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  #31  
Old 11-21-2011, 09:45 PM
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Quote:
Originally Posted by tangofox007 View Post
That is a lot like trying to measure three nanoseconds using a stopwatch.
Ahhh, but I didn't say the digital display would go up and down dynamically in response to the flex. I was going to measure the diameter of the line when the engine is off, then start the engine. If the line does expand, I'd expect the reading to increase and stay there.

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  #32  
Old 11-21-2011, 11:28 PM
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The metal line indeed expands and contracts with every injection event. I would seriously doubt that you will be able to measure the amount or even discern that there is a difference with calipers, tho. Tango's analogy is very apt.
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  #33  
Old 11-22-2011, 03:13 AM
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Quote:
Originally Posted by funola View Post
Ahhh, but I didn't say the digital display would go up and down dynamically in response to the flex. I was going to measure the diameter of the line when the engine is off, then start the engine. If the line does expand, I'd expect the reading to increase and stay there.
Sorry funola - won't happen.

Rigid fuel injector lines have and need a degree of elasticity. Without this elasticity the lines would be (more) prone to cracking and failing. The lines that fail are most likely lines that have been bent too much by enthusiastic mechanics so that the metal has been worked into the plastic region (elastic => plastic => bang!).

The injector lines pulse - flex in and out - by a very small amount. By how much I do not know but you could in principle measure it with a strain gauge with the engine running and then make a time capture of the measurement on a data acquisition system... (I've got to buy some of this kit soon)

Here are some numbers explaining these pulses.

At 800rpm (engine idle or there abouts) a cylinder fires 6.6667 times per second. (800 rpm / 60 seconds = 13.3333 rev per sec => 4 stroke engine so one bang for two revs => divide crankshaft rotational speed by two)

At 5000rpm (max chat!) a cylinder fires 41.6667 times per second.

I think to try and measure it under static loading you would be better off pressuring a line off of the engine. Cap one end of the line and attach the open end to a pop tester then try and measure the change in pipe diameter. I would be really surprised however if you could measure the deflection with a vernier caliper or a micrometer though. I think you'd need strain gauges...

...but as usual don't let me pee on your bonfire - give it a go.
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  #34  
Old 11-22-2011, 09:33 AM
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Quote:
Originally Posted by Army View Post
Sorry funola - won't happen.

Rigid fuel injector lines have and need a degree of elasticity. Without this elasticity the lines would be (more) prone to cracking and failing. The lines that fail are most likely lines that have been bent too much by enthusiastic mechanics so that the metal has been worked into the plastic region (elastic => plastic => bang!).

The injector lines pulse - flex in and out - by a very small amount. By how much I do not know but you could in principle measure it with a strain gauge with the engine running and then make a time capture of the measurement on a data acquisition system... (I've got to buy some of this kit soon)

Here are some numbers explaining these pulses.

At 800rpm (engine idle or there abouts) a cylinder fires 6.6667 times per second. (800 rpm / 60 seconds = 13.3333 rev per sec => 4 stroke engine so one bang for two revs => divide crankshaft rotational speed by two)

At 5000rpm (max chat!) a cylinder fires 41.6667 times per second.

I think to try and measure it under static loading you would be better off pressuring a line off of the engine. Cap one end of the line and attach the open end to a pop tester then try and measure the change in pipe diameter. I would be really surprised however if you could measure the deflection with a vernier caliper or a micrometer though. I think you'd need strain gauges...

