Topic: Effects of hammering a gas tank

[stereosilence]

I have seen several people on here make their own knee dents by hammering and then filling. On many of the popular professional builds I see now, they like to have the "invisible battery" look and I presume they put it up in the tank. Is there a downside (besides reduced capacity to hammering out a spot to stow a battery in the underside of the tank? Does it not mess up the tank liner or anything like that?

[flybox1]

'Most" relocate the (smaller) battery and electronics under the seat cowl or in a low profile tray directly under the seat

[754]

If it had a tank liner you would have to redo it. tanks dont come lined at the factory..

Its a no turning back modification, and I am sure there are lots of failed attempts, or HEAVILY  BONDOed  tanks out there.

[stereosilence]

Here is a photo of the style I am talking about. Cleared out, no seat hump. In this case, there is a lithium ion battery on the swingarm, but I think some put the battery under the tank. Maybe it is just a bad idea because of heat.

I agree on the liner. Maybe I'll give it a shot years down the road. If everything else looks real nice, I may get a professional paint job on the tank and that might be a good time to experiment.

[Don R]

You won't be able to "hammer" a spot to hide a battery.  The metal would tear and it would ruin the tank anyway. Many of the bikes you see are kick only and have hidden a very small very $$$ lithium ion battery somewhere under the seat or tank, even on the swing arm.

[stereosilence]

Why will the metal tear? Folks hammer in the sides for knee dents all the time it seems.

[lrutt]

LiFeP0 battery under the swingarm would be the best way to go. Very small and Very easy to hide.

[lone*X]

If you are refering to hiding the battery inside the tank just think about the way the tank fits the frame backbone.  You would most likely have to use tunnel space and the tank would no longer fit over the backbone.  The knee dents are placed on a large convex surface and simply hammered into a concave surface.  The sheetmetal has room to reform.   Underneath the tank things are more complex and more rigid.   Any hammering in this area will most likely break welded seams and screw up the petcock area as well.  And it still wouldn't fit the backbone properly after that.   

Lots of threads on what battery to use and to where to relocate it and the electrics so just do some searches.

[750K]

I had a cb450 tank given to me last year and for #$%*s and giggles I hammered the sides in, I got way to over zealous and hammerd it in to the point that the bottom edge of the tank pulled up and outward haha. It was going to be an art piece for a m/c tank show, so I just pitched it in the recycling box. Pretty funny how distorted a tank can get once you start wailing away with a hammer, haha

[lucky]

Here is a photo of the style I am talking about. Cleared out, no seat hump. In this case, there is a lithium ion battery on the swingarm, but I think some put the battery under the tank. Maybe it is just a bad idea because of heat.

I agree on the liner. Maybe I'll give it a shot years down the road. If everything else looks real nice, I may get a professional paint job on the tank and that might be a good time to experiment.

That twin engine design is not a dry sump engine like the CB750.
Completely different .

[Elan]

Here is a photo of the style I am talking about. Cleared out, no seat hump. In this case, there is a lithium ion battery on the swingarm, but I think some put the battery under the tank. Maybe it is just a bad idea because of heat.

I agree on the liner. Maybe I'll give it a shot years down the road. If everything else looks real nice, I may get a professional paint job on the tank and that might be a good time to experiment.

That twin engine design is not a dry sump engine like the CB750.
Completely different .

well he didn't actually say it was a 750...

[750K]

Yes, the cb400t doesn't have an oil tank like the 750. But it has a battery and a big honkin air box right there, the OP is talking about battery relocation Lucky. Not oil tanks...

[TwoTired]

Batteries can dump all of their energy very fast.  A short, from a collision or accident can make sparks, and even make the shorted metal glow red hot until the battery converts all of its chemical conversion energy.

And you want to put this potential fireball between your legs and in front of your eyes?

I guess there are those who wish to go out in a blaze of glory.  (Or linger as invalids for 50 years).  Personally, I'd rather not be that "stylish".

[Don R]

Imagine a dent the size of a battery in the bottom of a tank. Take off your tank and look at it. The bottom of a tank is flat and has only small areas big enough to hide a battery. Metal will only stretch so far and there are seams and the frame tunnel to worry about.
 But I say if you think you can, get an old tank and go to town.  Your best bet would be cut and weld. I would turn the terminals down for safety reasons. Also consider your fuel capacity, do you ride any distance at all?  And don't blow it up.

[lrutt]

Batteries can dump all of their energy very fast.  A short, from a collision or accident can make sparks, and even make the shorted metal glow red hot until the battery converts all of its chemical conversion energy.

And you want to put this potential fireball between your legs and in front of your eyes?

I guess there are those who wish to go out in a blaze of glory.  (Or linger as invalids for 50 years).  Personally, I'd rather not be that "stylish".

Ducati has been doing that for a very long time on the Monsters at least, and likely others.

[TwoTired]

Batteries can dump all of their energy very fast.  A short, from a collision or accident can make sparks, and even make the shorted metal glow red hot until the battery converts all of its chemical conversion energy.

And you want to put this potential fireball between your legs and in front of your eyes?

