The Craftmans Shop > New from Old

Thwaites 2 Ton Two Cylinder Dumper Running On One Cylinder

<< < (4/29) > >>

appletree:

--- Quote from: awemawson on November 07, 2015, 11:52:19 AM ---There is an injector pump for each cylinder, and their 'volume racks' are linked to move in synchronism to give equal volume to each. There is a governor in the bowls of the engine that moves the racks against a spring which at rest presses the rack end against an 'overload stop'.

The setting up requires that the racks are first synchronised so that a calibration mark on each is 13/16" from the spot face on the pumps - this is set by adjusting the length of the link rod that joins them. However this setting needs to be 'at rest' when the rack is limited by the 'overload stop'

Problem is the overload stop is hideously worn and flopping all over the place

--- End quote ---
Perhaps not immediately obvious to our readers the overload stop is disengaged for starting, it then drops back into place once the engine is running and the governor takes over.
The purpose of the device is to prevent over injection when the engine is under large/excessive load thus preventing over fuelling .

Manxmodder:

--- Quote from: awemawson on November 07, 2015, 11:26:37 AM ---  :scratch: :scratch: Now how odd is that  :scratch: :scratch:

It is drawing MORE current when cranking WITHOUT compressing than when the valves are closed - I can't explain that - it may be that the engine turns over faster, but it didn't seem to.

However the comparison between cylinders showed that they weren't miles off each other, but I do find those readings EXTREMELY odd  :coffee:
--- End quote ---

Andrew, what I believe you may be witnessing here is an atmosperic engine braking type of thing.

Decompressor engine brakes,usually only seen on 2 strokes, work on the principle that the piston has to work hard to draw air in through a small orrifice under only atmospheric pressure hence creating a partial vacuum in the cylinder.

On the subject of testing the cylinders for compression,why not make up a simple compression tester that replaces the injector with a suitable pressure range gauge fitted.
......OZ.

RussellT:
If you want a comparative reading rather than an absolute figure you could use your petrol engine compression tester.  If you used an extension pipe between the tester and the cylinder you would increase the unswept volume and decrease the pressure reading to a suitable amount.

I'm following with interest. :thumbup:

Russell

awemawson:
Thanks chaps but at this stage I think that the compression issue is a red herring. Given fine weather tomorrow I hope to go through the setting up procedure for the injection timing and metering.

Visitors today, but I did manage to make up a 'swan neck', that screws onto the output of the pump being set up, and acts as a 'stand pipe' to let you observe the 'spill cut off point' more accurately as you tweak the cam follower tappet adjuster.

The piston of the injector pump rises, and at one point covers the 'spill port' at which time the pressure starts to build and fuel is injected. The piston has an angled cut in it that, as it is rotated by the rack alters the effective point at which cut off occurs and hence changes the volume squashed though the injector. So it is important to set the rest point of the rack first, and that depends on that little brass 'overload stop' I re-made the other day.

awemawson:
Well not the best day in my life  :bang: :bang:

It all started quite nicely. I went through the procedure carefully to set the rack synchronisation and then went on to the  injection timing using the 'spill' method. I started by cleaning up the marks on the fly wheel - it carries TDC marks for both cylinders (as they are 180 degrees apart) and also for 24 degrees and 28 degrees before TDC as it seems 24 is for engines running up to 1650 rpm and 28 degrees for engines running up to 2200 rpm. No plate on mine so I decided to use the 24 degree setting.

Starting with #1 cylinder I removed the injection pumps one way valve as instructed, and installed the 'Swan Neck' slackened off the adjuster as per the book, set the timing mark bang on and then raised the tappet screw until the flow stopped - all went apparently as it should. I took the precaution of taking a picture before and after to be able to compare.

Navigation

[0] Message Index

[#] Next page

[*] Previous page