Any suggestions for a substitute vacuum tank check valve (5 below) for a 420G?
Hi Andrew, trying to keep the car as original as possible. Would be keen to find a replacement T piece that’s not plastic.
I would possibly have a one in my wreck, which I am pulling some more parts off later today by coincidence. so I will check
I presume brass would be suitable
I have a huge number of old brass pneumatic and hydraulic fittings in a big jar, and they have rescued me a few times over the years
I dont think it will work in this case, but the plenum reservac system, I have replaced in its entirety with a single aquarium check valve
of course I have retained all original parts,(in a box). but the Plenum Reservac system is completely redundant engineering, has zero additional functionality, mine functions as needed
It clears the crowded engine bay, and so despite enjoying an original engine bay as much as anyone, this is an improvement, and I will not be re-instating the system
Steve, I will PM you if I locate an original plastic valve…has yours failed ?
I understand the brake reservac system is different from the plenum reservac system
Thanks Tony. When I accelerate my scuttle vent closes, I believe this means that my check valve is stuffed.
I will do a write-up Steve soon,
Yes the plenum lid check valve fails, and is hard to fix or replace
You do not need to remove any item, (as I know your engine bay is concours)
You can simply place this tiny valve in line, and your plenum lid will now function exactly as it should.
In my case, I have removed the reservac chamber that sits above the dizzy.
All that does is “allow limited plenum operation after engine is switched off”
I will be rogered if I can think of why you would require that function ?
I believe If 2 of my valves were plumbed in, you could even retain that function
I bought a bag of 10 for about $5 off ebay
Ahhh that’s a good idea, put a one-way inline check valve somewhere where you can’t see it and leave the original where it is.
Use one from an E Type?
sort of, I think it is better to close off vacuum to the cannister, as it fills with petrol distillate, which in turn causes the valve diaphragm to fail, a minor vacuum leak, and another source of petrol vapor smell in the enhine bay
I will take a look at what I did and post a pic
On the matter of the plastic valve for the brake reservac system
First the good news. I have established that I have the complete unit with all original parts in my wreck, as you know they are tucked under the RH inner wing. Tank/hoses/ valve/clamps
The bad news is that circumstances conspired I was not able to remove them on the day, and I will be returning in approx 4-6 weeks, at which time I can remove them
you may PM me if you wish to wait that long
Steve,
the valve you need is not the Nylon plastic valve for the brake Reservac tank but rather the zinc alloy pot metal valve that was used for the heating system Reservac tank.
The part number is C19426 and was used on all the 60s saloons through to and including the XJ6 series 1.
However if the scuttle vent closes upon acceleration, which is when the vacuum produced at the manifold is at a minimum, then it’s more likely a leak at the hose to or at the HEAT, AIR, OFF selector switch.
Try this test. Engine at idle, operate the AIR switch and scuttle should raise and lower. Turn engine off and try again. You should get at least two operations before the reservac tank is evacuated.
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Thanks Nick, I now understand, I believe Tony was making exactly the same point but I was too daft to work it out. I now see the check valve and seems to be the same one as an e-type, glad it’s not the plastic 2-way one on the brake reservac tank.
Many thanks again.
Steve
I wasnt sure if you had one or both not working, as you showed the brake parts, I assumed that was it, but you may experience brake system and engine idling problems if that big valve is not working
Glad I did not wrestle to get the spare on out, as darkness fell, I was completely enveloped in fog, followed by a torrential downpour
With regards to the plenum control system, early XJ also used that valve, and if E-types also did, no worries…those guys have every spare part available to them, so its good when they crossover
As I mentioned, I removed the reservac and valve as it really gets in the way of any engine any work, especially dizzy
I doubt you will want to do this
The original system is of flawed design imo (but it does last for maybe 30yes…will that get you though mate ?
)
here is a basic pic and description of what i did, although it seems since my engine swap, I may not have hooked it up…but it was so discreet, it may be hiding, I will have to test the system to be sure, I have pics somewhere, cant find them atm
I think I placed the one way valve into the small hose from the valve, cut another short bit of small diameter hose, tucked it into the engine manifold hose, and a hose clamp, they are a perfect fit
As I mentioned, it was a very cheap plastic “aquarium” valve, fit small hose, I got a bag of 10, as I thought petrol vapors may gum it up, but it was still working after about 5yrs
The reservac always has red fluid in it. It is not ATF
My hypothesis is that is fuel vapor drawn from the inlet manifold, and due to the shape and location of the resevac container, it distills within, to a petroleum concentrate
This pretty potent and affects the rubber diaphragm inside the valve
They can be repaired by uncrimping, new rubber material, bond and re crimp
not wrth the efort though
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Thanks Tong, I’m going to do the test suggested by Nick tomorrow. I doubt I’ll get two cycles after turning the engine off but I hope I’m proven wrong.
