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  #1  
Old 06-02-2007, 03:42 PM
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M103 Valve Seals and Cylinder Pressurization

Hey guys -

I am lining up everything I need to replace the valve seals on my M103. In other threads I have seen on the issue, the cylinders are pressurized using shop air. Why is that? Is it critical?

If I don't need it, then I can replace them next weekend. If I need to get that, it could be another few months until I start working and can buy an air compressor.

Thanks!

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Old 06-02-2007, 04:55 PM
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Air pressure holds the valve shut and keeps it from dropping into the cylinder when the spring retainer is removed. If you lose a valve into the cylinder you will need to remove the cylinder head to retrieve it.
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Old 06-02-2007, 04:58 PM
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Keeps the valve from falling

The air pressure keeps the valves from falling down into the cylinder when you remove the valve springs.

Another way to keep the valves up is called the 'rope trick'. You remove the spark plugs. Then, with the piston for the cylinder which you are working on at the bottom of its motion, you feed a small diameter rope into the cylinder, rotate the crankshaft until the piston pushes the rope up tightly under the valves, holding them in place. I've not tried this but a search on this should help more than my description. The question I have about the rope trick is how much rope is needed to hold the valves but allow the engine crank to rotate to where the camshaft has allowed both valves to be closed.
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Old 06-02-2007, 05:02 PM
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Quote:
Originally Posted by Chas H View Post
Air pressure holds the valve shut and keeps it from dropping into the cylinder when the spring retainer is removed. If you lose a valve into the cylinder you will need to remove the cylinder head to retrieve it.
Yup, ok. That would be bad! The next question is where can I find the attachment / adapter required?
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Old 06-02-2007, 05:14 PM
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A good parts store will have what you need, or can order it. I use the hose whip from my compression tester. The quick release coupler on the whip mates with the end on my shop air hose.
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Old 06-02-2007, 08:44 PM
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My Sears compression tester came with the facility to add air to the cylinder like you need. You need about 80 psi and any small compressor would be ok. Beg, steal or borrow one!
You will need a valve spring compressor too.
Did you read our recent thread on this job, as we did it 2 weeks ago?
Here is the link.
http://www.peachparts.com/shopforum/showthread.php?t=168126

On our 300TE, we had to remove the radiator to get at the 27mm nut on the front of the crankshaft to turn the engine and then to lock it in place against the frame rail when we were working on the valve seals.
Oh, one thing you MUST do is when you get the rocker shafts off, before trying to compress the spring, get a socket big enough to fit over the keeper and give each valve a deft smack with a mallet. The caps are well stuck on the valve keepers or collets and all you will do is release the air in the cylinder! You will hear when they loosen.
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Last edited by Merkey; 06-02-2007 at 08:52 PM.
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  #7  
Old 06-02-2007, 09:34 PM
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I use about 30 lbs of air, enough to hold the valves (if one is gentle) but not enough to move piston. The write-up by Merkey is excellent BTW.

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