I guess there are those who wish to go out in a blaze of glory.  (Or linger as invalids for 50 years).  Personally, I'd rather not be that "stylish".

Ducati has been doing that for a very long time on the Monsters at least, and likely others.

The details are in the design, not the concept.  Do you assume amateurs can design as well, or have the foresight to consider all eventualities?  Or, just that it works to the end of the driveway, or placement in front of a camera?

[bjbuchanan]

Ducati's have space considerations for the battery to be there tho. With other bikes you are making the space. I don't want to sound to jerkish but to me the idea seems totally retarded. Unless you had a teeny tiny battery how do you plan on making the space for the thing?

Good bodymen can make magic happen with metal but you can't just make more metal appear there, square cutout and all for the battery.

Safety wise I don't think it matters one bit, just have a cover on your battery terminals, it should anyway for safety purposes. Hiding stuff has to be worked out on an individual bike basis because of oil tanks, space considerations etc

[davis96]

Here is a photo of the style I am talking about. Cleared out, no seat hump. In this case, there is a lithium ion battery on the swingarm, but I think some put the battery under the tank. Maybe it is just a bad idea because of heat.

I agree on the liner. Maybe I'll give it a shot years down the road. If everything else looks real nice, I may get a professional paint job on the tank and that might be a good time to experiment.

The battery in this example is mounted on the swingarm

[754]

I wish that pipe would follow the downtube angle, and guck under the motor..tighter.
 Yeah put battery under swingarm..or if arm is extended, put inside swingarm..behind pivot..

[Geeto67]

anybody want to take bets on whether the op was planning on doing his mods with a claw hammer and not precise bodywork tools?

[stereosilence]

Yeah, this wasn't meant as an acrimonious debate. I wasn't planning on doing this. I was just curious because I see people banging away to make knee dents. That looks pretty sketch to me. I would that would have some sort of negative effects on the tank.

[Geeto67]

It does have negative effects on the tank if done improperly (which is how 90% of the cafe kids are doing it these days):

- you lose capacity. Some friends of mine and I actually sat down and figured out how much you lose by making a convex surface concave. Depending on the tank it can be as much as a gallon of gasoline.

- Usually the body filler adds unnecessary weight. Worse than that though, most hacks use cheap talcum based body filler like bondo which absorbs moisture and can actually cause rust and rot issues in the tank if handled improperly. Only a good quality synthetic or fiberglass based filler should be used (like Marglass).

- If you are just using a claw hammer to do the dent you could be work hardening the steel (making it harder to dent and therefore prone to crack or pull the seam away). you could also be making the metal thinner. Real bodymen use hammers that shrink and streach the metal to help maintain the integrity of the work piece - it takes skill.

- It makes you look like you don't know what you are doing. This is a reputational risk more than anything else - but if I see a stock tank with bashed in knee dents I usually assume the builder is a hack. Traditionally speaking, there were only two reasons to have knee dents: to hold knee pads or to increase the size of your tank. Old british (and some japanese) bikes have knee pads in the tank to give you something to grip back when performance riding meant you glued yourself to the bike. Over time the glue holding these knee pads would weaken and the pad would fall out. They also made the bikes look like grandpas motorcycle. Some mfgs (triumph I am looking at you) recycled tank desing so much that when knee pads fell out of favor the tanks still had the indents because they were cutting production costs. The other reason was to be able to carry more fuel - for a while it was a given that you needed 5 gallons of fuel to do the long course at the IOM on any bike that could do near 100mph average speed. Where do you put that extra fuel? in front of the riders knees. The majority of people today putting "knee dents" into old honda tanks are doing it purely for "style" thinking it makes the bike look older than it is. I rarely see anybody using proper tools to do it and there is usually a metric ton of bondo involved. But don't take my word for it, just search for how people do it on this site - you'll see plenty of pictures. Such need to put style over function makes me question what other concessions the builder made. Usually I don't want to talk to the owner because I don't really want to hear some 20 something tell me about his scene...... However, when I do see a properly done tank (one that is usually cut and welded to add capacity) I am eager to talk to the builder about his bike because that guy is clearly thinking about performance motorcycles.

But that wasn't the question you asked - you asked about hiding a battery.

[lucky]

Battery in a gas tank NO,no.no
That reminds me of the plane crash that killed 300 or so.
Electrical wires inside of the gas tank.

Just asking for trouble!

[Elan]

just to play devil's advocate...

The coils are up against the tank, aren't they just as dangerous?

If the OP had this done correctly, IE basically a custom tank made/shaped (not just a hammer),and lined the space that the battery fits into with rubber, Then I dont think its any more risky than the coils.

Lucky, your taking it a little far, sit down and breath in a paper bag.

[Don R]

I'd bet I can hold a piece of steel against a coil lead longer than you can hold a piece of steel against the battery posts. A coil will throw a spark a battery will burn a hole or explode.
Not saying either way should or shouldn't be done. Proper precautions can be taken. Just because something  can be done doesn't make it a good idea. 
 Make your decisions based on fact and your abilities. Then proceed at your own risk.