03' Blaster leakdown

Discussion in 'Engine' started by Deej, Oct 28, 2019.

  1. Deej

    Deej New Member

    Oct 28, 2019
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    Hey, first time poster. Just bought a used 2003 yamaha blaster. Needed to do a top end rebuild which involved me buying a completely brand new Cylinder after breaking a bolt off putting the carburetor joint back on. Didnt do a bottom end but knew i should do both at the same time but after being laid off money is a bit tight so i just did the top end. So i put the new cylinder on, installed the gaskets and new piston and bearings and had stripped one of the 2side male threaded headgasket bolts so i had to put a heli coil in and so far its holding at proper spec. So my question is this, i built my own leak down tester with the help of forums and videos. I put the piston at tdc and then blocked the exhaust with an expanding freezer plug. Installed the leak down tester and performed the first test(had to use motoseal to seal my carburetor joint) at 7psi. The results. I lost 1.5psi. So my initial though was "anything more then 1 psi in 10 minutes means rebuilding the bottom end" but i figured one more test would be a good idea so i did my second test at only 6psi for 10 minutes and proceeded to spray soapy water at everything. Cylinder head, base, carburetor joint, exhaust port, the split gasket of the entire crankcase and lastly my leakdown tester. The second test showed i only lost 1psi and was just starting to dip a hair under the line of 5 psi so i was a bit confused on what to do. Nothing bubbled and i couldnt find any signs of a leak. What would be my next course of action im stuck on just trying to start it and see what it does and buying the bottom end rebuild kit (including crank) and going from there. Any advice? Maybe a spot i forgot to spray.
  2. Noxtol

    Noxtol Member

    Aug 15, 2018
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    Failing a leak down test does not mean that the crank is bad, it means that a seal or gasket is leaking somewhere, But usually, you only need 6psi for 6 minutes not 10. if it holds for 6 minutes you are fine.

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