Removing dents in RM fuel tank?

[Maicojames]

Hi, has anyone here had success removing dents in an aluminum RM tank(76-78)? I do have bodywork experience in autos...but frankly when a cycle tank came through, we would just fill the dent. This one is too deep to fill. I have heard of tack welding an alloy stud to tank-then pulling dent etc.
Thanks,  James

[cyclegod]

Try putting some water in the tank and adding a little compressed air, make sure the water covers the dent and slowly increase the pressure till it pops out.

[Maicojames]

Thanks, have you used this before? That would be cool isnce this tank has original paint with no rub marks, but a nice worn patina.

I will try it.

Thank you, James

[Maico31]

James i've removed dents like you said by welding a lug to the tank and pulling it out or by drilling a hole on the underneath and tapping it out with a rod then welding the hole back up. You have to be very carefull filling an alloy tank with compressed air because it tends to blow up everywhere and spread the tank apart.

[500Fool]

water covers the dent and slowly increase the pressure till it pops out.

Don't use anymore than 500lb though.

[GMC]

Avoid pressureising tanks to remove dents as it can destroy a good tank.
The pressure will spread the sides outwards, & at the same time the underneath will close in making it hard to fit back over the frame, & every slightly flat part of the tank will become rounded. This sort of damage is hard to reverse.
Best thing is to cut a small hole underneath to get some dolly bars in then weld the hole up later. The size of the hole depends on the size of the dent & how many dents. Sometimes a 1 1/8" holesaw is enough, sometimes a slot 3"-4" long will let you get at lots of small dents all over. Cut the hole in the underneath part where it won't be seen easily & usually, depending on the tank & how carefull you are at filling welding the hole back up it can be smoothed over so as not to be seen at all. If you have dents both sides then you will have to cut holes both sides of the tank.

I do however use a very low pressure to test the tank. Fit the fuel tap to the tank & turn it off, then fit the cap with the vent hose & fit an air blower to the vent hose, turn your regulator right down to 3-4 PSI (5PSI max.) & then spray with "spray & wipe"  or similar & look for bubbles. Test the tank all over as I have had some tanks that have had cracks away from the dented/ repaired area

[Doc]

Geoff the hole cutting is the exact method recommended to me for the repair of a few small dents in my RL250 alloy tank. I was quoted $300 to have the dents repaired, the rear mount rewelded/strengthened and the tank then polished to a high lustre and returned to me. Sounded reasonable taking into account the amount of work involved and how rare the alloy RL tanks have become but a fresh top end has precedence over a few small dents so it'll prolly be $500 by the time I get around to having the job done 

[Oldrodder]

On my CR250 that I am restoring the bloke I got it from had tried the air pressure method and totally stuffed the tank, now the bloke who does the repairs uses that tank as a model to show what not to do.
Bruce from Red Devil racing has a repair man that does alloy tanks, I eventually found another tank that still needs a bit of panelbeating, but better than the blown one.

[oldfart]

GMC
        Spot on mate .....I cut the tank at the back where  it rubs on the frame on both sides , at about 40mm wide by 100mm long slot in.
Cut up the broom handle and massaged away using a plastic welder heat gun to apply heat rather than oxy or mapgas .
Next fabricated some alloy patches that did the job and headed to nearest radiator repairer  ( welds alloy radiators )  ..... $80 latter all done 
I have seen tanks filled with water and air applied ....not pretty site and also the frozen water trick splits the tank along the bottom seam 

[Freakshow]

i thought the method was to use a strap. as in strap it so it dont move, and also strap it and fill with water and stick it in the freezer ?  I was told that is a good method if you strap it correctly and what how you freeze it  :OP

[GMC]

I was quoted $300 to have the dents repaired, the rear mount rewelded/strengthened and the tank then polished to a high lustre and returned to me.

That sounds about right Doc. I usually charge around $200.00 - $400.00 depending on degree of difficulty.

thought the method was to use a strap. as in strap it so it dont move

I don't believe you could strap it well enough to stop it moving in all the wrong directions. Pressure wants to expand in all directions equally, these tricks may work for a chamber that is round but a tank is the exact opposite of round.
I know a guy who tried to build a jig for his tank to stop it moving & while he managed to contain some of the major movement, it still bulged out & ruined the overall shape.

[Maicojames]

Thanks, I think I will spoon out and fill dents. ..or try pull rod.