570 crank in 550 cases?

tourist · Mar 4, 2016

Heya,

I often find myself idly speculating whether a 570 crank (and rod and piston) could be made to fit 550 cases somehow. Probably not! But what are your thoughts on the matter?

The 570 stroke is 2mm longer. I should look up rod and piston height too.

How much height can you add to the rotating assembly in 550 cases? None, right?

Borgschulze · Mar 4, 2016

Don't think it would be possible, the ends of the crank are probably completely different too?

570 is 70 degree engine, and 550 is regular?

Taffy · Mar 5, 2016

rod differences are 15-16mm in length. big ends are 3mm different.

bushmechanic · Mar 5, 2016

main problem is the 570 crank is 35mm diam (the actual shaft )

rod can be changed and outer diam of crank also but the mainbearing cavities in the 550 cases are not big enough for the nj207 that the 570 uses

so ... not really becasue of the main bearings

tourist · Mar 6, 2016

Thanks all!

And the pin probably couldn't realistically be machined down to fit a bit smaller bearing?, or the cases bored out to allow a little bigger bearings while retaining enough strength?, or altered to fit a dfferent bearing setup (cf. my rudimentary understanding of the JBS bearing rework)?

Fun discussion and gedankenexperiment. Thanks. The idea is to have what 550 cases remain in the world easily usable going forward, trying to use off-the-shelf stuff to fix the weaknesses we understand the crank itself to have.

tourist · Mar 6, 2016

Because I looooooove the 550 motor character. Love it.

bushmechanic · Mar 7, 2016

Ah I see

Crank works make 78mm billet cranks for the Ktm 525

They are closer to what you need than the 570 crank

spanner · Mar 8, 2016

you might be able to use these bearings on the 570 crank.

NJ1007 bearing Japan ntn-NJ1007

Big end pin might be a bit longer I think?

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570 crank in 550 cases?

tourist

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