How to measure length of stroke on crankshaft?

[lbo]

Like the title asks.

I bought a used crankshaft but don't know what stroke it is. Only ebay description is "Polaris 90 crankshaft eton kasea DRR " and can't find anything online. The one I am replacing is still in the case and just "unscientifically eyeballing" it appears longer then the one it's replacing but there should be some way to measure or determine stroke length.

Anyone know how I can determine what it is with rudimentary tools?

[lbo]

I know in theory it's the length from center of the crank to center of crank pin times 2, right? If so I can't get accurate measurement with my caliper as the pin is quasi blocked with the bearing still on the crank.

Just curious if there is an easier way or different method.

[90GTVert]

Other than measuring and calculating, I guess you'd have to stick the crank in v blocks or something and see how far the end of the rod will travel when you rotate it.

[lbo]

Looks like a 45mm from best guess with calipers, certainly longer than 42mm. Woo Hoo!

[90GTVert]

The Polaris 90 should be 42mm... but then I bought a stock crank for another 90cc ATV and it turned out to be 45mm. I think some get labeled Polaris 90 just because that's the most well known of them.

[lbo]

I have a cheap plastic set of calipers, the kind you find in the $1 bin while waiting in line at the hardware store.

I used the pin and the end and measured the shortest part of the rod at what would be BDC, then measured the rod at what would be TDC. After subtracting BDC from TDC measurements I got a difference of ~44.5, another time ~45mm. I know there are 44mm cranks out there but don't think for a Polaris so I am pretty certain it's a 45mm stroker.

I then used this method to measure the OEM crank in the scooter and got ~42mm. Also eyeballing this crank with the stock one it appears to be longer as well.

[reveeen]

You take a ruler..... starting at the base, you measure to the tip. OH! sorry wrong kind of crank!