Timing 2011 YZ450F - am I missing something?

Hey guys, just bought this bike and immediately had the head gasket let go.

Replaced the gasket tonight and thought I had it timed right but theres bugger all compression and it's blowing compression out the breather hose. I understand this is likely to be due to incorrect timing?

When I tried redoing the timing I found a spot where it all seemed much better, except there was a hard point when rotating the crank. Which I believe to be the exhaust valves and piston colliding. I just don't seem to be able to get it timed correctly. When looking at the crank through the timing hole there is a "stamped" kind of block mark and a small line also. Which am I meant to be lining it up with? Will using a screw driver down the spark plug hole help? Is it meant to be at TDC or slightly off?

Cheers for your help, James

Looking at the timing marks on the flywheel, the farthest mark clockwise (to the right) will be TDC, and that is what you line up with. Verify this with a probe down through the plug hole to clear it up in your mind.

Remember too that the intake and exhaust cams are reversed from normal in this engine. They still turn forward, but the exhaust is at the rear of the head. When you're using the right marks on the cams, the lobes should point slightly up and in toward each other. The "hard spot"is normal, at least to a degree. It's the compression stroke. On the other hand, if there's a spot where there is considerable resistance while cranking with the plug out, that's not a good sign.

It's also normal to push air out the breather. The piston displaces the same 450cc of air from the crankcase on the down stroke as it does in the cylinder on the exhaust stroke.

Looking at the timing marks on the flywheel, the farthest mark clockwise (to the right) will be TDC, and that is what you line up with. Verify this with a probe down through the plug hole to clear it up in your mind.

Ok, as I thought. However last night it didn't seem to actually be TDC when I checked with the probe. Maybe I was just tired and fustrated tho, I am about to head back out there now so will recheck.

Remember too that the intake and exhaust cams are reversed from normal in this engine. They still turn forward, but the exhaust is at the rear of the head. When you're using the right marks on the cams, the lobes should point slightly up and in toward each other. The "hard spot"is normal, at least to a degree. It's the compression stroke. On the other hand, if there's a spot where there is considerable resistance while cranking with the plug out, that's not a good sign.

Yup understand where the cams should be. Not having the 12 o clock marks to count pins and verify like the Suzuki's is a bit of a pain but I'm reasonably sure I'm getting those accurate in relation to each other.

The hard spot is definately not normal, well at least it doesn't feel normal. It's a point of resistance and like I say, feels like valve on piston considering when checking the spark plug hole the piston is up near the top and the cam lobe is pointing straight down.

It's also normal to push air out the breather. The piston displaces the same 450cc of air from the crankcase on the down stroke as it does in the cylinder on the exhaust stroke.

Good point, hadn't thought of it like that, possibly nohing but me looking for symptoms. So far you have kind of verified what I already thought (much appreciated to stop myself second guessing it). I'll head back out there now and see if a bit of sleep might have changed my perspective.

Cheers, James

The hard spot is definately not normal, well at least it doesn't feel normal. It's a point of resistance and like I say, feels like valve on piston considering when checking the spark plug hole the piston is up near the top and the cam lobe is pointing straight down.

That sounds like a problem, all right.

That sounds like a problem, all right.

Just been back out in the shed and I cannot for the life of me get this thing sorted. Had a setting that had compression and no contact of any kind but it didn't quite look right at the crank end, and didn't want to fire. Getting rather fustrated, I've never spent more than 10 minutes timing any of my other bikes! damn Yamaha!

FYI, it turned out to be that the flywheel had spun and sheared the key.

The guy I bought it off had removed his heavier flywheel and not put the standard one back on properly obviously. So it worked well for a while before letting go, strangely enough at the same time as the headgasket.

All sorted the next day after my last post and I've put 9 trouble free hours on it and she's going mint!

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