How to: Service a Blow off Valve
A lot of us are running aftermarket BOV’s on our MPSs, whether for the noise, or the common belief that the plastic one from the factory isn't quite up to scratch, like any piece of equipment it requires a bit of love every few months to keep it in pristine working order.
So heres how to service the more common brass piston type valves, this BOV in particular is the GFB GT Hybrid.
Items required :
-A cool engine to work on (optional, but highly recommended)
-Long nose & Multigrip pliers (for the hose clamps)
-10mm socket, extension, and 1/4 drive ratchet (for BOV flange bolts)
-Allen keys, or hex drive bits, size & requirements will depend on the specific BOV
-Metal polish, Brasso & most other auto metal polishes should work well.
-Isopropyl alcohol, or methylated spirits
-Clean rags, for polishing & resting parts on so they dont roll away
-Oil, a tiny coating of the moving parts will be required at re-assembly
-Loctite (blue), optional
-Eye protection is also recommended as the BOV is very tightly sprung, and a wayward part could do some serious damage.
You should not need to reset your spring tension after this exercise.
First remove the recirc hose, vacuum line, and finally, the BOV from the inlet manifold, if you find this first instruction daunting, I suggest you stop reading now, and go make a nice cup of tea.
All things going well, the BOV is off the car, and in your hand on its way to the garage.
Find a clean, flat bench to work on, with plenty of space around and good lighting....the top of the wheelie bin is probably not the best place to do this.
Remove all the ancillary bits (trumpets, blanking plates, recirc adapters etc) and set them aside on the bench, in the GFBs case these simply unscrew from the body.
Remove the top of the bov, on the GFB valve there are 4 hex bolts, I find it best to back them off a few turns, then while holding the top of the valve firmly, remove the bolts individually. If you dont hold the top of the valve, there is a good chance your stock valve will suddenly appear very appealing again as the innards of your BOV fly in all directions around the garage.
Place the screws in a small container so as not to lose them.
Now you have a top section, spring, piston, and a bottom section.
Place the top section to the side for now, and place the spring on a rag to prevent it from rolling away. Gently tip the bottom section of the valve upside down and the piston should slide clear of the body, a small push from the underside may be required if it gets stuck, note how tarnished the piston has become, and the accumulated “blow by” that is impeding its smooth running.
Place the bottom section on the bench and carefully remove the ring from the piston, and place that with the screws from earlier, in the safe container.
Give the piston a good wipedown with some alcohol (not beer), then take your choice of polish and start polishing the piston until its nice and shiny, give it one more wipedown with alcohol in case there are any wax residues from the polish you have used.
Mmmm, shiny.
Now give the other items a good clean with alcohol, particularly the cylinder the piston travels in, you could polish this as well if you like, also give the piston ring (if fitted) a good clean.
Place the ring back on the piston and smear a dab of oil over it.
Then reassemble the valve, check the top is correctly seated within the grooved areas for the vacuum nipple and bolt it all back together, you can place a drop of loctite on these bolts, but it is not crucial as they are held under load anyway.
Place the recirc outlet and trumpet / blanking plate back on the valve body, I use a little bit of loctite here for good measure ( I have already replaced one lost blanking plug ), it is important for the recirc fitting to go on the lower of the 2 outlet holes (there is also a notch in the flange indicating this), and the trumpet on the higher one, this ensures the initial part of the charge is recirculated to make your ECU happy.
Reattach the BOV to the car in the usual manner, start the engine and listen out for any leaks etc from the area around the BOV, you may notice a small amount of smoke upon startup, this is just a bit of the residual oil on the piston burning off, it is harmless and should clear quickly.
Warm the engine up and give the valve a few quick bursts on the throttle, you should hear the valve opening on lift off, and it should close again sharply, if there is any sign of hesitation or stumbling when the engine returns to idle, you may need to increase the spring tension slightly.
Most users of these valves report having the spring adjustment screw set level, or just below the top of the body for best results.
Nearly all men can stand adversity. But if you want to test a man's character - give him power.
Abraham Lincoln
LinkBack URL
About LinkBacks
Reply With Quote
Originally Posted by Nirvandan
