Why does your 1987 Yamaha Banshee keep blowing the head gasket?

Answer 1

1. make sure the cylinder surface is clean of all debris.

2. most important: make sure the stock cylinder head surface is flat and also clean. if the surface is not flat it will never seal right. you can get it milled or you can do it yourself with fine metal bodywork sandpaper, about 400 grit, a piece of non tempered glass, glass must be flat and tempered glass has waves in it so you must use raw glass. you can pick a piece at any hardware store for little money. lay the glass on a workbench, lay the sandpaper on top of the glass with the sanding side up, grab the head with one hand and with the other hand hold the sandpaper straight and flat on the glass and make several circle 8 patterns until the sanding marks become even on the head. you will see the difference from when you first start with a warper head to when the sanding marks become even. make sure you clean the head thoroughly when done. this will create a flat mating surface on the head. just dont go to far because you will get too deep in the squish band area, just go far enough to get the sanding marks even.

3. make sure the torque of the head nuts is correct and that the sequence numbers on the head are followed. i believe the torque spec is 15 lbs for the head nuts but check the banshee repair manual just to be sure.

4. make sure that the bike is not overheating while riding. purchase a inexpensive inline temp gauge that goes in the radiator hose between the engine and radiator. if you think the bike is overheating this will tell you for sure.

5. if overheating, check all cooling components, radiator cap, water and coolant level and mixture, overflow tank level etc.

hope this helps. MC.