A Couple Diesel Questions ?

Rick · Post by **Rick** » Thu Jan 11, 2007 11:57 pm

Still welding up my frame, but starting to lay out the drivetrain, and realized I don't have much experience with diesels. So I have 2 questions for those of you that have been there...

1. I know theres a return line from the injector back to the fuel tank. Does that HAVE to dump in at the top of the tank? On my clone, it dumps in about 2/3 of the way to the top. Could that be run back into the tank crossover hose? Or does it really need to be up at the top. Not a big deal either way, but I could stick a barb on the tank while it's still dry inside.

2. Do you guys use the compression release when using the electric starter? I know it has to be used for manual starts. It seems it wouldn't need a huge battery if you used the release priior to electric. Or am I way off base here?
Thanks, Gents

LocomotiveBreath · Post by **LocomotiveBreath** » Fri Jan 12, 2007 12:36 am

Hey Rick, the only stupid question is the one not asked.

1. The line in which your refering to is a return line from the injector(s), but keep it placed towards the top of the fuel tank. (See Photo) The two lines in the tank in the photo are injector return line, vent/air bleed line from the base of the injector pump. Fuel line can be seen coming from the fuel filter at the base of the tank.

2. If you want to use the compression release upon start up (with the starter), it would be best if the throttle/governor is off while motoring the engine over as every other revolution, the injector will inject/dump fuel into the cylinder, making a very smokey start up. On the upside is you will prelube the engine and while doing this, try to set the governor to start and and flip the compression release at the same time. Hope I'm making sense. But if you have an electric starter, I wouldn't worry about the compression release, that usualy used for hand starting, with out it, hand starting would be almost impossible.

Dave

Post by **Byrdman** » Fri Jan 12, 2007 5:16 am

1. The return line is a vent line as stated above but it also flows heated fuel back to the tank for cooling. Many engines use the extra return flow to cool the injector and in that case, I would dump back into the tank as far away from the fuel tap as possible. Cool fuel = powerful fuel.

sbrumby · Post by **sbrumby** » Fri Jan 12, 2007 6:56 pm

I dont think the reply you were given is strictly correct. My understanding is that the injector pump pushes out 215Bar (3225psi) this pressure is fed to the injector which is ineffect a needle valve with a hydralic piston above it. The pressure is fed down a hole at the side of the piston to the bottom. on the other side of the piston is a strong spring. 215Bar is required to push the spring and needle then the pressure is allowed into the injector holes usually 4. When the pump has done its work & stops the spring takes over & the needle reseals the holes. Hope I am not boring you. The piston is a very tight fit but not a perfect fit, if so it would not move. The diesel acts as a lubricant, so anythink that escapes up the sides of the piston has to be fed away LEAKOFF PIPE. So the answer to your question as to where the leakoff pipe needs to end up is probably of no consequence as the difference in pressure between top and bottom of the tank on a motorbike will be neglegible. If it were attached to the bottom of a 600gal tank the leakoff would have to overcome this pressure.

LocomotiveBreath · Post by **LocomotiveBreath** » Fri Jan 12, 2007 7:23 pm

Yes, I re-read the question and I corrected myself, thank you, I was assuming he was wanting to know about the air bleed vent line shown in this picture. Common on many Diesels, but not all.

Post by **Diesel Dave** » Sat Jan 13, 2007 12:24 pm

Regarding a return line from the injector, on all the standard tanks I've seen that are supplied with the Yanma 10HP clones these are fed back to a pipe welded into the base of the tank but extends inside for 2/3 of the tank height.

This pipe also acts as the air bleed from the top of the injector pump in case a bubble enters the feed line on some systems.

If you fit clear feed lines and watch a bubble in the system with the engine running you will see how much the fuel pulses in the line as backwash from the injector pump. It's not good practice to T the return to this line.

Regarding using the compression release, I use it for electric starting because it reduces the draw on the battery and also the rest of the electric starting system - price up a replacement starter motor and you will see why, it's almost cheaper to buy a replacement engine. This allows me to use a much smaller battery than the specs require. Set the throttle open a tad; left thumb slips open the compression release, right thumb hits the starter, 3 seconds later drop both at the same time and marvel at the ensuing miracle that is compression ignition.

If you have ever (attempted) pull starting a 10HP even with the compression release you should realise how much work you are asking the starter motor to do.

