time, saying all this wrong stuff again, and still no proof that I was wrong, just people telling me I am. So, I went to find what the problem was. Why I was saying things, and knew I was right, but everyone was saying I was wrong? I do my research, and did some more, and I found some interesting things. I was wrong in a few ways, but it's not my fault and I will explain.

Like I said, I was new, and I had my terminology right, but upside down because I just kept referencing the wrong thing; the bolt instead of the hole. If you read my first two post, and realize, everything I was talking about, was the hole. Which I though was strongly implied, being that I was talking about drilling out THREADS, I did keep saying bolt. So, everything I said about the bolt was wrong, but I was actually talking about the hole, and my math would be right then; kind of.

From what I have figured out, without the maker of the Tap & Dies that you are using, actually telling you the dimensions of the tap & die, you can never really know the true dimensions of a hole. Unless you can, I don't know? Before I came here, I said I took a ten minute crash course on threads and drill bit tapping sizes. I only looked at one threads terms picture, and one drill bit chart, because that's all you should have to look at. If there's this system out for threads that is universal, except for the American & Metric thing, every bolt and hole should be the same down to the hundredths, maybe not the thousandths, but, it's worse than that. A 7mm bolt can be up to .206mm smaller than 7mm, that's over 2 tenths off.

At this point; I was looking at a drill bit size for tapping chart (and should only have to look at one) and that's where I got the 6.75mm drill bit. I also was under the impression that there is .5mm of space between the crest of the bolt to the root of the holes threads (don't know where I got that knowledge) Anyways, As I was writing all of my previous post, I didn't realize how confuse I still was. Like I said, I do understand threads and the math but I really messed myself up by trying to learn about threaded holes, by obtaining thread info on bolts.

From this point on I'm going to leave my past mistakes behind, SORRY ALL, and talk about what more I learned about threads, and I'm pretty sure, I'mright this time.

As someone already said, A 7mm bolt's major diameter can be 6.794 - 6.974mm; it's not even 7mm.

The problem that exist, to the point that, people may be able to say .75mm of threads left behind will or won't matter, but there's almost no way to get the numbers to actually know if there will be .75mm of threads left behind; unless you get the actual dimensions of the tap and drill bit used to make the hole.

I have looked at 5-6 drill bit size for tapping charts, and they seem to never be the same. I've seen different drill bits to use to drill a hole to accept an M7, 6mm, 6.1mm, 6.4mm, 6.5mm, 6.75mm.

You have a hole with threads, and need to tap it. so you look at a chart for a drill bit size, and you see 6.4mm drill bit for a hole that accepts a 7mm bolt. The 7mm bolt is actually 6.794-6.974. then you think, the drill bit used to tap the hole was 6.4mm. The 7mm bolt has 1mm threads, so that means , the tap wil have 1mm threads. You take 6.4mm plus 1mm threads on both sides, you get 8.4mm. That says that the hole will be 8.4mm from root to root or crest to crest (not sure where the root is in the hole) You take (the biggest part of the hole)8.4mm, minus (the biggest part of the bolt) 6.974 and you get 1.42mm. Now you divide 1.42 by 2 (since threads are on each side of the hole) and get .713mm. That would mean that, on average, at any point in the hole, there would be.713mm of space between the crest of the bolt to the root of the hole.

Then again, what if the tap and die set you have, suggest a 6.1mm drill bit. That would mean that , when you tap a hole with it the major diameter of the hole would be 6.1mm + 1mm + 1mm = 8.1mm. 8.1-6.974mm=1.126mm. 1.126mm divided by 2= .563mm. So in this hole, the space between the crest of the bolt and root of the hole would be .563mm.

Now let say you have that same tap and die set that suggest a 6.1mm drill bit, but drill out the hole according to the chart on the internet, 6.4mm. That means the threads would only be .7mm thick and not the 1mm they should be. the threads in the hole would just be missing the tips and be just as strong, but the threads on the bolt will be holding on with only the very tips of the threads, since the hole is missing .3mm of it's threads.

I just thought of something. Obviously, if you are using a tap set that suggest a 6.1mm drill bit, that means the hole will end up having major diameter of 8.1mm. If they suggest a drill bit, that means that's the biggest you can use. If you go any bigger, you will not get the full 1mm of threads in the hole. By that theory, if there are many different drill bit sizes suggested, by different makers, that means a hole can vary in many sizes. If you have a tap set, all you would have to do, is mic the tap you have, and subtract 2mm. for the threads, and that's the drill bit you should use for that tap. Of course, all of this is based off of 1mm threads, the math would be different with different size threads.

