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Originally Posted by autozen
Please explain how radial pressure changes...................................... on the rings and cyl walls to get the sled moving. This would increase taper and effectively increase end gap.
Is the blow by tester you use the Sioux venturi vacuum gun with the disc on the end?
In conclusion. I do 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.
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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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