compression numbers ?

[catfish charlie]

guys ..my 78 merc. 140 stopped running today. i could not get it to crank at all. the compression numbers was in the 110-120 except number 4 which was 35..does this mean a rebuild is n order or could it be something else..

 

[andy6374]

Re: compression numbers ?

Better hope it isn't a rebuild. Could be a blown head gasket. Stuck ring (which a decarb could take care of). <br /><br />When you say you couldn't get the engine to crank, I think you meant to say that "the engine cranked but wouldn' start", right?<br /><br />-andy

 

[catfish charlie]

Re: compression numbers ?

yes it turns freely but willnot start.. how can i tell if its a head gasket or it needs a decarb..

 

[catfish charlie]

Re: compression numbers ?

why you say hope not rebuild.. are the parts hard to find?

 

[andy6374]

Re: compression numbers ?

A rebuild is expensive. Try a decarb and see if the compression picks up. Search FAQ for a how-to. Try this first.<br /><br />To see if it is the head gasket you will have to take off the cylinder head. If it isn't no big deal because you would have to pull the head for a rebuild anyways.<br /><br />-andy

 

[Chris1956]

Re: compression numbers ?

Charlie, That motor does not have a removable cylinder head, so it isn't a blown head gasket. You can remove the middle transfer cover on the starboard side of the motor, and visually inspect the #4 cylinder for scratches and the rings for breakage. The rings should also move a bit when you push on them. This shows that they are not stuck. <br /><br />Charlie, That motor should start up and run (poorly) with two bad cylinders. After the inspection, you may want to look for other reasons for the no run condition.

 

[SeaKaye12]

Re: compression numbers ?

From a range of 110-120.....down to 35 on #4?<br /><br />Seems like too much of a offage to be a stuck ring.<br /><br />Let us know what the inspection reveals.<br /><br />Chuck