Author Topic: [Fix] How to cheaply fix a leaking gear oil plug/bolt  (Read 1321 times)

mousejunks

  • Hero Member
  • *****
  • Posts: 585
    • View Profile
[Fix] How to cheaply fix a leaking gear oil plug/bolt
« on: May 09, 2021, 09:18:01 AM »
When doing the gear oil change for the first time, I noticed that the 8mm fill plug was on very tight and  I was never unable to torque it back on properly. Being overtightened and stripped, this caused the plug to weep oil over the course of hundreds of kilometres. My dealer wanted to take the whole transmission apart, which would have been an expensive exercise. As a DIY person I decided to find the simplest and cheapest way to repair the leak. I didn't like the idea of using a matching 8mm helicoil or timesert or tapping a larger 10mm hole as the drilling process of a blind hole would put metal shards all inside the transmission.

Looking into the stripped hole, I noticed that the stripped hole was deeper than the bolt and there was still some good thread remaining. Using this idea, I decided to replace the original bolt with a longer one.

The original bolt was M8 x 1.25mm and 12mm long with a flange. The new bolt to be used is a longer 16mm bolt (with a hex insert dome head because I like the shape). I also decided to use a 8mm Dowty washer, which is a special washer that comes with a bonded rubber seal, like an O-ring. If it's good enough for high pressure oil and hydraulic lines, it should be enough for a transmission.

The new 16mm bolt and Dowty washer was screwed into the stripped hole and torqued to spec (10 Nm) with no issues. I made sure that there was no metal bits or loose threads in the hole and that the tip of the bolt didn't make contact with any of the gears in the transmission. Just to be safe, I drained and replaced the gear oil to flush out any debris in the transmission.

Overall the fix cost less than $15 and all parts came from eBay. After a long ride there were no leaks, so the job is done. This may also work for engine oil drain plugs too.
« Last Edit: May 09, 2021, 01:53:09 PM by mousejunks »
'09 Kymco Espresso 150i
'11 Kymco Downtown 300i ABS - 79,500km
'17 Kymco Downtown 350i ABS

Ruffus

  • Hero Member
  • *****
  • Posts: 1733
    • View Profile
Re: [Fix] How to cheaply fix a leaking gear oil plug/bolt
« Reply #1 on: May 09, 2021, 09:49:21 AM »
@Mouse, first of all congrats to your repair. Thinking, tackling and solving a technical challenge, this is what counts.
Even taking off muffler, wheel and gear to repair/ insert a HELICOIL thread and taking your transmission off is not a big deal. It's just removing bolts.
Depends on space and tools available to you.

 In my experience, torque-figures are way to high in nearly any manual, and people additionally tend to use a 1/2 inch tools to tighten bolts, which is in most cases the kill of alu-threads.
But again, congrats.
Happy and safe scootering, Ruffus

CROSSBOLT

  • Hero Member
  • *****
  • Posts: 7760
  • West Tennessee, USA
    • View Profile
Re: [Fix] How to cheaply fix a leaking gear oil plug/bolt
« Reply #2 on: May 09, 2021, 01:32:33 PM »
Absolutely a genius, rightious repair! Gotta be a KISS and a KICK award somewhere for stuff like this! You wanna know what KICK is, doncha?! Keep It Cheap, Kid!
Karl

Three motorcycles 1960-1977 (restored a 1955 BSA)
Agility 50
Yager 200i
Downtown 300i
Navy tech, Ships Engineer, pilot and aircraft mechanic

Ruffus

  • Hero Member
  • *****
  • Posts: 1733
    • View Profile
Re: [Fix] How to cheaply fix a leaking gear oil plug/bolt
« Reply #3 on: May 09, 2021, 01:44:41 PM »
@CROSSBOLT, everyday something to learn from YOU mature guys...
😊
Happy and safe scootering, Ruffus

Stig / Major Tom

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 14674
  • Rural Ohio
    • View Profile
Re: [Fix] How to cheaply fix a leaking gear oil plug/bolt
« Reply #4 on: May 09, 2021, 02:36:04 PM »
Really, really old guys know better than to use a torque wrench on any small fastener in alloys.
On such tiny bolts a torque wrench has probably caused more leaks -- than prevented.
Stig
Boston Strong
Rural Ohio

And, I'm feeling a little peculiar.

mousejunks

  • Hero Member
  • *****
  • Posts: 585
    • View Profile
Re: [Fix] How to cheaply fix a leaking gear oil plug/bolt
« Reply #5 on: May 09, 2021, 02:53:16 PM »
Really, really old guys know better than to use a torque wrench on any small fastener in alloys.
On such tiny bolts a torque wrench has probably caused more leaks -- than prevented.
Stig

I always torque small screws and bolts by feel, just tighten until the surfaces meet and give an extra push, no more.

Also a pic of the prior oil leak after one ride.
'09 Kymco Espresso 150i
'11 Kymco Downtown 300i ABS - 79,500km
'17 Kymco Downtown 350i ABS

scooterfan

  • Hero Member
  • *****
  • Posts: 764
  • Durban, South Africa to Ankeny IA.
    • View Profile
Re: [Fix] How to cheaply fix a leaking gear oil plug/bolt
« Reply #6 on: May 09, 2021, 04:59:54 PM »
To my understanding the new 16mm bolt / plug is actually just holding to 4mm undamaged thread.
Sorry about being negative - but I think torquing that nut to normal specs (10Nm) is like playing with a lion's left testicle.
The Dowty washer obviously has nothing to do  holding the plug firmly - it only helps to prevent an oil leak. Whatever you do in future - I think you need to stay away from torquing that that to 10Nm - I think that 4mm thread will never last with such high torque.
Life is a journey. Just spend some time, and enjoy the trip.

