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F: Frame Comet Frame Tie


MartynG

Well Known and Active Website User
VOC Member
On behalf of another VRV member - In the Comet aluminium Frame Tie F106 there is an internally threaded bush F110 that the gearbox bolt upper F48/7AS screws into.

Here is the problem. At some time in the dim dark past a dastardly dodge was performed. The steel bush F110 was removed or lost and the bodge was to simply replace it with a nut! This left the end of the gearbox bolt with room to move about causing some distortion/enlargement to the hole in the Frame Tie that was designed to accommodate the F110 bush.

So now to rectify but there are some unknowns.

1. What should the ID of the hole in the Tie Frame for the bush be??
2. It is assumed the hole (once fixed) will need to be line bored to match up with the inside of F117 ?
3. What actually should be holding the bush F110 in the frame tie F106? If interference, how much?
4. Is there anything wrong (from a structural perspective) of enlarging the existing but misshapen hole in the tie frame and fitting a made to fit bush, keeping #2 in mind?
5. Given that there is no stress in that part of the Tie Frame, could the hole be repaired with a form of Liquid metal - Loctite has a few such products in their range?

Sensible suggestions sought.
 

erik

Well Known and Active Website User
VOC Member
I would recommend welding and line bored to standart size .Best done on a cnc mill.Erik
 

Bill Thomas

Well Known and Active Website User
VOC Member
Morning Martyn, Just took one apart.
First thing is the " NUT " Has a Spline, So for me it's tricky to tell you exact !.
The OVERALL length is 718 thou, The top hat lip is 110 thou ish.
The Male spline is 705 thou, But that is the outside of the spline !.

The hole in the Alloy Lug is 700 thou , But again the inside of the spline ???.
The width of the alloy Lug is 625 thou.
I warmed F106 in front of the Electric fire and gave it a big wack !,
So it's tight but not too much.
As you know the Alloy Tube that slides for alignment, Is not tight, So I don't think it has to be spot on ?.
Good Luck, Bill.
 

MartynG

Well Known and Active Website User
VOC Member
Morning Martyn, Just took one apart.
First thing is the " NUT " Has a Spline, So for me it's tricky to tell you exact !.
The OVERALL length is 718 thou, The top hat lip is 110 thou ish.
The Male spline is 705 thou, But that is the outside of the spline !.

The hole in the Alloy Lug is 700 thou , But again the inside of the spline ???.
The width of the alloy Lug is 625 thou.
I warmed F106 in front of the Electric fire and gave it a big wack !,
So it's tight but not too much.
As you know the Alloy Tube that slides for alignment, Is not tight, So I don't think it has to be spot on ?.
Good Luck, Bill.
Thanks Bill
 

Bill Thomas

Well Known and Active Website User
VOC Member
Just thinking Martyn, I don't think it has to be a spline ?, I would make up a nut a few thou bigger than the hole and Loctite it, Making sure the stud thread is a nice free fit, And grease the thread before fitting, To help if you have to take the Gearbox out later.
 

Attachments

vibrac

Well Known and Active Website User
VOC Member
I think that it will receive considerable torque on the 1/2" bolt and long term locktight may not be enough, a spline takes a considerable amount as any kickstart would tell you . My take would be entirely as above, but add either a spirol pin or a countersink cap screw of appropriate length up from the unseen underside of the boss into the plug nut since the new plug nut hole will be bigger (to remove residual spline groves?)there will be enough body. to be OK just run the tap down after.
 

Bill Thomas

Well Known and Active Website User
VOC Member
I don't do that bolt up too tight, I had the head come off a Stainless one, After not been touched for a long time, Trev seemed to think it was two different types of stainless, Where the nut was welded on the stud.
The old ones in steel were brazed.
 

vibrac

Well Known and Active Website User
VOC Member
Like most penny pinchers I make up my 1/2" bolts like front wheel spindles on racers I thread on a nut with good interference face off reduce part of plain portion to thread depth if appropriate and add a spirol pin.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Yes I love stainless, But I won't use it there again, Funny I found the old one, I knew exactly where it was after many years !, And fitted it.
I got a BSA Cad' one I will rethread, For the new bike.
 
Last edited:

oexing

Well Known and Active Website User
VOC Member
Not quite knowing much about this trouble why not fabricating a threaded bush and go for next size internal thread for the alu frame tie. So you´d make a bush with that oversize thread on the outer diameter that has the old size internal thread for the standard bolt. A Helicoil would be too slim but you can do your own bush instead. So no need for a flanged nut, the threads will hold the pull.
Spiral pins for locking nuts on their thread ??? Nooo, a bit of Loctite 270 and you´d be VERY challenged to undo this . . . .

Vic
 

davidd

Well Known and Active Website User
VOC Member
I have always made the F106's for the BAR gearbox. As a result, I used an American bolt and had to make the splined nut. I turned it up on the lathe and put a 1/2" x 13 tpi thread inside for my bolt. I made it to the dimension with no attention to interference, but I used a chisel to stamp a few splines in place. Pushed it in with some Loctite and none have ever failed. I did not line bore, but on the F106's I cast up I worked hard to get everything lined up.