...but as usual don't let me pee on your bonfire - give it a go.
I'd agree that it is not measureable with a digital vernier if the line flexes less than the lowest resolution of the vernier. How fast it flexes or the frequency it flexes at should not affect whether it is measureable by the vernier. I am wondering if the Snap-on pulse adapter is actually measuring line flex with a strain gauge or if it is just a contact microphone.
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  #35  
Old 11-22-2011, 09:47 AM
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Quote:
Originally Posted by funola View Post
I'd agree that it is not measureable with a digital vernier if the line flexes less than the lowest resolution of the vernier. How fast it flexes or the frequency it flexes at should not affect whether it is measureable by the vernier. I am wondering if the Snap-on pulse adapter is actually measuring line flex with a strain gauge or if it is just a contact microphone.
Huh? I already explained exactly how the snap-on pulse adapter works. The expansion of the line squeezes the piezo crystal and when the line relaxes at start of delivery the charge in the crystal is released. It's not a strain gauge. I suppose you could call it a microphone as it is the exact same concept as piezo guitar pickups, but it is not detecting and amplifying sound, it is detecting a change in the diameter of the line.
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  #36  
Old 11-22-2011, 10:37 AM
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Originally Posted by libbybapa View Post
Huh? I already explained exactly how the snap-on pulse adapter works. The expansion of the line squeezes the piezo crystal and when the line relaxes at start of delivery the charge in the crystal is released. It's not a strain gauge. I suppose you could call it a microphone as it is the exact same concept as piezo guitar pickups, but it is not detecting and amplifying sound, it is detecting a change in the diameter of the line.
Can you post a good photo of the pickup/ clamp?

Is this the Snapon model you have?

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  #37  
Old 11-22-2011, 10:51 AM
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Quote:
Originally Posted by funola View Post
I'd agree that it is not measureable with a digital vernier if the line flexes less than the lowest resolution of the vernier. How fast it flexes or the frequency it flexes at should not affect whether it is measureable by the vernier. I am wondering if the Snap-on pulse adapter is actually measuring line flex with a strain gauge or if it is just a contact microphone.
Sorry funola - totally disagree.

A vernier caliper is an instrument that measures static values. There is no way in which it can be used appropriately to measure dynamic deflections.

I could drone on about digital signal process and anti-aliasing filter till the cows come home but that is probably (even for me) a bit of a tangent.

If you're interested in that sort of stuff though take a look at

Anti-aliasing filter - Wikipedia, the free encyclopedia

Digital signal processing - Wikipedia, the free encyclopedia

Nyquist

I think you'll be better off getting an idea of the flex by trying to measure it statically.

(If I get the kids to bed on time tonight I'll do some calculations...)
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  #38  
Old 11-22-2011, 10:51 AM
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Libby,

I'm a little late to the party and I only skimmed the replies in the post, but there is something that I don't think has been mentioned.

In your efforts to time this engine, it is natural to ASSUME that the timing on the harmonic balancer is correct. There is something that you need to be aware of and check:

Unlike most other engines from various makers, the harmonic balancer on these engines are not keyed with a Woodruff key. Instead, there are two steel dowel pins that align half holes in the crankshaft with half holes in the balancer.

It is not at all uncommon for an unsuspecting tech to simply put the balancer in place and run it down using an impact wrench on the snout bolt. This often will ruin the half holes in both the balancer and the crank snout. Sometimes the balancer will get forced into place but will be out of position. If this is the case, then obviously timing off of the balancer mark will give incorrect timing.

To see if this is the problem, simply remove the pulleys so that you can see if the balancer is in place with the steel dowels and the holes intact. If there is distortion with the dowels and/or the holes, I'm afraid you will have bigger problems on your hands than simply getting the timing correct, but it will have to be seen to.

Hope this helps
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  #39  
Old 11-22-2011, 11:14 AM
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The only real way to be sure one is dealing with actual TDC is to measure piston travel with some instrument.... several degrees of crank travel Before TDC and then the same amount After TDC and then mark the place half way between those spots as represented on the crank end..... and this is often easier than taking off the harmonic balancer..... and if the item is messed up ...you will still need to do this to determine proper marking of it once fixed....
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  #40  
Old 11-22-2011, 11:29 AM
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Quote:
Originally Posted by Army View Post
Sorry funola - totally disagree.

A vernier caliper is an instrument that measures static values. There is no way in which it can be used appropriately to measure dynamic deflections.

I could drone on about digital signal process and anti-aliasing filter till the cows come home but that is probably (even for me) a bit of a tangent.

If you're interested in that sort of stuff though take a look at

Anti-aliasing filter - Wikipedia, the free encyclopedia

Digital signal processing - Wikipedia, the free encyclopedia

Nyquist

I think you'll be better off getting an idea of the flex by trying to measure it statically.

(If I get the kids to bed on time tonight I'll do some calculations...)
I agree a vernier caliper is meant for static measurements but it could also measure dynamic values but may get damaged in the process.

