Cylinder Stud broken

Discussion in 'Motorized Bicycle Welding, Fabrication and Paintin' started by _Spyder, Jul 29, 2015.

  1. _Spyder

    _Spyder New Member

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    Hi all! I've managed to over-torque one of my head bolts, and the stud sheared off at the top threading with 3 or 4 threads remaining. At this point I have the jug removed and the piston is hanging limply between the 3 good studs and the mostly-stud with paper toweling around it. The gasket between the cylinder and the crank case (the cylinder gasket?) is a mess - it took a **** of some doing to even pull the jug off.

    My problem is that no matter what I try, I can't remove the broken stud. I've chewed it up pretty good with my limited tools and bought a locking pliers, but it won't budge for the life of me. Wrapped rubber bands around it, tried gouging my pliers into the material for a grip, but nothing. There aren't enough threads for the double-nut trick, and I don't have a welder.

    Does anyone have advice for me before I take it to the auto body? Sorry if this has been asked. I did search, but all I see are motor mount studs - can't imagine no one has had this problem before, 12 lbs isn't too hard to exceed with your arm.

    Thanks!
     
  2. 2door

    2door Moderator
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    Did you or anyone use red loctite on the threads? If so, you'll need heat to get that stud out of the case. Even without the thread locker you might want to try applying a little heat to the case near where the stud threads into it. Don't over do it. A propane/MAP torch will be more than sufficient.

    If/when you do get it out you might want to replace the acorn nuts with hex nuts. The acorns are notorious for causing problems.

    12 pounds isn't too much. We suggest 120 to 140 inch pounds and 12 foot pounds is in that range.

    Let us know how you're doing.

    Tom
     
  3. Davezilla

    Davezilla New Member

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    Yup... it's either seized up or red locktite was used at some point. Heat will get it out either way. Like Tom said, just apply heat on the side of the case where the stud is seized, keep the vise grips locked on the stud really good, then just hold some steady pressure on the vise grips as the aluminum is heated, once it gives and starts to turn you can take the heat off and get it out, no need to keep the heat on after it starts to move unless it locks up again on its way out.

    During assembly a Thin coat of anti seize on the threads will prevent this from happening again, set the new stud, and torque the nut as usual. You can use regular he nuts instead of the problematic acorn nuts, ditch the split lock washers and use the star washers on top of a flat washer and it should stay put after assembly, but will most likely need re torqued a few times after the engine has run thru several heat cycles.
     
  4. Ninja Turtle

    Ninja Turtle New Member

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    Well, technically it's not.
     
  5. Ninja Turtle

    Ninja Turtle New Member

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    Are you saying to use anti seize on the stud into the case or on the nut?

    Thanks.
     
  6. Davezilla

    Davezilla New Member

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    You want to use it at the case, on the nut is optional, but at the case you got a steel stud going into an aluminum case, there's always a chance the 2 can get corrosion locked together, but the most common thing happening is that the aluminum tends to reshape it's self to the exact shape of the threads on the stud, imperfections and all so over time and several heat cycles it can for a thin film of oxide on the threads where they contact the steel stud, the stud is already torqued by the nut and strtched, then this film of oxide tries to for where there's no room to for and that's what causes the seizing. You may have noticed a white residue on the threads of a stuck stud or even on one that's not seized, most the time it's just a really thin powdery film but when it's seized, there's a lot more of this white oxide or rust from the stud, or both. The anti seize is usually a super fine aluminum, copper, or graphite powder suspended is some sort of grease so it prevents complete direct contact between the stud and the metal it's in and acts like microscopic tiny bearings when breaking torque and running the bolts or studs out of the metal.
    The stud can't come loose or out of the case with the anti seize applied to it due to the stretching it takes from being torqued, and this thin oxide film can't for as easily on either part since there's this ultra thin barrier between the 2. This solid barrier can't escape from between the threads so if you try to break torque 20 years later it'll break free just as easily as if you torqued it yesterday.
    you can usually get a small tube of anti seize at most auto parts stores where they sell the sealants and engine building supplies and sometimes in the same areas where they sell ignition components since it's also recommended on spark plugs in aluminum heads. The stuff is cheap and it just takes a really thin coat to work.
     
