2 Strokes Down Under

Have gone through two generator side crank seals in 8 months on my DS6 250cc.

Does anyone have any ideas on cause.
Thrashing bike understood as possible cause but bike used no harder than in past.

Now have checked timing, carby settings and oil supply.

Any comments appreciated.

John I

Crank taper bent or crank out of true would be my first impression. Ask our resident crank guru graham.

Hi 2TInsitiute.

Thanks for the advice, will investigate. Thoughts were not going in that direction.

The crank was running within manufacturers tolerences (at main bearing journals) when put in motor. Not sure about any seal surface run out.

The motor has done a lot of work and is most probably due for a new crank anyway. Think the Labarynth seal in middle could also be leaking. Making new funny noise above all the usual rattles.

Have accumulated most parts to build a new crank. So I will just have to get onto it.


John I

Are you using a genuine yamaha crank seal with the teflon coated lips or an aftermarket seal designed for another purpose. The difference in durability is substantial.....

The petrol and oil mix will destroy the sealing surface (lips) of a "normal" seal which is designed to only keep mineral oil in......

Crank seals are one place where the genuine seals are well worth the premium cost.....

Graham

Hi Graham.

Thanks for the tip.
Still using supposedly genuine ones. But bought as NOS on Ebay.
Never seen teflon coating on them.

Original ones from era long before Teflon and assumed the seals (Double sided) would no longer be available from Yamaha.
Will look into this. Have found it hard to find a Yamaha parts dealer interested in bikes this old.

John I