After finding to my delight that the 350SXF valves are in tolerance I turned my attention to an overdue check on the tuned 04 YZ450F. First gotcha was getting the motor to TDC as this tuned engine has a non-standard timing side crankcase cover. No inspection ports for the timing mark or for turning the engine over. You can see what I mean in the photos. It does, however, have a slotted, threaded, inspection cap on the valve cover (non standard AFAIK) between the cams. A tentative prod with a little finger suggested the cam chain was possibly loose. You can also see it has a manual tensioner. No problem to begin with, back to how I used to do the DOHC Gilera thumper. Plug out, valve cover off and in to top gear and use the back wheel to rotate the engine until the inlet valves had closed and TDC was reached. With care I could see the punch marks on the cam wheels end up where the should be. The bad news, at least a couple of clearances are significantly wider than spec. The possibly worse news. The cam chain hangs between the sprockets with lots of slack. I know there is a guide built in to the cover but should it be this loose at TDC with it at TDC and the cover off? Remember this has a manually adjusted tensioner so presumably it will be no tighter when running? Without a crankcase locking bolt KTM style I'm going to have to drain the oil (well that was going to be a given before long anyway) to remove the timing side crankcase cover so that I can check the crank doesn't move when it comes time to replace the cams after shimming. Before I get that far though, the manual refers to removing the carb to do the valves. Checking them seems possible without (but after withdrawing the hot start plunger to give better access), but is it essential if shimming is required? I've not had to shim valves before as the Gilera Bialbero though DOHC uses followers with screw and locknut adjusters. So I'm being very cautious.