Knocking at idle.

[Nospowered400]

I dont know the details but a guy at work just installed a 440 and he said he has a knocking sound at idle. I didnt know what to tell him so I thought I would ask.

[miken]

Cam chain?

[adrenaline]

either cam chain orrr....valves?

[Nospowered400]

I havent heard it run so Im not real sure what it is doing. He mentioned the rod but I dont think he really knew. I will tell him the suggestions yall have given so far.

[Fast350ex]

I don't now what this is. I wish I knew because, after every race, my 300ex does that. It starts knocking, if I let it rest for about 15 minutes, it runs fine until I start riding it hard again.
I also noticed that when it's hot, it will make a loud knocking sound when I start it.