115hp no compression in Cylinder #1

[danny9696]

Hi all I have a 75 1150 115hp that I had asked about a tapping noise earlier, I was able to work on it yesterday and found #1 cylinder had no compression and all others had 110psi. what little I had in #1 would bleed off, could that be the upper bearing and seal? The spark plug looked like it had a good burn and no deposits on the plug, can anyone point me in the right direction.

Also #6 cylinder spark plug was clean with oil on it but the compression is good and my ignition system checks out great could it be that my plug is fouled or what do you all think?

 

[Chris1956]

Re: 115hp no compression in Cylinder #1

Danny, It is likely that the #1 cylinder either overheated or ran lean. Both of these will scratch up the cylinder walls and trash the piston and rings. Remove the transfer cover (upper starboard side of motor) and inspect the piston top, rings and cylinder walls. You will likely need to disassemble the motor, bore out the #1 cylinder and install a new oversize piston and rings.

 

[danny9696]

Re: 115hp no compression in Cylinder #1

Chris I pulled it apart and you were right, the cylinder looks ok with just some aluminum on it but It is on its way to the machine shop to have her done up right, should I go ahead and replace all the rings while I have her apart? and do you think this bad cylinder could have made that tapping noise that I mentioned? oh ya and I also have carb kits on order so I can hopefully avoid this happening again

 

[Chris1956]

Re: 115hp no compression in Cylinder #1

Danny, You have pretty good compression on the other cylinders, so replacing the rings will not change it a lot. Rings are a few dollars a piece, so the investment vs the improvement is something to trade off.