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Supra Tech
1,750 Posts
Discussion Starter #1 (Edited)
Tech Tip: BOV Repair/Rebuild/Maintenance

I've recently seen threads about this and I've received many PMs/e-mails asking how I repaired my SSQV back to normal, and have have 3 SSQV's sent to me for rebuilds in the last 4 months. So I figured I make a write up so other can do this for themselves (not that I don't like making side money) but I'm the kind of guy that like to share information. Hopefully this will become a sticky. So here it is.


Remove rear cover and front nose cover. You only need to remove the screws at 1 o'clock, 4, 7 and 10 to remove the front nose cover. The other 4 screws hold the plunger seal to the main body of the BOV. Leave this on for now You'll know this if you've ever changed the insert/whistle.

With the rear cover off you'll see the one way bleed off valve.
Notice the very tiny hole in the 12 o'clock position on the valve. This is the bleed hole and it regulate how fast the valve closes after a blow off. If there is any obstruction in the hole the valve will stay open at idle after a blow off because the pressure in the front chamber can't bleed off. If the valve is cracked or I've even seen popped out of its housing completely then the valve will close prematurely and will cause flutter out the front of your turbo. On a brand new valve it stay open for ~1 sec after a blow off to relive all the pressure out of the charge piping. The only thing that secures the valve in is they roll the lip of the housing over the top of the valve. Anyone who knows what CTE is, (Coefficient of Thermal Expansion) knows that the CTE magnitude between plastic and aluminium is huge so when it gets hot, especially in the common directly over the turbo mounting on out MKIII's, the aluminium will expand making more room for the valve to pop out. There is a o-ring under the plastic valve.

Obviously, I've already repaired this valve, it was popped out completly and cracked from 6 o'clock to 9 o'clock. I repaired it by pre-heating the housing in a 250 oven for 10 minutes so it would expand a little, while it was in the oven I mixed my bond, turn the oven off and I quickly pulled it out of the oven, popped in the o ring and valve, applied the bond and I let it set in the oven while it is cooling down.
I actually re-sized the bleed hole a bit smaller,to ~0.008", so the valve stays open a hair longer after a blow off.

Pull on the diaphragm slightly and you'll see this

Using a pick, or something of the sorts, hold the shaft and remove the one way valve housing, one big washer, the diaphragm and the other big washer. Be very carfull not to tear the diaphragm.

Then it will look like this

Next remove the 4 remaining screws holding the plunger seal to the body. Remove seal and carefully remove the shaft making sure you don't damage the bushings in the body of the BOV.

Now take some high grit paper like emory cloth and LIGHTLY shine up the shaft and bushing's. Now is the perfect time for a trip the the parts washer to clean everything thoroughly. If you wanted to paint or polish the body of the valve now is the time for that as well, just tape of the chambers completely and have at it.

To reassemble:
-Apply your favorite lube/grease on the shaft and bushings and re-insert the shaft. careful not to damage the shaft or bushings
-Check to make sure that it slides easily in the bushings.
-Re-install the plunger seal with screws at 11 o'clock, 2, 5 and 8.
-Re-install one big washer on the shaft with the rolled lip facing in towards the body
-Re-install the diaphragm on the shaft with the "bubble" of the diaphragm facing out away from the body
-Re-install the other big washer on with the rolled lip facing out away from the body.
-Re-install the one way valve housing by holding the shaft with a pick.
-Re-install spring and rear cover. Put a little ultra black RTV bead between the main body and the diaphragm, and between the diaphragm and the rear cover.
-Re-install the whistle insert and the nose cover.

Remember "TIGHT IS TIGHT, AND TOO TIGHT IS BROKEN OR STRIPPED" Look at the size of the screw your tightening, you don't need to crank on them about 10 in/lbs is fine.

If anyone would like to add there rebuild/rebuild/maintenance experiences with any other styles and manufactures please post them with pics so there can be a common thread for this information.

225 Posts
rad thanks for the right up now i can school all these kids around town with broken ssqv's :p

Supra Tech
1,750 Posts
Discussion Starter #3 (Edited)
dolsen said:
In you BOV rebuild thread you mention applying a bond to the one way valve. What exactly are you talking about? applying an epoxy? just unsure of this step and want to have it all sorted out before I tear mine apart.

So if your looking at the one way valve you'll see that it is a plastic valve that is inside of a metal housing (which is the "nut" that holds the diaphragm in). It's common for the plastic valve to pop out of the housing under serious heat conditions because the metal housing is expanding much faster than the plastic so it creates a gap around the valve. And once you get into boost while that housing is expanded you'll pop out the valve and the BOV will not open any longer. So you'll want to bond a "ring" where the plastic valve is touching the metal housing.
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