Can you calculate how much the injection line expands at 145 bars?
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  #41  
Old 11-22-2011, 11:43 AM
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I understand the concept that piezo crystals when squeezed produce electricity....
But science is pretty strange and varied..
What is the possibility they are measuring the magnetic effect of the flow of carbon based fluid in the line as compared to the actual expansion of the STEEL fuel line ?
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  #42  
Old 11-22-2011, 12:24 PM
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Quote:
Originally Posted by funola View Post
Can you post a good photo of the pickup/ clamp?

Is this the Snapon model you have?

MT257B, Adaptor, Diesel Pulse
That is not the pulse adapter I have, but it may just be an updated case. Mine is metal and looks more old-school. The pickup is exactly the same. I probably won't take the time for a photo shoot. The pickup is an aluminum ring, a ring of crystal, and then a ring of aluminum the middle of which is cut out in a diamond shape, so that it can clamp on the line with four points of contact. I'm sure if you did some digging on the internet you could come up with a close-up picture.

Quote:
Originally Posted by LarryBible View Post
Libby... ...Hope this helps
I got it timed well enough that it starts easily without the clouds. It's good enough for me right now.

Quote:
Originally Posted by leathermang View Post
The only real way to be sure one is dealing with actual TDC is to measure piston travel with some instrument.... several degrees of crank travel Before TDC and then the same amount After TDC and then mark the place half way between those spots as represented on the crank end.....
I was considering this to confirm the actual TDC. I'd probably have to pull a pre-chamber and although I have the tools for the job, I don't relish it.

Quote:
Originally Posted by leathermang View Post
I understand the concept that piezo crystals when squeezed produce electricity....
But science is pretty strange and varied..
What is the possibility they are measuring the magnetic effect of the flow of carbon based fluid in the line as compared to the actual expansion of the STEEL fuel line ?
If you are asking about my diesel pulse adapter, then the possibility that it measures the magnetic effect is nil. I have accurately described how it works.
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  #43  
Old 11-22-2011, 12:55 PM
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Sure thing

Quote:
Originally Posted by funola View Post
...

Can you calculate how much the injection line expands at 145 bars?
Sure I can do a rough calculation. Do you happen to know the dimensions of the line? Sorry I am being lazy... I could go out to the garage but it is so cold today! (And it is bloody dark - crappy winter time - ***** ***** moan moan wish I had a second house in the southern hemisphere) And is the line really made from steel?
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  #44  
Old 11-22-2011, 01:09 PM
Goodentight
 
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The line is steel. Its OD is 6mm. I don't know the wall thickness/ID.
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  #45  
Old 11-22-2011, 02:13 PM
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Great stuff. Thanks for the data libbybapa.

Here's a really simple rough and ready calculation.

I'm assuming the thickness of the line is 0.5mm

In order to show you some "proof" that can be found on line I'm using this equation for thin walled cylindrical pressure vessels here

Strength of Materials

Rather than quoting a more complicated equation from "Mechanics of Engineering Materials" 2nd Ed Benham et al ISBN 0-582-25164-8 !!!!

Anyway about half way down the web page on eformulae.com you'll see an equation for


Stress at the outer pipe surface = { Internal pressure (P) X internal radius (r) } / pipe thickness (t)

Internal pressure P = 145 bar = 14.5 MPa (mega pascals)

Internal radius r = 5.5mm = 0.0055 m (metres)

Pipe thickness t = 0.5mm = 0.0005 m

Bang that into the equation to get a stress of

159.5 MPa

Assuming Young's modulus of steel to be 200GPa

(see Young's modulus - Wikipedia, the free encyclopedia for example)

Strain = Stress / Young's Modulus (E)

Strain = 0.0007975


Strain is a dimensionless ratio of the change in dimension to original dimension. For example change in length divided by original length.


So the expected change in the radius of the pipe line (from when the pressure in the pipe is the same as the ambient pressure out of the pipe to when it is pressurised to 145 bar) can be calculated by multiplying the original outer radius (6mm) by the strain.

This comes out as a change of 0.004785 mm

Vernier won't be able to measure it.


This is a bit of a meaningless number => in real terms it flexes by a very small amount that is going to be really difficult to measure.

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1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



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