View Full Version : A nasty runing blue band 70 hp merc

05-19-2003, 04:22 AM
Been having a problem with this dam engine She has heaps of spark Jumps 7/16 compression is great 110 on 2 all and 106 on the other carbs are good and clean reed valves are good seems to run on 2 and then seems to thump every now and again.
I was wondering although it has good compression could the ring s on one of the cylinders be stuffed so there is no vaccum in one pot I have looked into the intake side and noted that one piston has 2 rings on the piston and the other 2 pistons have three
Your thoughts are appriciated

05-19-2003, 10:38 AM
" Steve,

Merc made pistons with two and three rings. Functionally, they are the same, but I think you are better off with the three ring pistons. Someone rebuilt that powerhead.

Even though the compression is good, a piston may still need rings. If the rings are worn you can have compression, but as you stated, the vacuum may be low. When this is the case it can usually be diagnosed by turning the flywheel clockwise by hand and feeling the compression in each cylinder. If the rings are worn you will probably feel very little resistance in that cylinder when you do this.

Tony "