I need to change the valve stems seals in my 360 Magnum motor and need guidance. The engine is installed and want to know proper procedure to remove the old ones and install new ones.

Bring piston to TDC on that hole, replace spark plug with air fitting, apply air pressure to keep valves up, pop out the keepers on the spring retainer, remove retainer & spring, install seal.
With a shaft mount system it's probably easier to remove the rocker shafts; loosen bolts in stages to avoid the shafts getting bent. On my Street Hemi it was easy to just slide the rocker arms sideway on their positioning springs.
The keepers are small enough that they can easily fall into the heads, so use a lot of shop rags - preferably lint-free - to catch them.

I just went through this a week back with the AMC V8 in my Jeep.

You can "make" an Air-holding tool/fitting, by using a Spark-plug extender (available at autoparts stores) and 1/4-inch air-tool quick-disconnect fitting, plus some teflon-tape to seal.



You screw this fitting into the sparkplug hole for the cylinder you are working on and use compressed-air to hold/keep the valves from dropping down into the cylinders while you compress the valve-spring and remove the valve-keepers.

An older, alternative method, involves feeding small-diameter Rope, through the spark-plug hole, filling-up the cylinder. When the valve drops inward, the rope keeps it from falling all the way into the cylinder where it's un-retrievable (else you'd need to remove the cylinder head to get it out.)

You will also need an "On-Engine Valve Spring Compressor," to remove each spring. I bought a "Good" one for $40 at NAPA. I (also) bought a crummier one for $20 at Pep-Boys, though with weaker valve-springs, the cheaper one would likely work fine.



TIP: You should "hit/tap/smack" the valve-retainers (I used a wide, deep socket and rubber mallet,) to free-up the Keepers, otherwise they (sometimes) stick/bind in the retainer opening.

If you haven't got compressed air to use you can do the rope trick. Bring the piston up to TDC and then push some cotton clothesline into the cylinder until you can't get any more in. Then go ahead and change the seals. Pull the rope back out and do the same to the next cylinder. Be sure to have a long enough rope so you have a long tail hanging out of the cylinder when it's full. You don't want to have to pull the head to get your rope back.

Do you mean "Valve Seals?"

Viton Valve seals are likely a good choice. Autoparts stores and dealers sell them. Jegs, Summit Racing, etc, sell them too.

Example:

Viton Valve Seals

Thanks for the helpful info!!

Good Luck with your project.

BTW: If you use the Compressed-air method, as the air enters the cylinder, it is likely going to push the piston down and the crankshaft turns. At TDC it may not, but I never bothered to try to turn the motor by hand/starter to achieve it.

You can either try to achieve TDC,...

or place the transmission "In-Gear" Parking-brake "On" and block the wheels. When you apply the compressed-air, your vehicle "may" try to move a bit...

or, you can leave the trans in "Neutral" and just allow the crankshaft to turn freely.

Best thing with the TDC dealie is to do it RIGHT Take the time to measure around your balancer and mark the balancer every 90* This is easy if you have a small flexible tape measure