force 125 compression

[paul118]

Hello all...quick question, is it possible for the compression on a motor to read 150 across the board but a cylinder to still be bad? Reason why I'm asking is because I've been having a load issue on my boat and have changed and checked everything possible (thanks to you guys) and my mechanic was here today and told me the sleeve on number one was worn and the piston is moving around too much and not enough air is being sucked into the carbs so they are not firing the way they should. While running plugs 3 and 4 get pulled and the engine dies but when 1 and 2 get pulled there is just a slight hesitation. Any feedback would be great and thanks again.

 

[JB]

Re: force 125 compression

I would call your wrench's explanation balderdash, Paul. Sounds like he hasn't a real clue what is wrong. You got some critical information when you tested by pulling spark plugs. It is running on #3 and #4.

You need to look at what is common to #1 and #2 and causing a major loss of power. It is not a "bad cylinder" or even 2 bad cylinders, and it has nothing to do with compression..

I am not familiar enough with Force 125s to offer any prime suspects, but I would look first at common ignition or carburetion systems.

Good luck.

 

[Frank Acampora]

Re: force 125 compression

Yes! Most people are only concerned with compression ratio but equally important is the clearance of the piston skirt to cylinder wall. This determins the base compression and how much air is ingested, how much it is compressed inside the crankcase, and how much of the charge is blown into the cylinder.

Be leery though of "the sleeve being worn" These pistons are set up loose and will move side to side in the cylinder by hand, with the head off, while cold. While Chrysler and Force did not publish piston to cylinder wall clearance specifications, boring and honing to exact size will ensure a correct fit since the piston manufacturers will size the pistons to correctly expand under heat of running. With compression numbers that you showed, I would NOT expect worn piston skirts. While your mechanic is technically correct, he is jumping to confusions--as stated above, grasping at straws because he doesn't know what the problem is.

Check out electrical, carburetion, and reeds before you jump into re-boring cylinders with good to excellent compression.

 

[paul118]

Re: force 125 compression

Yes the reeds are ok but how to test the coils and the cd boxes? Carbs are rebuilt but the top isn't sucking any air when running. Top two cylinders are giving off spark but not enough. Stator? Trigger? How to test and what should they be?