History repeats itself. The turbo car is broken again and will be for a while..

Discussion in 'Small Block Tech' started by jay3000, Apr 24, 2011.

  1. tlivingd

    tlivingd BIG BLOCK, THE ANTI PRIUS

    First time reading this thread I was thinking as mentioned in one of the earlier posts of the cam being incorrect for this application.

    Are you properly torquing down the bolts and not over torquing them down? If your using a clicking type torque wrench is it properly calibrated? I've had one go out of calibration once and would only click on a much higher torque value. If you over torque them down you maybe torquing them past yield and over stretching the bolt.

    The impact loading over time can cause the bolt to fatigue and fail especially with the movement someone had mentioned albeit with an earlier design. And the additional bending stress put on the bolt mentioned by NoLift can also cause the failure. The only stress not on this bolt is shear.


    You maybe able to band aid it with a grade 8 bolt in the same size but I think that will also be on borrowed time.

    Is there a way you can somehow support the ends of the plate into the ends of the head above the oil drain? Almost girdle the plate into the head.
     
  2. tlivingd

    tlivingd BIG BLOCK, THE ANTI PRIUS

    The article is too big to attach to the board. it's nearly 6 mb of PDF.

    You can find it for 7 days at the link below. from the June 2011 issue.
    this is the Car Craft article about turbo camshafts. Sorry for the lousy scans but they're legible.

    http://www.filedropper.com/truthaboutturbocamshafts
     
  3. jay3000

    jay3000 RIP 1-16-21

    The cam is custom ground for this application by Crower and is based on their Turbomaster line of cams for SBCs..

    Their is no grade 8 fastener available like the one used on this application and there doesn't appear to be a way to fasten the ends or use a different style fastener without either re-inventing the wheel or re-designing this setup

    My opinion is the Mike hit the nail on the head.. Some BBCs even use a 7/16 stud for EACH rocker....
     
  4. sean Buick 76

    sean Buick 76 Buick Nut

    You said you used JB weld, can you tell use what was JB welded?
     
  5. jay3000

    jay3000 RIP 1-16-21

    Now keep in mind that this is after it broke the first time, and I got to looking at the setup more closely and thought " anything to help hold this down better would be good".. I put a very thin layer of JB weld on all of the flat mounting surfaces of the head. It squeezed every bit of it out during assembly and there was nothing left on the mounting surfaces upon removal.. Nothing.

    Once the fasteners were out, the plate lifted right off. Was not even stuck at all. I cleaned all of the surfaces very well before application. I did not over tighten the fasteners. I snugged them up, back them off then snugged them up again. Hard to quantify that.. No torque specs to go by, but it doesn't take much to round out an allen socket, and I was careful not to.. NONE of the fasteners had backed out. Guaranteed..
     
  6. Jim Blackwood

    Jim Blackwood Well-Known Member

    One problem I can see with those fasteners, and this may go to the root of your problem, is that they neck down right at the end of the thread where the chamfer on the back side of the head ends. Take a look, I bet that is where they broke off and they are probably only 1/4" diameter at that point, maybe less. The OEM hold-down bolts are weakest in the thread area itself. Also with that fastener you have to be absolutely on the money on your dimensions between the bolts or they will cock slightly and fight each other, adding to the stress. As little as a few thousands off will cause trouble. You may be able to change your fastener type and solve this problem. The best obviously would be if your bar is thick enough to allow the use of standard socket head capscrews countersunk into the bar. If it is 1/2" thick that might work, though 5/8" would be better. Next option would be the short headed SHCS which used a short fat head with a smaller allen socket. I've also shortened standard SHCS for shallow counterbores. another option might be a short stepped SHCS which has a larger shank, but I suspect you'd run into the same problems as with your existing fasteners.

    One last observation. I once worked on a project where a reciprocating mechanism we had built used an extra long setscrew and the design put a side load on the mechanism. After less than a million cycles the setscrews broke off. I replaced the setscrews (grade 11) with stainless threaded rod which is tougher and less brittle, though also softer and has less tensile strength and the mechanism then ran for over 13 million cycles with no signs of any sort of problem. It may be possible that the alternating side loads that your fasteners are experiencing are fatiguing them to the failure point. I wouldn't normally expect that with these fasteners but it is definitely a possibility, as they are usually in the same range of hardness as standard SHCS (grade 8-9 depending on manufacturer) which is not that far below grade 11. Stainless versions are available. You may find that simply switching to the stainless fasteners fixes the problem.

    JB
     
  7. mhgs

    mhgs it just takes money !!

    I agree with JB ...That and if the machined down towers for the plate are not EXACTLY true in plane you would now have torsional stress as well.
    I believe the system in theory is a good one...But I would rather have the steel plate with a recessed pocket for a cap screw...
     
