( yet another) Compression question

[RobDar]

( 1989 Johnson 60 Horse outboard)

I did a search on "compression" in the forums and found a little of what I was looking for...but my eyes are burning from all that reading...LOL!

...so someone mentioned to me that there are more reasons for low compression than just a failed cylinder that needs a rebuild.
What are some of those reasons?

 

[HighTrim]

Re: ( yet another) Compression question

Gunk goes downwards, and sometimes the bottom cylinders get filled with it, sometimes running deepcreep or seafoam helps free up cylinders, but an expert will give you better explanation. GL

 

[RobDar]

Re: ( yet another) Compression question

thanks for the reply...

my "expert" says rebuild the powerhead...I asked him..."well arent you even going to look into any other causes? I mean there could be something else going on right?"
he replied with..."not worth my time"

I just went through this with my van...the mechanic insisted on rebuilding the heads to fix a compression problem on the 3rd cylinder...my neighbor tested my spark plug wires ( which were brand new) with a high pot tester and found one that had a partial fault.

I dont want to rebuild a 89 outboard until all other options have been exhausted.

 

[BoatBuoy]

Re: ( yet another) Compression question

Rings stuck with carbon and not making full contact with cylinder walls; faulty head gasket; scored cylinder wall; obstructed ports, possibly faulty reeds.

Pull the head and take a look.

 

[Silvertip]

Re: ( yet another) Compression question

Spark plug wires on your van did not, nor can they create low compression. "Failed Cylinder" is a rather nebulous term and can mean lots of things. Not firing constitutes a failed cylinder but it is not necessarily due to a compression issue. Cylinder scoring, broken piston skirts, broken rings, stuck rings due to carbon or varnish build up, leaky head gaskets, and burned pistons, all have an effect on compression. Some require a rebuild and some don't.

 

[R.Johnson]

Re: ( yet another) Compression question

A leak-down test will give the answer.

 

[RobDar]

Re: ( yet another) Compression question

Spark plug wires on your van did not, nor can they create low compression. "Failed Cylinder" is a rather nebulous term and can mean lots of things. Not firing constitutes a failed cylinder but it is not necessarily due to a compression issue. Cylinder scoring, broken piston skirts, broken rings, stuck rings due to carbon or varnish build up, leaky head gaskets, and burned pistons, all have an effect on compression. Some require a rebuild and some don't.

just telling you what I was told...with the new wires it runs fine and the engine light is off.

 

[RobDar]

Re: ( yet another) Compression question

A leak-down test will give the answer.

I wonder how much difference there is in these...anyone know?
There are some fairly affordable ones and some expensive ones...it will probably be the one and only time I ever use the thing so durability is not an issue...but I wonder if the cheaper one is accurate/sensitive as the more expensive ones...

probably a "you get what you pay for" kind of thing huh?

 

[RobDar]

Re: ( yet another) Compression question

Spark plug wires on your van did not, nor can they create low compression. "Failed Cylinder" is a rather nebulous term and can mean lots of things. Not firing constitutes a failed cylinder but it is not necessarily due to a compression issue. Cylinder scoring, broken piston skirts, broken rings, stuck rings due to carbon or varnish build up, leaky head gaskets, and burned pistons, all have an effect on compression. Some require a rebuild and some don't.

I said I had low compression on one cylinder...not that I had a "failed cyliner"...
and that I had a COMPRESSION PROBLEM...not low compression on my van...I do not know what that compression problem was, it was the info offered to me and I was not there when the mechanic ran his tests...
he could have been scamming me.

I apologize for not being a mechanic...but then if I was I would not have to ask I suppose

 

[freddyray21]

Re: ( yet another) Compression question

no need to get an attitude. I think what they were trying to tell you was there is a difference and that a bad plug is not a compression problem. It is not going to hurt anything to do a decarb on the motor to see if the compression numbers come up. I would at least start there.