Final appeal for ideas!
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Tuned
Joined: Aug 2007
Posts: 287
Likes: 1
Final appeal for ideas!
1988 F250 351
#5 cylinder was oil fouled (threads were covered with oil) but the compression and leak down on it and all the other cylinders were perfect. Last weekend I removed the lower plenum and replaced the gaskets - this time using Ultra Black RTV as insurance. Put in a new plug. Less than 100 miles and #5 is just as oil fouled as before. Also the ACT sensor (which sits in the #5 intake runner was shorted out and had oil on it as well. All other plugs look great. Compression on #5 is still up. Is there any other place that could be letting in oil besides underneith the lower plenum without created a compression loss?
Any ideas before I have to cut my losses?
Thanks
#5 cylinder was oil fouled (threads were covered with oil) but the compression and leak down on it and all the other cylinders were perfect. Last weekend I removed the lower plenum and replaced the gaskets - this time using Ultra Black RTV as insurance. Put in a new plug. Less than 100 miles and #5 is just as oil fouled as before. Also the ACT sensor (which sits in the #5 intake runner was shorted out and had oil on it as well. All other plugs look great. Compression on #5 is still up. Is there any other place that could be letting in oil besides underneith the lower plenum without created a compression loss?
Any ideas before I have to cut my losses?
Thanks
New User
Joined: Nov 2007
Posts: 10
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Just a thought. Did you pop your valve cover off to see if somehow oil is getting in there from your intake valve. Maybe an oil valve seal? Wouldn't you still get good compression with a bad seal if the valve closes but it would allow oil to seep down the valve guide and in the intake chamber.
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Tuned
Joined: Aug 2007
Posts: 287
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Munypit,
You posted one second before my update. I could check under valve cover but I think you have to compress the valve spring to bet to the seals. Now the question remains, can it be done from the top?
You posted one second before my update. I could check under valve cover but I think you have to compress the valve spring to bet to the seals. Now the question remains, can it be done from the top?
New User
Joined: Nov 2007
Posts: 10
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I would pop the valve cover and take a look. Usually the seals get hard and brittle and start to leak oil. If they are not that old who knows. A flashlight might reveal a lot. If you're getting enough oil to foul the plug I think you be able to see what's going on without compressing the spring. If that's the problem, I think you can replace it from the top. It's been years since I've done it but if you hook air up to your cylinder when you compress you spring it will hold your valve up. I'm sure there are other methods.
Lead Driver
Joined: Aug 2006
Posts: 5,670
Likes: 13
From: Sand Lake, MI
Originally Posted by jemini
Could it be possible that the valve guide seals on #5 cylinder could be leaking from the get go? If so can new seals possible be installed from the top without pulling the head?
Get some cloth ¼” rope, with the piston you want to work on up on the compression stroke (rocker arms are both free) back the motor off until the piston is all the way down, stuff a few feet of the rope into the spark plug hole filling the cylinder. Now gently bring the piston back up so it presses the rope against the head so it will hold the valves up tight in place.
Now you can compress the valve spring and remove the keepers, the spring cap and then remove the springs, then remove the old seal. Put the new seal on and then the spring, cap and keepers. Back the motor off bringing the piston back down and remove the rope.
You can also use compress air to keep the valves up but a sudden loss of pressure could be bad, I’ve found rope to work very well.
Hotshot
Joined: Jul 2003
Posts: 12,177
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From: Newport, WA
Trending Topics
Lead Driver
Joined: Aug 2006
Posts: 5,670
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From: Sand Lake, MI
Originally Posted by superduty4x4
That rope idea is a GREAT one, reps sent!
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Thread Starter
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Tuned
Joined: Aug 2007
Posts: 287
Likes: 1
Thanks to everyone for the ideas.
I'll check under the valve cover to see what's what and then see if Auto Zone will loan me a spring compressor. I have plenty of spare valve seals so I should be in business.
This is a new remanufactured longblock so if the seal is bad it came from the rebuild work done by Rhino Engine and Transmissions. It would be far easier to do the repair myself than to try to extract a warranty claim from them. They have shown themselves to be a more than a real pain in the butt!
I'll check under the valve cover to see what's what and then see if Auto Zone will loan me a spring compressor. I have plenty of spare valve seals so I should be in business.
This is a new remanufactured longblock so if the seal is bad it came from the rebuild work done by Rhino Engine and Transmissions. It would be far easier to do the repair myself than to try to extract a warranty claim from them. They have shown themselves to be a more than a real pain in the butt!
Fleet Owner
Joined: Aug 2005
Posts: 23,667
Likes: 301
From: Easton,Ks
Originally Posted by Skandocious
Hey Bill mind explaining what the tool is and how it works?
After you put the rope in as stated above or air pressure to hold up the valve then you unscrew the handle all the way and hook the arms on the spring as far down as possible.
Then turn (screw) the handle in and as you screw it in the spring will compress.
Once it is compressed sometimes you have to tap the handle with a hammer to break the valve keeper free.
Take the keepers out and lift the spring off the valve stem.
Replace the seal.
Put the spring back over the valve.
Put the keepers back in and unscrew the handle.
Then take out the rope or remove the air fitting.