  7. Ninja Turtle

    Ninja Turtle New Member

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    Thanks for the detailed reply. That's the first I've heard of using anti seize instead of high strength loctite.
     
  8. Springfieldscooter

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    How much threads remain on the top of the broken stud?

    If you have enough threads, you can install 2 nuts on the broken stud. Then tighten the 2 nuts against each other as tight as possible. Then use a wrench on the lower nut only to remove the stud!
     
  9. Davezilla

    Davezilla New Member

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    He don't have but about 3 threads sticking out so double Nutting won't work in this case...
    I didn't think of this before but if you got a dremel and a cutting wheel you can cut a slot across the top of the stud so you can use a flat tip screwdriver on it, you may still need the assistance of a propane torch to get it to let go enough to get it out, but this trick has worked great for me in the past dealing with studs that have broke off too short to grab.
     
  10. allen standley

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    Found myself in this situation twice. Dremel a slot and heat, successful extraction on both occurances.
    Excellent explaination DaveZ!
     
  11. tgaydos

    tgaydos New Member

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    or if it's flat enough use a drill with the correct size drill bit and an easy out (sold at local auto stores), i had to do this with my front motor mount. just make sure to use a power drill (not battery) you'll have it out in mere minutes.
     
  12. 2door

    2door Moderator
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    What do you mean by that?
    Twelve foot pounds equals 144 inch pounds. That is within the recommended torque range for the cylinder head fasteners. We usually recommend 120 to 140 inch pounds but there are many who say to go as high as 160 inch pounds.

    What isn't "technically" right?

    Tom
     
  13. allen standley

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    What do you mean by that?
    Twelve foot pounds equals 144 inch pounds. That is within the recommended torque range for the cylinder head fasteners. We usually recommend 120 to 140 inch pounds but there are many who say to go as high as 160 inch pounds.

    Yes Sir - and when checking after a few hot/cold cycles, you're checking for looseness not tightness. If loose re-tourqe specs above.
     
  14. Ninja Turtle

    Ninja Turtle New Member

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    144 is not in the range of 120-140, it's just outside. I was just messin around anyways lol
     
  15. Davezilla

    Davezilla New Member

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    I didn't even think to mention using an easy out last night, but they are very effective for removing broken bolts or studs when they break right flush with or just a little short nub sticking out... just gotta drill thru the center of the broken stud, and the combination of hammering and turning will usually make just about any broken faster give up and come out... if it's still really tough, heat can still be applied.
    One more weapon I got in my arsenal is a screw knocker, basically it goes into a rivet gun or air hammer and has a 3/8 drive on the other end so you can put a Phillips or standard screwdriver tip or a small socket to hold the easy out, pul, the trigger while turning the wrench on the knocker and it shakes the **** out of the broken fastener until it has no choice but to give up and come out. This tool isn't very common for automotive or motorcycle use, but very common for aircraft so look at an aircraft tool site for these...
     
  16. Davezilla

    Davezilla New Member

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    For the head torque, 144 in/lb is about as far as I would go using the studs provided in the kit, if I wanted to torque the studs higher than 144 in/lb I would get the higher grade studs just to prevent one from breaking or stretching. You will know right away if one stretches because right before you reach the desired torque it'll start to turn easier instead of tighter. Torquing does actually stretch the bolts or studs, but they can also over stretch and when you remove it you'll see where it looks like a piece of taffy that was just pulled because you'll see a narrow spot somewhere on the fastener. Proper torquing only stretches the stud or bolt a few thousandths of an inch at best...
     
  17. 2door

    2door Moderator
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    I don't disagree with anything Dave said above, but, my guess would be that the threads in the aluminum case would let go before a steel stud stretched enough to actually break. Stripped threads is one of the most common things I've seen in engines that were returned to a supplier. I'm not saying a broken stud is impossible but a believe damaged case threads are much more common.

    Of course with either failure over tightening is usually the culprit which is why we stress the use of a torque wrench when working on these little engines. And not exceeding the set torque value. Check the fasteners but checking them for tighness doesn't mean seeing the wrench turn. It means checking to see if they are still at the torque recommended. If they are, leave them alone.

    Tom
     
  18. Springfieldscooter

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    Good advice above!

    Also, its interesting to note......

