fact. i have often wondered why they would stay in the same spot. i guess we take the trouble to make sure they dont line up just for starting up the first time.

thanks for sharing.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Very interesting. I have wondered about this for years, considering Mercedes even states in their manuals that it is possible for the rings to line up.

__________________
Auto Zentral Ltd.

The same company....tested end gaps of rings on blow-by and effeciency.

The supposition was that large end gaps would/did result in low compression and poor performance.

I think it was a Ford Kent 4 cylinder 4 stroke 'petrol' engine that was the 'mule.
It was stripped and prep'd for new piston/rings. The ring end gaps where set at
0.015" with less than 0.002 side gap.
The engine was run up and loaded to set the rings and performance measured.

They kept doing this with ring gaps enlarged to 0.025" and all the way up to 0.050".......Results........

The end gaps had little impact on engine operation ! There was little to measure between the 0.015" gaps and the larger ones.

The test revealed that RADIAL pressure of the rings against the cylinder bore where the critical part that made or broke piston ring seal

Also it must be remembered that all tests where done with new piston/ring packs.

Looking at this result brought up the question as to why every piston ring company insisted the ring gaps be held at 3 to 4 thou' per inch of bore ?

Public re-education was not going to improve ring sales.
These's test where filed and apart from those of us in the know...forgotten.

SO......a NEW set of rings on a good spec' used piston will usually bring the engine back to OE spec' compression levels......regardless of the end gap....within reason.

However, I have of late done my own tests.
I have used 'file fit' rings on several VW diesels using a gap of 0.003" to 0.005" in the unworn....lower cylinder bore area...which usually produces 0.020" to 0.30" at the top on the worst case bores.
I have a fixture to measure blow-by on the piston/block without a head.

Blow-by of 2% or less will produce close to 500 psi cranking pressure cold ( 65 F ambient.)
Also found that NOT honing the bore produced good results very quickly.

So, end gaps seem most important on cranking speed, not dynamic speeds.....and on a diesel this IS important.

Both these results seem at first to be contradictary to popular engineering accepted results from doing this. However, my own tests prove this is very effective on diesels for cold start performance......once the engine is running , time/angle operating losses are conciderably reduced and even a low compression diesel will run reasonably well under load.......

Here's a little test for you.....start your diesel and remove the oil filler cap, ( Watch out for oil spray.)..note the amount of blow-by.....now raise rpm's a little ....what's the result ?


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__________________
[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

Please explain how radial pressure changes. Is it because of increasing end gap with worn bores? I am well aware of the fact that a diesel witl 100k on the clock that has been driven around town is in poorer shape than one with 300k of highway miles, because of the radial oressures exerted on the rings and cyl walls to get the sled moving. This would increase taper and effectively increase end gap. Correct me if I'm wrong.

Is the blow by tester you use the Sioux venturi vacuum gun with the disc on the end?

In conclusion I go agree with you that cranking compression can drop off to where you don't get the 900* or so needed to ignite the fuel, but I maintain that a valve job which is cheaper will give you more bang for the buck than a lower end overhaul. I can elaborate more on this later.

looking forward to hearing from you.

__________________
Auto Zentral Ltd.

The radial pressure decline or reduction, is a function of time/heat/fatique.
Honda uses a very low radial pressure ring set....this increases usable horse power/ reduced ring drag..

( I used DYNO 2000 to 'build' a V8 with 1'' inch bore and a 9'' inch stroke.....the engine would not produce any power above 5/6000 rpm due to internal friction..ie: power output: ZERO.).

...but this also causes problems if the engine should fuel wash and rings loose oil sealing. Another reason Asian cars use a 'Clear Flood' programme in the ECU.

By using a 1st or 2nd or even 3rd oversize ring sets you can increase radial pressure to get good cranking pressures.............this is no help if cranking rpm is low....For example....if you rotated a cold engine at 1 revolution per hour, it would not start no matter how high the compression ratio.

Speed of compression is critical to raise air temperature to flash point...typicaly 1,100 degrees F.

The 'ignite' point of the fuel is helped by the glow plugs and as you know...very few MB or VW diesels will start without glowing.

The leak down tester is a MATCO dual gauge set. I use it with an Assenmacher bore tester.

It seems that low cranking speeds are primary reason for no start besides low temperature and heat sink.
We used to start old Atkinson and Thornycroft diesels with a blow torch....those where the days !


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__________________
[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

start the engines?

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

i don't want to hijack this thread.. but i just wanted to say thanks....

__________________
Mike

----------------------------------
1975 200 - Sold (no pix);
1978 200 - Sold - http://www.pbase.com/hboy/redbaron
1979 300TD - Sold
http://www.pbase.com/hboy/greenwagon
http://www.geocities.com/hboy726/300TD.html
1985 230E - now my daily driver...

you're hijacking our hijacking!

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

These two old yard shunters where hand crank started. In fact, the starting handle was made long enough to allow two people to swing on it.
The Thornycroft had a decompression handle.

When temperatures where low, the yard boy would wheel out the welding bottles and heat the intake manifold .....after this, two of the heaftiest guys around would swing the handle....until one day someone came up with ether .

Apparently they squirted ether into the warmed manifold, set the de-comp' lever and swung.........the lever clicked off...the flywheel brought the engine to
nearly tdc and the ether fired.......just one problem.......it fired off in reverse rotation..........the old Thornycroft ran the engine up higher and higher until the starting handle flew off taking one headlamp with it and then a few seconds later the engine disintergrated..........I was hiding around the shop with the guys who'd run for cover when this happened at 4.30 am .....I had just arrived to do a run to London.

Later on...around 1969/70 the new trucks came equipped with Ky-Gas bottle start fluid systems.

__________________
[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

No problem...

The new plugs are in and, surprise, surprise, she still won't start.

Apparently I'll be spending winter break replacing the bloody headgasket.

Question: how long should fast plugs be glowed for? I did a 20 sec heat-up but I think that may have been a little long.

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'84 190d 2.2 - Silver
Converted to 5-Speed
'84 190d 2.2 - Blue
Factory 5-Speed

'76 300D (W115)
Sold, found again in less auspicious circumstances

Glows can be glowed for a long time.....don't forget they live IN a 1200/1400 F enviroment !

..........ya know....that brings up a question.....I'm gonna glow a plug to destruction and see how long it takes.....stand by for NEWS !



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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

Hmmm....

This is rather curious. Your 300D sure doesn't idle like it has a blown headgasket.

Were all the plugs getting appropriate power, fuses good, and a strong battery?

Its in the high 30's here and even my 240D with 300k and a bad glow plug or two starts...

Try spraying a little wd 40 penatrating oil into the intake manifold at the end of a glow plug cycle when you start to crank engine. Get a friend to help. If engine comes to life you possibly might have a fuel supply problem of some sort. I was trying to suggest my thoughts earlier on perhaps why your compression readings where as they are in my post. You have loosened an injector line off to acertain that fuel is available when cranking? These two tests are cheap and easy to do. Just might reveal something. Certainly will not hurt anything. You of course remove the top of the aircleaner and spay directly down the throat as the wd 40 will not pass through the aircleaner filter.

That trick doesn't work anymore unfortunately.

When you spray the new gen wd-40 into the intake the engine slows down and defintely doesn't help light the fire.

No propane anymore I believe...