ORIGINAL: gphil
The tank I have now is square and fits snug against the firewall
GP now think about that just a moment. Now I am sure you have read about packing the tank with foam and such to prevent foaming but here we are jamming the tanks front end and bung hard aginst the highest point of vibration in the entire airframe aft of the engine mount.
Kinda contradictory Huh well seems that way to me. Heres the disclaimer - in my opinion - That is a very poor design and left over from many years ago. There is no need to force the tank up aginst the firewall, none at all.
Your airplane is pretty much a genaric forty sized trainer and there is no way you could not use at minimum an eight ounce hayes or any other style tank for that matter. You likely could even fit an eleven ounce hayes.
The trouble with stock tanks is inconsistancy most arfs will have differant tanks included from time to time or even from container load to container load. And searching for an exact copy is often a waste of time. Now is the time to improve your fuel system.
Also on conventional tanks you said they are all for three line systems in an earlier post but that is not normally the case. Every new aftermarket conventional tank I have ever used or seen has three holes in the compression caps but the rubber bung has only two holes fully opened. So its up to you to puncture the third hole if you want to use a third line.
Try the Hayes and you will not be sorry.
John
Here are closeups of the Hayes fitting to get an idea of how they work. The plug is hard plastic and has an 'O' ring. The steel ring prevents any splitting that can occur on older designs. The tower website does not illustrate these at all.
The Hayes is a bit longer but is is also narrower allowing plenty of room for the throttle in a genaric trainer and the tank is usually positioned high enough to allow the nosewheel pushrod to go underneath. There is no problem allowing the tanks rear to be slightly further aft.