    Fred from CR machine shop suggests the following torque values:

    "Coarse thread cylinder head nut torque spec: 60 inch pounds"

    "Fine thread cylinder head nut torque spec: 48 inch pounds"

    (I assume this is for the 8mm studs with coarse being 1.25 and fine being 1.0)
     
  19. Davezilla

    Davezilla New Member

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    I agree with Tom, in these cases the threads may pull out or strip before a stud stretches or breaks from overtorquing. This is also why I never use a bolt in the aluminum unless I absolutely have to. Studs go in hand tight, then the nut on the other end is where all the torquing friction is, this prevents premature wear or stripping of the holes in the aluminum, but the threads can still pull right out of the aluminum if excessively over torqued.
    In places where a bolt has to be in the aluminum it's always best to helicoil or install steel inserts, especially if it's somewhere that a bolt will be installed and removed frequently.

    I've also seen Fred's recommendations for torquing the heads at really low values and I know why he recommends such low values. His reasoning is because the gaskets can smash down when torqued too far, not the aluminum head gasket as much as the fiber base gaskets, the aluminum can smash a little too but pretty much a neglidgeable amount... unless you're running a really Really tight squish band, then the extra smashing of the gaskets could cause the piston to hit the head. It would be really rare that this would happen, but if your squish clearance is less than .010" and the paper fiber gasket can smash down by about .005" or more, and the aluminum gasket .0005" that's leaving you only .0045" or less of clearance between the piston and head, now warm up the engine and the rod stretches a little from heat expansion this distance becomes even closer... you pretty much know what's next.

    The other reason he recommends the low torque values is because as the torque goes up, the clamping force of the studs goes up and can warp the head enough for the gasket to leak between the studs, but as thick as his heads are this is highly unlikely.

    To combat both these issues I use copper base and head gaskets since they won't smash down as much from torquing, the copper is rather soft and will require a retorquing, but then it hardens up from the engine's vibration and won't smash any more but will have a perfect seal by this time. Copper work hardens and you can actually see this in action by bending a piece of copper a few times, you'll feel it bend really easy as it starts off super soft, then you'll notice each subsequent bend you do that it becomes more and more difficult to bend, and if you keep going it'll eventually crack, this won't happen between a head and cylinder, but the vibration of the engine, even a very smooth running engine will cause the copper to match up perfectly to the micro contours of the head and cylinder causing it to need to be re torqued, but then it hardens up to a certain point after it seals. Copper gaskets can be reused numerous times before they wear out too much, but they need to be annealed between each use by heating up to cherry red then quenched quickly. I've tried cooling it both ways, letting it cool on it's own, and dipping in cool water to cool rapidly and both methods leave the copper dead soft after being heated to cherry red.

    The reason less torque is needed with the fine threaded studs is also in the clamping force applied as the finer threads will apply more clamping force at a lower torque value, you can also go into lubed vs dry torquing and how much it effects the clamping force and on and on as well.
    I understand his reasoning for the low torque values, but on a street engine it's not going to be that much of an issue as on a race engine where tolerances need to be as accurate as possible and smashing a gasket a fraction of a thousandth could effect the engine in a bad way. It also distorts the jug ever so slightly as well but that's also going into a totally different area...
     
  20. 2door

    2door Moderator
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    Lots of good discussion in this thread.

    As for fine thread verses course, here's another fly-in-the-pie. I've seen many engines with cylinder studs having course threads on one end and fine on the other. I've had folks say they've never seen this and argue with me about it but regardless, it is a fact.

    These engines have fine threads in the case and the course threads on top where those pesky acorn nuts go. What I've seen is a builder will not notice the thread difference and will attempt to thread a stud in, forcing the course threads into the fine threaded case. You can guess the results. Then he tries to put an acorn on the fine threads on the other end of the stud. Same results. Damaged threads, leaking head gasket and the engine won't run worth poopy.

    I realize this odd stud issue isn't universal but I've seen enough of them to believe they are a source of trouble. In addition to the use of fine and course threads I've also seen studs of different lengths used in the same engine. Add this to the case threads not being precisely the same depth and you have the potential for even more head gasket problems.

    And get rid of those stupid chrome acorn nuts. Grind the tops off or replace them with hex nuts.

    In defense, I've seen some newer engines coming with taller (longer) acorn nuts that will accomodate the stud threads even if they're a little long.

    Tom
     

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