stripped threads in case to hold cilynder

Discussion in '2-Stroke Engines' started by jasonpadilla, Jun 6, 2010.

  1. jasonpadilla

    jasonpadilla New Member

    i stripped the threads in the case that holds the cilynder in, then i put loctite in ad threaded it down more it seems to be holding but what do i do if need be?

  2. Al.Fisherman

    Al.Fisherman Active Member

    Like Marko told Liam Neeson in the movie Taken ..... "Good luck". I doubt very seriously it will hold very long, much less surprised it's holding at all.

    1. Are you still using the factory hardware?
    2. Might need to drill and tap for a insert.
    3. Tap to a larger stud. This one requires both cylinder and head drilled to accommodate the larger stud.
    4. Torque on 8mm studs is to be 150-200 INCH pounds, and 6mm 50-60 INCH pounds. I use 50 and 150 with lock tite. Never a stripped hole, stretched or broken stud. (upgrade hardware if you haven't.
  3. MikeJ

    MikeJ Member

    Hi Jason -

    Here is another proven fix method, because I stripped a stud in my engine. I just about threw the fool thing away. Here is what I did; other writers have successfully used 8 mm threaded rod in their fix. If you have a drill press at your disposal, that would ensure drilling is as error-free as you can get it. Treat a buddy to a six-pack if he has a drill press. It is important to note that my original engine studs were 6mm, not 8 mm:

    1. Remove all four studs. Remove cylinder and head. Be careful to save the gaskets.

    2. Go to hardware store. Purchase a drill (13/64 I believe) and a 5/16 x 24 tap. (I went the next size up over 6mm (1/4 inch). If your cylinder studs are 8 mm, get more advice than what I am providing here.) Important: Get a friendly hardware store guy to help choose the right combination. Purchase four each 5/16 x 24 bolts. Any US made 5/16 bolt is stronger than the engine's original cylinder studs.

    3. Drill and tap all four engine block holes. Do not drill into the crankcase. Be careful to keep metal chips from falling into the crankcase. A buddy with tapping experience may be willing to help.

    4. Use a drill very slightly over 5/16 inch diameter to ream out the cylinder head holes and gasket holes. Maybe the cylinder holes. It won't take much effort.

    5. Get your four steel bolts: 5/16 x 24 by four inches long. Get a washer for each bolt.

    6. Bolt together the cylinder and gaskets into the crankcase. The drilling and tapping may break through the very thin wall to the outside world where the crankcase is threaded. The bolt will extend into the crankcase hole by about 1/2 of an inch or better. There is plenty of gripping threads.

    7. Slowly tighten bolts in a criss-cross pattern until each bolt is about 8 ft-lbs (about 100 inch-pounds) of torque. I did not have a torque wrench, so I used a foot length of pipe over my wrench handle. Slowly hang a gallon of water jug (8.3 pounds) on a string on the pipe one foot from the bolt. That is approximately 100 inch pounds of torque. You will have to reposition the wrench as the bolt turns until it stops turning. Use a table and lay the engine on its side during this process. If you have a helper holding the engine during this process, you will save yourself a lot of anxiety.

    8. If successful, you will have a good, tight assembly. After a run or two, break the bolts loose by turning backward a quarter turn, then re-tighten by max of an eighth of a turn; not much. I consider this optional; I saw no benefit after I did the re-tighten. But it does follow the recommendations of going to a higher torque value.

    I did these above instructions over 1200 miles ago and have not opened the cylinder since then. Aluminum expands at twice the rate of steel when it gets hot, so the hotter your cylinder runs, the tighter the gasket seals become.

    Keep an eye on that cheap default spark plug. Mine leaked gases during the compression and power phases. I replaced it with a recommended better plug. Make sure you can remove the screw-on top of the replacement spark plug if the original did not have it. Else replace the CDI wire.

    Wait until you start researching oil ratios and break-in procedures! Have fun!

