Hello

I know Ken did a good article of this on 2CVGB but I have a few more questions.....

1. Does the tube HAVE to be exactly 8mm - and is that 8mm bore, or 8mm overall diameter?

2. Is the required 50mm of pull - 50mm difference between the left and right 'leg' or 50mm up the right hand leg from the zero point on the scale?

3. I'm on DOT 4 and don't have any LHM on me - can I use sunflower oil?

Sorry if this post drives you insane with banality - but it usually takes a few goes for the penny to drop. I wish I'd listened more in GCSE Physics...I really do!!!

Thanks All
Willami

It would be great to have a feature on how to make a manometer on here, I've probably misplaced that edition of 2CVGB news but it would be handy to have one.

Ken? Pretty please.......................

No, but a smaller bore will give more "pull" for the same amount of vacuum, whilst a larger bore will give less. The outside diameter's irrelevant - apart from you having to be able to see through the walls of the tubing...



Anything that'll mix nicely with engine oil (in case it sucks too hard) and is nice and visible against the background.

Unless you're out to impress the neighbours with your Blue Peter skills, 1.5 metres of 5mm windscreen washer tubing will do the job.
I don't even bother to attach it to a board, since some tie wraps can be used to fasten the loop of tubing to a steel rod, which makes it handy for use 'in the field'
Wrap enough turns of insulating tape around one end to make it a tight fit in the dip stick tube, add enough LHM/cold tea/stale wine to part fill the 'U' shape and you're ready to roll.

Some technical waffle...

1.The free end of the tube needs to be open to atmosphere, not plugged.

2. Internal diameter of the tubing is irrelevant, the height difference will be the same for any size of tube.

3. Liquids such as LHM which are less dense than water will show a greater difference, so a correction needs to be made.
Citroen specify 50mm difference water gauge, so if the liquid used has a specific gravity of 0.9, the difference should be 55mm.

4. The second part of the test is, if anything, even more important than the test at tickover. Citroen specify that the reading should not go positive at any engine speed.
Just as with checking/setting the timing, what's happening at typical working rpm is what really matters...

5. If the reading does go positive, but only slightly, don't panic.
Bear in mind that 50mm water gauge is equivalent to only 0.07 psi.
In many instances, oil leaks are due to worn out or ancient, hardened seals, in my experience anyway.

ken.

Your getting your schoolboy physics muddled with scool boy hydraulics!

What you see is the relative differance between the air pressure the bore wont matter the wider the bore the more air pressing down on the open end.

technically its not sucked in but pushed in by the column of atmosphere at the open end

ideally if you make an all singin all dancing one you could put a damper in which is just an obstruction in the u bend so slow down any rapid changes

fill with parrafin, diesel redex etc
sean
(now, wheres the picture of the anorack)

I use water with fruit colour red or green.

Probably...

Once again, thanks for the low-down on these suckers, or is it blowers?

I've taken the dump valve off and cleaned it in petrol, taken the massive kink out of the tube from the breather to the valve (ummm, yes...) but

my main ball-ache is now finding that, after doing a compression test, i'm getting 110 psi on the OS cylinder and 140 psi on the other!

i'm not losing power - it will do a top of 65, isn't bad through the gears (the Ami is heavier too) and it's white smoke on the cold mornings, not black/blue....maybe i'm getting worked up about all this...

bye for now
Will

Willami,
if that was with engine warmed up and wide open throttle, both readings do seem low.
To allow for possible inaccuracy of a gauge, some folk recommend looking for an imbalance between cylinders rather than absolute values, with anything more than about 5 to 10 psi difference being cause for concern.

Also worth noting that valve clearances can have quite an effect on the readings obtained during a compression test, especially if they're too tight, which is why I always re-torque the cylinder head studs and adjust the valve clearances beforehand.
0.25 exhausts, 0.20 inlets...

nil desperandum,

ken

Hi ken

the engine was fully warmed up, throttle out, i did have the choke open fully too??? can't think that would make a difference but maybe??

on the lower of the two, the plug was a bit oily around the thread - not on the ceramic or core though - but more oil than just the bit i put round it. plugs a bit sooty though, that's more to do with rich mixture though, isn't it?

cheers
Will