The early Polaris engines did take the BPR8ES plug! Only about in 1990 or 1991 I think that they went to the BR8ES NGK plug.I really don't know if the heads were shaved down a bit on the later models. Does stand to reason since they went to the standard depth plug. The "P" stands for extended probe (projected). Here's a chart that explains. NGK Sparkplug Codes
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I blew up the cyclone this weekend. Took her down the road for the first time and on the way back it seized up on me. Gotta tear it down and check it out and see if it's worth rebuilding it.

 

Well,sorry to hear about the Cyclone seizing up. Be sure to check the rod for any up and down play along with any rough sounding,rough feeling crank bearings as you turn the rod around. Just my on this one,if you're going to repair it,best to do it right and start at the bottom and work your way up to the top on rebuilding the engine. Keep us updated.