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  #46  
Old 11-22-2011, 02:24 PM
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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..... 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....
Hey Greg we're back to this again aren't we?

I'm gonna have to get my act together and get that finding TDC thread I've got planned up and running - one of these day eh? I hope you join in when I finally get round to sticking my neck out!

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  #47  
Old 11-22-2011, 02:38 PM
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TDC or not

I have considered making a hydraulic TDC tool out of an old injector body. Using a clear pipette attached to a hard injector line. A small amount of diesel could be squirted into the cyl and the engine rocked back and forth( I know that is not great but just for the sake of argument) The same level checked before and after TDC & split the difference on the harmonic pulley. Seems like it should work to me. Easier than removing a prechamber & using a dial guage. Accuracy would depend on attention to purging air and the diameter of the pipette. Comments anyone. Cheers Dan
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  #48  
Old 11-22-2011, 03:14 PM
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Quote:
Originally Posted by libbybapa View Post
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.



I got it timed well enough that it starts easily without the clouds. It's good enough for me right now.



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.



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.

Libby,

I'm glad you have it timed so that it will run good. The problem is that this could be a sign of an impending problem. If the balancer has indeed been incorrectly installed, it is likely that it will come off some day while on the road, or it will turn further making the engine run poorly again or quit altogether.

What you described was an indication of this problem. It wouldn't be too much of a job to pull the pulleys and inspect the balancer to crankshaft fit.

Best of luck with it.
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  #49  
Old 11-22-2011, 03:19 PM
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Quote:
Originally Posted by Army View Post
Hey Greg we're back to this again aren't we?

I'm gonna have to get my act together and get that finding TDC thread I've got planned up and running - one of these day eh? I hope you join in when I finally get round to sticking my neck out!
This is the only subject I have ever seen you engage where you just did not get it. I hardly know how to argue it any better than I already have...and I posted several sites which describe exactly what I was taught was the most accurate way to find it.. and I have explained the mechanical logic of it also..
AND it does not even require any measurement..... except to split the marks on the crank... the piston to top distance can be done with a mechanical device having no measuring capability...
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  #50  
Old 11-22-2011, 03:22 PM
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BigblockChevy.... you are dealing with needing a very accurate measurement of liquid... at the same time that liquid will be seeping down past the piston rings...LOL
The correct method has already been found and described..no use re inventing a lesser method....
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  #51  
Old 11-22-2011, 03:51 PM
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Quote:
Originally Posted by leathermang View Post
This is the only subject I have ever seen you engage where you just did not get it. I hardly know how to argue it any better than I already have...and I posted several sites which describe exactly what I was taught was the most accurate way to find it.. and I have explained the mechanical logic of it also..
AND it does not even require any measurement..... except to split the marks on the crank... the piston to top distance can be done with a mechanical device having no measuring capability...
Over adjusting a valve so that it was poking down enough to interfere seems like a relatively easy way. Similar amount of work to pulling a pre-chamber and using a dial indicator on the piston crown down through the injector hole.
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  #52  
Old 11-22-2011, 03:51 PM
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Quote:
Originally Posted by LarryBible View Post
What you described was an indication of this problem. It wouldn't be too much of a job to pull the pulleys and inspect the balancer to crankshaft fit.
In this thread I initially described three vehicles. One runs well and shows the correct timing on the scale. That one is mine and there's certainly no reason to mess with it at all. The second runs well, and shows timing off the scale. I am completely convinced that the balancer is on 180° out. It is a friend's car and so I'll let him decide if he wants to mess with it in the future. That car is in such rough shape I doubt he will do anything to it that isn't totally necessary. The third car showed relatively correct timing but ran like crap. I advanced it a few degrees and in the process discovered that the inlet banjo was not tight and very likely sucking in air. The combination of tightening the inlet banjo and getting the timing correct has significantly improved the cold start and running. That car is also not mine and so I will let my friend decide if more work is necessary. That said, I don't see any reason to think that the balancer has ever been off of that engine and wouldn't mess with it if it was mine.
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  #53  
Old 11-22-2011, 03:55 PM
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Quote:
Originally Posted by libbybapa View Post
Over adjusting a valve so that it was poking down enough to interfere seems like a relatively easy way. Similar amount of work to pulling a pre-chamber and using a dial indicator on the piston crown down through the injector hole.
Are you describing taking off the spring retainer and letting the valve rest on the top of the piston ?
Anything less than that will not allow you enough pre and after piston placement to be accurate.
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  #54  
Old 11-22-2011, 04:02 PM
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Quote:
Originally Posted by leathermang View Post
Are you describing taking off the spring retainer and letting the valve rest on the top of the piston ?
Anything less than that will not allow you enough pre and after piston placement to be accurate.
I'm not familiar with the degree of interference of the Merz engine with the valve open, but on the VW, which I know have a more significant interference, one can add a shim between the cam and valve and have the engine clunk to a stop quite accurately. I'm not a fan of rotating the engine backwards, tho, so would personally opt for pulling a pre-chamber and measuring with a dial indicator if I had to find TDC.
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  #55  
Old 11-22-2011, 04:42 PM
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No suggestion of rotating the engine backwards..... very bad idea pretty much forbidden by the FSM.

