A pair of idiots trying to use a home made manometer

[Fanum]

6 foot plank, 20 feet of silicone tubing, a bit of Sae90 gear oil and (as it turned out) 4 inches of smaller diameter tubing (from the diesel bleed back system on a landrover actually)

Now, as I understand it, a manometer like I tried to make is just a loop of tube going from the vacuum nipple under one throttle body, to the vacuum nipple on the other throttle body.

Then when started up, an imbalance between the two bodies creates more suction on one side than the other, so the oil, in this case laid in a parallel vertical looped tube, moves towards the side with the least vacuum.....

Then using the threaded adjuster and having loosened the 10 mm lock nut, you adjust the LHS to match the RHS and the oil stops moving. EDIT....no, in fact it should return to the level position on both sides, so equal vacuum on both sides, therefore TBs are balanced)

Correct?

This is what actually happened......


On my bike.....

Set up plank in vertical position, oil level in tubes.
Tried to connect silicine tube to nipple on TB.....doh! wrong bore.....
Dug out two tube reducing connectors (nylon) and a foot or so of smaller bore tube, added a few inches of smaller bore tube to each end, fitted (tightly) on to both nipples.......

Ready to go......oil level in paralell tubes

Start up......One side starts moving up at about 2cm a second......I wait for the column pressure to overcome the imbalance so it stops moving, but it carries on moving

Switch off bike, allow oil to settle.......

Try again, tweaking adjustments on cable adjuster LHS, unable to slow progress of oil.

Get peed off after an hour of farting around with it, then after another hour, Speggo turns up on his almost identical (but made for shortarses) bike....

We set his TPS correctly, then bung the manometer on his as well....

Same result

Ok, so either both bikes are similarly unbalanced, or the tube on one side of the manometer is letting air in, so the suction from the cylinder opposite the seepage carries on dragging the oil towards it......

So we swap the ends around to confirm this, plugging the end that was on the right onto the left and vice versa....start engine up, expecting to see oil go up but THE OTHER WAY....does it fekk

At this point, it just doesn't make sense to either of us.....we double checked we hadn't got the ends mixed up in the shuffle around, removed a joint I'd put in to add the oil with another nylon tube tail, got the same result

From videos I've watched on YT, I Was expecting the oil to be unbalanced by maybe 4-6 inches in the tubes, but in mine, it kept going up and up

By moving the throttle body shaft cam that the cable wraps around, we were able to get the oil to stop, but the bike was so rough that it couldn't have been right.....


I'm obviously missing something totally obvious and stupid here, but neither of us could see what it is

It doesn't matter what length of tube is between each nipple and the oil meniscus (according to my logic) because all we're trying to do is establish a balance......the two ends could be at totally different heights on the plank as well, for the same reasoning......

I'm probably totally stupid, and I will take any abuse that shows it up, but honestly, it didn't make sense

And no, before some smartarse says 'go buy a twinmax or a harmoniser'....I can't.


I don't want to borrow one either, I just want to understand WTF we were doing wrong, and be able to fix it so I can balance my TBs from here onwards

 

[pablo666]

In my humble opinion, both sides should be identical lengths for a balance to be achieved.

My experience was, I made a manometer same as you using ATF, and on my 1150 GS it worked well, allowing me to easily set the TBs as you have discribed, BUT, my TB's must have already been pretty much well set up.

I tried same on a friends 1100RT, and got the same result you are getting, and had to switch off before the ATF oil was sucked into the engine. Try as I might I couldn't get the fecker to work on the RT and ended up buying a twinmax.

Ever since Ive used the twinmax and it's a peice of piss. Manometer got thrown in the bin.

