OIL FILTER TUNNEL LEAKS...Some thoughts.

[shaunstaples]

Thanks Duncan, I can look at pictures but not the same as having one in bits.

Dave, Yes read that Viton just over 200'c, so probably best choice.

Les, I read the Info. posted earlier but as said before "I worry", and feel that reducing the material outside the O ring would be a sacrifice? Especially as the RTV has shown its strength.

For me the inner edge of the groove will be the hardest thing to get right, if the groove is too wide then will it offer any benefit being there? the O ring could be reduced to say 28mm and provide a little more area for a smear of RTV to play its role?
Also without the inner wall it might make it more tolerant to varying thickness / material of the O ring?

[shaunstaples]

I could replicate this on both sides of the end plate, on the test rig...

[Les Howard]

Hello Shaun. The way I see it is this: The O ring method should create the perfect seal against the high pressure oil in the filter chamber. Maximising the area OUTSIDE the O ring for the benefit of allowing a touch more RTV to be in situ is, I think, of no advantage. All areas outside the confines of the O ring will see the same low pressure as the rest of the crankcase and can use the sealant of your choice: Wellseal, Loctite 518, Threebond etc...
As regards the inner diameter of the groove: As said, for internal pressurised flanged joints, the Outside diameter should be the same as the O/S diameter of the O ring. This is because the internal oil pressure will ram the O ring against the outer edge of the groove. The inner groove edge itself simply creates the space and houses the O ring...The inner diameter is NOT that critical (see the calculator I link to above) It serves no other purpose than to house the O ring somewhat initially before tightening. The seal would work if there was no metal on the inside of the O ring as long as it was in position when clamping up. However if you make a groove the same width of the O ring rubber then it cannot get deformed as it should by the SQUEEZE of the flange metal clamped up. In fact it could even hold the cases apart, so it needs space to squash into. The MINIMUM of the groove width must allow that spreading of the rubber but the inner edge of the groove DOES NOT need to be in contact with the inner edge of O ring when fully tightened up...see diagrams..Hope this creates a better picture?

[shaunstaples]

I was thinking of the varying thickness and material you seem to get these days, but I guess were all buying from china so probably over thinking...

The inner grove, if in a perfect world could be achieved then it would provide just enough space for it to squash, but hitting the inner edge provide a slight increase in pressure of the o ring, whilst still allowing the cases to fully mate. Beyond my paygrade to achieve I'm afraid! and back to consistency on the O rings you can get hold of.

The 28mm would still give 0.5mm inside before the filter housing, also was thinking if the O ring failed, then the sealer might be your prayers answered...

[Les Howard]

Knowing BEFORE I START that the next time I rebuilt the engine it was guaranteed Not to Leak would be my Prayers answered, Shaun ha ha...
No, the pressure needed to seal is created by the SQUEEZE on the O ring (the difference of the depth of the groove compared to the O ring thickness). Something around 20% is optimum. Secondly, the oil pressure itself forces the O ring outwards into the joint line of the 2x flange faces. The more pressure the more ramming. The inner wall of the groove does ABSOLUTELY NOTHING so no need to be too critical sizing it up....just make it big enough and not too small width wise. PS My offset between the halves of the tunnel would be very nearly at least 0.5mm so I would want the O ring further away...

[Joker_Bones]

Somewhat off topic but somewhat on topic...

I took took this carburettor off recently, which I have to admit I also fitted.

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I imagine there was insufficient space for the O ring to deform into.

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The inner edge of the recess had deformed inwards turning an 1 1/8" bore into a 1" opening.

In this case the pressure differential is reversed, the higher pressure on the outside, so the inner edge of the recess is theoretically needed.

[Les Howard]

Hi J Bones: Yes, the O ring should butt up to the inside edge of the carb's groove (the carb is sucking inwards). Very often one sees a fat O ring in the groove which when tightened down is too big to be accommodated inside the groove. This results in the Flange unable to settle flat on the manifold and the carb sits on the O ring. Further tightening bends the carb flange towards the manifold....How many have you seen like that? The correct groove and O ring thickness combination should allow the O ring to be squeezed slightly before the flanges meet with the O ring close to or gripping the inner edge of the groove...If the O ring fills the groove, it's too big, but the correct size O ring will enable full tightening of the carb without bending the carbs flange. In your carb, it is possible a fat O ring was forced to move inwards at some point with heavy tightening pressure and bent the weak metal (zinc/alloy ?).

[shaunstaples]

Well good news and bad news, did a few pressure tests last night and good news is I can’t make either side fail getting > 2500psi
Bad news is chamber side won’t hold pressure and falls back to zero whereas grove side is holding just over 200psi.
Used two o rings and swapped them round and got same results so must need inner face? It probably put it in more compression?
I’ve set up RTV and o ring so will retest today

Nip on o ring was about 9 thou, both sides but it was difficult to measure

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[Les Howard]

Hi Shaun...can't quite make out what you mean with this sentence: "bad news is chamber side won’t hold pressure and falls back to zero whereas groove side is holding just over 200psi."

[shaunstaples]

I’ve had help and we managed to machine the 1mm x 0.8mm deep groove and that’s sealed but on the reverse side we cut a 0.8mm groove but then machined in to centre to create another chamber. The groove held just over 200 psi but the reverse chamber side wouldn’t hold pressure