    1,248 miles on a jackshaft kit and my Frankenmotor. Not all have been trouble-free...
    Last edited: Jun 6, 2010
  4. Al.Fisherman

    Al.Fisherman Active Member

    If you choose to use bolts, don't use RED lock tite. I use RED as that is the strongest, and needs heat to be removed. With studs the head and cylinder can be removed and the stud heated to be removed. Hard to do with bolts. I would not use bolts on any thing on these engines that needs to be torqued. You might bottom out and the end result will be improper torque. Also you may want to remove the head and or cylinder from time to time, using bolts requires the removal through the aluminum threads, where studs require the removal of a nut and the stud stays in place. Much better on these engines. Bolts are a all around a bad idea on these engines.
  5. MikeJ

    MikeJ Member

    Bolts a bad idea? I have not seen published engineering data one way or the other. Maybe some day I will actually look for it.

    I refer back to my growing up days when I used to take apart Briggs & Stratton almost-pot-metal aluminum lawnmower engines. They were held together by bolts, and still are. I used to disassemble and reassemble them any chance I could. I would put a couple drops of any old lube oil I found lying around on the head bolt threads before assembly. Torqued to "This feels about right" tightness. If I did not mess up the spark system too badly, they ran some more. (Growing up on the farm, a high-tech tool was a box wrench that actually fit!)

    I suppose studs were engineered into these engines for a reason. Probably for cost reasons. Bolts are more costly.

    Either way, I am sure Ron will agree that larger diameter studs or bolts equate to better holding strength.

  6. Al.Fisherman

    Al.Fisherman Active Member

    Larger diameter...why yes. 8mm much better then a 6mm depending on application. Mike you need to think about this and I was sure someone would bring up your point. First of all B & S engines are built to B & S specs, no matter where they are made, be it here, China, or Mexico. The make up of the material (alloy) in these HT engines are in no way comparable to the material in a B & S engine, not positive but pretty sure. There are different grades of cast aluminum. I, like most likely you, have torn down more then my fair share of B & S engines in my 50 years of fooling with them. The less a thread hole is used the better off you will be. Actually that goes for anything that uses a threaded fastener.

    "Aluminum Grades: Aluminum Association alloys 319, 356, 514, 535, and 713 are available on a certified bases. Other alloys can be cast upon request. A standard blended alloy is available for non-critical, non-certified applications."

    So what do you think the Chinese (as proud of their products that they are ROFLMAO) use???? Does the word CHEAP AS POSSIBLE ring a bell?
    Last edited: Jun 7, 2010
  7. MikeJ

    MikeJ Member

    Hi Ron -

    Your points are well taken, especially your last emphasized phrase. That gave me a round of the giggles.

    I concur, insertions and removals of bolts do leave some thread damage every time, expecially where the bolt is much harder than the recipient metal. I have seen where over time and many cycles, the recipent hole is worn out of specs and is in danger of failing.

    I should have known before writing to ask about comparing B&S metal alloys against China's Best. B&S certified alloys (probably traceable to to ISO specs) and manufacturing processes are certainly better than the "cheap as possible" combinations. Maybe I will remember for next time.

  8. Al.Fisherman

    Al.Fisherman Active Member

    No problem, sometimes we just don't compare apples to apples...heck I'm as guilty as the next guy every now and then.
  9. jasonpadilla

    jasonpadilla New Member

    UPDATE.... ok the bolt vibrated loose so i took the cylinder off and now i have to re thread it i have the grubee 66cc skyhawk with angle fire head what size are the bolts? and what size should i tap and re thread with? do i have 6mm studs? or are they 8mm? from the posts i couldnt tell, hey thanks guys for all ur help on this 1, im stuck riding the bus tomorrow but when i get home im gonna listen to you guys and fix this problem, just need to know what to buy from the hardware store and go from there, thanks sooo much for all your help, this forum is a life saver to ur motor bikers.. keep up the good work much thanks AL and MIKEJ, AL do u know the stock stud size that r in there now?
  10. Al.Fisherman

    Al.Fisherman Active Member

    IF the studs through the cylinder are the SAME diameter as the engine mount studs you have 6mm studs, otherwise they are 8mm. If it came loose why do you NEED to re thread it? Use a 6mm/1.0 or a 8mm/1.25 bottom tap depending on what size studs you have. You need to get rid of the stock studs and replace ALL of them, and lock tite them in. There are a number of suppliers of hardware here including my self. Also do you have ANY gap between the engine mount and the bike tube? ANY AT ALL?

    Do it right (as in correctly) NOW, or do it later, hoping that you can.
    Last edited: Jun 8, 2010