 

[ChrisH Kerry]

The way I understand it and balanced mine (then checked with gauges I have as well ...) is that you set the idle balance with the brass screws to get the oil level - it will continue travelling up one side/down the other until balanced, it willnot reach an equilibrium (but my manometer is only on a metre rule) when you have that done, you open the throttle to see what happens. Depending on whether the cables are opening the butterflies in sync or not the oil will travel up one side or if you are very lucky will stay balanced. You then mess about with the cable/s until you get an even balance in the manometer as you open the throttle... and I got all that info here

 

[Fanum]

The way I understand it and balanced mine (then checked with gauges I have as well ...) is that you set the idle balance with the brass screws to get the oil level - it will continue travelling up one side/down the other until balanced, it willnot reach an equilibrium (but my manometer is only on a metre rule) when you have that done, you open the throttle to see what happens. Depending on whether the cables are opening the butterflies in sync or not the oil will travel up one side or if you are very lucky will stay balanced. You then mess about with the cable/s until you get an even balance in the manometer as you open the throttle... and I got all that info here

TY

Forgot piccies.......piccies are nice.

Yes, I know my carpet needs cleaning, TYVM

 

[Fanum]

In my humble opinion, both sides should be identical lengths for a balance to be achieved.

Why though


There's only one tube....it's a loop, with each end attached to the throttle bodies
It's working by using the imbalance of vacuum/pressure(depending on which way you look at it, it's the same) in a closed loop

You could 30 metres of tube on one side and 2 on the other, but the oil will still find the level........then, the vacuum affects both sides and moves the oil regardless of the length of tube (within reason of course....there will be a slight theoretical difference as the tube sucks itself in and exerts its own pressure outwards)

 

[Ogmios]

Even i can follow the logic of one of these yokes.
Providing the distance from top of oil at rest to open end of tubes is the same*,
it can only be an air leak surely?

*not even sure if that's essential - but i'd figure it would make some difference.

It's a lot of trouble to go to for a bong though.
...................................
EDIT:

In my humble opinion, both sides should be identical lengths for a balance to be achieved.

Why though

Equal lengths = equal suction or flow or pressure

 

[DollyRocket]

When I use manometer in my line of work I always leave one pipe open to atmosphere, that way you can use the difference in water level as a real measurement.

In your setup you have a pressure (or vacuum against atmosphere) on both ends of the tube, which means if the pressure is equal on both sides then the liquid will stay level (like it does when there is no connection at all). If there is an inbalance in pressures, the liquid will move in the direction of the lowest pressure.

So, what you are seeing (if I read it correctly) is matching physics . If your TBs are perfectly balanced then the liquid will not move (or barely move at all?) The movement of liquid and the height that it will move to is dependant on density / pressure etc. For water, you can get a pressure difference of about 1m per 100mbar, mercury you will get 760mm for 1 bar. You can look up the oil density and determine what the estimated movement is likely to be. (What is the expected pressure drop of the vacuum within the TB?)

 

[brassmonkey001]

If the throttles are balanced then the oil should not move other than a bit of oscillation even if it is not level. Uneven vacuum will draw the oil towards the body with the lower pressure.
I suspect you've got a leak somewhere either on your manometer or on the body when it's connected.

 

[Fanum]

When I use manometer in my line of work I always leave one pipe open to atmosphere, that way you can use the difference in water level as a real measurement.

In your setup you have a pressure (or vacuum against atmosphere) on both ends of the tube, which means if the pressure is equal on both sides then the liquid will stay level (like it does when there is no connection at all). If there is an inbalance in pressures, the liquid will move in the direction of the lowest pressure.

So, what you are seeing (if I read it correctly) is matching physics . If your TBs are perfectly balanced then the liquid will not move (or barely move at all?) The movement of liquid and the height that it will move to is dependant on density / pressure etc. For water, you can get a pressure difference of about 1m per 100mbar, mercury you will get 760mm for 1 bar. You can look up the oil density and determine what the estimated movement is likely to be. (What is the expected pressure drop of the vacuum within the TB?)

If the throttles are balanced then the oil should not move other than a bit of oscillation even if it is not level. Uneven vacuum will draw the oil towards the body with the lower pressure.
I suspect you've got a leak somewhere either on your manometer or on the body when it's connected.

Both spot on

That's why we changed the ends over......suspecting that one 'end' was letting air in so that the oil never stopped moving even after the vacuum had equalised.

