Gear oil drain plug over-torque '93 K75S

1993 K75S

OK, I had my first and last (hopefully) senior moment last night and would like to solicit your opinion on the drain bolt over-torque event I created.

After draining the transmission gear oil, I replaced the drain plug with a new crush washer. I set the torque wrench to 20 NM but really it was 20 Ft-Lbs, I didn't have my darn glasses. The required gear drain plug torque is: 20 +/- 3 NM. So in actual case, I applied 27 NM instead of 20 NM or the max allowable 23 NM. I actually stopped torquing when the wrench gave the audible click, but I had already started getting the "uncomfortable" this seems weird feeling.

It's been a few years since I wrenched, but I do remember from way back when that torque values are posted as accurate on dry bolts only. Lubrication of any kind skews the tightening torque value actually applied. Gear drain plugs are obviously always lubricated. So, with that in mind, my over torque may be even greater than 4 NM.

So what is your take on my stupidity, I mean, brain fart, considering the size of the drain plug and the metallurgy of the transmission case? In other words, do you think an over-torque of 4 - 8 NM will equate to internal thread damage to either the gear casing or magnetic drain plug?

Since the plug is steel and the trans case is aluminum, there is no chance that you damaged the plug.

There is a chance that the threads in the tranny case have started to deform (strip). But there's not any easy way to tell. Hopefully, what you felt was the deformation of the crush washer.

What I would do is back off the plug and retorque it to the low side of the torque spec. You want to do that now, while it is still easily broken loose. Otherwise you could have problems breaking it loose in a year or two and possibly cause more strain to the threads.

If it doesn't leak after being retorqued, relax and don't worry about it. If it does, worst case, you could put a heli-coil in it.

I thought of loosening the drain plug. However, if I go ahead I believe I should go all the way, dump the oil and replace the crush with a new one as it will have flattened and releasing it may also lead to some oil leaks. What do you think?

Just try loosening and retightening. Crush washers on drain plugs (unlike brake lines) can usually be used a couple of times. What's the worst that could happen? Just a slight seep.

It's probably going to be fine. If it leaks, THEN replace washer.

You don't need to drain, just put your finger in the hole while you swap washers with your other hand. Replace plug ,tighten, wipe off, top off.

I'd forgeddaboutit until the next service. The extra 7Nm isn't going to make a bit of difference IMHO. If it's not leaking, it's fine. If it needs work (which IMHO it won't) worry about that at your next service next year..

BTW - added the year/model to the thread title. It's a shame users can't edit their own thread titles, but that's Vbulletin for you..

I followed your advice(s) and let off the drain plug without removing the plug. I retightened and that's the end of this first lamentable maintenance action on my part. But, it won't be the last time I make mistakes, that I am sure. However, I refuse to shy away from tinkering on the fine piece of German liquid cooled engineering.

Thanks for the input and words of wisdom.

BTW, I was extremely surprised to see the color of the drain gear oil: it was almost jet black! Is that normal for hypoid gear oil? And is it me or does used gear oil ever wreak?

Now I am tempted to dump the final drive oil and take a peek at the drive splines. Then, it will be bleeding the brakes. I need some input on those gizmos that help with the bleeding of brakes.

ghyber said:

I followed your advice(s) and let off the drain plug without removing the plug. I retightened and that's the end of this first lamentable maintenance action on my part. But, it won't be the last time I make mistakes, that I am sure. However, I refuse to shy away from tinkering on the fine piece of German liquid cooled engineering.

Thanks for the input and words of wisdom.

BTW, I was extremely surprised to see the color of the drain gear oil: it was almost jet black! Is that normal for hypoid gear oil? And is it me or does used gear oil ever wreak?

Now I am tempted to dump the final drive oil and take a peek at the drive splines. Then, it will be bleeding the brakes. I need some input on those gizmos that help with the bleeding of brakes.

Click to expand...

Did you install the previous gear oil? What color was it? If not, who did?

I always use a moly gear oil additive and what I pour in goes in black. K75s don't have greased, sealed bearings like some R11xx bikes, which can make gear oil suddenly a muddy brownish black when the grease seals leak and the grease washes into the gear oil.

I'd guess there is moly in the gear oil.

ghyber said:

And is it me or does used gear oil ever wreak?

Click to expand...

yes, it's a very "unique" smell. new gear oil has the same odor, just not quite as intense.

PGlaves said:

Did you install the previous gear oil? What color was it? If not, who did?

I always use a moly gear oil additive and what I pour in goes in black. K75s don't have greased, sealed bearings like some R11xx bikes, which can make gear oil suddenly a muddy brownish black when the grease seals leak and the grease washes into the gear oil.

I'd guess there is moly in the gear oil.

Click to expand...

Man, you guys are good! I just spoke with the former owner, and he changed the gear oil two years ago (hardly covered any kilometres) and added MOTUL GEARBOX mineral oil with is reinforced with molybdenum bisulphide which happens to be brownish black right out of the can. Bravo Zulu! You guys are on fire!