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Low Compression Cyl 4

  #1  
Old 12-23-2014, 07:28 PM
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Default Low Compression Cyl 4

Well I have replaced Rings, Head Gasket, and new timing chain kit. I still have the same compression in no.4 60 PSI. Now considering Valve job, but can't get an answer on could Valve Seal be the cause. Many in forum say compression has nothing to do with seals. When I do a leak down test I lose no pressure for over 2 hours and then very little. I should have changed the seals when I did the head but it is easy enough to do now without removing the head. Just want opinion from anyone who has solved a compression problem by changing valve seals.
 
  #2  
Old 12-29-2014, 10:37 AM
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I've never known valve seals to be part of low cly compression on internal combustion engine.

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Last edited by sw2cam; 12-29-2014 at 10:42 AM.
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Old 12-29-2014, 05:13 PM
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EDIT: Article below describes function of valve seals only.

https://www.hastingsmfg.com/ServiceTips/valve_seals.htm

Are you sure it's not leaking? Most compression testers I've used capture the peak compression---a "measurement & hold" situation, so I would not expect to see the measurement change on that type of gauge. Of course, if you're using something professional grade that lets you read the compression as a function of time, then disregard the above.

Valve guide seals on s cars are known to wear and let oil pass into the combustion chamber.
 

Last edited by derf; 12-29-2014 at 11:05 PM.
  #4  
Old 12-29-2014, 06:41 PM
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Leak in the cly if a valve is open....or leak onto the top of the valve when closed. When the valve is closed the seal on the valve stem is at the other end. If the valve seal had anything to do with the clylinder compression we would have a lot of cars without it.

Look it up, do a wet and dry compression test. Problems could be a valve, piston, rings, head gasket, or head. Hell could even be the block deck.

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Last edited by sw2cam; 12-31-2014 at 03:53 PM.
  #5  
Old 12-29-2014, 10:43 PM
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what's the compression on the other 3 cyls BEFORE the rebuild?
what's the compression on the other 3 cyls AFTER the rebuild?

Did this suddenly become a problem as a misfire or was it a slow onset deal?

Per my edit above, the valve seals are the oil barrier when the valves are open---at which point compression is not the issue.

Did you check that the
block bore
block trueness
head trueness
valves were all in tolerance?

And the things Joe mentioned above?

If you still have the same TRULY crappy compression after the rebuild you did (I'm assuming the valves and valve seats were also done), there is something fundamentally wrong going on. Yes I am stating the obvious. I'd prob rule out head gasket itself but the block and head may not be true and thus if the head is warped you'll have trouble. The possibility of a cracked or porous head is not out of the question either.
 

Last edited by derf; 07-16-2016 at 01:26 AM.
  #6  
Old 12-30-2014, 10:58 AM
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derf is 100% on the money right down to ebay.
 
  #7  
Old 12-30-2014, 09:14 PM
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Default Thanks all for info.

185, 186, 186, 60 We have found the issue. We took the head off again and did a leak test on the valves. To my surprise the #4 cyl. intake valves leaked bad. No issues on any of the exhausted side. So my head is off to the machine shop. Now I'm going to have a $1,000 engine in a car worth $500. But at least the 2 teardowns have educated me on how to do it in the future. When it is all back together I should get a good 150K miles out of the new rebuild as long as the trans. hold up.
 
  #8  
Old 12-30-2014, 11:10 PM
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....and you keep up with those oil changes.....

Glad the culprit has been identified.

MAKE SURE YOU GET THE VALVE SEALS REPLACED
 
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Old 01-03-2015, 10:46 PM
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Tom? Top right you'll see your username, next to it a drop down. Click the drop down and then signature. Add your first name, state, and car to your signature. Get your post count up to ten so your account stays useable.
 
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