OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Victa Lawn Mower Frames Causes of a scored piston? Please help urgently!!!

Hi all,

I have been advised by my mower repairer that the Two-Stroke Victa Tornado Self-Propelled Mower that I bought 11 months ago has a scored piston. I was told that it was most likely due to insufficient oil in the fuel. I have worked as a gardener for five years now and admit that this problem occurred to me once (a few months ago) as I must have forgotten to add oil to one of my tins. However, ever since I been extremely careful with ensuring the correct amount of oil in my mix and have only used Shindaiwa oil. I can't understand how it could happen again so soon and despite me being ULTRA careful. Can anyone advise me whether there are other possible causes? (I noticed that before the mower stopped running properly, it was over-revving, and so I ran it at about a 1/3 throttle speed). Thank you

Hi Stephen Sounds like a lean mixture may have caused the high revving. Lean mixture may be caused by shotage of fuel thru several causes such as stopped up vent in petrol tank, partly bocked main jet in carby. Carby manifold leaking air thru coming loose. etc etc . Whether the high revving caused the scoring its hard to say. The oil content may not have been high enough to cope with the higher speed ,it would depend I would think on just how high it did rev and for how long.
Without seeing the piston itself it is hard to guess the cause..... If it is just one deep type of score then it may be possible thru some foreign body passing thru the engine, A chip off a engine bearing. or screw form the choke valve ot the throttle valve . I have seen this type of damage afew times . Bits of big end needle bearing were a common cause on various makes of chainsaws causing bad scores on the piston..
I dont know the design type for the engine you have so cant say much more Cheers Joe

Stephen,

What Joe is saying is correct about the air leak etc.

Can you post a picture of the piston so we can look at it.

Another thing is what ratio was the oil mixed at as that could be an issue as well.

Thank you very much for the info guys!

Stephen B