You can not get an accurate reading crankwise just noting the top point hit by the piston..
You can use a dial indicator and mark on the pulley or flywheel a place as you get near the TDC and note the position of the dial indicator... then rotate the engine in the CORRECT direction to past TDC to that same indication on the dial indicator... you have marked that position both times... then you measure half way between them and mark that... that is TDC...
Any other way has too much ' margin of error' ... since there is almost no movement of the piston for several degrees of crank rotation at near TDC... crude at best... want it accurate... choose places where there is observable movement, mark them and interpolate between equal distances from TDC..
This has been standard procedure on all sizes of engines for many decades.
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  #56  
Old 11-22-2011, 04:56 PM
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Quote:
Originally Posted by leathermang View Post
AND it does not even require any measurement..... except to split the marks on the crank... the piston to top distance can be done with a mechanical device having no measuring capability...
When you said that I assumed you meant it. How are you recommending to "do the piston to top distance" without a measuring device? Now you are saying to use a dial indicator which definitely does have a measuring capability.
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  #57  
Old 11-22-2011, 05:06 PM
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You can make something like a ' stop' ....mark going up, fold up or unbolt, replace as it goes down, re- mark... split the difference on the crank or pulley or flywheel...
There are pics someplace..
However, HF has nice dial indicators with huge faces on them plenty accurate for this really cheap.... you may need the screw on extension for the end ...
You are just needing to mark equal distance from the top of the bore... thus you do not need the actual measurement..
Dial indicator much more fun....
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  #58  
Old 11-22-2011, 05:24 PM
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The dropping the valve on the piston crown and then measuring the motion of the piston crown via direct contact with a DTI is the official procedure in the FSM. It is described in chapter 03-345 for the adjustment of the tachometer mount on the pointer next to the crankshaft pulley.

With the OM617 / 616 / 615 you've got a vertical valve "drop" onto the piston crown whereas the per-chambers are canted at an angle. Measuring small changes in piston height is likely to be more error free in a vertical sense than when done at an angle.
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  #59  
Old 11-22-2011, 06:09 PM
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Thanks for doing the research and calculation. I measured a spare VW idi injection line which uses the same injector body as Mercedes. Let's assume the injector lines are the same.

o.d. is 6 mm , i.d. is 2 mm so the wall thickness is 2 mm.

Can you recalculate using these numbers? I am too lazy.

My digital vernier has a resolution of 0.01 mm so would not be able to measure the tiny amount of flex.

Quote:
Originally Posted by Army View Post
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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  #60  
Old 11-23-2011, 03:29 AM
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Quote:
Originally Posted by funola View Post
Thanks for doing the research and calculation. I measured a spare VW idi injection line which uses the same injector body as Mercedes. Let's assume the injector lines are the same.

o.d. is 6 mm , i.d. is 2 mm so the wall thickness is 2 mm.

Can you recalculate using these numbers? I am too lazy.

My digital vernier has a resolution of 0.01 mm so would not be able to measure the tiny amount of flex.
OK will do but I should be using a different equation - the wall thickness is meant to be much much smaller than the diameter of the pipe.

With a wall thickness of 2mm I expect it to be even smaller.

I do wonder if the vibration of the engine (as a result of ignition) is producing a bigger signal at the line than the flexing of the pipe due to pressure build up.

In an ideal world it would be nice to compare the output of this type of piezo-electric sensor clamped on the outside of the pipe with the output of a pressure sensor that directly measures the pressure in the line - all done as a function of time. This might explain libbybapa's observation that 10 - 12 degrees BTDC is better than the 14 degrees BTDC suggested by Brain Carlton (in the the thread I linked to way back when).

I wonder where Brian Carlton got this value for 14 degrees BTDC? (Calling BC!)

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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



Don't leave that there - I'll take it to bits!
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