Stripped Final Drive Drain Threads

[SoCalR1200RS]

I don't know what gods I must have pissed off today...

I was attempting to change my final drive oil for the first time. I've done it before on my old R1100R multiple times without issue and was trying to be extra super careful. After letting it drain for a bit, running some clean fresh oil thru (and draining), I then went to reinstall the drain plug.

I did this as carefully as I possibly could. Starting the threads by hand and going by hand as long as I could. Eventually, I needed a rachet and slowly and smoothly cranked it until it was snug. I had written notes beforehand and my notes said it needed 20ft/lb of torque!!! I realize now that was supposed to be 20Nm! (god I hate that there are two measuring systems for the same things...). A quick maths check tells me that 20Nm is roughly 14.75ft/lbs.

When I was tightening, I thought it felt like too much force, so I used my torque wrench to check the pressure, which at the time was roughly 10ft/lbs, and I slowly, 1ft/lb at a time, worked my way up to around 18lb/ft at which point I really didn't feel comfortable tightening any further, and already suspected I had done something wrong. I had tightened to something like 24-27Nm. At this point, I decided to back the bolt out and inspect and sure enough, I saw the worst, little bits of threading came out with the plug.

Now - I'm stuck and afraid to move forward. Visual inspection of the bottom of the housing shows the very outermost thread was damaged, likely sheared off the bottom 1/4" of threading. The rest of the threads look fine however when I attempt to reseat the plug, I can only get a couple of turns by hand before it jams.

No clue what to do next. I don't want to force the plug in place and wind up stripping the rest of the threads. I also don't have access to die taps or similar tools to re-do the threads.

Oh, and the main reason for doing the maintenance now, is that my fiance just totalled our car (it was an accident) so I needed to make sure the bike was all set to be my only vehicle for now... So I'm really in a jam now - without this bike, I'm pretty much stranded.

Any and all advice would be greatly appreciated. Below are some photos of what I'm looking at.

[Grumpy Goat]

Please post a side picture of the plug in way of the broken threads.

[SoCalR1200RS]

This is the best view I could get of the threads. The plug looks fine. Can't see any threads that look wider or damaged at all.

[Grumpy Goat]

So the piece of thread that came off came from the housing and not the plug, correct? Sorry if I missed that point.

If that is the case then the threads don’t look to be cross thread damaged, but you may have a sealing problem since the underside of the plug head expects to bear up against a flat surface. Can’t hurt to ask a dealership service technician for advice. They may have come across this before. Some sort of crush washer gasket may hold but I don’t know how hot this gets, which would determine the material that can be used. Just some thoughts.

[Lee]

A Tap or insert can be used to fix the threads, but if the sealing surface is damaged I don't know how to fix that.

Edit: Looks like Time-Serts may have enough sealing surface.
https://www.timesert.com/

[SoCalR1200RS]

Thanks for the input gents. Seems like the best long term move would be a time-sert, however, as I'm imagining it, that repair is going to be quite involved. Wheel off, remove the final drive, and probably even open up the case, yeah? Otherwise, even if you can clamp it into a vise, how will you prevent metal shavings from remaining in the oil and damaging the gears?

It'll be a repair that will outlast the motorcycle, and I'd never have to worry about over-tightening again, but yeah, ball park estimate for a shop to do it I'm guessing like $100 parts and 2.5 HR labor?

Considering all metal thread insert repair kits require drilling out the remaining threads, I'm thinking about just reinstalling the plug as carefully and securely as I can manage, and if I feel comfortable, test riding and monitoring for leaks. If it's holding for now, that can buy me some time to find the best repair plan asap.

[Lee]

I'm thinking about just reinstalling the plug as carefully and securely as I can manage, and if I feel comfortable, test riding and monitoring for leaks. If it's holding for now, that can buy me some time to find the best repair plan asap.

It's worth a try.

[Ray]

I'm thinking about just reinstalling the plug as carefully and securely as I can manage, and if I feel comfortable, test riding and monitoring for leaks. If it's holding for now, that can buy me some time to find the best repair plan asap.

Should't take much time to try to run a quick tap through and screw the bolt into a die for some peace of mind on re-assembly. And sometimes, just a new bolt with do the trick. Just my two cents (and worth about as much).

[Grumpy Goat]

Thanks for the input gents. Seems like the best long term move would be a time-sert, however, as I'm imagining it, that repair is going to be quite involved. Wheel off, remove the final drive, and probably even open up the case, yeah? Otherwise, even if you can clamp it into a vise, how will you prevent metal shavings from remaining in the oil and damaging the gears?