Sorry all, on the other hand; I pretty sure I understand this time. I still don't actually know if, you are changing pitch, should you always remove all old threads. Meaning if you change pitch sizes, you would at least have to tap up 2 sizes to remove almost all old threads. But I'm over it, I'm using time-serts anyways. But, If I am still misunderstanding things, please let me know, and back your claim up, so I can believe you are right. Thank You.

tdmidget said:

AND there is a vast difference between a "setscrew" and a stud.

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Saying there is a vast difference between a set screw and a stud, is like saying there's a vast difference between a Suburban and a SUV. Or there's a vast difference between cake and junk food.

The definition of stud is, a large-headed piece of metal that pierces and projects from a surface.

So when you have a set screw in your hand, it's a set screw, but when you screw it into something, it's a stud. Once it's installed, it's almost more a studs than a set screw.

janvanruth said:

m7 x 1mm?
never seen that one on a european car

exhaust studs are mostly m8

m9?
never seen that either as a standard in use

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I keep on getting asked this question by many people, and everytime I recheck, I always find m7x1x39.

So please, if you find somewhere that it's not an M7, let me know. I am under the strong belief it's an M7, but if it's not, I do need to know.

To help prove it:

RealOEM.com   BMW E46 325i Cylinder Head

NWOrphan said:

Saying there is a vast difference between a set screw and a stud, is like saying there's a vast difference between a Suburban and a SUV. Or there's a vast difference between cake and junk food.

The definition of stud is, a large-headed piece of metal that pierces and projects from a surface.

So when you have a set screw in your hand, it's a set screw, but when you screw it into something, it's a stud. Once it's installed, it's almost more a studs than a set screw.

Click to expand...

No, you are wrong.

NWOrphan said:

The definition of stud is, a large-headed piece of metal that pierces and projects from a surface.

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Studs, by definition, have no head.

NWOrphan said:

The definition of stud is, a large-headed piece of metal that pierces and projects from a surface.

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Perhaps, you meant "threaded" ?

NWOrphan said:

So when you have a set screw in your hand, it's a set screw, but when you screw it into something, it's a stud. Once it's installed, it's almost more a studs than a set screw.

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NO.

Set screws rarely "project from a surface", and usually remain flush or below the hole they are threaded into.

Set screws never use nuts, whereas studs always do.

Set screws put compressive force on another component to lock it into place;

Studs are in tension to clamp two components together.

Im sure there are some rare exceptions to these rules, but any exhaust manifold held on by set screws wouldn't last long.

NWOrphan,

I gave up reading #14 after the first paragraph. I don't give a damn why you were/are wrong. Certainly, I don't care enough to try to make sense out of your explanations. Blah, Blah, Blah!

You defined the issue, not very well, but it was your thread. You got quite a few legitimate replies with constructive recommendations. Be satisfied with that. Whining because nobody held your hand while attempting to unravel the knot of a mess that you posted is a waste of time. You will be able to get better answers when you learn to ask better questions. Do your research first. Learn the correct nomenclature for your subject. Then post your question. Doing a post mortem at this point is of no interest.

janvanruth said:

m9?
never seen that either as a standard in use

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Top of the strut towers on the old Datsun Z's.... Only place I've ever seen them.

Changing my struts one time I lost 2 of them... I never knew you couldn't buy them ANYWHERE....

Everytime I hit the junkyard after that, I always swiped all the 9mm nuts off the strut towers,
I ended up with a bag of them.

NWOrphan said:

Before I came here, I said I took a ten minute crash course on threads and drill bit tapping sizes.

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I guess you should have signed up to the 20 minute course then if you wanted to start your posts on this forum by calling the very experienced people who are trying to help you "condescending a-holes"

In the meanwhile, most of us "a-holes" would have run an insert of the flavour we like best into the aluminium, thereby doing the job correctly with a high probability that the STUD could be removed in future should it need to be, instead of some bodge job tapping it oversize and either stripping or breaking it a second time.

However your milage is clearly different so I'm off to park in a handicapped space.