1986 yz250 stroked engine questions

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8/31/2018 12:34 AM
Edited Date/Time: 8/31/2018 1:11 AM

I have an engine that I came across when I picked up a bunch of parts from a guy on Craigslist and I’m just curious if anyone can identify what someone was trying to do with it... anyways it’s a 1986 yz 250 motor that, from what I can gather, has been stroked (haven’t measured rod length but, the cylinder has roughly a .340 thick spacer welded to it)... The head has been milled a ridiculous amount (I’m assuming to both raise compression and set squish)... the power valve arm has also been extended to account for the additional height of the cylinder...and then the cylinder has been ported a ridiculous amount on the intake side (doesn’t look like the greatest port work)... Auxiliary boost/boysen ports are huge! Transfer ports have been worked on a little bit same with exhaust and powervalve... If anyone has any insight that would be appreciated, just trying to make heads or tails out of what it is... thanks in advance Photo
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8/31/2018 5:39 AM
Edited Date/Time: 8/31/2018 5:39 AM

Like you said, it looks like it was stroked. Check the stroke length, not the rod length as you mentioned. I noticed that the transfer port divider is cracked. 1st pic right side.

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8/31/2018 7:14 AM
Edited Date/Time: 8/31/2018 7:14 AM

Brett Campbell wrote:

Like you said, it looks like it was stroked. Check the stroke length, not the rod length as you mentioned. I noticed that the transfer port divider is cracked. 1st pic right side.

Yes I see that as well... and I know I have to figure out the stroke length little harder to measure without a piston in the bore was just going to check rod length as a quick way to see if longer than a stock rod... I guess more or less what I’m asking is what somebody would have done all this for? ... I’d imagine this engine was all top end with a short powerband

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8/31/2018 9:20 AM

Got cha! Let us know what you find out.

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