Crank loose on old Pegasus mountain bike

[Bike28472]

Hello, I have an old Pegasus mountain bike and the crank is loose. I think it just needs to be tightened. I pasted links to pictures. What tools do I need and from the side with the gears middle is flat with metal engravement. Is that a cap I need to get out by banging something thin from the outside and prying it off? Thank you

 

[Ajax Bay]

Is there an 'inside' thread where the left hand crank attaches to the spindle? Is its diameter 20.8mm?

 

[Bike28472]

Is there an 'inside' thread where the left hand crank attaches to the spindle? Is it's diameter 20.8mm?

Yes, it's 20.8 or near that.

 

[Cycleops]

Looks like the drive side and spindle are one piece and it tightens from the opposite crank which is removable. You haven't shown us a pic of the non drive crank properly, please post one. I can see some threads but nothing more.

 

[Bike28472]

Thank you, here are more pictures.

 

[Cycleops]

It seems what you have there is a Thun Thompson crank set. Found on older continental bikes. This was on YouTube, but has a cottered attachment, yours is retained by a bolt but otherwise the same. The German video shows yours.
Check the bearings as the looseness you thought was in the cranks could be wear there. Fairly unlikely that just the cranks are loose on the spindle.
A standard crank remover should work but the threads on your cranks look damaged but give it a try (Pic below)
Don’t know what size the bolt is. You will find a standard square taper spindle under. If you can’t use the extractor a metal rod and hammer will have it off.

View: https://youtu.be/U3NFZ_zD5as

View: https://youtu.be/E8i6o5PFo8U

 

[Bike28472]

Thank you

 

[Ajax Bay]

Remove bolt. Screw in and screw clockwise crank puller tool. Left crank will pull off. Then attack BB (see @Cycleops video).
Have good supply of grease ready.