Home

Head with leaky valves advice needed

Posted By: rshaw125

Head with leaky valves advice needed - 02/10/19 10:48 PM

A buddy of mine had persistent misfires on his Taurus. Compression test showed two weak cylinders. He pulled the head and laid it on it's side. Filled the ports with water after a few minutes a tiny dribble out of one valve. 1 of 6 intake valves. DOHC Ford. Then exhaust side . Two valves with little dribbles after a few minutes. Are these little dribbles enough to cause the misfire and low compression? The engine has around 150,000 miles. Is this just normal wear??
Posted By: 46Harry

Re: Head with leaky valves advice needed - 02/10/19 10:56 PM

Since the head is off and there is leakage from the valves, now would be a good time to get the head reconditioned especially since the engine has 150,000 miles on it.
Posted By: KneeGrinder

Re: Head with leaky valves advice needed - 02/10/19 11:02 PM

Pouring water in the combustion chamber now? Yes it will show the leaking valve seats if they a fairly bad. Will cause lower compression, yes, but he really should have done a comp test before removal. compression is often lost thru rings or valves. At this point he is in no man's land till he has a valve job done and mounts heads back on motor. Yes, seems like fairly normal wear for a Taurus....

As for valves causing misfire? IDK, If its the intake, and they leak bad enough, yes. The ECU should show a code for misfire if its OBD2, and its the ignition system. Atleast it should...If its back firing thru an intake valve, probably is not going to log a code.

O'pps my bad, he did a comp test, sorry! Nice German car you have by the way! I approve...
Posted By: rshaw125

Re: Head with leaky valves advice needed - 02/10/19 11:12 PM

Thanks for the replies. Yes a compression test revealed the weak cylinders. Wet and dry. Rings are tight. After codes for misfires. The leakages are just dribbles. i was expecting a flow of water. No obviously burned valves.
Posted By: StevieC

Re: Head with leaky valves advice needed - 02/10/19 11:53 PM

There could be different reasons. Slightly bent valve, weak valve springs, worn seats.
Best to take the head in and have it rebuilt and put it back on.
Posted By: mattd

Re: Head with leaky valves advice needed - 02/11/19 12:22 AM

What exactly were the compression test results? Valve leakage can certainly cause misfires
Posted By: rshaw125

Re: Head with leaky valves advice needed - 02/11/19 12:32 AM

The two bad cylinders were 55 and 65 PSI. The good cylinders were 145 - 155.
Posted By: DeafBrad

Re: Head with leaky valves advice needed - 02/11/19 12:54 AM

I don't claim to be a professional mechanic or anything. But what is a dribble with water should be significant when the air is under compression.
Posted By: Chris142

Re: Head with leaky valves advice needed - 02/11/19 01:19 AM

Originally Posted by DeafBrad
I don't claim to be a professional mechanic or anything. But what is a dribble with water should be significant when the air is under compression.

Yep. If liquid will pass air will really leak past.
Posted By: Linctex

Re: Head with leaky valves advice needed - 02/11/19 01:50 AM

Originally Posted by rshaw125
Are these little dribbles enough to cause the misfire and low compression?


Little dribbles after several minutes?

No - - Those will not affect the way the engine runs.

I have seen heads where liquid would almost run out as fast as it poured in - - STILL, no misfires!

But you could SURE hear the whistle in the exhaust when cranking it to start it!!!!!!
Posted By: Linctex

Re: Head with leaky valves advice needed - 02/11/19 01:51 AM

Originally Posted by rshaw125
The two bad cylinders were 55 and 65 PSI. The good cylinders were 145 - 155.


You should have done a "DRY" test followed by a "WET" test.

I honestly do not think the head is your problem, if you got "Just a tiny dribble" after several minutes.
Posted By: Trav

Re: Head with leaky valves advice needed - 02/11/19 02:18 AM

Sure, numbers like that can and do cause misfires, under 90 psi can cause it and the lower it goes the greater the odds. That kind of leakage is enough to cause the low compression.
Seeing as a wet and dry test was done I think you found the issue.