  8. jay3000

    jay3000 RIP 1-16-21

    Here's what I think would work.. I'm far from an expert.. A thicker plate. It can be wider by about 1/4 " as well toward the springs. Mill the heads down slightly more to accomadate the thicker plate. (if that is possible)Drill and tap the heads for a 7/16" fastener and use a fastener similar to what holds down the seat belt in a car recessed into a pocket on the plate. Something with a wide head to spread the load and a shoulder on the fastener to align the plate.. THe fastener would ideally have a torx socket.. That would be one beefy connection.. That may well even work with the current plate..The current plate works fine if you could just keep it attached..

    I don't know all of the correct terminology, but I hope that makes sense..

    One thig I have noticed each time this has broken is that it bends the plate not only upward, but also twists it toward the springs..

    I have a ton of pictures I made for another member if anyone wants a particular view..
     
  9. jay3000

    jay3000 RIP 1-16-21

    JB you were right. It did in fact break both times right at the end of the taper. The original fasteners were stainless I believe.. That sent me in search of the strongest fasteners I could find which was a hardened alloy as seen in a link a few pages back.

    This has lasted since Nov of last year.. The original setup lasted almost a year before it broke in a different place..
     
  10. sean Buick 76

    sean Buick 76 Buick Nut

    And to be honest I am a little surpsired the engine stayed together considering how stock it is!

    Just goes to show the 350 loves boost!:3gears:
     
  11. Jim Blackwood

    Jim Blackwood Well-Known Member

    So Jay, how long did the stainless fasteners last compared to the grade 8? That might give a clue. Very likely all you really need to do is step up to a 3/8" fastener of the same type, if there is room, and that will hold up without failing. No sense in redesigning it if a simple solution will work.

    OTOH, most guys are more comfortable with socket head capscrews countersunk into the piece, and that design has the advantage of allowing for sideways misalignment between the holes. Also a 5/16" SHCS is stronger than a 5/16" countersunk CS. IIRC you need 5/16" of depth to properly recess a 5/16" SHCS so with a 1/2" bar that would leave you 3/16" below the head, which seems a little thin but should be enough. You are limited on thread depth so milling the head down to use a thicker bar may not be a great idea, but if you could go to a 3/8" SHCS that would almost certainly be strong enough, I would think.

    JB
     
  12. jay3000

    jay3000 RIP 1-16-21

    The original fasteners were on for close to a year, and I'm guessing that they were stainless based on looks alone. That being said, the car was NA at the time or most of it, and did not see the beating it has seen now that the turbos are on and the tune is good.. So, it's hard to draw any conclusions from that.. The fasteners I used did not advertise themselves as "grade 8". They were just a hardened alloy made to some exacting specs. I could not find a grade 8 countersunk fastener like that.

    There is room to put a 3/8 countrersunk fastener and maybe even a 7/16. The flat bar is 3/8 thick.. There is not room to put a SHCS nor is the bar machined for that..
     
  13. Jim Blackwood

    Jim Blackwood Well-Known Member

    Then the first thing I'd do is try the 3/8" size and go with the stainless, then if it breaks again try the grade 8. They might not put the grade numbers on those screws, but the black hardened ones are manufactured in the same process and with the same materials as regular SHCS. You really have to dig deep into the technical specs to get the tensile numbers and such. IIRC they are actually a bit stronger than grade 8, which is why I referred to them earlier as grade 8-9. That's about where they sit in the range. So... better than grade 8. And no matter what anybody tells you, there IS some variation between manufacturers.

    Anyway, I'd go in small steps. Try the 3/8 stainless, try the hardened (the risk here is more brittleness and/or work hardening) and if that fails maybe the 7/16".

    JB
     
  14. jay3000

    jay3000 RIP 1-16-21

  15. bammax

    bammax Well-Known Member

    http://www.boltdepot.com/fastener-information/materials-and-grades/bolt-grade-chart.aspx

    Seems to me the 18-8 stainless may not be strong enough based on that chart above.

    This may help narrow it down a bit.

    http://www.americanfastener.com/technical/grade_markings_steel.asp



    What I can tell you though is to read this link very carefully as it breaks down each type of cap screw and explains the differences between them

    http://www.earnestmachine.com/Onlin...eCatalog_TechnicalLibrary/SocketProducts.tech
     
  16. online170

    online170 Well-Known Member

    Hi Jay;

    DO NOT USE STAINLESS STEEL! Anything Gr8 is usually good. If you want to see something thats easier to pick out, go to www.mcmastercarr.com

    Use their search function, pick a bolt and then go to your favorite hardware supplier and order it. McMaster carr is not a producer they are just a distributor. Most hardware places will recognize the McMaster number and give you an equivalent part.

