xflow inlet m/f torque settings

[ashaughnessy]

Can anyone tell me what torque settings should be used for tightening the bolts holding the inlet manifold to the head on a supersprint (twin weber 40s, normal caterham manifold)? Also is there a particular tightening sequence?

 

Also, the carbs are attached to the manifold using little rubber things that look like cotton bobbins with a metal cap on each side, and between the carb and manifold there are four aluminium plates with an o-ring on each side. How tight should I do up the nuts that hold the carbs onto the manifold? I've heard about leaving a 40-thou gap somewhere, but that might be with the thackery (sp?) things and I don't think I've got those.

 

Anthony

[Nick T]

The haynes webber carb workshop manual says

 

Where thackery double-coil spring washers are fitted tighten to maintain approx 0.020 in (0.50mm) clearance between adjacent coils

 

or

 

Where anti-vibration mounting is fitted, tighten the locknuts in a diagonal sequence until the covers just contact the grommets, which should also be in contact with the carb flanges. Now tighten each locknut a further 1 and a half turns and check that the v-section of each rubber gromet is equal

 

Hope that this is of some use

 

Nick

 

[ashaughnessy]

Thanks Nick. To rephrase, do the nuts up until they just touch the caps on the rubber thingies and the rubber thingies are touching the carb, so that everything is touching but there is no compression on the rubber thingies. Then tighten up by one and a half turns. Does this sound right?

 

Any ideas about the manifold bolt torque settings, anyone?

Anthony

[R2D2]

I think that tightness of Thackery washers or the "rubber bobbins" may be a bit more subjective tahn just measuring gaps.

 

The type of O ring plate has some influence. The traditional plate has two O rings but the newer style has a split O ring bonded to a thin aluminium plate.

 

I tend to find that the bonded O ring type needs more force to make a good seal than the older style plate. I changed all the plates to the bonded type on my Twin Cam a couple of months ago and when I gapped the Thackeries to 20 thou there were significant air leaks at the O rings.

 

[Casbar]

Just completed this exercise on my xflow.

 

Tighten the carbs until they are level and you have the same gap between the back of the carbs and the manifold. On mine that equates to the two sides of the bushes just about touching. The carbs must be able to be moved slightly. Once on, and with the engine running, spray some wd40 around the carbs, to see if there are any leaks.

 

Be careful not too pull the carbs around too much, as you will break the inlet manifold seal.

 

As to how tight do you tighten the inlet manifold, not very tight!! If you strip the bolts, you are stuffed. Just tight enough to stop the water leaking.

[Roger King]

Tighten the inlet manifold to about 8lbft.

 

If you tighten your carbs so that you have about 10mm up and down movement at the air filters (without using brute force), that will be about right. To some extent this is a bit of a black art, but the carbs MUST be flexible or they will vibrate and froth the fuel.

 

If I had a penny for every time I've seen a car where someone noticed that the carbs were 'loose' and tightened them rigid................

[R2D2]

Roger,

 

I have used new "swedish Plates" on my Twin Cam and if I adjust them to this sort of movement they leak through the O rings.

 

I tightened them just until theu stopped leaking air and i have about 1mm movement.

 

They dont seem to be frothing but I am quite concerned. Any ideas?

[Roger King]

Chris,

 

Difficult to answer this one. To some extent it depends on what you consider to be a reasonable force when you move the carbs up and down.

 

1mm is far too little if you need to go this tight to stop air leaks. In fact the carbs can often be absurdly loose and still be OK. I should mention that I am talking about 10mm movement at the part of the air filter that is furthest from the engine.

 

It sounds as if you may have something stopping the carbs from seating properly, but the only way to be sure is to have a look. It may just be that we are measuring in a different way.

 

The Swedish mounts are our preferred choice, so there are no problems there.