I'm helping my cousin with this craiglist special he picked up and we are scratching our brains, hopefully someone here can help. The bike is a 2007 YZ450F. The bike was bought with a trashed motor. Was told it needed a piston and cylinder but the damage was much worse. cylinder was cracked, crank out of spec, rod bent, head completely destroyed. A new Wiseco crank was installed, new cylinder works cylinder (replaced what was on the bike) OEM yamaha head OEM cams (bike came with hot cams) OEM cam chains OEM chain guides. The issue is, the 2007 cam chain is waaaaaaaay to tight, we cant even get it over the cams. The tensioner is removed and we even unbolted the chain guide from behind the mag. still wont go on. We ordered a 2010 cam chain which is about 4 links longer and thats too loose. The cam chain tension is fully extended and isnt even removing slack. We COULD make it work but we have the fear that there will be too much arch on the chain and that will wear away the chain guide very fast. The gear on the crank appears to be the same diameter, the cam gears appear to be the same diameter, the cylinder is the same height, the head is the same height, the height of the cam saddles appears to be the same height. I measured with primitive tools. Even if there is a variance I cant see, it would only be 1/32 of an inch off and thats not going to take the slack out of the cams. Not sure if it makes any difference but the OLD head was stamped Y-1, the new one is stamped Y-2 and then under that 093 is stamped under it. I have inspected everything to the best of my ability, when I got in on the mess, the motor was already together so I cant do a 100% side by side comparison. What am I over looking? Did they re-design the chain guides to put more arc in them?????? im lost.