How To Replace Valve Stem Seals Without Removing The Cylinder Head

Hi guys and gals, today we are looking at how to replace the valve stem seals on an engine without having to remove the cylinder head. Typically you would be doing this repair because of exhaust smoke after letting the engine idle for some time or the engine blowing smoke when accelerating after coasting for a bit with a closed throttle or smoke of start-up (See the image below). The reason an engine with worn valve stem seals will blow smoke during these times is because the vacuum level is at it’s highest at idle which will draw oil past the seals, down the valve stem and into the cylinder and likewise when the engine is off for a while the oil will seep down the valve stem, past the seal and into the cylinder. When accelerating or revving the engine the vacuum level drops so the effect isn’t as bad. Keep in mind that worn valve guides can also cause this and the only remedy for that is a cylinder head overhaul. Better to try the cheap option first sometimes though!


The engine we are using for this tutorial is a Ford 4 litre single overhead cam engine, but I think you will find this tutorial relevant to just about any overhead cam unit, although typically double overhead cam engines will require a more complex tool than the one we can get away with using on this single cam.

Talking about tools (no, not me 😛 ), before you start you will need to get yourself organised with a few things. First up, an air compressor and an air line fitting or hose that will screw into the spark plug thread on the cylinder head. We need to fill the cylinder with compressed air to stop the valves from dropping down once the collets, retainer and spring are removed. You can get these from EBay at a reasonable price if you don’t already have one – Air Line Fitting. There is one other option if you don’t have access to an air compressor, it’s threading a soft rope into the cylinder via the spark plug hole and basically filling the gap between the top of the piston and the valve faces and therefore preventing them from dropping down. Crude but relatively effective!

You will also need an overhead valve spring compressor, as opposed to a typical valve spring compressor that is used when the cylinder head has been removed from the engine. As I said earlier, you can usually get away with a fairly simple tool (no I’m not referring to myself again) for a single cam engine such as the image below –


But for double overhead cam engines there simple isn’t the room and you will need something like this –


Once again these are available from EBay – Valve Spring Compressor

Removing the seal can be done with multi-grips or vice-grips IF YOU ARE SUPER CAREFUL, but I do highly recommend getting the right tool for the job in the form of pliers or the small slide hammer type. You can check these out here – Valve Stem Seal Remover

And finally, as well as the tools needed to remove the rocker cover from your engine, having a magnetic pick up tool makes life a lot easier when removing the pesky little collets, you’ll see what I mean shortly. And finally these can also be had from EBay – Magnetic Pick Up Tool

Ok, on with the show. The first thing you need to do is remove the rocker or valve cover. In the case of the Ford engine this involves removing the air intake and placing a rag in the throttle body to stop any crap getting in, removing the brake booster vacuum hose, removing the pcv valve from the cover or removing the vacuum hose to it, removing the accelerator cable and numbering the ignition leads and removing them from the spark plugs and hanging them over the intake manifold.


Next up we removed all the spark plugs and the four 13mm bolts securing the rocker cover and lifted it off and placed it upside down close to the engine, you’ll see why shortly.


The rocker gear is the next to come off. A couple of notes of caution here – in the end of each rocker arm is a lifter or lash adjuster. With the AU engine they typically won’t fall out when you remove the rocker assembly but in the earlier engines (and other makes of engines as well) they are likely to come out. The easiest way around this is to loosen the rocker gear bolts (see the caution about this next) and wrap electrical tape or similar around the end of the rocker arm and lifter to secure it in place. This is handy for reassembly also.

Lash Adjusters taped to rocker arms

And a caution about the bolts. Certain rockers will be pushing their respective valve springs down due to the position of the camshaft so the rocker gear can be under a bit if pressure. To prevent breaking bolts or stripping threads out undo the bolts evenly and in a circular pattern starting from the middle. A couple of turns each time is advisable until all 28 of the suckers are loose. You will feel the rocker gear move up as you loosen the bolts and the valve springs decompress.

With all of the 10mm bolts loose (i.e. all of the way out of their thread but not removed from the assembly) you should now be able to lift the rocker gear up and out of the way. I like to use the upside down rocker cover to store it, with the front to the front and the back to the…. well you know what I mean (and the rocker gear not necessarily upside down like in the pic!).


To avoid losing the small valve collets down into the timing case or down one of the oil drain holes in the head I highly recommend stuffing rags into these before going any further. See the diagram below for a typical valve setup.



