compression question

[kd7isf]

Hi,

Looking at a friends boat.

early 90's searay 16.5 with merc 3.0 alpha1

It has been sitting in his driveway (uncovered!!) for a few years.
He Said it wouldn't start, so he rebuilt the carb, and after the carb rebuild, it ran rough and would not idle.

So, I checked the carb -- float level and drop were way off -- corrected that, but it still ran rough and refused to idle.

I then checked the spark plugs -- all have some carbon, but not too bad (black, not brown, and dry) It should be noted that 3 and 4 were rusted to the block -- very difficult to get out.

Then I checked compression: 1 = 175, 2 = 170, 3 = 105, 4 = 100

I pulled the manifold off and checked the ports. all exhaust ports were dry and black, all intake ports were dry, but 3 and 4's had some light corrosion in them

I squirted some oil into 3 and 4 and rechecked compression -- 170 - 175 in both of them but only momentarily

Is there a way I can determine weather the rings are stuck or broken without dis-assembly?

Thanks

 

[Barnacle_Bill]

Re: compression question

Since the pressure came up after squirting oil in the cylinders there is a problem with rings. You could try soaking them with some PB Blaster. You might get lucky.

 

[Alpheus]

Re: compression question

You need to let it run and get up to operating temp to really gauge the compression numbers. Your rings may be stuck but getting the piston nice and hot usually releases them if its not corroded too bad...

 

[LippCJ7]

Re: compression question

The way I see it is you have already started taking the motor apart may as well keep going and freshen the motor with new rings and a head job. Just the way i roll I guess

 

[jerryjerry05]

Re: compression question

PB or Marvel Myster Oil.Let it soak for a couple of days(keeping it full).Remove the oil,if it didn't already leak past the rings.Then run it up to operating temp for a while.Then do another comp test.
If the comp is still low check the head gasket.J