stripped thread in engine casing fix?

Discussion in '2-Stroke Engines' started by Danjr1, Apr 3, 2010.

  1. Danjr1

    Danjr1 New Member

    i changed the head gasket and basically one of the head studs seems to have stripped a thread in the engine casing. anyway i can fix this? thanks for your help in advance
     

  2. Al.Fisherman

    Al.Fisherman Active Member

    There are a few ways of repairing your problem, but to cure this problem from happening I start off first when building a HT set up is to change all the hardware from the Chinese soft studs to a grade 8.8 in metric, followed by red lock tite...never a problem. Second don't over torque.. 8mm uses a max of 170 (I use 150) inch pounds, (for foot pounds divide by 12) due to the case material and not that of the stud.

    Now for a fix
    1. Tap and insert the next size up in standard. Remember you have to drill the holes in the jug. Least prefered for me.

    2. Drill, tap and use a insert and origional size stud. Caught in the middle, sometimes I use this method.

    3. I use aluminum wielding rods to fill hole and re drill and tap. Best way

    4. Last thing I prefer is to replace the case for obvious reasons.

    Always remember the softer the material the easier it is to expand and contract. Thus with a soft stud and max torque the applied torque will be greater when heated, thus a chance to pull threads.
     
    Last edited: Apr 3, 2010
  3. MikeJ

    MikeJ Member

    I did the same thing you did (follow instructions; strip the casing threads) and then did basically what Al described. Here are some specifics that may help you...

    I did some research and determined that 1/4 inch by 24 threads per inch by 4 inch long bolts would be ideal for me. (Note that when you drill and tap your own holes, you don't have to stay metric.) I went to Ace Hardware and found a #17 drill. But I think that was matched to a 1/4 inch by 20 threads per inch bolt. So I bought a 1/4 inch by 20 threads per inch taper tap and handle. I think that is what I finally ended up using.

    The bolts I used were Grade 8 bolts. If they are good enough for a high-perf Chevy big-block, they are good enough for me.

    The 4 inch bolts are not long enough to bottom out in the hole, so need to worry about drilling too far, just don't push the #17 drill through the bottom of the hole. On my engine, the drill and tap broke through the outside wall of the threaded hole, but that turned out to be a non-concern; there was still plenty of thread to grip the bolts. If you had access to a drill press, your holes will be more accurate.

    You will have to ream out the holes in the head to at least 1/4 inch diameter, so a 1/4 inch or maybe a 5/16 inch drill will act as the reamer. Do the same with the lower and upper gaskets also after determining if necessary.

    During drilling, I cleaned away the drill chips, ensuring none fell into the crankcase. That could be a bad thing. During assembly, I used just a drop of oil on the bolt threads. I know, some guys advocate blue or even red Locktite. If you do, you will not be able to go back later and easily retighten head bolts.

    I used a steel flat washer under the head of each bolt, then tightened them down to about 9 ft-lbs (108 inch-lbs). (I used a gallon jug of water hanging from the end of a foot-long wrench as a means of measuring the applied torque. It works!) During running, the cylinder will try to expand in length when it gets hot. The bolts expand at half the rate. In the end, the gaskets will be compressed more while running, providing a better seal. Later, when the engine is cold, you can back-turn the bolts a quarter turn and retighten to a final torque. I did that once after the first tank of gas and have not done it since in over 900 miles.

    I did put a little plumbers thread sealant from a tube around the base of the spark plug. It was leaking cylinder gases and oil until I put that stuff on.

    Have not opened my engine since. Mind you, it would probably improve with custom intake, exhaust, etc. But someday when I have a second bike I can ride while the first is in pieces....

    MikeJ
     
  4. cigron

    cigron Member

    I did the same thing. If you have 6mm studs 1/4 in heli coil for
    the head about $20 at pep boys. They also have metric heli
    coils.I did the motor to frame holes with 6mm both front
    and rear, pluss the exhaust. For the head I took 1/4 by 6in.
    I took A nut A lock washer A nut and another lock washer.
    Put bolt in as far as it will go then then tighten the nuts
    and washers down. then take A hacksaw and cut off the access.
     
  5. cigron

    cigron Member

    I did the same thing. If you have 6mm studs 1/4 in heli coil for
    the head about $20 at pep boys. They also have metric heli
    coils.I did the motor to frame holes with 6mm both front
    and rear, pluss the exhaust. For the head I took 1/4 by 6in.
    I took A nut A lock washer A nut and another lock washer.
    Put bolt in as far as it will go then then tighten the nuts
    and washers down. then take A hacksaw and cut off the access.
     
  6. Al.Fisherman

    Al.Fisherman Active Member

    I use metric all thread (8.8) which equals a US Grade 5..Grade 8 SAE is overkill, (you can't come close to the 8.8 torque specs as the case won't take it) one can use standard if desired. Using lock tite isn't a concern with all thread and if you need to remove them they are easy to heat. Also hold all together with nylon locking nuts. Using bolts...yes no lock tite, or you will most likely be asking for trouble.
    I have access to both 6mm and 8mm Grade 8.8 foir making studs vrs using bolts. When using bolts you might bottom out and never realize it.
     
    Last edited: Apr 3, 2010
  7. Al.Fisherman

    Al.Fisherman Active Member

    When using two nuts don't use washers between them. You loose the jam nut effect. All my mounts are double nuted with a regular first followed with a nylon locking. Jam the two nuts together. I only torque 6mm to 50 inch pounds only...4 foot pounds. This isn't quite enough to keep the engine from rotating on the bike tubes so I made a "L" bracket to keep the engine in place. NEVER...NEVER a mount problem.
     
    Last edited: Apr 3, 2010
  8. cigron

    cigron Member

    Learn something new every day. I thought the second lock washer was I good idea at
    the time. live and learn.
     
  9. Danjr1

    Danjr1 New Member

    so that a yes or no to using bolts instead of threaded bar or double ended?
     
  10. Al.Fisherman

    Al.Fisherman Active Member

    Unless you know what you are doing (bolt can bottom out before the head is torqued correctly)....no I wouldn't use bolts with a head on them. I have, for a temp get me going, but you can't lock tite them. There are a number of vendors that sell them, I myself make them.
     
    Last edited: Apr 5, 2010
  11. cigron

    cigron Member

    Thats A yes.I used A 1/4 in number 20 thread 5 inches long put the nuts and
    washers up as far as they will go.With 1/4 hile coli all ready installed.
    Put the bolt in run your nuts and washers down.Then cut off the
    head of the bolt then tighten to 10 foot pounds.
     
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