Thread size

[Flying Scotsman]

What is the thread size for the lower frame rail bolts.The 2 bolts on each side at the back of the frame rail.I know its M8 but was wondering if its a M8-1.25 thread in the frame.Anyone know the pitch.

[Arnie]

Pretty sure you're correct that its an M8-1.25

However, the hole in the rail is 10mm, and IMO the best way to stop these bolts from breaking or loosening is to drill and tap the threaded hole in the frame so that you can use 10mm bolts.

Arnie

[Flying Scotsman]

Thank you Arnie.
Yes i know I can tap it bigger.
I already have a bag of M8 1.25 helicoils I use on my GP1200 cylinders if the frame is solid enough there I can pop a helicoil in there.Saves me looking for new bolts.

[Paul1965]

What is the thread size for the lower frame rail bolts.The 2 bolts on each side at the back of the frame rail.I know its M8 but was wondering if its a M8-1.25 thread in the frame.Anyone know the pitch.

Scott, you could always text me a pic of the bike where the bolt is and I'll pull one out of mine and measure it for you.

[Flying Scotsman]

I can check when I get out to the garage in the next couple of days.

[FJmonkey]

Confirmed, M8-1.25 x 35MM, I took the bolt from this spot.



Then used the proper tools to measure"

[Flying Scotsman]

Awesome I have a bag of those have the drill tap and insert tool as well.
My 85 has 2 stripped on the left side.

[Pat Conlon]

Look at getting grade 10.9 if you want to stay at M8x1.25 which is what I did on my '84
On my old '92 (now Paul Lawson's) and on Jason Lawson's '93 we replaced the M8's with M10's
2 of the M8's were sheared on the '92 and 3 (of the 4) were sheared on the '93.