CROSSBOLT

  • Hero Member
  • *****
  • Posts: 7760
  • West Tennessee, USA
    • View Profile
Re: [Fix] How to cheaply fix a leaking gear oil plug/bolt
« Reply #7 on: May 09, 2021, 07:12:21 PM »
I always torque small screws and bolts by feel, just tighten until the surfaces meet and give an extra push, no more.

Also a pic of the prior oil leak after one ride.
Following is opinion-BEWARE!
Now, I understand what it was, why it leaked, how it stripped and what my fix was.
Fill bolt originally supplied with NO WASHER of any kind.
It leaked because of rough metal.
It got stripped because original owner or some tech cranked it to stop the leak.
I used an appropriate solt aluminum washer which is effective. Your rubber insert washer is better.
Karl

Three motorcycles 1960-1977 (restored a 1955 BSA)
Agility 50
Yager 200i
Downtown 300i
Navy tech, Ships Engineer, pilot and aircraft mechanic

mousejunks

  • Hero Member
  • *****
  • Posts: 585
    • View Profile
Re: [Fix] How to cheaply fix a leaking gear oil plug/bolt
« Reply #8 on: May 10, 2021, 03:23:16 AM »
Has anybody on this forum actually been successful in repairing a stripped gear oil hole using a helicoil or timesert? I'd like to see some photos of the process. How do you not get metal swarf inside the transmission?
'09 Kymco Espresso 150i
'11 Kymco Downtown 300i ABS - 79,500km
'17 Kymco Downtown 350i ABS

CROSSBOLT

  • Hero Member
  • *****
  • Posts: 7760
  • West Tennessee, USA
    • View Profile
Re: [Fix] How to cheaply fix a leaking gear oil plug/bolt
« Reply #9 on: May 10, 2021, 10:56:59 AM »
Has anybody on this forum actually been successful in repairing a stripped gear oil hole using a helicoil or timesert? I'd like to see some photos of the process. How do you not get metal swarf inside the transmission?
Hook an air hose to the drain to have a constant fairly strong flow of air out the boogered hole you are drilling/tapping. Coat the drill and tap with heavy grease before you start.
Karl

Three motorcycles 1960-1977 (restored a 1955 BSA)
Agility 50
Yager 200i
Downtown 300i
Navy tech, Ships Engineer, pilot and aircraft mechanic

mousejunks

  • Hero Member
  • *****
  • Posts: 585
    • View Profile
Re: [Fix] How to cheaply fix a leaking gear oil plug/bolt
« Reply #10 on: May 11, 2021, 02:51:55 AM »
Hook an air hose to the drain to have a constant fairly strong flow of air out the boogered hole you are drilling/tapping. Coat the drill and tap with heavy grease before you start.

Very smart, although I don't have an air compressor (yet).
'09 Kymco Espresso 150i
'11 Kymco Downtown 300i ABS - 79,500km
'17 Kymco Downtown 350i ABS

JJJoseph

  • Hero Member
  • *****
  • Posts: 892
  • Kymco Sento
    • View Profile
Re: [Fix] How to cheaply fix a leaking gear oil plug/bolt
« Reply #11 on: May 11, 2021, 05:25:35 AM »
Has anybody on this forum actually been successful in repairing a stripped gear oil hole using a helicoil or timesert? I'd like to see some photos of the process. How do you not get metal swarf inside the transmission?

I would just take the transmission apart.  It only takes about 15 minutes, and is almost a no-brainer.  It comes apart in two pieces, one of which holds all the gears.  Your problem bolt is in the case & is easy to access. It can be tapped to the next larger size and re-assembled in another hour.  You might need a gasket, which can be cut from gasket sheet. Put away the torque-wrench!

CROSSBOLT

  • Hero Member
  • *****
  • Posts: 7760
  • West Tennessee, USA
    • View Profile
Re: [Fix] How to cheaply fix a leaking gear oil plug/bolt
« Reply #12 on: May 11, 2021, 01:45:12 PM »
I would just take the transmission apart.  It only takes about 15 minutes, and is almost a no-brainer.  It comes apart in two pieces, one of which holds all the gears.  Your problem bolt is in the case & is easy to access. It can be tapped to the next larger size and re-assembled in another hour.  You might need a gasket, which can be cut from gasket sheet. Put away the torque-wrench!
I can't even get ready to ride in 15 minutes!
Karl

Three motorcycles 1960-1977 (restored a 1955 BSA)
Agility 50
Yager 200i
Downtown 300i
Navy tech, Ships Engineer, pilot and aircraft mechanic

JJJoseph

  • Hero Member
  • *****
  • Posts: 892
  • Kymco Sento
    • View Profile
Re: [Fix] How to cheaply fix a leaking gear oil plug/bolt
« Reply #13 on: May 22, 2021, 07:17:57 PM »
I can't even get ready to ride in 15 minutes!
Haha!  Just slow down!  Everything's going to be all-right!

An Error Has Occurred!

Call to undefined function split()