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Sir Paolo

Mounting Carbs to Inlet M/f

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Gents,

Having invested in some new 'Cosworth' washers/rubber mounts, the fitting advice seems unclear.

 

Some parties suggest anything from 3mm to 0.8mm as a gap between the two washers, sandwiching the rubber one.

I settled on about 1.5mm as a gap, but then noticed that some of the washers weren't machined vary flat. Which meant the compression on the rubber washer was uneven.

 

As a 'sanity' check, after fitting the carbs, I then measured the distance between the carb rear faces and the inlet manifold face.

In order to make this gap uniform and 'square up' the 'O' rings, I loosened/tightened the lock-nuts as necessary (and therefore adjusting the compression on the Cosworth mounts).

 

Please can anyone advise me if this is correct. I did reference Des Hammil's book on this but this section wasn't at all clear.

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I think the cup washers that surround the rubber mounts must not be touching to allow some flex. I think the 1.5mm dimension is the gap between the cup faces.

 

Buddsy

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I assume you've replaced the "O" rings between the manifold and the head? Tightening up the carbs isn't a hugely critical operation. They need to move a little bit - the alloy faces of the head and manifold not touching - and not leak through the "O" ring seals. As long as that's OK, all should be fine.

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Thanks, Gents.

And, yes, I did replace all (8) spacer 'O' rings.

 

Looking at it again last night, I decided that the nominal 1.5mm gap between the cup washers was too hit and miss. This is largely due (as mentioned previously) to the fact that some weren't machined flat to start with.

 

It would seem that air exclusion with a little flexibility is required, along with the carb faces being in parallel to the inlet m/f. 

As such, I squared all (carb to m/f) gaps to 6.5mm (or about 0.255 in Christian money).

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Without checking the service book I am pretty sure for  my 88n/a the manual  just states to tighten up to get the gap on the carb to manifold join to 1mm and doesn't give a gap for the cup washers. I replaced mine with new and side by side on the work bench the old ones  were half the size and hard.

Edited by mdw

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Tbh, not that I was penny pinching, but I wasn't going to replace the rubber washer until I found, as you did, they were hard and mis-shaped. As such I doubt they would've given any of the much needed flexibility.

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