under crank drain plug
Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
RE: under crank drain plug
That is not a drain plug, and further more, it should never be removed for any reason. If you remove it, or try to tighten it then the result will surely be a stripped plug.
This plug was used to plug a hole that the factory provided to assist with the machining passages of the engine as it was being built. One of the worst ideas they ever had!
Just inside the hole are the flywheels.....about a quarter inch away from the end of the plug. There is no way possible to re-thread this hole with a tap unless you pull the entire engine apart and split the cases because there is no room inside for the tap end.
This plug has a long unhappy story associated with it for owners who either stripped it out trying to tighten it up, or removed it and could not get it back in place. It is just really bad news............pg
This plug was used to plug a hole that the factory provided to assist with the machining passages of the engine as it was being built. One of the worst ideas they ever had!
Just inside the hole are the flywheels.....about a quarter inch away from the end of the plug. There is no way possible to re-thread this hole with a tap unless you pull the entire engine apart and split the cases because there is no room inside for the tap end.
This plug has a long unhappy story associated with it for owners who either stripped it out trying to tighten it up, or removed it and could not get it back in place. It is just really bad news............pg
Thread Starter
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Novice
Joined: Oct 2007
Posts: 23
Likes: 0
RE: under crank drain plug
thanks for the info but i recieved this 72 ch motor with the plug missing and i would like find out the thread size so i could turn one out , i know it not a drain plug but it is a plug
Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
RE: under crank drain plug
I do not know the thread pitch/size myself, but just take a thread gage and stick into the hole to measure the thread pitch. Then just measure the hole. The thing will be a 5/8-11, 9/16-12, or a 1/2-13. Something like that. Whichever size it is, it will be a std thread.
Use a lot of caution when you tighten the plug, and if you are going to turn a plug be sure to make it short enough to miss hitting the flywheels. I would also urge you to carefully check the condition of those threads in the case.........pg
Use a lot of caution when you tighten the plug, and if you are going to turn a plug be sure to make it short enough to miss hitting the flywheels. I would also urge you to carefully check the condition of those threads in the case.........pg
Thread Starter
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Novice
Joined: Oct 2007
Posts: 23
Likes: 0
RE: under crank drain plug
thanks , when i picked up the engine it was supposibly completly redone top and bottom ,clutch and trany so i put it on my stand and tore it down to make sure , alot of new parts but not assembled very good retainer tabs not bent over ,primary tenioner bolts lose, heads not alined for intake, lot of silicone etc. but tolerenses were in range through out so i reassembled it and threw it in the frame and tonight i poured in the oil and holding the return line and hand cranking it waiting for the oil to come out of the return hose then i seen all the oil pumping to the floor ,looked under and couldnt beleived what i saw no plug ,i cant beleive i missed that ,but anyways i took a quick look at the threads and noticed there fine thread and look good so i went in and tried to find it at bikebandit no deal so i came here instead of going back out and puting the pitch gauge on it
Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
RE: under crank drain plug
Whenever I hear that 'The entire engine has just been rebuilt' BS I have to take it with a small grain of salt. So, good for you for not being too impressed with that either and tearing it down to check it out yourself. Just exactly what I would have done. It sounds like it paid off for you because as exampled by the lock ear not being bent over and sloppy assembly is a sign of a careless built. Let something like that work loose and it could cost you some big dollars.
If the hole has a fine thread on it, that does not surprise me. The drain plugs for trans use a coarse thread because the purpose is to be removing them on a regular basis. That plug you need was meant to be installed one time at the factory, and no more.
I suggest that you go to a Harley shop if you have one close by and see if they can order it.
Try to get the part number for the plug, even if they cannot order it. That way you will have a cross reference for it if you try VTwin or J&P. There may even be a thread per inch listed on the callout in the parts book, but that is probably wishful thinking. As much info as you can get though will be helpfull.
Other than that, just put the thread gage on it to see what thread it takes. Very short length required, the whole short end of the plug should be full thread and this thread should run up to the shoulder of the plug's head......This ain't gonna be an easy thing to make, even if you do have a lathe and are pretty goog turning threads, but it can be made. The big problem is going to be making the plug the correct size so it fits tight but does not wipe out the threads in the crankcase piece.........pg
If the hole has a fine thread on it, that does not surprise me. The drain plugs for trans use a coarse thread because the purpose is to be removing them on a regular basis. That plug you need was meant to be installed one time at the factory, and no more.
I suggest that you go to a Harley shop if you have one close by and see if they can order it.
Try to get the part number for the plug, even if they cannot order it. That way you will have a cross reference for it if you try VTwin or J&P. There may even be a thread per inch listed on the callout in the parts book, but that is probably wishful thinking. As much info as you can get though will be helpfull.
Other than that, just put the thread gage on it to see what thread it takes. Very short length required, the whole short end of the plug should be full thread and this thread should run up to the shoulder of the plug's head......This ain't gonna be an easy thing to make, even if you do have a lathe and are pretty goog turning threads, but it can be made. The big problem is going to be making the plug the correct size so it fits tight but does not wipe out the threads in the crankcase piece.........pg
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Road Master
Joined: Mar 2006
Posts: 775
Likes: 2
From: OC California
RE: under crank drain plug
Always a big issue with these plugs. They are 1/2x13 in size and available from dealers and the likes of J&P.
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Stellar HDF Member
Joined: Feb 2006
Posts: 3,035
Likes: 17
From: Houston Texas
RE: under crank drain plug
Thanks Cal. So, the plugs are 1/2-13 thread after all. I was pretty sure that they were a coarse thread instead of a fine thread. With the relative thin crankcase and using coarse thread that means you have what, maybe 3 or 4 threads at most on the length of the plug? Another reason they strip so easy.
Thanks also for the tip on J&P carrying them. What are they listed under? I tried to find them but could only find the trans drain plug listed. That info should help cruncher a great deal.........pg
Thanks also for the tip on J&P carrying them. What are they listed under? I tried to find them but could only find the trans drain plug listed. That info should help cruncher a great deal.........pg