It didn't work though, hence the major head scratching.....we expected to see the oil move the same degree but in the OPPOSITE direction.

It didn't

I'm glad Speggo was there to see it, because it just sounds so ridiculous.

 

[GSTourer]

In this day and age shouldn't it be a 'non gender specific ometer?'

 

[brassmonkey001]

Why though


There's only one tube....it's a loop, with each end attached to the throttle bodies
It's working by using the imbalance of vacuum/pressure(depending on which way you look at it, it's the same) in a closed loop

You could 30 metres of tube on one side and 2 on the other, but the oil will still find the level........then, the vacuum affects both sides and moves the oil regardless of the length of tube (within reason of course....there will be a slight theoretical difference as the tube sucks itself in and exerts its own pressure outwards)

Hmm, I would think that having the length of tube identical is not exactly critical, but I think a 28m difference would have a definite effect. Even if the throttle bodies were perfectly balanced I should think that the oil might be drawn along the shorter length at first due to the difference in volume of air within both lengths of tube.
I'm sure a physicist will be along shortly to explain it properly.

 

[Fanum]

Hmm, I would think that having the length of tube identical is not exactly critical, but I think a 28m difference would have a definite effect. Even if the throttle bodies were perfectly balanced I should think that the oil might be drawn along the shorter length at first due to the difference in volume of air within both lengths of tube.
I'm sure a physicist will be along shortly to explain it properly.

Aye Al.......that's why I added the caveat 'within reason'

Air IS compressible (and whatever the opposite is) , but left in a sealed system (Ie no leaks) the pressure would have evened out eventually......so you're right, it would have gone along the shorter tube by a factor related to the degree of compressability (is that a word?) of the air and a ratio of the two tube lengths.

In this case though, the two 'ends' were of similar (but not exactly the same) length.

 

[Fanum]

In this day and age shouldn't it be a 'non gender specific ometer?'

No.

Mine has a penis.

 

[GSTourer]

No.

Mine has a penis.

 

[roddy]

Assuming the pressure is equal and fluid will always want to equalise to the same level, if your tubing is longer on one side than the other, it'll try and equalise more on the longer side.

Hence why you need the tubing to be the same length so the pressures are acting the same on both sides.

now if you connect them up the oil will still move but you get a better representation of whats happening, when I made mine I found the oil jumped about too much so I bung equal sized but of sponge about 10mm long down each end of the tubing to slow the pulses down.

It will also be worth looking at the butterflys are the correct way round, I had this with my first GS and it caused a bit of head scratching till I worked it out as I just couldn't get the TB to balance at all

 

[Fanum]

it can only be an air leak surely?


...................................
EDIT:

Equal lengths = equal suction or flow or pressure

Marc that's exactly what we thought, and why we swapped the 'ends' around (not actually ends, just sections inside the loop IYSWIM, effectively trying to reverse the flow in the loop between lower and higher vacuum)

We were both expecting the direction of travel to reverse......it's the only thing that SHOULD have happened, but it frikking didn't

 

[Fanum]

Assuming the pressure is equal and fluid will always want to equalise to the same level, if your tubing is longer on one side than the other, it'll try and equalise more on the longer side.

No, it's a sealed loop......

The oil will try and equalise to the level of gravity, plus or minus the suction (vacuum) on either side of it, which should be constant apart from the fluctuations caused as each cylinder fires in turn (hence the heavy oil)


Within reason, the lengths of tube either side should make no difference

 

[cookie]

Air is quite susceptible to pressure drop dependant on tube length.

At least it is when using compressed air.

Having tried a home made manometer, I've decided they are an utter waste of time (and space).

 

[brassmonkey001]

Try spraying WD40 all around the take-off point with your manometer connected and the engine running. See if it makes a difference to how quickly the oil flows towards one side.

 

[brassmonkey001]

Air is quite susceptible to pressure drop dependant on tube length.

At least it is when using compressed air.

Having tried a home made manometer, I've decided they are an utter waste of time (and space).

Mine works fine.