Hole above cam tensioner?

I have a 2007 YZ450 that i just rebuilt the top end. I had a local shop machine the head and install the new valves. Upon putting the cylinder and head back on I noticed a 6MM hole to the left of the intake, right above the cam tensioner. Was wondering if someone could enlighten me as to what that hole was for?


That hole should have a bolt with a copper washer in it. It is a oil pressure check port. When the engine is running, you loosent the bolt to see if oil starts to drip. This is how you check to make sure that the valves are getting pressurized oil. It sounds like the machine shop removed the bolt, and forgot to replace it.

Thanks for the reply, now I can rest easy knowing I did not forget to install the auxillary cam tensioner ;)

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