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valve stem seal replacement

Big Block Mopar valve stem seal replacement-on the vehicle

This article is to be used as a reference for replacement of valve stem seals on a big block Mopar engine, installed in a vehicle. All safety precautions must be taken, to include the use of proper tools, safety glasses, etc. The author and this website are not responsible for any problems which may be associated with those folks who may use this as a reference for their own projects.

Step 1: Assess the situation

Valve stem seals which are "on their way out", so to speak, will allow engine oil to pass through the valve guides, particularly when the engine is cold. This allows the oil the pool in the combustion chambers, sometimes, right on top of the pistons themselves, depending upon where the pistons are located in relation to their cycle. This causes a puff of oily, blue smoke upon startup, usually until the engine warms up, or, when they’re completely gone, the engine will burn some oil as it goes down the road. Some may confuse this with bad rings. Bad rings will present themselves upon acceleration-oil passes (blows by) the rings as the engine cycles, particularly during acceleration (coming away from a light, etc.). The best way to diagnose if you have bad rings is to do a compression test on each cylinder.

My ’75 New Yorker Brougham St. Regis has a 400, 2 BBL, and has just 71K miles on the odometer. I purchased the car off of ebay fall of ’04. At first, the engine was OK, but as time wore on, it became apparent the valve stem seals were bad. This is common on older cars, as well as cars which have been sitting for some time. I figured the car must’ve sat for some time, most likely at least once during the last 30 years. The engine ran great, but, as time wore on, it burned more and more oil upon startup. Ugly clouds of black/blue smoke would appear, then, would go away as the engine warmed up.

So, I went ahead and purchased a compression test/air hose adapter set from  Sears Craftsman™, which included the gauge to measure cylinder pressure, as well as the adapters to inject air into the cylinders in order to keep the valves “up” into the head. Also, the valve compressor from Craftsman™ comes in handy. I modified this tool by setting it against a vice, and lightly tapping the handle back and forth with a small hammer, until it was a loose enough to move by hand. This comes in handy in tight spots, such as near the alternator and the brake booster on a C-bodied Mopar. You can use sandpaper on the handle, too, to make it slide more easily.

Step 2: Attack

Here is our victim-a 400 motor. Valve covers are easy to remove-just get the air cleaner, wiring, pre-heater thingy, etc., out of the way on both sides, and remove the 6 screws which hold each cover on each head.

Here’s another shot, this time from the passenger’s side.

This shot shows our valve compressor tool doing its thing. It’s important to have the tool at the lowest possible part of the spring, for maximum compression of the spring. Properly installed, the spring will be compressed within a matter of seconds. Sometimes, you may have to nudge it in between the two lowest coils. Practice, and you’ll be a pro after a few springs!

This shot shows our all-important air hose attachment screwed into the spark plug hole on the #1 cylinder. This is absolutely important; otherwise, the valve will most likely drop into the cylinder. There are two other methods to make sure the valve stays up; use a length of rope stuffed into the cylinder through the spark plug hole, or turn the motor over until the piston for the cylinder you’re working on is all the way up in its travel. I prefer using the air hose attachment method, which almost became my undoing, despite being the most straightforward approach. This illustrates the importance of attention to detail and coordinating things properly when doing a job like this, with the engine in the vehicle.

I thought the air hose was attached while doing the intake seal on the #7 cylinder. Well, it wasn’t, and the valve started going down into the cylinder! Let my lack of attention to detail be a lesson; always make sure the air hose attachments are, well, attached. You’ll hear air in the cylinder, which is what I thought I heard. At any rate, keep a small diameter magnetic retriever handy (under .250”), in case something does happen. I connected the hose, and made a quick trip to Advance Auto to purchase yet another retriever, which helped me fish the valve stem out of the valve guide. Stock valve stems on big block Mopars are .375” in diameter. Consider me lucky.

Above pic shows one spring, retainer, and valve lock assembly removed. This is how the spring seat area should look. With plenty of air in the cylinder, go ahead and gently try and move the valve stem back and forth; this is to test the valve guides. The valve stem should be stationary, side to side, within the guide. Any excess movement may indicate a bad guide.

This pic illustrates the need for modification of the valve compressor tool; clearance at both the brake booster and alternator is a bit tight, so, the person doing the repair must be able to move the handle back and forth to make both compression and release of the spring easy.

Here, I use a magnetic retriever (stronger than that used during my near mishap with the valve going down into the cylinder). I use the magnet to retrieve the valve locks, of which there are two per valve. Compress the spring, use the magnet to get the locks halves out, then remove the spring and compressor as one assembly. Piece of cake, once you get moving.

Above pic shows a quick and dirty method of using grease on the locks, which makes reassembly easier. The grease helps to hold the lock halves in place while placing them on the valve stem grooves, during reassembly. Notice cheap fender cover, which comes in handy during projects like these.

Above pic shows using a little coercion used to get the valve retainer to come loose from the valve stem and locks. A slim, but blunt, object, and light tap with a small hammer makes everything come loose.>


After replacing the worn out or non-existent seals in my ’75 NYB St. Regis,  doing a tune up, and an oil change, the car started up great, and quickly burned off any oil which was in the cylinders. The engine settled down into a nice idle, and the job was done. The engine doesn’t burn any oil now; there are no clouds of smoke anymore, etc. It’s a job which will give the average backyard wrench some satisfaction. Take your time (it takes a few hours, minimum). Again, I feel the air hose approach works best. Make sure to use crocus cloth or very light sandpaper on the valve stem seals before reassembly; this prevents tearing of the new seals. Another tip; slather a little grease on each valve stem and each seal as you prepare to slide the new seals into place. This helps to prevent tearing of the seals, too.

The new seals from Fel Pro came in a kit, and are of a better material then the originals. Also, the exhaust seals are of a different design, which kinda threw me for a loop, when I first opened the box. The intake seals are of the deep “umbrella” type, which helps to keep the vacuum of the cylinder from sucking oil into the chamber, when the intake valve is open. The intake seal fits completely around the top part of the valve guide. You’ll need to press it into position. The exhaust seal is of a “hat” type, which makes sure if there is some wear in the valve guide, the oil will weep back into the open side of the head (by the force of compression and the open exhaust valve). Once I’d replaced a few seals, it became apparent why they designed these newer seals in this manner.

All prices on the price list are in U.S. dollars. Auto parts were purchased locally from Advance Auto, in the Rochester, NY, area.

One of these days, I’ll create another article on how to install Mopar Performance™ valve covers on one of these cars. Looks to me like the manifolds just need a little cleanup in a few spots with a die grinder. Hmmm

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