Verry annoying bolt and thread issue

[dufflespank]

Today I finally got around to changing out my injector nozzles on my 603. Changing nozzles is no sweat. My next step was to bolt the intake back on. Every single bolt threads perfectly, except for one. The malevolent bolt will screw in half way before creating a significant amount of resistance; enough to let me know that I'm on the verge of stripping the thread.
I tried another bolt, same issue.
I'm trying to get things up and running for my wvo road trip on Thursday. What it the best way to handle this issue?
Two ideas I have: 1) Create an enormous shim (the bolt goes in about half way before showing any signs of trouble) or 2) Cut the bolt in half. I figure that 25 nM isn't enough pressure to make this idea a bad one. Also, drilling and retapping is way out of my range (of skill and patience). I would like to do this in the easiest way possible.
Your thoughts and advice would be GREATLY appreciated.

[BobK]

Stick a small screwdriver or a long allen wrench down the hole and use it to measure the depth of the hole including manifold and measure against the bolt you are trying to put in there. Be sure you have not mixed up bolts. If you are sure you have the correct bolt and that you aren't forgetting something else that is held on by that bolt (thus being your "shim"), then you should try running a tap down the threads to clear them. A lightly oiled tap will hold the crud that it will remove from the threads. Just be gentle. Should be able to do this with manifold on if need be.

[t walgamuth]

i would suspect dirt in the female part of the threads. i would take a nail and probe the hole, then perhaps a drill or a tap to open it up.

i would not shim or cut the bolt off. this will half the holding power of the bolt and likely result in a failure.

be patient and get the threads cleaned out. some oil and a tap is best i think...then put your bolt in.

good luck

tom w

[rebreath]

Originally Posted by dufflespank

Today I finally got around to changing out my injector nozzles on my 603. Changing nozzles is no sweat. My next step was to bolt the intake back on. Every single bolt threads perfectly, except for one. The malevolent bolt will screw in half way before creating a significant amount of resistance; enough to let me know that I'm on the verge of stripping the thread.
I tried another bolt, same issue.
I'm trying to get things up and running for my wvo road trip on Thursday. What it the best way to handle this issue?
Two ideas I have: 1) Create an enormous shim (the bolt goes in about half way before showing any signs of trouble) or 2) Cut the bolt in half. I figure that 25 nM isn't enough pressure to make this idea a bad one. Also, drilling and retapping is way out of my range (of skill and patience). I would like to do this in the easiest way possible.
Your thoughts and advice would be GREATLY appreciated.

not to sound like a jerk,but did you make sure that the hole is cleaned out of any debris?
Is the bolt showing any sign of damage after being put in to where it sticks?
when you pulled the bolt originally,did anything come out with it.shavings,pieces,crud...anything at all?

[dufflespank]

I initially thought that the female thread would be gunked up, so I sprayed brake cleaner down the hole and then shot some air in. Still no. Also, the bolt shows no signs of damage when pulled out.

Now, if I get a tap which is the same size as the bolt and has the same thread, could I run the tap down the hole and "create" a new thread where the old thread has gone bad? Wouldn't there be a lack of metal once the tap removed the faulty stuff? Do I have this whole concept absolutely wrong?

Thanks so much for the help and suggestions! I'm starting to feel more confident about this.

[jnc19610]

If you have any sence of feel, you can run a tap down the existing hole, and chase out that crud. If you do it right, you won't have any metal shavings, you'll just shave off the crud that is blocking the bolt.

You'll will want a bottoming tap to do this job. They are made a little differnt.

[dufflespank]

Unfortunately, I am entirely inept when it comes to using a tap. Will there be any drilling required? If I push lightly with tap, will it thread with the old hole? Will it create resistance where the threads have gone bad? Do I keep turning the tap even when there is resistance? Will I be able to find the right tap at Home Depot?

Sorry about all the questions. I'm a newb in need.

Also, how would I go about determining the tap size?

[riethoven]

Originally Posted by dufflespank

Unfortunately, I am entirely inept when it comes to using a tap. Will there be any drilling required? If I push lightly with tap, will it thread with the old hole? Will it create resistance where the threads have gone bad? Do I keep turning the tap even when there is resistance? Will I be able to find the right tap at Home Depot?

Sorry about all the questions. I'm a newb in need.

Also, how would I go about determining the tap size?

Something here does not make sense. Logic comes into play. If the bolt came out with no resistance it should go back in with none. As stated in an earlier post, make sure you have the right bolt in the right hole. If the bolt came out OK then there was no crud in the bolt hole when it came out. The only time something could have gotten in there is when everything was apart.

To "clean up" threads that may have a few burrs or a bit of damage you just have to screw an oiled tap that matches the diameter and pitch of the existing threads. This will remove any crud or light damage to the threads. If it was cross threaded, this may not work because the tap will start following the crossed threads and really mess things up. To determine the diameter measure the bolt, to determine the pitch, buy a metric thread gauge. They are cheap - less than $5. My guess is it is a 8mm x 1.25. 1.25 is the thread pitch and it means that the thread goes one revolution around the bolt in 1.25mm. Standard threads go by "threads per inch" or TPI. You should not need a bottoming tap which as it is called is used to tap all the way to the bottom of a hole. Most holes will be deep enough so that a bottoming tap is not needed to accomodate the bolt going in the hole.

