What is this hole? Went for a ride today when i stopped my 04 YZF450 was steaming. It was something dripping on the exhaust. I thought it was water from a cracked radiator but it smelt weird(not oil). When i pulled the fins and shroud off and started it i heard air coming from this hole. It is blowing through the radiator. I may have a cracked radiator and I'm no mechanic and don't have a manual. Just want to check up before i start spending money.

Any help appreciated

Check to make sure the large rubber plug is still intact that fits into that casting facing the radiator. It is a left over casting from where the decomp shaft went on earlier models. The rubber plug was prone to coming loose.

one of two things that could cause air to come out of the radiator,

1- the coolant level or it's condition needs attention.

2- the head gasket is defective.

if the air is coming from the location where the decompression lever used to be, as mentioned earlier, check rubber plug

It Smelt?

Your bike has apparently ejected the cheesy little rubber-coated plastic plug that blocks the bore where the decompression shaft once went. Don't bother replacing it with the same part, except as a short term fix. Use an 18mm steel or brass freeze plug you get from an auto parts store, or one of These, from the TT Store

You should also check to see if your breather hose is pinched at one of the two metal clips holding it to the frame, or elsewhere. It's a common cause.

Definitely no plug in there! Thanks guys. Will check the rest now

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