Yes, I believe the FSM says 4 cycles, nut as I mentioned, there is no use for this function. like a rubber crutch really.
By bypassing it, what you have is crisp no leak operation of the plenum lid upon command, when the engine is running
I seem to recall symptom of failure is it flaps up and own in response to throttle position (manifold vacuum), an undignified situation for such a grand car, and one that simply cannot be tolerated
If you would like, I will free mail you a couple of ebay check valves, just PM me your address, I will likely be out of action from Tuesday though
I emphasize no Jagur part is harmed, my reservac and valve is in the boot, in a box marked “original parts removed from this 420G”
I have read the reproduction check valves are not reliable
One other thing to be aware of is the ornate push button switches that control the system cam also leak, listen closely for a whistling sound. Can be repaired by judicious use of JB weld or similar
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Yes I agree it is not necessary to use the scuttle vent while the engine is off and the car is not moving. I did the test suggested by Nick and after switching off the engine the scuttle would not open. I don’t care about that of course,but, as Nick has suggested this might mean there is a leak somewhere and perhaps this is why the scuttle goes down when accelerating, and not because of the check valve. Very annoying, I hate removing the console to get to the controls. Maybe I can just suffer the indignity of a flappy scuttle or just keep it closed 
The leak could also be at the vacuum valve which is behind the glovebox fascia which means dashboard put etc.
As a matter of inquisitive curiosity, take the old check valve apart. With a small bit of effort, it fell in half and I found mine to be rusty, the diaphragm stiff and had a very oily appearance. 50 plus years of living in that area of the fender-well certainly takes its’ toll. Is it possible to put a vacuum gauge on the line going into the fascia with a “T” tap, start the engine, build up vacuum and see if this is the culprit of your leaks? These valves seem to be readily available and if not, perhaps something from the hot rod vendors.
The old 1955 Chevy’s had vacuum operated wipers, which on acceleration would cause the wipers to pause mid stroke. Somewhat frightening! Chevelle’s have a “cowl induction system” which opens the scuttle on full acceleration. A bit of research into those topics could give you some insight on repairs.
ON the MK2 I seem to remember that one “nipple” on the valve was for inlet and the other went to the booster. The FSM noted it one way and one of the vendors had it another orientation. It does make a difference.
Gerard
Dont despair yet young man
Your results are consistent with a failed check valve, removing it will not help
I suggest you try what I outlined. Your total cost will be $5
Bear with me on the hypothesis…the vacuum operates a big plunger valve that is connected to the plenum arm on the LH side behind dash (on a RHD car)
If this was leaking your plenum lid would not move at all, as it held down by a surprisingly thick spring…so it must be working if the lid raises…good!
Problem; the ported vacuum that controls the plenum varies with throttle position
So when you press the throttle hard (from memory) the lid will drop, then rise again when throttle is near closed (could be the other way around)
The job of the check valve is to prevent this loss of manifold vacuum
This allows the in cabin valve (which is quite large) to do its job
I hope this makes things clear from and engineering perspective
(I can always be wrong, should be in my signature )
I advise follow the exact instructions I issued earlier
I would be only to happy to mail you one for free, but I am out of action after tomorrow for a while
PM if you wish, if not, its a “one way check valve” sold as an aquarium valve, probably get one in pet shops, or online as I did, sized for the small line is best
I would bet anyone a cyber beer…or even a real one if there are any takers, that once you install that valve, your plenum lid will operate better than it ever has, making you proud
(I think the original system gets leaky, with no leaks, the lid snaps up and down like crocodile jaws )…but only on command
Mine opens and closes on demand. I will ask my mechanic to make the modification, no need to send a check valve, thanks for the offer.
Despair indeed, I have still not recovered from the trauma of the 12 month restoration process. Getting better, however. Slightly helped by the fact that I took out overall winner of the JCCV concours d’Elegance, with the highest score ever achieved (99.57%).
Congratulations,
Your engine bay was an inspiration before I even knew it belonged to you, and I have been gradually working on mine to improve it.
Maybe it would be easier for you to just send up your cheque book please