77' Primary Chain Plug Stripped

[craig (DE)]

I decided to get my 77' XLH back out on the road. I went for a ride to heat up the fluids so I could change the primary and engine oil. My primary drain plug will no longer tighten up. I ran a thread chaser up into the case to see if any threads were boogered. So the stripped threads appears to be a common problem on older Sportys. With that being said, what's the best method for repair? I see some use heli-coils or self-tapping oil pan repair kits or piggyback drain plug repair kit. I would like to keep the original style drain plug if possible.

[chuckthebeatertruck]

By "primary" I'm assuming you mean the transmission cavity drain plug at the rear of the cases.

What you've discovered is one of the "oh crap" moments that affects most ironhead owners at one time or another -- and most then end up accepting a truism of ironhead ownership -- do not touch the drain plugs in the cases ever, for any reason, period.

In essence, the threads get destroyed easily and then get even more screwed up when folks try to "tighten them up." Running a tap through them seems logical, but it often makes the situation worse as the threads aren't "stripping" as much as they are "pulling and deflecting." When you run the tap through -- you "bend" this action back and the normally tight fit between the male and female threads is actually opened up and suddenly you're putting more force into the plug to try and feel the same "drag" -- thus pushing the situation further into the red zone cause it never feels "tight."

Compounding the problem is that you have very little clearance between the countershaft gear set and the "top" of the plug when it is inserted. This means that yes, you can try a variety of repair methods in situ, but all require careful thought and all have a risk of alloy shavings getting exactly where you don't want them.

At this stage, for me, the "safest" repair would be to reinstall the plug with a touch of yamabond on the threads and the underside of the head. Snug but do not try to tighten it. Let it sit overnight. Draw a line on the plug that indexes to the case and keep an eye on it for 500 miles or a few tanks of fuel. If it moves, you're gonna have to do surgery. If it leaks, it depends on how bad the leak is. If it it doesn't leak or move -- leave it until you have reason to be in the transmission cavity. Then, when you are next in the transmission, repair as you like (helicoil, etc). It is a lot easier to complete a sound repair with the transmission out of your way. The only thing to be cautious of in a repair is welding up the hole. Due to the proximity to the parting seam . . . it has a tendency to warp cases and screw up the sealing surface.

So you know where I'm coming from -- I feel your pain.

We just had to deal with this on my '64CH whilst the cases are down for boring. The front plug was eh but not bad enough to warrant full repair, so we reset it as described above with yamabond. T he transmission plug, however, was truly screwed. So, it was set up in the mill, bored oversize and retapped 9/16-18. A custom plug was made from brass stock and it will be yamabonded in place and not come out again in my ownership. If I was restoring the bike, we would have done the repair differently -- but this is a full on rider and keeping the trans oil tight was more important to us than making an indistinguishable from stock repair. Your desire may vary.

I know it seems counter-intuitive to have what appears to be a convenient drain plug and to be told by a stranger on the internet not to use it . . . but seriously this is a well known issue and the vast majority of ironhead riders come to the same conclusion about the plugs -- they are much more trouble than they are worth.

About now you're gonna ask -- if I don't use that "drain plug" how will I change the fluid? Simple -- pull the primary cover. Yes, it is more work -- it also eliminates the chance of stripping that plug and gives you a chance to better inspect everything in the primary from the adjuster shoe to the chain itself. Then, you seal her back up, reset everything, and ride merrily until the next fluid change is due.

Murphy's law dictates you will strip the plug when it is least convenient for you.

[chuckthebeatertruck]

Photos of a repair

So you can understand better where I'm coming from, here are a few photos from this past weekend's repair work to the buggered plug in my own cases.

First photo shows the rebored and tapped hole.

trans plug threading.jpg

Then, the custom plug:

custom plug.jpg

And, finally, in this photo you can see how even when the plug is flush with the "back" edge of the cavity hole, the front edge stands proud. We still have to check whether the end of the plug needs some grinding.

plug inserted.jpg


Hope this helps you weigh your options.

[craig (DE)]

By "primary" I'm assuming you mean the transmission cavity drain plug at the rear of the cases.

What you've discovered is one of the "oh crap" moments that affects most ironhead owners at one time or another -- and most then end up accepting a truism of ironhead ownership -- do not touch the drain plugs in the cases ever, for any reason, period.