At this point I suggest lining up the first cylinder you are going to do to Top Dead Centre, where the piston is at the top of it’s stroke. To do this, rotate the engine clockwise using a 22mm socket on the front crank bolt until the two camshaft lobes for that cylinder are facing down (see pics below). It’s important to do this for each cylinder as you move along because if for some reason you loose air pressure the valve will only drop as far as the piston will allow it but if the piston is at the bottom of the cylinder it’s possible that the valve will drop enough to fall out of the guide and then the it’s cylinder head off – not good! Also if you are using the rope method for keeping the valves up you don’t want to have to thread 50 feet of rope in there each time!

Exhaust Lobe facing down
Intake Lobe facing down

Next up fit the air line (or thread the rope in) fitting and connect it up. We don’t need a lot of pressure to keep the valves up, I had it set at 20psi and had no problems but if the retainers or collets are a bit sticky you may have to use more. Be aware that the engine may rotate a bit initially as the cylinder pressurises.

I find it a good idea to grab a socket around the valve retainer size and place it on the top of the retainer and give it a couple of taps with a hammer. Nothing too serious, just enough to loosen things up a bit. On the first tap it will probably feel pretty solid but on the next couple it should be a bit springy. BE CAREFUL TO KEEP THE SOCKET IN THE CENTRE AWAY FROM THE VALVE STEM!!IMG_1441

With that done we now need to fit the spring compressor. The claws should go on the lowest possible coil that you can get them on to as the spring needs to be compressed quite a way to be able to get the collets out. Also, the retainers on the Ford engines have a small diameter so it’s important to have the top of the compressor lined up properly as well.


And now if you push down a bit on the valve compressor tool the retainer and spring should move enough to be able to get the collets out with the magnet.



And then the retainer and valve spring can be removed and the seal will be visible.


Removing the seal can be quite tricky, and I highly recommend using the correct tool for the job as mentioned above, however if you are EXTREMELY CAREFUL you can remove them with multi-grips and vice-grips. The idea is to grip them just enough so that you can rotate the seal and pull upwards at the same time. Grip the seal too hard and you risk damaging the boss that the seal locates on and you MUST BE CAREFUL NOT TO MARK THE VALVE STEM IN ANY WAY OR THE SEAL MAY BECOME USELESS. This method does work but use it at your own peril!


After checking that the valve stem has no marks or damage it’s time to fit the new seal. I use a long socket that is the same diameter as the outside of the seal (12mm in the case of this engine) and after fitting the seal over the valve stem and locating it on the boss give it a few taps to drive it down into place. You don’t have to be particularly forceful and you should be able to feel when it is driven all the way down.


Once the seal is in place it’s time to put everything back together. On the Falcon engine there is a shim that acts as the valve spring seat, be sure that these are fitted if you notice these on your particular engine. Usually they will stay in position but it’s worth checking before starting on the reassembly.


With the valve spring and retainer still in the compressor tool, fit them over the valve stem and fit one collet (tapered end down) and make sure it has located into the grooves in the valve stem.


And then with a non-magnetised flat blade screwdriver, rotate the collet around the valve stem 180 degrees, ensuring that it remains located in the valve stem grooves.


Now you should be able to fit the second collet in the space previously occupied by the first collet, hope that makes sense!

Both collets fitted

Now you can start releasing the valve spring compressor, ensuring that both collets stay in position. If one or both come out of the grooves in the valve stem you will need to tighten the spring compressor and have another go at fitting them, this can be tricky but try to have patience!

With the valve spring compressor removed the assembly should look like this –


One down, eleven to go! (depending on your engine type). I’m not going to do all them as it’s just a junk engine used to set the turbo gear up but the process is the same for the rest of the valves. If you are using the rope method to keep the valves up don’t forget to rotate the engine to Top Dead Centre for each cylinder that you are working on. And DON’T FORGET TO REMOVE THE OIL DRAIN AND TIMING CASE RAGS YOU HAVE IN PLACE ONCE ALL VALVES ARE DONE!

The rocker gear can be refitted once all valves are done, being careful not to dislodge any lifters or lash adjusters and ensuring that the rocker arms are correctly located on their respective cam lobes and valve tips. As with removing the rocker gear, the bolts must be done up evenly and in a spiral pattern starting from the centre to avoid rocker damage,valve damage, bolt damage or thread damage and don’t over-tighten these bolts, 25-30Nm of torque is all that is needed here.

The rest of the reassembly will just be the reverse of what you did to remove the rocker cover etc.

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