22% Blow by in #5 Cylinder

[Stavis Bay]

A prospected buyer had my 1994 150XR6 Merc checked out by his Mechanic today and the mechanic said that I have a 22% blow by in the #5 Cylinder. The compression checks come back at #1 130, #2 125,#3 135, #4 140, #5 135, #6 145. Any ideas on the high Blow By and is this a big concern? I have never heard of this.

 

[rodbolt]

Re: 22% Blow by in #5 Cylinder

try a good decarb carefully folowing the procedure on the can. 22% is showing excessive leakage. very poor cyl sealing. could be rings or head gasket leakage. yes it can be a big concern I will scrap most anything over about 15%. the next step is to determine if its leaking past the reeds or past the head gasket.if its past the headgasket cooling issues will occur due to combustion gas in the cooling system. if its past the rings lubrication issues will occur due to contamination of the incoming fuel mix and hot gasses blowing past the piston.

 

[Stavis Bay]

Re: 22% Blow by in #5 Cylinder

Thanks rodbolt. What will the decarb do? Could that help solve the problem. The motor seems to run great, I have had no problems.

 

[rodbolt]

Re: 22% Blow by in #5 Cylinder

could be some carbon in the ring grooves or on the ring land preventing a good seal. could also be the start of a head gasket leak. they dont last forever.