MerCruiser 4.3 Low compression in #1
 

Hello-
I recently purchased a used boat - 2002 Monterey with only 35 hrs on
it. Mercruiser 4.3
The compression numbers:
#1 130
#2 185
#3 180
#4 185
#5 180
#6 180

The mechanic who looked at it said that with so few hours on the boat,
its obvious that its sat for a while and that after use - the
compression in #1 would go up.
Should I be concerned? If so, what are the likely reasons for the low
compression in #1?

Thanks!

"JaxDawg" wrote in message
ups.com...
Hello-
I recently purchased a used boat - 2002 Monterey with only 35 hrs on
it. Mercruiser 4.3
The compression numbers:
#1 130
#2 185
#3 180
#4 185
#5 180
#6 180

The mechanic who looked at it said that with so few hours on the boat,
its obvious that its sat for a while and that after use - the
compression in #1 would go up.
Should I be concerned? If so, what are the likely reasons for the low
compression in #1?

Thanks!


Yep, but I would have questioned it before I bought it.

A 3+ year old boat with only 35 hours on it? Hmmm.

Why would sitting idle cause it to lose compression in only one cylinder?

"JaxDawg" wrote in message
ups.com...
Hello-
I recently purchased a used boat - 2002 Monterey with only 35 hrs on
it. Mercruiser 4.3
The compression numbers:
#1 130
#2 185
#3 180
#4 185
#5 180
#6 180

The mechanic who looked at it said that with so few hours on the boat,
its obvious that its sat for a while and that after use - the
compression in #1 would go up.
Should I be concerned? If so, what are the likely reasons for the low
compression in #1?

Thanks!

Rings or valve seats.

It *could* be a stuck valve, loose spark plug, leaking head gasket, or a
hole/defect in the piston, but those are unlikely.

I would guess it the rings...riding on some rust in the cylinder. I would go
ahead and run it, and see if it comes out.

Good luck.

--
-Netsock

"It's just about going fast...that's all..."
http://home.columbus.rr.com/ckg/

The 35 hours figure comes from a digital read from the engine. Based
on the condition of the boat, I believe it. Its been stored in dry
dock and in excellent condition.
Why didn't I question it? I'm an idiot, I guess - and I didn't note
anything from the sea trial.
My question is... what are the common causes of low compression, how
much $ to fix, and is it something that I need to address right away?

thanks

"JimH" wrote in message
...

"JaxDawg" wrote in message
ups.com...
Hello-
I recently purchased a used boat - 2002 Monterey with only 35 hrs on
it. Mercruiser 4.3
The compression numbers:
#1 130
#2 185
#3 180
#4 185
#5 180
#6 180

The mechanic who looked at it said that with so few hours on the boat,
its obvious that its sat for a while and that after use - the
compression in #1 would go up.
Should I be concerned? If so, what are the likely reasons for the low
compression in #1?

Thanks!


Yep, but I would have questioned it before I bought it.

A 3+ year old boat with only 35 hours on it? Hmmm.

That is not that unreasonable, if someone bought it at the end of the
model year, and then found they jst didn't use it.....in a northern climate,
I can see how it would have low hours.


Why would sitting idle cause it to lose compression in only one cylinder?

"JaxDawg" wrote in message
ps.com...
The 35 hours figure comes from a digital read from the engine. Based
on the condition of the boat, I believe it. Its been stored in dry
dock and in excellent condition.
Why didn't I question it? I'm an idiot, I guess - and I didn't note
anything from the sea trial.
My question is... what are the common causes of low compression, how
much $ to fix, and is it something that I need to address right away?

thanks


Sorry if I came across the wrong way. I only wanted to express my view that
35 hours on a 3+ year old boat is suspicious.

Low compression normally comes from cylinder wear, something occurring over
time. The fix in that case is rebuilding the engine (reboring the cylinders
to a slightly larger diameter and putting in larger pistons), something that
can normally be done only once on an engine.

With only one bad cylinder and with the low hours you report the problem, as
Netsock previously suggested the problem is likely to be with a piston ring
in cylinder #1.

#1 cylinder gives a hint that maybe some water got into that cylinder and
sat, causing some corrosion. I'd run it, check the oil condition frequently,
and hope, if the corrosion isn't too bad, that it gets better after running
it for a few hours.


"JaxDawg" wrote in message
ps.com...
The 35 hours figure comes from a digital read from the engine. Based
on the condition of the boat, I believe it. Its been stored in dry
dock and in excellent condition.
Why didn't I question it? I'm an idiot, I guess - and I didn't note
anything from the sea trial.
My question is... what are the common causes of low compression, how
much $ to fix, and is it something that I need to address right away?

thanks

JimH wrote:
"JaxDawg" wrote in message
ups.com...

Hello-
I recently purchased a used boat - 2002 Monterey with only 35 hrs on
it. Mercruiser 4.3
The compression numbers:
#1 130
#2 185
#3 180
#4 185
#5 180
#6 180

The mechanic who looked at it said that with so few hours on the boat,
its obvious that its sat for a while and that after use - the
compression in #1 would go up.
Should I be concerned? If so, what are the likely reasons for the low
compression in #1?

Thanks!



Yep, but I would have questioned it before I bought it.

A 3+ year old boat with only 35 hours on it? Hmmm.

Why would sitting idle cause it to lose compression in only one cylinder?



I would run some Marvel Mystery oil in it. A little in the crank and
some in the gas to help free up the rings.

Capt Jack R..

Rust or stuck ring. Run it for a while and see. Even if it stays low I
would not let it worry me unless it gets lower and starts missing on that
cylinder. You could run a thousand hours like that.

"JaxDawg" wrote in message
ups.com...
Hello-
I recently purchased a used boat - 2002 Monterey with only 35 hrs on
it. Mercruiser 4.3
The compression numbers:
#1 130
#2 185
#3 180
#4 185
#5 180
#6 180

The mechanic who looked at it said that with so few hours on the boat,
its obvious that its sat for a while and that after use - the
compression in #1 would go up.
Should I be concerned? If so, what are the likely reasons for the low
compression in #1?

Thanks!