compression question

[JOFO17]

I recently picked up an early 80's Evinrude 185. The first thing i did before even putting it on a boat was to see if it had good compression. All were good except for #1 and it was very confusing. It will only pump up to about 30 psi on the compression stroke and drops down to zero the rest of the time. The needle never rises above 30 psi. What might cause this reading?

 

[BonairII]

Bad rings/scored cylinder? Or maybe valves aren't opening/closing properly?

Was the motor free? If not, why didn't you check the compression BEFORE buying it?

 

[emdsapmgr]

Sounds like you've got a dead hole. The best situation you could hope for is that the head gasket has a bad seal ring on that cylinder. A head gasket is an easy/cheap fix. You'll need to pull the head for sure to check the seal. If it's intact, then do a visual inspection of the cylinder walls (check for cyl liner scuffing) and check to be sure the top piston ring is still intact. Also, check the placement of the 3 rubber water diverters by each cyl.

 

[racerone]

There are no valves involved with compression in the cylinder !

 

[JOFO17]

For what I paid it was worth it for the lower unit and the starter and pump etc. I was just hoping it was a good motor. Now that my grass is cut I can take the head off tonight and take a look. I'll let you all know what I find. And I was also thinking that if a valve were stuck open I wouldn't get compression.

 

[racerone]

When you get the head off you will see very clearly that there are no valves in sight when compression starts in the cylinder !!!

 

[JOFO17]

Just an update.... When I took it apart I first found the thermostat clogged up and then found the piston pitted and the walls scored pretty good on the bad cylinder. The others look Ok.. Just like Racerone said... Not a valve issue

 

[JOFO17]

And wihile I still have this compression post going, there is something I'm not sure of. In the "official" I Boat compression test procedure JB said that the big JohnnyRude V-6 motors usually will read a bit lower. What should I be looking for????