reinstalling cam: lobes up or down?

2003 XR 400. New piston. Putting it back together, I have everything aligned, crank and sprocket. I can put the cam in with the lobes up or down. Manual does not say one way or the other.

So, sure, I'm on TDC. But it seems to me that my spark will be right one way and 180 out the other. Can someone explain to me how the cam should go, and how I make sure my spark isn't 180 out?

Thanks very much!

Lobes down.

Not possible to get the cam 180 out, the ignition is wasted spark, fires every crank revolution. With the lobes down, it is much easier to replace the head cover.

X2 on the lobes down for the valve cover...i just did that yesterday.

Now that's what I'm talking about! Thanks!

It will be interesting to see what the bike does. It was bone stock. Now new HC piston, just did airbox, snorkel, grind exhaust pipes and drill exhaust can, add 36 Mikuni.

Not only the mods, but bike was jetted (probably) for sea level, we're at 2300' minimum.

Creeky, are you still riding - you're 73? I'm 62 and it's getting tougher.

easier with lobes down,

but either way is correct,so long as the cam wheel marks line up with top of head when at tdc

Creeky, are you still riding - you're 73? I'm 62 and it's getting tougher.

Yeah, I'm still hanging in there, but as you say, it gets tougher all the time. I have decided to slow down a bit and reluctantly sold my '05 KTM450EXC recently and will be riding the 650R on easier dual sports as long as the old body will take it.

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