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Dry compression test Ok -wet not so good. Rebuild???



 
 
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  #1  
Old September 9th 03, 01:07 AM
CaptMP
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Default Dry compression test Ok -wet not so good. Rebuild???

tom wrote:pretty good dry compression
..approx 150 in all 6 cylinders. In a couple of cylinders the wet test
shows 210 and 185. ....


Tom, I'm thinking that the two cylinders that are high "wet" are OK, though the
one at 210 sounds high. Probably due for a valve job as the other cylinders
did not show a rise in pressure when wet. Normally I'd expect to see a moderate
increase when doing a "wet" test. Actually the absolute numbers are less
important (within reason) than the difference between cylinders anything over
10% or so is suspect.
Good luck
Mike
Ads
  #2  
Old September 9th 03, 04:39 PM
Bill Kiene
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Default Dry compression test Ok -wet not so good. Rebuild???

I think I understand. I will try that next time.

Thanks Gene.

--
Bill Kiene

Kiene's Fly Shop
Sacramento, CA
www.kiene.com

"Gene Kearns" wrote in message
...
On Tue, 09 Sep 2003 04:25:08 GMT, "Bill Kiene"
wrote:

Hi Tom,

I have been working on reciprocating engines for over 40 years as a

hobby.
My grandfather, father and uncle were professionally trained mechanics. I
have taken lots of compression tests in my day but have never heard of a
"wet test"? If you have 150# in all 6 cylinders and it is not burning oil
and goes pretty good, I don't think I would rebuild it unless you are

going
to do a real high-end rebuild or a brand new motor.


Ever squirt a teaspoon or two of oil in a cylinder to sort out ring
problems from valve problems? The rings are wet......

--



Grady-White Gulfstream, out of Southport, NC.

http://myworkshop.idleplay.net/cavern/

Homepage
http://www.southharbourvillage.com/directions.asp Where

Southport,NC is located.
http://www.southharbourvillage.com/autoupdater.htm Real Time Pictures

at My Marina
http://www.thebayguide.com/rec.boats Rec.boats

at Lee Yeaton's Bayguide




  #3  
Old September 9th 03, 10:18 PM
F330 GT
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Default Dry compression test Ok -wet not so good. Rebuild???

Hi Tom,

I have been working on reciprocating engines for over 40 years as a hobby.
My grandfather, father and uncle were professionally trained mechanics. I
have taken lots of compression tests in my day but have never heard of a
"wet test"? If you have 150# in all 6 cylinders and it is not burning oil
and goes pretty good, I don't think I would rebuild it unless you are going
to do a real high-end rebuild or a brand new motor.

--
Bill Kiene

Kiene's Fly Shop
Sacramento, CA
www.kiene.com

"tom clark" wrote in message
. com...

My 1972 Mercruiser in-line 6 cyl. has pretty good dry compression
..approx 150 in all 6 cylinders. In a couple of cylinders the wet test
shows 210 and 185. It doesn't burn much oil though ( can smell some
blow by) and the oil pressure is still good. Top end RPM's are good
too although top speed is not what it should be but still ok.

Perhaps I screwed up the wet test but is this common... to have bad
numbers on a wet test and good on the dry test?

Should I be thinking of a rebuild?



I agree with you Bill. I've never heard the "wet test" one either. I think any
mechanic would know you squirt a couple drops of oil down a cylinder with low
compression to tell you whether or not it's bad rings or a valve.

A couple of squirts of oil in a high compression engine would certainly
increase the compression. You'd be changing the compression ratio. A couple of
more squirts and you could easily break something.

In building a high performance engine you can increase the compression ratio
just by going with a thinner head gasket. Can you imagine how much difference 3
or 4 squirts of oil will do?

Barry
  #4  
Old September 10th 03, 01:09 AM
Lawrence James
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Default Dry compression test Ok -wet not so good. Rebuild???

If the compression goes up when you put a little oil in the cylinder it
means the rings are leaking. Too much oil could change the compression some
I suppose. Make sure you crank each cylinder until the gauge stops rising.

I would not worry about it if you are happy with the performance and the oil
consumption is not much. There is no good number, what you are looking for
is all the cylinders to be about the same. My 350 has 65# in all the
cylinders, think that is bad ? :-) It's not, I have a high overlap cam.

"F330 GT" wrote in message
...
Hi Tom,

I have been working on reciprocating engines for over 40 years as a

hobby.
My grandfather, father and uncle were professionally trained mechanics. I
have taken lots of compression tests in my day but have never heard of a
"wet test"? If you have 150# in all 6 cylinders and it is not burning oil
and goes pretty good, I don't think I would rebuild it unless you are

going
to do a real high-end rebuild or a brand new motor.

--
Bill Kiene

Kiene's Fly Shop
Sacramento, CA
www.kiene.com

"tom clark" wrote in message
. com...

My 1972 Mercruiser in-line 6 cyl. has pretty good dry compression
..approx 150 in all 6 cylinders. In a couple of cylinders the wet test
shows 210 and 185. It doesn't burn much oil though ( can smell some
blow by) and the oil pressure is still good. Top end RPM's are good
too although top speed is not what it should be but still ok.

Perhaps I screwed up the wet test but is this common... to have bad
numbers on a wet test and good on the dry test?

Should I be thinking of a rebuild?



I agree with you Bill. I've never heard the "wet test" one either. I think

any
mechanic would know you squirt a couple drops of oil down a cylinder with

low
compression to tell you whether or not it's bad rings or a valve.

A couple of squirts of oil in a high compression engine would certainly
increase the compression. You'd be changing the compression ratio. A

couple of
more squirts and you could easily break something.

In building a high performance engine you can increase the compression

ratio
just by going with a thinner head gasket. Can you imagine how much

difference 3
or 4 squirts of oil will do?

Barry



  #5  
Old September 11th 03, 03:08 AM
Ron Thornton
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Default Dry compression test Ok -wet not so good. Rebuild???

What is the purpose of a high overlap cam?

Ron

  #6  
Old September 11th 03, 03:55 AM
Mark Browne
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Default Dry compression test Ok -wet not so good. Rebuild???

Better breathing at very high RPMs.

Mark Browne

"Ron Thornton" wrote in message
...
What is the purpose of a high overlap cam?

Ron



  #7  
Old September 11th 03, 04:11 AM
Calif Bill
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Default Dry compression test Ok -wet not so good. Rebuild???

More Power! Basically a racing cam. Is a source for real bad damage in a
boat, as the high overlap can cause negative pressure in the exhaust and
suck water into the cylinder. Most likely used on Dry Stacks, or stacks
where a little water is injected near the exit to meet the exhaust laws.
e.g. V drive ski boats (Mandella, etc.) Or jetdrive low profile ski boats
Bill

"Ron Thornton" wrote in message
...
What is the purpose of a high overlap cam?

Ron



  #9  
Old September 11th 03, 09:43 PM
Ron Thornton
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Default Dry compression test Ok -wet not so good. Rebuild???

Mark, Bill and Gene,

Thanks for the replies. I understand now.

Asskisser and jerkoff,

Why don't you guys take your personal bull **** to e-mail.

Ron

 




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