    The helpful thing about the website is it gives you alot of information like tensile strength etc...


    Did you end up getting those stock 350 heads to get your car going?
     
  17. DaWildcat

    DaWildcat Platinum Level Contributor

  18. gsjohnny1

    gsjohnny1 Well-Known Member

  19. Jim Blackwood

    Jim Blackwood Well-Known Member

    Now see, there you go. Just what I was talking about, the tensile numbers are all over the map, there is only one reference to a tensile range for only one grade of stainless, and the guy who says, "Don't use stainless" can't even give a reference or a reason why.

    What I'm telling you is this. All of these high quality fasteners are made of alloy steel and the compositions vary in significant ways, as does the heat treatment. Unless you are a metalurgist or have studied it intensively (as I HAVE) you have no understanding of what that means, but the alloying content and type is the key to understanding how the material behaves. Compounding the difficulty is the heat treatment process, which can be convoluted and very specific. Only a very small part of that information can be put in a chart comparing hardness numbers. For this application, the crucial qualities of brittleness, ductility, and work hardening are all important. Do you see them in the charts?

    When you alloy steel, you are already beginning with an alloy. It has iron, a very small quantity of carbon, and a few other trace elements such as silicon in minute quantities, and it cannot be heat treated. You add elements to give it specific qualities. The most common is carbon, which allows it to be heat treated and reach very high hardness but also makes it brittle. You add things like chromium for hardenability, strength and corrision resistance, nickel for strength, ductility, and corrosion resistance, Cobalt, Molybdium, Vanadium and others for superior hardenability, toughness and other desireable qualities. All of these are used in a mind numbing variety of proportions and are usually categorized by the major alloying element. On top of that you have two general categories of so called "stainless" (which is nothing more than an alloy with levels of chromium, nickel, or both above a rather fuzzy value) one of which is magnetic and one of which is not, but you also have it divided between two groups one of which is hardenable and one that is not. So immediately there are at minimum four grades of stainless but it's far from over.

    The grades of stainless are comparable in all respects to the alloy grades. In fact you might for instance find something like a cobalt tool bit for machine work which has a much higher level of chromium than a grade of stainless used for tableware. Maybe not the best example but it serves to illustrate the point that a blanket statement like, "Stay away from stainless" has no basis in fact unless a specific grade is mentioned for a specific application.

    Bottom line, the stainless grades almost universally contain alloying contents that give them higher than usual toughness compared to carbon steel and alloy fasteners usually selected for a specific application. As you might expect there is a trade off and that usually is slightly less ultimate tensile strength and higher cost, but in applications like this one, where repetitive stretching and bending are involved, toughness counts for more than tensile strength, and work hardening is to be avoided at all costs.

    Therefore an alloy should be selected with moderately high levels of nickel for toughness and ductility and enough chromium to give good tensile strength which generally means hardenability. Which stainless alloy to choose? Well, 316 is a pretty good alloy but I do not recall without looking it up whether it is heat treatable or not. Seems though like it isn't. Pretty tough stuff otherwise and it takes a pretty good grade of medium carbon steel to match it. The 18-8 alloy seems to be one that was developed mostly for sheet metal screws and such and as used in those applications has good hardness at the cutting edges but is somewhat soft in the core, which would seem to indicate the use of a case-hardening process in manufacture, or possibly work hardening which would be undesireable. I would check with the Fastenall rep and pick the one with the highest tensile strength. I suspect it will be the 316. But to go further, there are probably better grades available and a specialty supplier or even McMasterCarr might have what you need. Bear in mind that even a black heat treated alloy fastener such as a SHCS might well be considered stainless based on it's alloy content. What you are looking for here is a fastener that is optimized for toughness and then strength, not the other way around. For those characteristics, oddly enough an alloy of the type used in fasteners for structural steel used in highrise construction might give good characteristics, as it has to be strong but also has to give long service under continual changes in strain loading. Undoubtedly the one you need is out there. You just have to find it. Happy hunting.

    JB
     
  20. bammax

    bammax Well-Known Member

    With the exception of the 18-8 Stainless all of those bolts are listed as F835

    Here's some info on that designation


    3ASTM F835 Socket Button & Flat Countersunk Head Cap Screw

    Medium carbon alloy steel: quenched & tempered

    #0-1/2 min tensile strength 145,000 Core hardness (Rockwell) min C39 max C44

    over 1/2 min tensile strength 135,000 Core hardness (Rockwell) min C37 max C44

    It's listed on the bottom of page 1
    http://www.fastenal.com/content/feds/pdf/Mechanical Properties of Inch Fasteners.pdf
     

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