Air filter can to plenum chamber fit

rossbraithwaite · Post by **rossbraithwaite** » Wed Apr 17, 2013 3:25 pm

I have a S1.5 that has been converted back from fed spec to UK spec. I recently tried to replace the split grommet between the air filter and the plenum chamber but found that the short 'trumpet' that the grommet sits on is no where near centre of the air filter cannister. There is no adjustment in the location of either item. I have read in another post about there being different brackets in the plenum chamber for US cars but I can't see how this would solve the problem- either the plenum is too big or the pipes that come off the carbs are too long. Is it possible that something was missed in the conversion?

Post by **Heuer** » Wed Apr 17, 2013 3:46 pm

Have you got any pictures?
e.g.:

rossbraithwaite · Post by **rossbraithwaite** » Wed Apr 17, 2013 4:16 pm

I'm afraid not. Also, I am currently estranged from the car for a few weeks and am still not sure about the whole photobucket thing!
I will get some pics soon and re-post if I can't sort it.

Post by **Heuer** » Wed Apr 17, 2013 4:33 pm

As long as you have the entire SU air filter assembly - trumpets, plenum, cannister, brackets - there should be no need for any adjustment although the cannister attachment allows some movement. Clearly something is amiss if it is not approximately central.

38E · Post by **38E** » Wed Apr 17, 2013 4:40 pm

Are you sure that the engine is sitting centrally and vertically in the mounts?

The slotted mounts do allow a certain amount of sideways movement which could partly account for the problem.

PeterCrespin · Post by **PeterCrespin** » Wed Apr 17, 2013 4:42 pm

Have you got the right plenum with notch and trumpets with notch? Does the fibreglass sit fully home INSIDE the backing plate (allowing for seal)? The drum brackets should line it up but if you have the base one wrong or side one wrong it could be tilted inwards if the base was too far outboard or side bracket too far inboard. If you have the wrong carb spacers like MkX /420G metal ones with double o-rings they can push the carbs and plenum too far out.

Pete

Post by **Heuer** » Wed Apr 17, 2013 4:44 pm

For reference:

rossbraithwaite · Post by **rossbraithwaite** » Thu Apr 18, 2013 8:57 am

PeterCrespin wrote:Have you got the right plenum with notch and trumpets with notch? Does the fibreglass sit fully home INSIDE the backing plate (allowing for seal)? The drum brackets should line it up but if you have the base one wrong or side one wrong it could be tilted inwards if the base was too far outboard or side bracket too far inboard. If you have the wrong carb spacers like MkX /420G metal ones with double o-rings they can push the carbs and plenum too far out.

Pete

Hi Peter, Thanks for your response. Is the notch you refer to the one to the right of the right hand bracket in the plenum chamber (item 10) in the illustration below? I think this might be the problem as I know I had to cut and adjust the notch in item 11 near the rear trumpet due to the fibreglass NOT sitting fully inside. What is the notch for and is it different on US cars? Does this sound like non-matching parts from US and UK cars? Which would you suggest I look to replace?
Thanks for your help (again!)
Ross

PeterCrespin · Post by **PeterCrespin** » Thu Apr 18, 2013 11:11 am

All triple carb plenums had the notch as did all triple trumpets. Think it was to clear the Kelsey/Heyes servo on RHD cars? Dunno - all my sixes have been LHD. Twin carb plenums don't have the notch as there were no RHD twin carb Es. You can inverts and relocate the brackets to fit a triple trumpet plate but would need to make a notch underneath. AFAIK the location of the filter can spigot underneath is the same distance from the carb face as before.

Without seeing your car I can't say more, but clearly any misalignment in one spot is going to have ramifications elsewhere. Couple that to an engine which may be slightly right-leaning on the adjustable rubber mounts and you could have a number of smaller tolerances adding up to a significant displacement of filter can and plenum. You'll just have to organise things to fit better.

Pete

rossbraithwaite · Post by **rossbraithwaite** » Mon Apr 29, 2013 12:32 pm

Heuer wrote:Have you got any pictures?
e.g.:

This just shows how far out of alignment the plenum chamber and air filter can are:

rossbraithwaite · Post by **rossbraithwaite** » Mon Apr 29, 2013 12:39 pm

plenum chamber profile does not match that of the plate on the trumpets but that is not causing it to be out by 1 inch.

The brackets have been moved around a bit in the plenum chamber (partly by me and there are lots of holes but again; that is not causing the misalignment.

Is it possible that the trumpets are too long?

PeterCrespin · Post by **PeterCrespin** » Mon Apr 29, 2013 3:27 pm

The misalignment appears to be the dustbin tipped backwards from vertical.

I have seen some support brackets underneath with asymmetric ends IIRC, and if you put it on back to front you can end up with a tilted base support. The side bracket has a measure of adjustability too, with slotted holes.

I would concentrate on getting your canister vertical and then possibly reform the rear lower corner of the fibreglass plenum, or tap out the notch in the backing plate, to get the lateral alignment correct. The whole purpose of the flexible top grommet is to allow for some movement and misalignment, so it doesn't need to be millimetre perfect.

Pete

rossbraithwaite · Post by **rossbraithwaite** » Tue May 07, 2013 8:03 am

Having flattened out the notch in the plate and adjusted the position of the air filter can the grommet can just about accommodate the non-concentricity. Thanks for all advice and suggestions.

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Air filter can to plenum chamber fit

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