Jinma 254 starting problem

[greg_g]

I'm pretty sure that kero has better lubricating properties than does diesel fuel. And anyway, there's likely already some diesel fuel mixed with your pump oil. That's why I try to drain/refill my pumps twice a year - to get rid of the diesel that's gotten past the rings.

Kero should need less than a minute of the engine running to flush that little pump. No guarantee it will actually free a stuck piston though, you should actually try to do that first - then drain/flush and refill with clean lube oil

//greg//

 

[Affordable]

The stuck piston is below where the hard lines attach to the top of the pump,you can remove all the hard fuel lines,carefully take the head off,under it are 3-springs and disc's one for each cylinder,the disc are what stick most of the time or have debris in them,it also could be a stuck fuel rod.You do not have to remove the pump to do this,

Tommy
Affordable Tractor Sales
Home of compact Jinma, Foton, and Koyker Tractors and Parts, Wood Chippers, Backhoes - Affordable Tractor Sales Company

 

[psj12]

Kerosene does not have the lubrication quality of diesel. In fact jet fuel, which is kerosene, has to have lubricity additives put in it to make it compatable with the army's diesels. The army and all the services now use JP8 in ground equipment and aircraft. We experimented with the older diesels prior to the army adopting this standard and found it did shorten injector and pump life even with the additives. The difference was not signifigant enough to stop its' adoption. Newer military diesels are more compatable. Also kerosene produces on average about 11% less power per volume than diesel. In the older style pumps found on Chinese tractors it is all about volume.

 

[greg_g]

Fair enough - but this is about cleaning (flushing) the pump, not the engine. Perhaps you assume the pump shares engine oil - it doesn't. The vast majority of injection pumps on these Chinese utility tractors have their own little sump. Filling the injection pump sump temporarily with kero flushes the pump only - and has nothing to do with the engine.

//greg//

 

[psj12]

The oil sump in the pump lubrecates the cam and followers for the pump and the govenor assembly. The pump piston itself is lubrecated by fuel only.

 

[Ranch_Hand_Supp]

Kerosene does not have the lubrication quality of diesel.

.

I agree.
Doing a un-educated test by rubbing Diesel fuel then Kerosene between your fingers will allow you to feel the difference.


Ronald
Ranch Hand Supply

 

[greg_g]

I stand corrected. I drew my own unscientific conclusion after obtaining exactly the opposite of Ronald's uneducated test. Yet the 2-1 margin pushed me to actually look it up. Kerosene and #1 diesel fuel do in fact contribute less lubricity than does #2 diesel fuel.

But I'm skeptical about diesel fuel lubricating the pump piston. A rotary pump maybe, but these are inline pumps. As such, I thought that the piston rings (or discs) drew oil up from the sump to lube the cylinder wall. It's always been my understanding that the lubricity characteristic of (sulphur in) diesel fuel was for the benefit of the seals, valves, injectors, etc. So I'm still thinking that temporarily replacing the pump's lube oil with diesel or kero will wash the cylinder walls, against which a ring (or disc) may be stuck.

But I was wrong about diesel versus kero lubricity, so please educate me if the above is incorrect or inaccurate as well.

//greg//

 

[psj12]

Diesel high pressure fuel pump pistons do not have piston rings. They are precisely lap fitted to bore of the pump cylinder. The clearance in the pump piston and cylinder are measured in hundred thousandths and even millionths of an inch. This gap would not allow lube oil to work. The upper end of the piston gallery is sealed from the lower end of the pump assembly to prevent oil sump contamination. The clearances are so small that when handling the pistons you should never touch them with your dry fingers. Always wet your fingers in fuel or light oil first. The dry spot caused by touching them could cause them to sieze. Pistons are permanently mated to the bore they are in. A very small amount of fuel that gets by the piston is returned in a return line. The small clearances are the reason pump pistons sometimes freeze in their bores due to contamination. Water and solids being the worst. The only thing that returns the piston from an up stroke is the spring on the lower end of the piston.

Sometimes a piston can be manually freed and will continue working. Sometimes it becomes siezed in place permanantly. When this happens if the pump has individually removeable pumps then that one has to be replaced and the pump calibrated. If it has integral pumps than the entire pump assembly must be replaced.

The piston has a helix cut in it that opens a small port on the side of the piston bore that allows fuel to flow into the bore of the pump. The rotation of the piston determines the position of the helix in relation to the port thus changing the amount of time the port is open during the down stroke thus how much fuel enters the bore. The rotation of the piston is controlled by the rack which is moved by the govenor.

When you press on the throttle all you are doing is putting more pressure on the govenor speeder spring that has to be overcome by the flyweights. So the flyweights have to spin faster to overcome the spring pressure before returning your fuel rack to a lower fuel position.

 

[greg_g]

Diesel high pressure fuel pump pistons do not have piston rings. They are precisely lap fitted to bore of the pump cylinder. The clearance in the pump piston and cylinder are measured in hundred thousandths and even millionths of an inch. This gap would not allow lube oil to work.

Bear with me, it's clear that I'm still climbing the learning curve here. I admittedly have zero design knowledge of these Chinese tractor pumps. But that said, methinks you may be attributing tolerances to them that may not typically exist. Elsewise, how is it that fuel-contaminated pump oil is reported so often in these Chinese tractor forums? Can't blame one specific pump either, cuz both my current tractors use different pumps - and I still find myself draining fuel-contaminated oil from both about twice a year. And I say we collectively - since this specific issue has been reported here across the manufacturer and model spectrum.

Or am I also incorrect in assuming that compression pressures force fuel down the cylinder walls and into the sump? Is it leaking in from somewhere else? Yet - if there isn't even molecular tolerance between the piston and the cylinder wall - what makes a formerly reciprocating piston stick after sitting idle for a while? I thought it was from wet fuel. And if the tolerances are as tight as you state, how does diesel fuel "lubricate" the cylinder walls in the first place? Matter of fact, why then do they have lube oil sumps beneath the cylinders in the first place?

Again, I'm not challenging your knowledge - you obviously know more about injection pumps than do I. And your descriptions are very clear. Unfortunately - for me - they have created more questions than answers.

//greg//

 

[Bob Rooks]

If I may interject here, psj12 is correct on all counts.
What may cause plunger/barrel sticking after sitting idle for some time is moisture in the fuel causing oxidation or bugs. Bugs live in the water/oil interface layer and can completely ruin entire fuel systems, hence the necessity to keep fuel clean, very clean.