Hello all! I am slowly learning more and more about these bikes. I have a 16v K100 and I need to get a tank for it, but have noticed that there seem to be two styles. One with the mounting points on the side and another with a single mounting point in the center. 

I also noticed that some of the tanks seem to have a access hole on the bottom center, and others seem to have some sort of plug on the bottom left. 

I am curious how interchangable these tanks are? I am not worried about the mounting points, as fabricating isn't a problem for me, but was more concerned with the difference in the other parts of the tanks.

Thank you all very much for your help!

Not interchangable.

The old tank (83-84-85) had the middle mount, and plug on the bottom left is for a device wich should be a floater, and connection for the pump.
Later models (86 -> ) were different.

+1 on Arlina’s comment.
the 83-84-85 tank I believe they changed mid year (85) production to the 86 and newer tank.
BTW The earlier vintage tank had the single hole mounting rear of tank and was prone to damage. 
check max bmw parts online catalog.
good luck!

also... I believe the 16 valve were the newer models.

The early tank that has the single bolt at the rear and the plug at front left is not interchangeable to the later tanks.

The clue is the earlier tank has 2 fuel lights, a red 4 litre and an orange 7 litre. The later tank has a singe red 5 litre fuel light.

Alright! Thank you guys very much! Hopefully should have the majority of the major parts now!

There is also I think a later change in the plug connection. I have a numbers of Ks and K1100 over different years and you just need to check the plug connector at the back of your clocks.

Paddy1 wrote:also... I believe the 16 valve were the newer models.

Yes and no....
Yes, because the 16V models came later than the first series K, after 86.
Also the 16V tanks are in 4 different shapes.
The 86 and later tanks of the K75 and K100 2V are in 4 different shapes. Mostly to fit with the right fairing/panels.
The 83-84-85 tanks only were for the K100, 1 shape, K75 came later.

DevilDesign wrote:I also noticed that some of the tanks seem to have a access hole on the bottom center, and others seem to have some sort of plug on the bottom left. 

A float-type fuel level sender is inserted through that "access hole". The sender's mounting plate that has wires through its center is bolted onto the tank at that point. Aftermarket replacements for that fuel level sender model are available.

Earlier fuel level senders were inserted through a hole in the floor of the tank's left side, near the fuel delivery and return ports, then coupled to the tank by means of a circular plastic nut that has wires through its center. That might be the "plug" you describe. Aftermarket replacements for that sender are not available.

Laitch wrote:

DevilDesign wrote:I also noticed that some of the tanks seem to have a access hole on the bottom center, and others seem to have some sort of plug on the bottom left. 

A float-type fuel level sender is inserted through that "access hole". The sender's mounting plate that has wires through its center is bolted onto the tank at that point. Aftermarket replacements for that fuel level sender model are available.

Earlier fuel level senders were inserted through a hole in the floor of the tank's left side, near the fuel delivery and return ports, then coupled to the tank by means of a circular plastic nut that has wires through its center. That might be the "plug" you describe. Aftermarket replacements for that sender are not available.

Thats exactly what I was wondering! Thank you very much. There is a lot of different varients of these bikes compared to the hondas I am used to!

one more thing… the early pre-mid 85’ design required a different pump designed screen filter installed below the pump inside the tank.
always use the bikes vin # when sourcing parts for the early K100rs

BMW K100 K75 Ignition Switch | eBay ....... this person has the tank and parts you need , i bought a frame and engine off him and he has the rest of the bike RS, great person to deal with for K parts which he is slowly listing

Another thumbs up here for that seller. I've bought stuff off him too with absolutely no problems.