Bored out CR 125 blown head gasket

Gage`s Dad

Aug 28, 2009
My son just bought a CR 125 with a bore kit. He rode it for maybe 3 hours and the head gasket developed a hole beside the water jacket and filled the engine with water. Now Im waiting on a new gasket (cometic) that wont be here til next Friday. Wonder what caused the gasket to get a hole in it? This engine was just recently built, and we were going through the break-in period. The three hours of riding were not consecutive. When I got home from work and looked at it the head bolts were not torqued tight enough, although not really loose.
Anyone have any suggestions?

Oh yeah, is it possible for the carb to be full of water also?

Thanks in advance for any help....


Apr 18, 2006
Not torquing the head down properly can definitely lead to a blown head gasket. There will be a specified torque that the bolts should be tightened to and a pattern that the bolts should be tightened in sequence. I always snug the bolts first, then torque them down in several steps so that the last step is only tightening them 1 foot-pound or so.

I also recommend checking the torque of each bolt after the engine has been run once or twice.

As for water in the carburetor: Are you talking about in the float bowl or in the venturi area?

If you managed to get water from the cooling system into the venturi area of the carburetor then I would recommend taking a close look at your reed valves as they may have been damaged. I sure don't see how water could get from the cooling system into the float bowl area.

On the flip side, if the bike managed to ingest water through the carburetor I can see how that could cause the head gasket to blow. Your son didn't ride the bike full throttle into a lake, did he?



Pantless Wonder
Dec 26, 1999
Was the head & cylinder checked to make sure the surfaces were flat? Are the fasteners past their service life?
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