In essence, the threads get destroyed easily and then get even more screwed up when folks try to "tighten them up." Running a tap through them seems logical, but it often makes the situation worse as the threads aren't "stripping" as much as they are "pulling and deflecting." When you run the tap through -- you "bend" this action back and the normally tight fit between the male and female threads is actually opened up and suddenly you're putting more force into the plug to try and feel the same "drag" -- thus pushing the situation further into the red zone cause it never feels "tight."

Compounding the problem is that you have very little clearance between the countershaft gear set and the "top" of the plug when it is inserted. This means that yes, you can try a variety of repair methods in situ, but all require careful thought and all have a risk of alloy shavings getting exactly where you don't want them.

At this stage, for me, the "safest" repair would be to reinstall the plug with a touch of yamabond on the threads and the underside of the head. Snug but do not try to tighten it. Let it sit overnight. Draw a line on the plug that indexes to the case and keep an eye on it for 500 miles or a few tanks of fuel. If it moves, you're gonna have to do surgery. If it leaks, it depends on how bad the leak is. If it it doesn't leak or move -- leave it until you have reason to be in the transmission cavity. Then, when you are next in the transmission, repair as you like (helicoil, etc). It is a lot easier to complete a sound repair with the transmission out of your way. The only thing to be cautious of in a repair is welding up the hole. Due to the proximity to the parting seam . . . it has a tendency to warp cases and screw up the sealing surface.

So you know where I'm coming from -- I feel your pain.

We just had to deal with this on my '64CH whilst the cases are down for boring. The front plug was eh but not bad enough to warrant full repair, so we reset it as described above with yamabond. T he transmission plug, however, was truly screwed. So, it was set up in the mill, bored oversize and retapped 9/16-18. A custom plug was made from brass stock and it will be yamabonded in place and not come out again in my ownership. If I was restoring the bike, we would have done the repair differently -- but this is a full on rider and keeping the trans oil tight was more important to us than making an indistinguishable from stock repair. Your desire may vary.

I know it seems counter-intuitive to have what appears to be a convenient drain plug and to be told by a stranger on the internet not to use it . . . but seriously this is a well known issue and the vast majority of ironhead riders come to the same conclusion about the plugs -- they are much more trouble than they are worth.

About now you're gonna ask -- if I don't use that "drain plug" how will I change the fluid? Simple -- pull the primary cover. Yes, it is more work -- it also eliminates the chance of stripping that plug and gives you a chance to better inspect everything in the primary from the adjuster shoe to the chain itself. Then, you seal her back up, reset everything, and ride merrily until the next fluid change is due.

Murphy's law dictates you will strip the plug when it is least convenient for you.

Yes Chuck, I'm talking transmission/primary chain oil drain plug. I will take your advice and try some sealant on the plug and it let it set up for a day or two. This bike might see a couple hundred miles a year max as I have others to ride. I have own this bike since 1980 and the motor has never been apart.

[craig (DE)]

So you can understand better where I'm coming from, here are a few photos from this past weekend's repair work to the buggered plug in my own cases.

First photo shows the rebored and tapped hole.

[ATTACH=CONFIG]27040[/ATTACH]

Then, the custom plug:

[ATTACH=CONFIG]27041[/ATTACH]

And, finally, in this photo you can see how even when the plug is flush with the "back" edge of the cavity hole, the front edge stands proud. We still have to check whether the end of the plug needs some grinding.

[ATTACH=CONFIG]27042[/ATTACH]


Hope this helps you weigh your options.

Great looking repair! Maybe someday if the motor ever gets torn down, I will rebore and make the permanent fix.

[ChiefTwoKicks]

77' primary chain plug stripped

I have used a LocTite product, PC3967 Stripped Thread Repair, aka "LocTite Form-A-Thread" several times over the years. Although I have NOT used it in an environment where the threads are subjected to oils or trans fluids. I believe, in your application, I would give it a try. Of course the repair must be absolutely clean (clean the threaded hole with lacquer thinner, not solvent). You should be able to re-constitue your threads well enough to tighten the plug. About never removing the plug again, well thats up your own discretion. The product is a 2-part epoxy with a mold release agent. Worked great for me. C2K

[craig (DE)]

I have used a LocTite product, PC3967 Stripped Thread Repair, aka "LocTite Form-A-Thread" several times over the years. Although I have NOT used it in an environment where the threads are subjected to oils or trans fluids. I believe, in your application, I would give it a try. Of course the repair must be absolutely clean (clean the threaded hole with lacquer thinner, not solvent). You should be able to re-constitue your threads well enough to tighten the plug. About never removing the plug again, well thats up your own discretion. The product is a 2-part epoxy with a mold release agent. Worked great for me. C2K

Thanks C2K!