I am not suggesting that this is the best way. It worked for me with good alignment, etc.,

David
 

Black Flash

Well Known and Active Website User
VOC Member
Maybe you can remake this lipped nut with a course o. d. thread instead of the splines and tap a thread into f106.
then screw in the nut with 638 or 648 loctite. I would believe this will do the trick permanently.

Cheers Bernd
 

Marcus Bowden

Well Known and Active Website User
VOC Member
These are not splines, as Frank Griffin calls them serations, I make them with a knurling tool with straight teeth, same hole and sleeve/nut knerl it then fit with assistance of a strong vice.
The damaged one you are talking about, how much is the hole out of round? If not too bad make slightly larger O/D knurl it and force it in, I removed this one and fitted a S/S one because Eddy s/s Stevens did it too !.
bananaman.

IMG_1379.jpg
 

Marcus Bowden

Well Known and Active Website User
VOC Member
Certainly Bill,

Straight knurler. use it to make battery clamp knobs and rear wheel adjusters and some where I also have a straight knurling wheel mounted the other way to use as a boring when I do bearing housings to make a bearing fit more tightly
Diamond knurler uses two oposite handed helical wheels but is a little chunkier as it has 6 wheels in pairs and it all revolves round on a central axel but that is down on the big lathe down the road in Harvey's big workshop.
Not that he uses it much but handy for me.
IMG_1387.jpg
 

Bill Thomas

Well Known and Active Website User
VOC Member
I am getting better !, I was only 13 thou wrong, That's good for me, I am a feet and inches man.
 

oexing

Well Known and Active Website User
VOC Member
I cannot see any benefit of the splines, they do not hold any pull from the bolt, just prevent a threaded insert from turning in its bore while doing up the bolt. You´d typically go for a helicoil but I guess the mangled bore is too large for that. So instead I´d fabricate a bush with threads inside and out after finding a tap for the oversize F106 bore. With that lipped nut all the force from bolt load goes into the small cross section at the lip/head. So no wonder you can snap it and pull the knurled part into the frame tie - not great.
An even easier way is to line ream the frame tie to get a nice parallel bore out of the mangled hole. Then you can do a decent measure of the bore and fabricate a nice threaded and lipped ss bush with the 1/2 " thread and loctite it into the frame tie with type 638 or 648. Still all load will go into the lip cross section but there will be a bit more material after reaming to oversize first. No need for knurling,the Loctite cares for locking the bush safely while tightening the bolt.

Vic
 

MartynG

Well Known and Active Website User
VOC Member
Thanks for all your input. The bike in question is not mine, its not a matching numbers and it has been somewhat 'enhanced' 600cc kit,electric start and lots more so no need to fuss about keeping it original.

Based on comments received I propose to recommend to the owner that the elongated hole in the F106 be enlarged to a 'standard' size that is in alignment with the hole on the other side then make up a bush from aluminium or brass that is a light press fit (helped out with loctite) into F106 and has a bore that will accept a new shaft that will replace the gearbox upper bolt - this new shaft will be approx 3/4" longer than the original so when fitted it protrudes a sufficient distance out from the F106 to fit a washer and nut.

Other than purist cosmetics - are there any problems with this?
 

Bill Thomas

Well Known and Active Website User
VOC Member
Just check it is clear for the chain and sprocket, I made a long bolt from a BSA stud and thought it should not go too long, Not sure why. Cheers Bill.
 

Bill Thomas

Well Known and Active Website User
VOC Member
I cannot see any benefit of the splines, they do not hold any pull from the bolt, just prevent a threaded insert from turning in its bore while doing up the bolt. You´d typically go for a helicoil but I guess the mangled bore is too large for that. So instead I´d fabricate a bush with threads inside and out after finding a tap for the oversize F106 bore. With that lipped nut all the force from bolt load goes into the small cross section at the lip/head. So no wonder you can snap it and pull the knurled part into the frame tie - not great.
An even easier way is to line ream the frame tie to get a nice parallel bore out of the mangled hole. Then you can do a decent measure of the bore and fabricate a nice threaded and lipped ss bush with the 1/2 " thread and loctite it into the frame tie with type 638 or 648. Still all load will go into the lip cross section but there will be a bit more material after reaming to oversize first. No need for knurling,the Loctite cares for locking the bush safely while tightening the bolt.

Vic
Vic , The bit that snapped on mine was the other end, Standard it is 1/2" stud with a nut brazed on the end, But the new one I bought was Stainless !, The stud was one type of stainless and the nut was another,
It had been on there for a long time and some sort of reaction had happened, I put photos of it on the Forum,
I was a mechanic all my working life, Not known for over tightening things, But I had put a spring washer under the head, And one day as I was about to go for a ride, I looked down and saw the nut part was on the piss,
Soon as I touched it, Off it came. Cheers Bill.
 

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