It'll be a repair that will outlast the motorcycle, and I'd never have to worry about over-tightening again, but yeah, ball park estimate for a shop to do it I'm guessing like $100 parts and 2.5 HR labor?

Considering all metal thread insert repair kits require drilling out the remaining threads, I'm thinking about just reinstalling the plug as carefully and securely as I can manage, and if I feel comfortable, test riding and monitoring for leaks. If it's holding for now, that can buy me some time to find the best repair plan asap.

If, as you said, the threads seem to be not stripped with the end thread broken off then if it were me, I would not be focused on damaging the remaining threads. I would be more interested in seeing how to flatten the sealing surface between the plug and the housing.

Your last paragraph makes sense to me. Its not like you have a choice if it is now being pressed into primary transportation duty.

[Lee]

I think the seal is made by the o-ring touching the wall of the drain opening.
If that's true, maybe he's ok.
Am I screwed up with my thinking?

Here's a picture of the plug without the o-ring in the groove.
   

[Grumpy Goat]

I think you're right, Lee. I forgot that this plug was not like the oil drain plug and this one has an O-ring.

This is good then as the seal should not really be affected, and since it is only part of one thread that came off, and the tightening torque is low then the plug should stay in place without much difference.

Just wondering why this was an issue in the first place, i.e. why it presented resistance and why that first thread came off. Defective manufacture, it seems. But this experience reinforces the need to be careful when reinstalling this plug as it is done from an unusual position upside down. The FD housing material is much softer than the plug.

[SoCalR1200RS]

So I went ahead and reinstalled the plug. I didn't torque it to exactly 20Nm - I had the wrench set correctly, but stopped when I felt it was "good n tight". I rode it about 20 miles, including highway, and see no leaks. I put a little piece of painter's tape over the bolt so I'd spot any leaks. I will continue to keep an eye on it, and will update this thread when I return to do the permanent time-sert repair.

[Boxerboy55]

So I went ahead and reinstalled the plug. I didn't torque it to exactly 20Nm - I had the wrench set correctly, but stopped when I felt it was "good n tight". I rode it about 20 miles, including highway, and see no leaks. I put a little piece of painter's tape over the bolt so I'd spot any leaks. I will continue to keep an eye on it, and will update this thread when I return to do the permanent time-sert repair.

Having read the above, I think you missed a complete thread strip by the skin of your teeth.

So I would have also simply checked the plug was running in and out ok, then re-fitted with O Ring.

My tip - DO NOT EVER use a torque wrench on small screws.

You’ve achieved the obvious, common schoolboy error, when trying to use a torque wrench way down at the bottom of the scale.

(I’m not being rude - just a figure of speech)

Save it for wheel bolts at 60Nm.

You need to develop a “feel” for fasteners of all kinds when tightening small screws and/or screwing anything into soft alloy or any other non-steel material.

Can you guess I’ve got a little grey hair left and a large tool box.
And the Torque Wrench is least used.

[Lee]

. I put a little piece of painter's tape over the bolt so I'd spot any leaks. I will continue to keep an eye on it,

Are you seeing any seepage?

[Duccrazydave]

I, unfortunately, have had the experience of completely botching an otherwise flawless cam swap on an old KZ1000, by the method Boxerboy55 speaks of. 0-50 lb ft wrench tightening ( I mean stripping) a 20 lb ft bolt. However, if you're that particular about torque values when it comes to smaller fasteners, Park tools is a good source.
https://www.parktool.com/en-us/product/r...rque+Tools

[Liteitup]

Yep, the only bolts I have ever broken were small sized ones done with a torque wrench. The first click I heard was more of a "snap!".

[Grumpy Goat]

Of course, with small fasteners an “uncalibrated wrist” can have the same result. I’d rather get a good small torque wrench if a torque is specified.

[runnerhiker]

Of course, with small fasteners an “uncalibrated wrist” can have the same result. I’d rather get a good small torque wrench if a torque is specified.

+1

[Ray]

I had the wrench set correctly, but stopped when I felt it was "good n tight".

Right - as a once-upon-a-time professional bicycle mechanic, I spent my share of time shearing cheap, small bolts.  

Your comment demonstrates you have a better feel than your torque wrench. 

I'll only note that finding accurately calibrated torque wrenches that were better than my judgement was always a challenge. Finding accurate estimates of torque settings for specific bolts and uses was even harder. 

That said - I'm with Dave. I grew up with and have invested a small fortune in Park tools through the years (and Darrell and MrVvrroomm appreciate, this is a US company that contributes significantly to the tax base of the Twin Cities in MN).

[Lee]

I have a Craftsman 5 to 80 ft-lbs torque wrench. I don't trust that for small torques and keep thinking about a Park Tool wrench for the small stuff.