1st oversize tolerance ?
 

Hi,
what tolerance piston/barrel do you recomend for 1st oversize ( 100,5 diameter of piston ) on XTZ 660? According repair manual, minimum is 6/100 mm. Any quality expirience? XTZ 660 is well known oil consumption bike, and i am thinking that making minimum tolerance will decrease consumption?
Regards,
AnteK

Hi Ante,
I have 100,5 piston also but have no idea what tolerance the machine shop made for me.
But oil consumption maybe has something to do with the engine not warming up well enough most of the time. This affects a lot of things such as carb mixture, expansion of piston and other parts etc.
I noticed that just after I change oil consumption is always less. So maybe the oil
deteriorates quickly.

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Fred, XTZ660, Holland.

Antek,

Stick to the specified tolerances. If you go smaller, you increase the chances of seizing the engine when it gets hot. The tolerance is there to allow the components to EXPAND under use. Too little tolerance will result in an expanding piston grinding to a halt in a cylinder that is not quite big enough. A trip over the handlebars could be the end result (speaking from experience here!)

Tolerances are specified by the manufacturer & determined by materials & the thermodynamics of that particular engine.

Oil consumption can also be due to worn valve guides, perished valve stem seals, worn rings etc.

When running the new piston in, do not use a a fully synthetic oil. Use a basic oil that meets minimum requirements - this will allow the piston to bed in properly. Once the running in is complete, change the oil & filter, using a higher quality oil. Using a fully synthetic oil when running in will NOT allow the piston to bed in as well.

Steve

Steve, you must be joking when you talk about the engine getting HOT. It's a 660. We have problems getting it warmed up to normal working temp.
But you're probably right when you say that we should use the factory prescribed tolerances.

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Fred, XTZ660, Holland.

Not had the misfortune to own such a machine......

Leaving the oil out should help the engine get up to temperature....

Steve

They are perfect in the Sahara when it's 45 degrees and if you really do your best you can even get the oil to rise to 100 degrees.


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Fred, XTZ660, Holland.