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Tank bolts shaking loose

danno

Well Known and Active Forum Website User
VOC Member
Hi
The front tank bolts on my Seies C Rapide seem to gradually undo themselves
due to vibration.
The RH thread in the headstock is worn so may need a helicoil.The LH bolt tightens
but still tends to undo even when threadlock is used.
They do seem to be difficult to tighten as they need to be pushed in while being rotated
due to the rubber sleeve.
Any ideas as to what thread size/type they are?
Any help appreciated.
 

Albervin

Well Known and Active Forum Website User
VOC Member
Try to find some (slightly) longer bolts with a tapered end. The taper will help centre the bolts (hex screws is what engineers call them, I think) and the extra length will bite into the unused section of thread.
All in KTB plus other enlightening books. Use a rubber grease to ease them through a bit easier although that does in some way undo the job of the rubber preventing the bolts from undoing themselves. And make sure the rubbers are inserted correctly, NOT the way depicted in the drawings.
 

danno

Well Known and Active Forum Website User
VOC Member
Thanks. The bolts have quite a short thread,just over 1/4" with a shoulder.
I do have some similar 5/16" BSF & BSW bolts but the thread is not the same
when inserted.
The bike was renovated mid 90's so I'm not sure if they're the same type as the originals.
 

Howard

Well Known and Active Forum Website User
VOC Member
Have a look at how well the threads work without the tank on, or at least without the rubber bushes. If loctite and the tight rubber doesn't stop it vibrating loose, I suspect the threads are stripped or possibly different sizes.
If it's stripped in the UFM you may find enough good thread with a longer bolt (as Alyn says). As a quick fix you could use a long bolt (or setpin) to use the maximum good thread, and slip a piece of tube over it, the same length and o/d as the original shoulder (assuming you don't have machining facilities to knock up a longer shouldered bolt).

Good Luck

H
 

danno

Well Known and Active Forum Website User
VOC Member
Thanks. I think I'll have to take the tank off to have a good look.
I assume tank removal is fairly straight forward. First time I've done it!
 

1660bob

Well Known and Active Forum Website User
VOC Member
Hi Danno, are the bolts tightening fully to a dead stop on the shoulder on the bolt? I found that with all new bolts/rubbers/ washers that the rubbers were being horribly "oversquashed" and squelched before the bolt could be tightened onto its shoulder (it was actually bending the tank inwards!!), so I spent some time undercutting the bolt heads in a lathe to relieve pressure on the rubbers so that only the last 1/2-3/4 turn actually nips the rubbers (which is plenty) and the bolt bottoms out on its shoulder nicely to nip up securely.
 

stumpy lord

Well Known and Active Forum Website User
VOC Member
Hi Standard bolts are 5/16 B.S.F.
When fitted correctly the shoulder is supposed to be tightend down hard against the boss on the head stock( thats why they are shoulderd), if not the torsion built up in the rubber when fitting tends to cause the bolt to undo.
If you carry out a helicoil repair to the head stock then you must have a pair of tank bolts made up that have a larger diameter on the shoulder, other wise when you tighten the bolts down the, the shoulder will be bearing against the end of the helicoil insert and not the boss on the head stock, you will of course have to enlarg the hole in the rubber bush to acomodate the larger dia of the new tank bolt.
Hi
The front tank bolts on my Seies C Rapide seem to gradually undo themselves
due to vibration.
The RH thread in the headstock is worn so may need a helicoil.The LH bolt tightens
but still tends to undo even when threadlock is used.
They do seem to be difficult to tighten as they need to be pushed in while being rotated
due to the rubber sleeve.
Any ideas as to what thread size/type they are?
Any help appreciated.
 

danno

Well Known and Active Forum Website User
VOC Member
The LH bolt tightens ok but I find I have
to pack out the socket on the ratchet spanner with nuts so pinward pressure can be applied.
Otherwise the bolt just rotates
The rubbers do seem to be bulky and



they grip the bolt making it difficult to
turn it.

I've got plenty of taps and dies but no metlathe so unable to turn up a modified bolt.
 

danno

Well Known and Active Forum Website User
VOC Member
Made a bit of a mess of that last post.Trying to do it on my phone!
Any ideas why I'm unable to edit my posts?

Have just checked and neither bolt tightens up against the headstock.Must be stripped.
They are difficult to turn,being gripped by the rubber which does tend to squash down a fair bit.

Thanks for the info on helicoiling. Handy if I need to do that.
I have loads of 5/16 BSF bolts but they didn't seem to fit although the thread looked the same.Are there various thread types?

As 'Albervin' suggests, I'll try and find a bolt without a shoulder that fits and see if there's any extra thread available.
 

Howard

Well Known and Active Forum Website User
VOC Member
Hi Danno, are the bolts tightening fully to a dead stop on the shoulder on the bolt? I found that with all new bolts/rubbers/ washers that the rubbers were being horribly "oversquashed" and squelched before the bolt could be tightened onto its shoulder (it was actually bending the tank inwards!!), so I spent some time undercutting the bolt heads in a lathe to relieve pressure on the rubbers so that only the last 1/2-3/4 turn actually nips the rubbers (which is plenty) and the bolt bottoms out on its shoulder nicely to nip up securely.

It's a long time since I had a proper Vin tank, but I'm pretty sure that if you're bending the tank, you've got the rubber bushes in back to front. The bushes should go into the tank from the inside of the brackets before the tank's fitted. From memory, I think the spares drawing shows them the wrong way round.

H
 
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