F: Frame Petrol Tank Bolts

J

James B

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Hi all

Currently struggling with tank attachment - one of the threaded holes for the tank bolts in the headstock has decided to surrender its threads
I’m looking to repair it but first need to identify the thread. My current best bet is 5/16 BSF. Is this correct? Know thy beast, my normal go to, was unhelpful in this regard.
I’m planning to attempt a helicoil - unless there is a better way?

James
 
greg brillus

greg brillus

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Yes 5/16 BSF...... a helicoil will work fine, apart from one issue that can happen, and that is the replacement bolts are generally made of stainless steel. As stainless is about as forgiving as a brick verses glass, be sure to lube the bolt threads with some grease or antiseize which is best but messy. If you don't do this, it is very possible that when the bolt is removed it will extract the helicoil with it. Be sure to use grease on the drill and tap when you carry this out, as any swarf that is allowed to fall into the headstock will settle atop the lower bearing race, not ideal for the bearing assembly. Good luck with it all............ Greg.
 
davidd

davidd

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5/16" X 22 BSF FT84

Often the thread is longer and I think the Club offers a longer version of the bolt thread. It is in KTB.

David
 
davidd

davidd

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Did I give the wrong number? I just read it off the bolt head. It must be a series B trick!

David
 
vibrac

vibrac

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A good tool for fitting those bolts is a socket with an extension and a short 5/16 socket ( mine is ground down) so you can get a good push I also grind a bit of a taper on one side of the large dia rubber it helps slip it in Without looking for the MO drawing isn't the rubber shown the wrong way round there?
Why the minutia? Time is short in the paddock and you get that sinking feeling to hear the words "the tank will have to come off":(
 
B

BigEd

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vibrac said:
A good tool for fitting those bolts is a socket with an extension and a short 5/16 socket ( mine is ground down) so you can get a good push I also grind a bit of a taper on one side of the large dia rubber it helps slip it in Without looking for the MO drawing isn't the rubber shown the wrong way round there?
Why the minutia? Time is short in the paddock and you get that sinking feeling to hear the words "the tank will have to come off":(
Click to expand...
Interesting that fellow sufferers (Vibrac) come up with similar solutions. I use a speed brace and socket to hold the bolt straight and keep a little pressure on until the bolts starts to screw in square. If you don't want to shorten your socket drop a 5/16" nut into the socket first so the bolt head doesn't disappear too far into the socket. Don't tighten them up too tight and risk stripping the thread. (Over the years it is most likely these bolts have been put in cross threaded at some time.) I only just nip them up so the rubber is not compressed or you end up with a rigid rather than flexible mount.
 
Albervin

Albervin

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vibrac said:
A good tool for fitting those bolts is a socket with an extension and a short 5/16 socket ( mine is ground down) so you can get a good push I also grind a bit of a taper on one side of the large dia rubber it helps slip it in Without looking for the MO drawing isn't the rubber shown the wrong way round there?
Why the minutia? Time is short in the paddock and you get that sinking feeling to hear the words "the tank will have to come off":(
Click to expand...
Yes, the drawing is wrong and is a trap for new/young players. Silicone grease on rubbers and nickel/copper slip on the bolt is the answer plus a bit of "feel" before you screw it in.
 
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