Oil change, using different SAE to recommended.

[Moxey]

Doing the MZs oil and filter, just curious if using 10w40 would cause any major mechanical fuck ups.

Recommended is 20w40 for regular use and 10w30 for winter, the engine is pretty much the same as yamaha XT660, SRZ660 and XTZ 660 singles so anybody know of much harm from doing this?
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Current: 02 FZS 1000 & 91 Royal Enfield Bullet 350 Some Bike Pics...
'I was too busy paying attention to pay attention'

[weasley]

It'll be fine. In fact you might struggle to find many 20W-40 oils, as they're a bit old hat.
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Yamaha XJ600 | Yamaha YZF600R Thundercat | KTM 990 SMT | BMW F900XR TE

[Moxey]

Reassuring to know cheers
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Current: 02 FZS 1000 & 91 Royal Enfield Bullet 350 Some Bike Pics...
'I was too busy paying attention to pay attention'

[tahrey]

Seeing as the lower number is it's cold viscosity rating, it'll probably be better for the engine in fact. So long as you still have that 40 for summer or 30 for winter that means it won't get too thin as it warms up...