Airbox backplate seal?

[jimbo]

Forgive me for bringing up an old favourite ... I've spent some time searching but just want to confirm the facts.

Should there be a gasket between the airbox backplate and the carbs? I can't find any evidence of one in any of my books/manuals, but metal to metal seems a bit nasty and unlikely to form an air tight seal.

The same goes for sealing the airbox front to the backplate. The service manual shows a gasket. Are these still available or shoud I just use Silicon sealant on both joints?

Thanks in advance,

James

PS - It's a 72 Sprint on Webbers

[Vanden Perre]

James,
All I can tell you is what I have on mine (S3). No gasket between air box back plate and carburators but well one between air box and air box back plate.
I believe it is standard.
Olivier.

[DJThom]

I made gaskets to go between carbs and airbox. I avoid metal to metal whenever possible.

Regarding the seal between the airbox and backplate. I ordered some from one of the suppliers and got the same seal used on my trunk lid (S2 small lid). Not sure thats the original type or not, but it works fine.

D

[jimbo]

Thanks for the replies ... I ordered a couple of these which I think should do the trick!

James

[gordonlund]

There are definately gaskets available between carbs and air box but whether Lotus actually fitted these to Elans is debateable. They are not shown in the workshop manual but In Fuel System Additional Information in the Workshop Manual, commencing at Engine No C 22414, the air trumpets are sealed with "Hylomar SQ.32M before being fitted to the carbs. This is shown at Section L - Fuel System page 55/56.

I was advised at a Club Lotus Technical Seminar that Elan twincams run better with a depression in the air box, caused by pressure drop across the air filter. If there is not much of a pressure drop then unfiltered air is getting into the engine. Hence the need for a good seal between carbs / air box backplate / backplate to air box / air box / trunking / trunking to filter casing. This also reduces tendency to backfire, and will result in extended engine life.

Gordon

[jimbo]

Hi Gordon,

Is that the same as Hylomar Universal Blue?

Also your manual must be different to mine, as in my copy pages 55/56 in Section L refer to the "Fuel tank filler cap", "Starter housing" and "Evaporative loss control" ...

Cheers,

James

[Dave-M]

James,
Forget Hylomar and use Wellseal. (ref Miles Wilkins book). It,s the best.

Gordon,
I think the real reason for sealing the air trumpets is not to prevent air getting in, but fuel getting out and into the airbox.
Fuel can leak from around the auxilliary venturi and then into the airbox, assisted by the depression in the airbox, sealing the air trumpet will prevent this.

All Airboxes (plenum chambers) will be at below atmospheric pressure while the engine is running (ignoring turbo & supercharging) and the greater the pressure drop across the filter the greater the depression in the airbox.
External air leaking into the airbox will always carry the risk of dust being drawn in, but assuming flat mating surfaces and the relativly clean underbonnet environment, I would think the lack of gaskets would not be too critical.
Having said all that, what I did when I fitted my modified airbox was to attach some 3mm closed cell foam, (the type used for camping mats), to the flat mating face of the airbox, and fitted the same gakets as per James between carb and backplate.
Regards
Dave

[dusty]

The seal for use between the two halves of the airbox comes up on ebay quite regularly, I bought one and it fits perfectly.

[gordonlund]

Sorry James, I was looking at my +2 Manua!! All good stuff and anything to stop fuel from dribbling onto a sparky dizzy must be a good thing!!!

Gordon

[jimbo]

Its all good info Gordon. Thanks!

PS - Excellent book! Sorry to read that Custard is no more (at least in original form).

[ddddumas]

I've gotten the Elan airbox gasket, in factory-sealed Lotus packageing from Ray at r.d. enterprises, www.rdent.com. It is a 1/2" O.D. continuous loop of round Buna-N rope, with a 1/16" W x 1/4" D reglet cut-in to make it C-shaped in section.
Paul Garrett

[umbyfer]

Hello,

same problem: any gaskets between weber carbs and backplate? what is standard originally and wich advise?

Reading this topic I remain a little confiused...

Thank you,

Umberto
Elan Sprint 7108000193K

[pereirac]

I bought a cork gasket many years ago which fitted between the two halves of the air box on my Sprint. It looked very similar to a cam cover gasket on a early push rod engine. I have never managed to source a replacement (yet)...

Carl

[umbyfer]

And between carbs and backplate do you have something?

thanks.

Umberto
elan sprint

[twincamman]

well after worrying about nuts getting loose and air leaks into the air box heres my solution ---cost $6.00 [thats huppence tuppence and a penny ] for a shop vac filter and 4 tie wraps ---works a treat -and looks ' real boy racer 'too --ed