Lotus Elan

Sprint Servo Non Return valve query

PostPost by: silverlink » Mon Jun 01, 2020 8:10 pm

Hi,
After having a failure of my Girling Mk2A servo I sent it away for a complete rebuild which I posted a comment on here about a while ago. I am now in the process of refitting it and have a question, on my Sprint engine I have a non-return valve at the back of the engine for the headlamps and another at the front of the engine on the number one inlet (see photo)
Engine Servo non return valve.jpg and

The servo has a non return valve fitted so why do I need another on the inlet? I understand my engine was originally destined for a Plus 2 but was probably installed in my car due to shortage of Sprint engines. Unlike the Sprint the Plus 2 has a valve on No 1 and No 4 inlets due to the greater clearance at the back. I had mine modified with a 90 degree angle so it didn't foul my bulkhead.
Also the garage that originally took the servo out of my car has lost the valve on No1 so does anyone know where I can get another the same.
Cheers
Ian (confused!!!)
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PostPost by: TeeJay » Tue Jun 02, 2020 9:28 am

Ian.

My car has a non return valve on the back and the front of the Inlet manifold.

The one on the back goes to the Servo, the one on the front goes to the chassis vacuum chamber for the front lights.

But note it is an early +2, which does have the Girling Mk2A Servo.

My understanding is the Mk2A does not have the Non Return valve, that was fitted to the modified MK2B
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PostPost by: silverlink » Tue Jun 02, 2020 4:26 pm

Trevor,
Many thanks for your reply, I think I made a mistake with my Girling! it should read Mk2b.
Ian
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PostPost by: vxah » Tue Jun 02, 2020 10:15 pm

I think you should have a non return valve as close to the intake runner as possible, like the one screwed into the manifold even if your servo has one built in.
This is because on this engine there is a lot of pressure pulsing at low rpm’s due to single cylinder per throttle. That means that without a close up valve the pressure in that long servo hose will also be pulsing, changing the vacuum signal to that carburettor barrel and dragging fuel into the servo pipe which you really don’t want?
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PostPost by: andywatts » Wed Jun 03, 2020 8:04 am

A quick search on 64949063 which is the Girling part number for the Mk2B non-return valve gives quite a few hits, but none with availability as far as I could see - worth keeping an eye open. Otherwise as a remporary fix you could find other valves (such as "Mercedes Brake Servo One-Way Non-Return Check Valve A2710180329") which just fit in-line in the vacuum tube. It would be worth giving Classicar Automotive a ring, as they are useful. Good luck.

For info mine is a 69 +2S with the Mk2B servo, and has the non-return valve in the vacuum pipe. Works fine but gives a bit of a rattle at tick-over as the valve operates on each piston stroke.
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PostPost by: TeeJay » Wed Jun 03, 2020 9:25 am

Ian.

SJ have both Non return valves listed.

The one for MK2B:- https://www.sjsportscars.com/parts-and- ... J6081F.htm
The one for inlet manifold:- https://www.sjsportscars.com/parts-and- ... /SJ566.htm
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PostPost by: TeeJay » Wed Jun 03, 2020 9:50 am

Just looked at PM, they also do the Inlet manifold non return valve (NRV), which requires 2 other items.

I am sure that the SJ item would require the other 2 items.

NRV :- https://paulmattysportscars.co.uk/produ ... urn-valve/
Union:- https://paulmattysportscars.co.uk/produ ... -straight/
Adaptor:- https://paulmattysportscars.co.uk/product/tube-adaptor/


This probably makes the assembly to long for the No4 inlet position??

My +2 needs a replacement NRV, looking for one similar to the one on your photo, IMI Norgren sold something similar years ago, suitable for the heat from the engine.
So I am looking into it, seems they changed their name to IMI Precision
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PostPost by: silverlink » Thu Jun 04, 2020 9:02 am

Hi all,
Just by luck I had a quick look on Ebay yesterday afternoon and would you believe there was a Non-return valve for sale just like the one in the photo I posted. I managed to win it last night for £10, I just hope it's the same as the one I lost!
Ian
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