Not certain what Hz is. Well if you want a mechanics drama story.. read on. If not the updates are at the bottom paragraph. My CRF Short story. Bought the bike with a hot cams in it. I rode the bike last season on and off and noticed the burning of the oil and often hard starts. Checked the valves probably too late and they were way off. I decided to open the machine up to see what would cause the burning and was expecting to replace piston and rings. Wrong. I have some cracked and missing valve seats hence the purchase of the new 250 r head. So read the prior posts to understand the current assembly experiences. Well late last night i decide to pull out the current hot cams and replace it with the stock cam that was given to me by prior owner. Assembled it, started it, and wham... we are good to go, it purrs as it should. I should have stopped there. But no.. i wanted the spiffy more powerful cam and was curious as to the problem. I stopped working and waited until this morning. I took it out and measured tolerances between the 2 and seen they had big differences. I reduced the shims by one as I had installed them more on the tight side and not the loose side. Got the hot cams back in and buttoned up and started. Crazy loud same drive me crazy noise. I say screw it and start to put the Honda original on in. Once that decision was made i was happy with an end in site. In the process of assembly i drop the cam chain. No biggie get a pick an pull it up and re-assemble as I have done no less than 10 times before. button it up and go to turn it over by hand. It seizes up.. WTF I go look at the marks and they are off. pissed as hell i uninstall everything and reassemble everything verifying everything 2 times. button it up and turn it over. It seizes up again. Again... wtf. I step away to consider my assembly and think i must have dropped something. So i go to disassemble the cam and chain to rotate the bottom end alone. With the cam off and turning the crank it locks up. Turns out i dropped the chain off the bottom gear. So i pull off the left hand assembly to realign the cam chain and leave the bottom case off during the whole process. Get the chain cam and other bits and pieces on yet again and rotate it by hand. Boom we are golden. Again.. end in site, again. Well i button up the bottom left hand side again and check everything again then rotate it again and all is smooth. Its now time to hear this baby purr. I add oil my temp oil splash guards and insert the spark plug wire and turn the key push the e-start button and the motor spins and spins. It spins so nice with the starter pushing it. Problem is it should be running like the other 7 times it has in the past 24 hours after being all buttoned up. Frustrated, I check fuel, yup got fuel. Check air, yup not in a void of that at the moment. check spark, no spark. Im assuming I did something to the wiring along the way when I removed the bottom left hand case. I reseated the connections and checked with prod light and nothing. So now I am off to get a multi meter. Fun stuff. Thanks again for the suggestions so far.