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3.5 cc diesel needs needle valve

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Wanted Re: 3.5 cc diesel needs needle valve

Post  pkrankow on Wed Oct 04, 2017 7:48 pm

A Fox slant head 15 NVA is about the correct span, but the diameter is too big at 0.156

The OS NVA previously linked has a minimum span of .523, with the same diameter of .156 as the Fox.  

A COX press fit NVA has a diameter on the knureled area of about .125with a difficult to measure span of around .310 (I measured a backplate with NVA)  Consider inspecting the hole for signs of a press fit.  Use a magnifying glass or loupe.

There is a concern over drilling out the intake for a larger NVA.  The choke area will be reduced which will change the operation of the engine from as-designed.  Reduce the choke area too much and the engine will not run well.

Yet without an NVA the engine cannot run at all...

Phil
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Wanted Re: 3.5 cc diesel needs needle valve

Post  pkrankow on Wed Oct 04, 2017 8:13 pm

http://brodak.com/brodak-049-and-061-spraybar-closeout.html
http://brodak.com/brodak-mk-ii-049-needle-valve-and-spring.html
I wonder if these might be more suited. I also wonder if they fit together. Brodak's is pretty accommodating so give them a call during business hours or fire off an email with your measurements.

Phil
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Wanted Re: 3.5 cc diesel needs needle valve

Post  kendias on Fri Oct 06, 2017 7:58 pm

Thanks Phil. Tried Brodak, no luck, they don't have either the NVA or spray bar.
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Wanted start the 3.5 cc diesel

Post  kendias on Mon Nov 27, 2017 7:38 pm

Did manage to get the needle valve/spray bar. Now want to try and start it.I guess I use ether and castor oil mix - in what proportion? Any tips on how to start?
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Wanted Re: 3.5 cc diesel needs needle valve

Post  Ken Cook on Mon Nov 27, 2017 8:32 pm

35% kerosene, 30% castor oil, 30% ether and a small percentage of ignition enhancer can assist. This mix is good for plain bushed engines.
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Wanted Re: 3.5 cc diesel needs needle valve

Post  kendias on Tue Nov 28, 2017 3:15 pm

Thanks. Should the needle valve/spray bar assy be in the vertical pos'n or does it matter. Can I start it by hand or need a starter?
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Wanted Re: 3.5 cc diesel needs needle valve

Post  Oldenginerod on Tue Nov 28, 2017 8:33 pm

kendias wrote:Thanks. Should the needle valve/spray bar assy be in the vertical pos'n or does it matter. Can I start it by hand or need a starter?

Orientation of the spray bar shouldn't effect performance other than setting tank hight to suit.

Most diesel folk strongly recommend not using a starter as it is way to easy to damage a diesel when flooded.  You'll need a strong arm, a well-padded/gloved finger and lots of patience.  

Don't try to start the engine with the needle open and don't prime it through the intake.  Raise the piston to close the exhaust and place a drip of fuel into the exhaust port just to wet the side of the piston.  Give it a couple of sharp flicks and see if you can get it to fire.  You're looking for a short run (2 seconds) rather than a single pop.  If it runs with a single drip prime then open the needle about 2 turns, prime and try again.  If it runs briefly like before, watch closely to see the fuel being drawn up the line.  If fuel continues to run all the way to the engine once it stops running then close the needle and lower the tank a little.  If it stops when the engine stops, then prime & try again.

If on the first try you only gert a single pop or nothing, you may need to raise the compression a little- only about 1/8 turn in should be enough.  You should still be able to turn it over fairly easily by hand.  If it strongly resists being turned over then be very careful.  Back the compression off a turn and start over.  Diesel's have a bad habit of sticking the cornta-piston, so when you back off the screw and turn it over it won't push back up.  Sometimes if this happens the engine needs to fire to free the contra-piston.  Over-compression is the biggest killer of diesel engines, and starting fingers.

Rod
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Wanted Re: 3.5 cc diesel needs needle valve

Post  kendias on Thu Nov 30, 2017 5:46 pm

Thanks for the detailed instruction. What is a cornta piston?
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Wanted Re: 3.5 cc diesel needs needle valve

Post  Oldenginerod on Fri Dec 01, 2017 1:28 am

kendias wrote:Thanks for the detailed instruction. What is a cornta piston?

The contra-piston fits into the top of the cylinder to form the top of the combustion chamber.  The compression screw on the top of the engine forces the contra-piston down, reducing the size of the combustion chamber thus increasing compression.  When the adjusting screw is loosened the contra-piston remains in position until compression forces it back up the cylinder until it contacts the adjusting screw.  They are a very tight fit in the cylinder and often stick.  If this happens you cannot lower the compression if you go too far with the compression adjusting screw.  If it remains stuck with the compression too high, then the connecting rod can be bent if you try to rotate the crankshaft, or the crank-pin can break.  As I mentioned, sometimes it actually takes the engine to fire to force the contra-piston up in the bore.  If it doesn't, your only option is to dismantle the engine and physically press the contra-piston up.  Varnish caused by castor oil makes a very good glue for sticking contra-pistons.  It may be a good idea to dismantle and thoroughly clean the engine.  If you are not confident in doing this yourself, I would seek out somone with diesel experience to help out.

Rod.
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