Unequal lower fork tree pinch bolts on 1980 SE

[Trev]

Hi All, I'm new to the XS650 and I've just started looking at my project '80 SE.
One of the first jobs is a front fork rebuild. On striping them out of the frame I noticed the lower tree pinch bolt pairs are uneven. I've got M8 in the upper positions and M6's in the lower. Anybody come across this before? All the references I've found so far are M8's in both positions.
This bike is an all in one piece basket case that appears to have been subjected to some dubious work, so everything is getting 'questioned'.
Thanks for any input, Trev.

 

[Jim]

Can you put some pics up here?

 

[jpdevol]

Welcome!

Perhaps a measurement of the upper fork tube's diameter too?

 

[Trev]

Thanks!
I will try to get the measurement and a photo hopefully tomorrow.

 

[gggGary]

From the 80 parts fiche.
PErhaps someone snapped off the bolts, drilled inside the remains and retapped?

 

[Trev]

Sounds horribly viable. Thanks for the fiche shot. Trev.

Doh! didn't press the post button last night...

 

[Trev]

Working on the bike round a mates and he's put the legs away safe, so no measurement. I think the nail has been hit though...
I'm reasonably sure both holes should be blind?
Thanks, Trev.

 

[Jim]

Those bottom holes are not blind. What you're looking at is normal..... other than the buggered threads that is.

 

[Trev]

Thanks for the info Jim.
The buggered part appears to be the remnants of the M8 where they went a bit off plumb. In the darkness lurks about 2D of M6 thread, like the nearside photo shows better.

 

[gggGary]

Kinda looks like the original bolt remains are slightly to the left, of a new hole drilled and tapped?
Other one looks like the hole stayed centered in the old bolt.
a light clean up with an angle grinder or file should reveal if that's the case.

 

[Trev]

Yep, that's what I'm seeing with eyeball, didn't manage to capture it so well with the photos.
I've never had this beast running, so the target is a safe MOT and a couple of hundred miles clocked up before winter if nothing goes wrong...
With a nominal torque of 14.5 lb/ft I'm leaning towards cleaning them out with a thread chaser and if the threads are all good and 2xD I'll use them until I can helicoil them back to M8. Note: Grade 10.9 HT bolt minimum!

 

[Trev]

Just to finish this thread off, this is what is in place for the time being. The tensile specification for these bolts is 12.9 Zinc Plate, which means 14.5lbft (≈20Nm) is right on the recommended seating torque. Length selected to see the nose at the other end.
If anyone else ever has the misfortune to be in this zone, do not do this with the more commonly available 8.8 grade bolts. Something will go horribly pear shaped.