Edit: You should check the valve guides and cam lobe/lift also, worn guides can cause erratic seating in the running engine and worn lobes can cause low compression, a dial indicator is be the easiest way to tell on a cam in block engine.
Posted By: KneeGrinder

Re: Head with leaky valves advice needed - 02/11/19 03:14 AM

Originally Posted by DeafBrad
I don't claim to be a professional mechanic or anything.

"But what is a dribble with water should be significant when the air is under compression."


Correct!
Posted By: demarpaint

Re: Head with leaky valves advice needed - 02/11/19 12:24 PM

Originally Posted by 46Harry
Since the head is off and there is leakage from the valves, now would be a good time to get the head reconditioned especially since the engine has 150,000 miles on it.

+1 And in all honesty if he plans on keeping the car he might as well do the other head, and check the cam.
Posted By: Donald

Re: Head with leaky valves advice needed - 02/11/19 12:35 PM

Originally Posted by rshaw125
Thanks for the replies. Yes a compression test revealed the weak cylinders. Wet and dry. Rings are tight. After codes for misfires. The leakages are just dribbles. i was expecting a flow of water. No obviously burned valves.


What was done to determine "rings were tight"?

What year Taurus?
Posted By: rshaw125

Re: Head with leaky valves advice needed - 02/11/19 12:55 PM

It's a 2004 DOHC. Dry compression test followed by wet. The two bad cylinders saw no improvement from added oil.
Visually the cam lobes look like new.
The head in question is going to the machine shop Wednesday. Trying to decide if the other head should go even if it does not leak water.
Thanks for the replies.
Posted By: mattd

Re: Head with leaky valves advice needed - 02/11/19 01:47 PM

Did you perform a leakdown test?
Posted By: demarpaint

Re: Head with leaky valves advice needed - 02/11/19 01:49 PM

Originally Posted by rshaw125
It's a 2004 DOHC.
The head in question is going to the machine shop Wednesday. Trying to decide if the other head should go even if it does not leak water.

Many years ago I worked in a machine shop, I learned quite a bit from some of the best machinists on L.I. The other head has just as much wear as the head in question, only it is not showing any symptoms, yet. You're halfway there labor wise to having that head done. Having said that, and forgetting ethics, if you're looking to sell the car fix the head in question and let the next person worry about it. If you want to keep the car, or care about ethics I'd do both heads. Imagine 6 months from now, or possibly less having to rip everything apart to do the other head. We are not talking a low mileage car here. I would say 8 out ten times we did heads in pairs.
Posted By: meep

Re: Head with leaky valves advice needed - 02/11/19 01:51 PM

stretched timing belt caused misfires/stumbles at idle and low rpm for me.

~50psi is very low pressure.

leaky EXH valve can also cause misfire if it's developing hotspots and causing preignition.
Posted By: WyrTwister

Re: Head with leaky valves advice needed - 02/11/19 01:52 PM

Originally Posted by 46Harry
Since the head is off and there is leakage from the valves, now would be a good time to get the head reconditioned especially since the engine has 150,000 miles on it.



Exactly what I was thinking .
Posted By: rshaw125

Re: Head with leaky valves advice needed - 02/11/19 02:12 PM

Originally Posted by mattd
Did you perform a leakdown test?


No. The two low compression cylinders were also the one's that were misfiring. Also the one's with the leaky valves.
Posted By: ragtoplvr

Re: Head with leaky valves advice needed - 02/11/19 02:40 PM

Water is a poor choice to leak test valves, it normally does not wet out the surfaces and with the surface tension it normally takes a pretty big hole to leak thru without pressure. Alcohol is a better choice. Bet those valves would gush with alcohol. If the head is still on the engine the alcohol will burn off evaporate much quicker but you still must worry about hydrostatic lock.
Posted By: Propflux01

Re: Head with leaky valves advice needed - 02/12/19 12:42 AM

Leak down test would have given more info. Since the head is off, recondition it, and press on with pride. If the misfire stops, you will know why.
© 2019 Bob Is The Oil Guy