CB550k3 petrol tank not fitting snuggly

[davidrsmith]

Hi

I have just put the petrol tank back on the bike ready for an MOT, however, at the front where the tank sits on the two rubber mounts the tank seems to able to move around a lot, as if the tank has been widened or pulled open underneath. There appears to be nothing visually wrong with the tank. I have ordered new mounting rubbers.
If anyone has a tank off a bike could they give me the measurement from tank side to tank side inside of the metal collars which locate on the mounting rubbers.
I don't remember there being such a gap on my original 550. I just don't want it to fail the MOT for this as during the winter I intend to respray the tank.
Many thanks
Dave

[Menno]

Yeah, I've seen that problem before.

I'll take a look for you to see how much the space between the tank...

So the old one should have 11,4 cm
The new one 10,4 cm between the brackets for the rubbers...

[davidrsmith]

Thanks for doing that for me, it will give a reference when I take the tank off and measure my tank

Dave

[Seabeowner]

Can happen if someone has tried air pressure to remove dents. I did it on a z650 in my youth. Yes, yes, the dent is coming out, oh s*** the tank now looks like a duck with fat wings.
Also had a 500 tank that was about 10mm wide and used it for years with a couple of spacers on the mounting stubs behind the rubber mounts.

[Tomb]

Can happen if someone has tried air pressure to remove dents. I did it on a z650 in my youth. Yes, yes, the dent is coming out, oh s*** the tank now looks like a duck with fat wings.

The trick is to use a ratchet strap wrapped round the tank several times, holds it all in place whilst the dent comes out.

And can be used to pull the shape of the tank back in when they have gone a bit wide, DAMHIK

[davidrsmith]

Hi

Just measured the gap on my tank and it is 11.6 cm, I was thinking of a couple of spacers on the mounting rubber stubs, or making the mounting flanges on the tank a little wider by pop riveting on some new strips onto the flanges.
Having never tried it, but wouldn't putting straps around the tank to pull back into shape just dent the tank even more?

Dave

[Tomb]

but wouldn't putting straps around the tank to pull back into shape just dent the tank even more?

Dave

Never has yet. Ratchet straps are flat fibre banding so don't do any harm to the tank, keep the ratchety thing under the tank

[matthewmosse]

I think I found swapping out my tank rubbers for another set sorted mine, both were used, I never buy new if it can possibly be avoided. Being my bikes, the rubbers that had too much play were from a job lot of cb550 bits and so were the replacements but being cheap job lots either could have been wrongly sorted. It's a hazard of old bikes, any used part might be mixed up from elsewhere. I have been known to pack the rubbers out with washers behind and electrical tape wrapped around which is surprisingly effective at compensating for worn out mounting rubbers. Means you can keep riding whilst you wait on spares to pop up at a sensible price.

[Ashdowner]

Both my spare K3 tanks are 10.6cm or as close as I can measure them

[Menno]

Please be carefull trying to 'rattle' the tank back into shape with these straps.
If done wrong the tank can 'knick' in the upper corner and at the rear.
Those two points are the only two preventing the tank from bending.
If the tank bends to fast you'll get two very strange dents on the tank causing the tank to shift in height a couple of mm.

Seen that as well...

[Tomb]

Very true, hence the DAMHIK

The best way is to use the strap BEFORE using compressed air to stop the bending happening

The trick is to use a ratchet strap wrapped round the tank several times, holds it all in place whilst the dent comes out.

And can be used to pull the shape of the tank back in when they have gone a bit wide, DAMHIK

The old saying "If you never do anything - you never do anything wrong" is right. And when a tank is dented its worth having a go.

I have one to do on a Chinese Keeway 125 I'm getting ready for my son, that will require air pressure and a glued on slide hammer, and another on an XJ1100 Maxim that should pop out easily. All with ratchet straps to stop the bending (or probably better described as "straightening")