Topic: '73 CB750 Oil line bolt (6x25) hole stripped

[Mark K]

Installed the oil line 6x25 bolts that connect oil lines to engine case. Noticed when I tightened one of the bolts, felt like it slipped and was somewhat loose again. Uh-oh, stripped threads I thought. Removed bolt, tapped hole with same size tap, used a slightly shorter length bolt, worked until I had to remove the line and when I reinstalled line, the shorter bolt did the same thing. Time for a helicoil, right? Never used a helicoil before, and finding there are SO many Heli coil kits for sale, my questions are;

1. Is there enough thickness in the case oil line bolt holes that it could be drilled out to the next larger size? And if so what size Helicoil would I use?

2. If there isn't enough thickness in the case holes, could I use the next smaller size Heli coil (5mm??) and go to a smaller bolt? And would this cause any issues with the smaller diameter bolt holding the oil line in place?

3. Would this be a good kit to buy? I've attached a picture.

Thanks in advance.
Mark K

[bryanj]

There should be enough metal to take a helicoil as its basicaly a 7mm thread fitted with a steel coil but try and fit a 2d  not the standard 1.5d length

[CB750R]

I helicoiled them 2 of the them on my old cases, the holes are blind, just don't go crazy with the drill bit as if you drilled through the back of  the hole you'll be in trouble.

[PeWe]

I have found one of those threads gone when assemble.  Used a longer bolt to use not used threads.
Measure depth to bottom first, too long bolt might pop the bottom.

About thread repair kits. Find M6 since this is the size. Most of the other not needed.
M8 sometimes for exhaust assembly to head.

[Mark K]

Thanks for the advice, really like the forum and the wealth of knowledge the members share with 'newbies' like me.

[MauiK3]

I'll just say, as others have, be sure you don't go too far and break out the bottom of the existing hole.
Bad berries!

[PeWe]

Pop bottom possible when using right bolt, but wrong hole
The 3 front case beside front sprocket. CB750.

I used a torque wrench it felt different at around 3-4 Nm. I planned to tighten 9Nm.
Checked and saw a hole to transmission. Thought it could have been an old damage entering dirty threads.

Found the bottom when removing oil pan which I had to do later. My fault only. A few chewing marks. Could have been expensive.

[Mark K]

There should be enough metal to take a helicoil as its basicaly a 7mm thread fitted with a steel coil but try and fit a 2d  not the standard 1.5d length

What is 2d? 1.5d??

[bryanj]

It is the length of the coil insert in relation to the diameter, 1.5 on a 6mm thread is 9mm deep, 2.0 is 12mm

[CB750R]

There’s standards of strength published by helicoil. https://www.stanleyengineeredfastening.com/-/media/Web/SEF/Resources/Docs/Heli-Coil/Tensile_Strength_Bulletin_Metric_LR.pdf

I have not had an issue with any of the helicoils I’ve used in my repair, unfortunately the previous owner of my bike had a very uncalibrated arm for torque.

[Mark K]

It is the length of the coil insert in relation to the diameter, 1.5 on a 6mm thread is 9mm deep, 2.0 is 12mm

Thanks for explaining it to me.

[Mark K]

Oil line bolt hole heli-coiled (?) succesfully!