just got one of the last fo these bikes so hapy but there is a distincted rattle anyone else have this problem
The rattle noise has been discussed in another thread ... It's caused by piston slap due to the Chinese using a piston with the wrong clearance in a ceramic bore ...
They may very well have HAD to run that clearance to allow for expansion/contraction of their alloy cylinder ... When engineering a bore kit that runs no iron sleeve but nikasil coated onto the bare alloy ... You have to take into account how much the alloy cylinder will expand in proportion to the piston ...
My bet is that due to the fact that these engines are air cooled , they can't run tight enough piston to bore clearances to keep the cylinder to bore clearance to the minimum at full operating temperature ... The bore more than likely expands more than the cast piston does as the engine heats up so the operating clearance grows with the resultant rattle noise you're hearing ...
A forged piston running more static clearance would be better because the forged alloy being denser , expands at a greater rate than the cast alloy cylinder would ... So you'd clearance the piston to bore so that you achieve the minimal clearance at full operating temperature ... That means you'd have to put up with a rattle sound in a cold engine ... until it warms up ...
With a forged piston the fuel/air ratio would be more critical ... too lean a mixture and the piston could expand enough to seize in the bore ... I'm pretty sure Coolmodee had problems a few years ago with forged pistons seizing in ceramic bores ... and it would have been due to a combination of too little piston to bore clearance combined with excessive engine heat due to too lean an A/F ratio ...
Cast pistons run much tighter clearances than forged pistons because cast alloy has lower expansion ... When these new skirtless pancake pistons are used , the piston to bore clearance is even more critical than if a full skirt piston is used ... And maybe the Japs have also tinkered around with the alloy to control the expansion better than the usual forged piston material (Mahle alloy which Porsche used to use) ...
Ceramic bores should really only be used on water cooled engines where the cylinder expansion rate can be controlled much better ... otherwise you'd have to put up with the rattle noise which water filled jackets would tend to dampen out ...
As a note of point I see that twin oil coolers are used in most chinese bikes which run ceramic cylindered engines such as the 175z's ...
I've read where people were complaining because the chinese didn't listen to their requested jetting specs and supplied the bikes with bigger/richer jets ... Logically , they'd do that to keep the piston and bore cooler during run-in to minimise the expansion and therefore minimise the slap noise and also to prevent seizures caused by people thrashing their new engine ... So maybe the chinese aren't so ignorant after all ... but are merely just protecting themselves against a flood of complaints that they KNOW are likely to occur if they run the leaner jets ...
I know I'd make sure I ran a richer A/F ratio during run-in ...
The only REAL way to know for sure about the bore clearance thing would be to measure the temperature of a cylinder on a running engine ... then let it cool ... remove it and the piston ... measure the piston and bore diameters cold ... place them both in an oven to heat them both up to the measured operating cylinder temp ... then re-measure them to see if the piston to bore clearance changes ...
Iron cylinders and sleeves tend to hold their size and shape better than alloy ones ... that's why iron is used in heavy duty engines that are subject to high loads and heat ... Most OEM manufacturers choose to run iron cylinders on their air cooled horizontal engined production bikes ... and iron sleeved cylinders on their air cooled vertical engined bikes ...
Car manufacturers prefer to use cast pistons and iron cylinders or sleeves as well to avoid complaints from customers about piston noise during engine warm up ...
