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Posted by: cheezy400

would at 86 crank fit into a 88 250r

Posted by: ZRider400

yes but then you will need to run an 86 style piston.

Posted by: wilkin250r

The connect rod is a different length, it's 5mm shorter than the 88. This is why you need the 86 piston, because the 86 piston is designed to work with the shorter rod.

With an 86 piston and 86 crank, it will fit right in, no worries.

Posted by: 310ESR

wilken, what about the piston port?

Posted by: stocktires

quote:
Originally posted by 310ESR
wilken, what about the piston port?

All is fine, the 88 rod is longer than the 86 rod, BUT the 86 piton has a lower mounting position (therefore making it the same height). So as long as you have the same year model piston and crank you will be alright

Posted by: wilkin250r

Correct. Picture the piston at TDC. The height of the piston crown from the crank is determined by the rod length plus the distance from the piston pin to piston crown.

On the 87-89 crank, the connecting rod is 5mm longer, but the distance between the pin and crown is 5mm shorter, so the piston crown is at exactly the same place.

Now, this will cause a very slight change in the piston crown position at 90 degrees after TDC because of the differing lengths and angles, but it's a very small difference.

Basically, the long and short of it is, an 86 crank and 86 piston will work in any year cylinder, and bottom end, without modifications. An 87-89 crank and 87-89 piston will also work in any year cylinder and bottom end. The only time modifications are needed is if you run an 87-89 crank and an 86 piston, then you need a spacer plate.

Posted by: ZRider400

this pretty much explains it all.

http://webpages.charter.net/vogt26/images/quads/top_end_differences.jpg