Servo vacume pipe

[Alex'n'Ane]

I am fitting a good second hand servo along with disc brakes. I am mounting it in the nearside engine bay, attached to the inner wing just off the floor, as the new engine will have the exhaust on the opposite side. The servo however doesn't come with the vacuum pipe or one way non return valve. My question is where can i get these bits from? And is there a specific diameter or is it a standard size? I already have a tapped 1.5" heated manifold so that is also not an issue.

[RobThomas]

The hose is probably 1/2 inch ID (or 13mm) and the consruction of it is different from water/coolant hose. A scrapyard ought to yield something suitable or ThinkAutomotive sell the right stuff near Heathrow.

[TomLS]

Vacuum hose of any diameter can be found on ebay. Not sure about a non-return valve, can't see one on mine and it works just fine.

[Alex'n'Ane]

Having looked at a few at the local meet none seem to bother with the non return valve, nor the 'u-bend' in the pipe. I have measured the hoses which are currently attached (cut off) and they appear to be 10mm, is this particularly surprising?
I was going to order this? http://cgi.ebay.co.uk/10mm-Silicone-Vac ... 1039wt_880

[chrisryder]

most servo's have non return valves built in. never bothered fitting in-line ones on any of our minors.

for the hose, vacuum hose is a must. otherwise it will collapse with the vacuum inside. normal hose is designed for positive pressure inside, not the other way around.

if you've got a union on your inlet manifold already, measure the OD of that and that'll be the ID of your hose!

[Alex'n'Ane]

Surely the od of the union will be bigger than the internal of the pipe required? The pipe needs to be tight fit over it? I measured the internal of the union to me 10mm?

[chrisryder]

ok, the ID of the hose wants to be no more than the OD of the union, otherwise it will bunch up. It'd be ok to fit 10mm ID hose on a 10mm OD union, just make sure it has a good hose clip!

not sure if that silicon hose will stretch well over the union, it's tough stuff!

[TomLS]

Mine doesn't even have a hose clip! It's an interference fit but not a particularly tight one. All the time the engine is running its under negative pressure any way so it will always try to pull itself together.

[Alex'n'Ane]

Thanks for the advice, i measured the od at the manifold to be around 10mm at minimum point so have gone with that I have also ordered a 13mm breather/ filter to go onto the rocker cover, to match the k&n on the new carb

[TomLS]

If your engine trickles oil, it will often be found that the trickle increases somewhat when the negative pressure, supplied by being plumbed into the air intake, is removed and breather filters fitted instead (as the engine warms up, the pressure will be very slightly positive). Mind you if it is a new engine you shouldn't have any problems at all.
Some say that the oil vapors given off give them headaches / nausea - I haven't found this to be the case on either of the 2 cars I've owned, but my V8 did develop a tiny oil seep when I removed the negative pressure to the crank case.

[Alex'n'Ane]

Thanks tom, hopefully this carb and engine wont be on forever, till the end of summer at the longest (i hope!) I will see if i get an issue with leaks on the trip down to the national, then if i do i will try to reattach the older filter with vent pipe.

[bmcecosse]

The 'breather filters' are a very bad idea - as above -you MUST have the suction of the inlet taking away the fumes. Your 'filter' will cause back pressure/blue smoke/increased oil consumption and oil leaks -especially from the rear of the crankshaft onto the clutch...... It also allows the carcinogenic oil fumes to run out into the engine compartment - where they get into the cabin with nasty smells and health advisory. Just a thought - you aren't hoping to run your servo (why??) from the little brass inlet on the side of the carb........are you ???

[Alex'n'Ane]

I already have a tapped 1.5" heated manifold so that is also not an issue.

No its from the manifold as required.. The reason is I got a good condition second hand one with the disc brake set up, and thought i might as well fit it since this will be a daily driver, and often used for long runs.
What would you suggest to use as an airfilter for the 1.5" carb?

[bmcecosse]

The K&N airfilter is fine - as long as it's the taper type of course - but you MUST have a breather connected to the inlet suction. Most later carbs have a brass pipe on the side for this....

[TomLS]

Most later carbs have a brass pipe on the side for this....

Just make sure its the right one - they also have a fuel overflow pipe. If you connect it to this it will cause problems, not to mention if your carb float gets a hole you will rapidly fill your crank case with petrol!

I've no experience with a servo on discs in a minor, but with drums it makes a world of difference (or maybe the other minor I drove without one just had crap brakes).

[bmcecosse]

That's odd - because most 'experts' feel that servo with drums is quite unnecessary........ . I certainly wouldn't want my brakes to be any lighter than they are!

[chrisryder]

what 'experts' are these? yet more people that havent tried it themselves?

[bmcecosse]