Motorcycle frame design question

[peterdallan]

Hi,

    Just beginning to sketch out a couple of designs for my frame for next year.

I will be going in the 650cc Pushrod Fuel/Gas classes, Special Construction frame.

Question, can I have a frame where the top tube is the gas tank and the downtube is the oil tank?

thanks 

Peter

[Dakin Engineering]

For gas class, the tank must be sealed.
They like to visually verify the tank is empty before filling and sealing.

Sam
#6062

[ol38y]

I don't know of any compliance reason you can't. But, you'll severly limit your capacitys , especially gas. JMO

[peterdallan]

Thanks Sam,

                  Alternative is to fit a couple of tube tanks alongside the top frame rail, however wouldn't I come up with the same problem regarding checking the tank is empty as they would be quite long and thin?

JMO, what would be an ideal capacity for a run in your opinion? I was planning to have a much larger diameter top tube than normal if I went this route.

Cheers



Peter

[ol38y]

IMO 1 to 1.5 gals for gas with the twin alum. tubes. Then you'd have the top rail and the down tube for oil. But, JMO

[Vinsky]

You said fuel/gas class.  If you are running Alky, you need a much larger tank than for gas.

[55chevr]

I race a 1000cc pushrod bike at Bonneville and it uses more then half a gallon during the run ... it is 3 miles wide open ... youop are gonna need a really big top rail ... also your fuel weight drops as you consume the fuel during the run.   A lot of special construction bikes use a fabricated fuel tank that fits conveniently into the frame design.

[ol38y]

You said fuel/gas class.  If you are running Alky, you need a much larger tank than for gas.

Yup, I glossed right over that. If you're running fuel you'll probably want 3 gals available.

[peterdallan]

Ok all good info, thanks, will help with the frame design choice.

Peter

[RidgeRunner]

Gravity feed for carburetor is one thing.  Any type of FI with  a return to tank could bring on aeration where the return dumps into the tank in which case baffles and/or larger capacity might be need to be considered.

Ed

[ol38y]

Gravity feed for carburetor is one thing.  Any type of FI with  a return to tank could bring on aeration where the return dumps into the tank in which case baffles and/or larger capacity might be need to be considered.

Ed

Nuther good point. Also, when determining fuel line size, bigger is better..

[bak189]

What engine are you using?.......1.5 gallons should be enough if you are using gasoline for fuel........
We ran a 750c.c Triumph with a top tube frame tank on gas (record still stands) with no problem.......
To show the tank is empty ....just disconnect the fuel line and show the man the tank is empty..Simple..

[wobblywalrus]

My experience with oil-in-frame is they are difficult to thoroughly clean out if the oil is contaminated, for example, by an engine failure.

[peterdallan]

We are using a 1960 Triumph 6T engine as the basis for our build.

Peter

What engine are you using?.......1.5 gallons should be enough if you are using gasoline for fuel........
We ran a 750c.c Triumph with a top tube frame tank on gas (record still stands) with no problem.......
To show the tank is empty ....just disconnect the fuel line and show the man the tank is empty..Simple..

[bak189]

With the 6T Tri. engine on gas (petrol to you) about 1 gal. should be enough......Our frame tank was a 3 inch dia. tube, 2 feet long.....after our run on the salt we had about a couple of pints left in the tank.....
our engine was a pre-unit Tri. using a 750c.c. Morgo Kit, running thru a BSA close ratio gearbox.......
The bike has been retired and sold and is on display at some Texas truck stop....Oh, the shame of it all....