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Trashed the crank today... Anyone know if a crank can be re-threaded/ inserted???


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Just a thought here...By chance the inside of the balencer might have a slight taper to it? Try and put it on backwards just to see if it will start on. You never know.

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Mike, since some of the threads are now MIA, it would be best to use a stud to screw into the crank to take advantage of all the remaining threads, then use a nut on the stud to pull the balancer on. This takes advantage of all the existing threads and spreads the load out over the threaded area still there. Use some anti-sieze on the snout, and hone the balancer so about 50 ft-# of torque will pull it on the snout. I'm not a big fan of heating the balancer because if you get halfway on and it cools enough to start tightening up you've got problems, and it can be a bear to get the balancer off in the future.

 

John

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Mike - How many threads per inch in that hole? How many threads left? I am not sure what I would do, if you are missing a good inch of threads i may look into a size up stud and bolt idea, that sounds strongest. Someone should be able to chime in with a minimum thread 'area' needed to safely hold that ballancer on GRUMPY???

 

 

Ferd/289 - Everyone's suggestions on removing taps are good and Jolane makes a very good point, it's just not fun!

 

Depending on what the tap is made of and what the material you are tapping in to, it can be very difficult to remove the tap once broken, and the smaller the tap the more difficult it is to get that little dude out of there.

 

Most of my experience is with carbide taps into inconel (a very high grade SS ) using 1/4-20 taps for set screws. Most of the time we try to chisel them out, by shatering the carbide and hope you can clean the threads out. Tap burners are messy and not very accurate and can easily burn a hole in your part if your not careful so we don't use them too much, but every situation is different.

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On further inspection, It appears I've got a good 1.25 inches of thread in the crank that are good, a little over half an inch of missing threads, and I think JT1's idea makes a LOT of sense... I'm going to look into a stud kit for this unit and also get a flap attachment sander and bore out the balancer. I'm just glad that there is something to work with, and that there appears to be mre than enough threads left to do the job. I'm REALLY concerned about getting the hole drilled straight and re-tapping it at perfect straightness. With the crank in the motor, I'm just not certain that is a good idea.

 

Mike

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Mike, do you have a drill press that uses your hand drill? You may be able to mount that to the block, that would be the only way I can think of doing this accuratly while the block is together. Be creative but make sure what you come up with is stable...dunno, still a bummer situation....

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When the thread length exceeds the diameter of the bolt, the threads shear strength, "holding power", typically exceeds the tensional strength of the material. Exceptions to this are influenced by thread pitch, thread depth, type of thread and material of the host of the threads and bolt, stud, etc. If you have more than an inch of threads, then there should be sufficient material to "hold" a balancer bolt which is what 7/16 or 1/2 inch fine thread.

 

Studs always hold better, due to the lack of shear when tightening, which can gall threads.

 

The harmonic balancer or the crank obviously has a problem. I doubt that heating the balancer will completely solve the problem since it takes so long to install it and the heat sink area is ever increasing on a large mass. Measuring tools would definately help. A dial bore gauge would tell you more about the balancer than feel. A mic on the crank snout in several directions would also provide usefull information. I'm not sure what the interference fit should be, but .0005 to .001 would seem sufficient to me. I've encountered this problem several times and I always try the balancer on another crank first, if that works, then I work on the snout so I can use the balancer on another crank later on. Of course if you don't care about the crank or balancer then you could resort to the "bubba" method of a brass plate and a MFBH.

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