A bit convoluted this, hope I can get across what I mean. Engine originally destined for my '83 MK1 GTI was it's standard 1.8 DX. Things have moved on and a slightly later '85 MK2 GTI 1.8 EV is going in. I understand the heads on each are essentially the same save for a few differences, but for the sake of this post it's mainly the addition of 'air shrouding' for the injector valves in the '85 I'm concentrating on. I'm not using the air shrouding function and will be capping off the inlet pipe on the rear of the head. Straight forward enough. I already had the '83 non-shrouded injector valves and matching fuel lines that have the earlier, coarser thread. The DX uses the stubby brown plastic injector holders seen in the first image, the EV uses the brass ones in the second. These however have a different diameter and means they're not interchangable between DX / EV heads. So I'll be putting non-air shrouded valves into the brass holders for shrouded ones. Again, so far so good. From what I can see this isn't going to be an issue, but was looking confirmation the (longer) lower brown plastic part for shrouded injectors doesn't need to be fitted to the brass holder if using non-shrouded injectors (or if I do use them, it'll make no odds). The thinking is the brass holder has an O ring of it's own and to my eye it will (in addition to the injectors own O ring) be enough to seal things into the head and the additional longer plastic part is redundant for my needs? Just to confuse things further there appears to have been a third type of fitting (cream coloured) used briefly during 1984 for air shrouded valves that didn't have 'top hats', I've added an image just for reference. The brass holder, with separate plastic part seems to be an evolution of it?
I've only got the brass ones on my mk2 so can't really help. Although I did buy new brass inserts from Classic Parts, but dont remember seeing the Orings.... Hopefully that is just my memory. But what does that o-ring actually seal against?
Been puzzling with this all day and trial fitted various combinations to see what 'fits' naturally / correctly. No longer happy it goes where I've shown it above, like you say, in that position just what would it seal against for a start, plus it also partially obscures the air shrouding vent holes which seems counter productive? 7Zap is a little confusing in the way they place the O ring on the schematic, think that's where I've been going wrong. The diameter of the ring itself means it won't fit between the brass holder and the inside collar of the plastic insert, the only natural place it sits is as pictured below. When like this it would seal the plastic insert against the bottom of the injector port of the cylinder head when everything is screwed into place. Seems to imply the threaded part of the brass holder must be sufficient to seal it with the cylinder head and no added help is needed. The injector valve is sealed at its top by the larger donut ring and the bottom by the smaller, slim O ring that goes around the 'top hat'. I think in my circumstances the plastic inset and it's O ring plays no part as I'll have the air shrouding blocked off ie. that'd prevent any leaks in itself. If you're using the air shrouding and airs instead circulating around the brass holder / plastic insert it's looking like you do need the O ring(s) to ensure air goes where it's meant to.
Going to fit these even though there's no air shrouding going on in my set up and in that regard they're redundant. However you can't use the O ring without it being placed over the plastic insert and that's what creates the seal between the combination of valve / holder / insert when the unit as a whole is screwed into the head. No O ring'd mean you'd have the bottom of the brass holder seating against the bare metal of the head. ... and this is to also assume it screws completely down to the bottom, which I'm not sure that it does. Either way it creates the risk of an unwanted leak. Without the injector valve fitted the plastic insert has a very small amount of movement against the brass holder, but that tightens up to become rock solid when the valve is pushed in, further strengthening the seal as you're screwing down onto it. If you are utilising the air shrouding, this is my understanding of how leaving the O ring off might effect it even more. Air enters the head via the pipe on the rear of the head, that's roughly situated between injector valves 3 + 4. If you look at either end of the head there's one small bung on each. There's a channel runs the entire length of the head between them, I'm guessing this is machined right through and not cast with the bungs simply there to close off the open ends. That channel passes through each injector valve port and also adjoins the incoming air pipe. The air gets into the brass holders via a hole on either side, goes down the inside of the plastic insert and into the 'top hats' via openings between it and the injector valve. The top hats have their own seals that prevent the air leaking passed them from within the plastic insert. Back to our O ring... it prevents air escaping the injector ports at the point where it should all be going into the brass holders. if it weren't there some air could potentially pass along the outside of the plastic insert and not within them instead. The top hats are a tight fit, but they're also a pentagonal shape because of the way they're pressed and not perfectly round. Those 5 x gaps are what allows the air to enter the hats before then exiting via further holes on their circumference. Oddly there's room for 5 of these holes evenly spaced, but there are just the 4 with one being a blank. Be interesting to know why that is, perhaps something to do with disturbing / improving the atomisation?
Now seeing the picture of the seal on the plastic part reminds me that I did have them. At the time I was wondering if they were a good idea being so close to such heat, but I also dont doubt VW.