[dufflespank]

So should I get a bottomless tap? Or no?

I agree with BobK and Reithoven. Check the depth of the hole first with a skinny screwdriver to check if the hole is deep enough for the bolt. Perhaps some of the bolts are different lengths?? If you don't know anything about tapping a thread you might run the risk of trashing it.

[kip Foss]

I do a lot of this kind of work in my job. Here are a few pointers.

1.) Use common sense. A bolt came out of the hole and one should go back in. As stated above make user that this hole depth is not different from the others or that there is not some thing mounted to the bolt external of the manifold that would take up the extra length of the bolt. If you have to pull out all the other manifold bolts to check that there is not one odd size in the lot it is worth the effort. This in not likely but can happen.

2.) I always run a clean up tap through holes like these that are not used very often and tend to rust inside. BE CAREFUL with a tap, esp., when you are going into a blind (dead end) hole. Taps are very strong but very brittle. I snapped one off in the side of a Diesel generator last month, using what I thought was only moderate pressure. Luckily I was able to get it out with a tap extractor. Lesson one is that you can not drill out a tap. They are made of the same hardness steel of which drills are made. You can get them out with a tool called a tap extractor, if you are real lucky, or one called a spark eroder but it is costly and time consuming. Also you will be doing this work with the engine still in the car while leaning over a fender, which increases the difficulty factor by about 3 times.

Also, if you have to take the car to a machine shop to get the broken tap out they, as nice as they may be, realize that you are over a barrel, or car fender as it were, and will not hesitate to charge you full price plus an 'I gotcha' fee.

I am not trying to scare you away from something that you, as a budding mechanic, should learn, but am only trying to warn you not to go in there like John Wayne. That millisecond between the time that the tap bottoms out and you hear the 'snap' will be one of the most rememberable in your life.

[dufflespank]

So I pulled the intake back out in order to get a closer look at the hole. There is no debris other than a few metal shavings that I must have created when intitally tightening the bolt down. I never actually stripped the threads, but I must have done some damage to them. Can I still get away with just retapping the hole?

Also, I can't figure out if the bolt is 7mm or 8mm. My caliper says it is 7.6, but the thread appears to be 1.0. Does anyone know exactly what kind of bolt it is? Just to reiterate, it is one of twelve bolts that hold the intake manifold down on the 603 engine. Thanks!

[BOMC]

i find oyur problem interesting because i am pulling my intake (for the first time) next week to degunk and change my plugs. now, on inspecting my comming work i noticed on my 603.960 at the very rear of the intake (closest to the windshield) there is a hook for an engine hoist, this bracket shimms out the bolt marginally. maybe this may account for your shortage.

[t walgamuth]

you must have left the hook off inadvertantly. so then the bolt is longer than the others, right? if you want to leave the hook off you can buy a bolt that matches the others or install with some washers. you just want to engage the same amount of thread as the other bolts. not less cause it will strip out from overstressing the threads. not more cause it will bottom out in the hole and not draw the intake down.

if you are not clear on this dont hesitate to ask more questions.

good luck

tom w

[Shorebilly]

Interesting thread here.....what some of us take as common everyday tools and skills......are quite intimidating to others.....

I use a MAC 40pc Rethreader Set......contains rethreading taps and hex dies in Metric, National Fine (NF), and National Coarse (NC)...plus 2 thread files (Metric & American).......Snap-On makes a similar set.....I suppose one could be had thru Grainger.......

I run a rethread (thread chasing) tap down every bolt hole, and a hex die over every bolt....on everything that I disassemble.....a habit that I got into when I was a Cadet.....this assures me that the threads are clean, free of debris, dings and damage.......makes for a good repair in the long run.

Rethread sets are also useful in determining what sizes of bolts and nuts you are dealing with.

You can take your old bolt to any NAPA store and run it into the test device that they have above their nut and bolt bins.....this will determine size as I do with my rethread set.

Taps come in sets of 3...taper, plug, and bottom.....they are designed for threading a hole of proper size...as determined by a "tap and drill chart"...or your "Modern Machinist's Handbook" ...if you have one.
Taper taps are...tapered....and also the smallest in diameter....and are used to make the initial threads....
Plug taps are a little more blunt and slightly bigger in diameter, and they make the second cut when threading.
Bottom taps are cylindrical all the way to the bottom....and also the largest, and correct, finished size.....they finish the threads all the way to the bottom.

Thread Files....are specially designed with 8 different "thread pitch" cuts on each file......they are used to clean up damaged threads.....

I hope that this helps someone here, It was not my intention to confuse anyone. Bear in mind that there are many different thread patterns and pitches.....and any rethread set, or screw plate will only have "common sizes".

Be thankful that you are working on German machinery, and not British stuff....Whitworth Taps and Dies are harder to find and quite a bit more expensive!!!

SB