Hope this helps
Dave

Rick · Post by **Rick** » Sat Jan 27, 2007 12:16 am

Yeah, I thought it was a return line, too. On my clone, it goes through the side of the tank about 2/3 of the way up. But I can't see what it would hurt to return it to the crossover hose. Or maybe just use the crossover nipple opposite the petcock strictly for the return. It's a 4 gal tank, so I'll have plenty of capacity to spare....

About the comp release on starting... The book says to flip it down (and it STAYS down) Ease the recoil start past comp, the pull it hard! The release pops back up off it's own accord. Does that sound correct to you all?
I'm figuring on using a smaller battery, and pull starting it if necessary.

PS.. Nice to see our numbers increasing here...

balboa_71 · Post by **balboa_71** » Sat Jan 27, 2007 4:48 pm

I've got my return line going into a soda bottle (beer can is just as good) so I can see how much really is bled off.....turns out to be very little. I can always unscrew the bottle and dump back into tank or get rid off if it becomes contaminated. I don't like xtra holes in my fuel tank, but will eventually route to brazed up fitting in top of tank.....

Cris

DEZEL INGEN · Post by **DEZEL INGEN** » Sat Jan 27, 2007 6:51 pm

just my 2cents. how about just tee ing back into your fuel supply line.

LocomotiveBreath · Post by **LocomotiveBreath** » Sat Jan 27, 2007 7:28 pm

DEZEL INGEN wrote:just my 2cents. how about just tee ing back into your fuel supply line.

My 2¢ worth, bad idea, the reason for the line returning to the tank is to purge any air bubbles that get traped in the fuel system. A tee would just reintroduce the air back into the fuel system upstream of the pump and injector(s).

Dave

DEZEL INGEN · Post by **DEZEL INGEN** » Sat Jan 27, 2007 7:40 pm

where are ya pickin the air up from?

LocomotiveBreath · Post by **LocomotiveBreath** » Sat Jan 27, 2007 7:54 pm

Well I notice I pick up a small amount of air when my tank is less than half full and I slow down (traffic lights, stop signs, naked female hitch hikers). I notice this as I have transparent fuel lines. My motorcycle moves and the fuel sloshes around, just like my truck etc.....

Homework assignment, take a clear gallon jug, fill it with Diesel/biodiesel, put the cap on, and shake, notice the little air bubbles? Diesel fuel is a light "OIL" and traps air bubbles! If you look hard you will notice the bubbles in the jug. My little Hatz engine shakes my bike enough, not to mention the fine suspension of a Dnepr.

Dave

Rick · Post by **Rick** » Sat Jan 27, 2007 8:29 pm

First off, I just checked the tank I plan on using.. NO crossover . It's an old HD SuperGlide tank that I ran on the bike for years.. Never noticed there wasn't a crossover before.. Go figure..
Second, Maybe I'm just dense here... but won't any air bubbles in the line go UP?

LocomotiveBreath · Post by **LocomotiveBreath** » Sat Jan 27, 2007 8:37 pm

Sure, the bubbles will go up, unless there is a vacuum on the line like a fuel pump? Injector pump? Maybe engine builders put all those extra return lines on because they got a great deal on tubing?

balboa_71 · Post by **balboa_71** » Sun Jan 28, 2007 2:07 am

I should have mentioned this before in my last post regarding my attempts....When I first got my bike on the road, I was using a very common (cheap) store bought filter that has 3 ports:
In, Out (both 5/16 dia.) for fuel to go from tank to injector pump, and a third port (into the side of filter, 1/4" dia.) which I used for my return line to tap into. It worked fine for a few days and then I developed fuel leaks up at the injector. I proceeded to waste a few weeks of time screwing around with my high pressure injection fuel line, thinking I had a lead from there....biggest damn waste of time and money screwing around..... After all but giving up, I ported the re turn line to a soda bottle and all was good with the world.....no more leaks.

I pissed off 3 weeks of phucking around, thinking I had some sort of leaking going on where the HP line attaches to the injector.

For the present time, I don't give a rats ass about the few drops of fuel that collects into the soda bottle over time.... I just don't want another leak

Cris

DieselBike.net

A Couple Diesel Questions ?

A Couple Diesel Questions ?

Your Questions

Re: Your Questions

return line

I stand corrected

Return lines and compression release.

return line

Air?

Bubbles going up?

fuel return line