Kubota V1702 engine - Is 200-250 PSI too low compression to run?

[moocowman]

Compression is 200, 230, 230, 250PSI. I know this is lower than ideal (350PSI?), but shouldn't it still run at this compression? This engine died several years ago. Owner never had time to find out why, but suspects a fuel issue. Now I'm trying to get it running. Even with a constant spray of starting fluid, one of the cylinders might fire just once after 10-15 seconds of cranking. I'll deal with fuel system problems later, but I know it's getting some fuel. When I crack open injector lines, small amounts of fuel pulse out of each line. After a few seconds cranking, white diesel smoke starts coming out of the exhaust. But again, I'm using starting fluid just to make sure the engine has the right conditions to run at all.

 

[Shawn T. W.]

Starting fluid is probably the cause of the low compression, it should be more than double that ..

 

[Tinhack]

It might run on 250psi but will have no power. That could be the single fire you're getting. Check the valve clearance/adjustment before digging in too deep. After that, you could be looking at major disassembly to fix.

 

[moocowman]

It might run on 250psi but will have no power. That could be the single fire you're getting. Check the valve clearance/adjustment before digging in too deep. After that, you could be looking at major disassembly to fix.

Thanks for the answer. I guess next step is checking valve clearances. If they're ok, remove the head and check for valve leakage, check cylinder walls.

 

[rScotty]

Compression is 200, 230, 230, 250PSI. I know this is lower than ideal (350PSI?), but shouldn't it still run at this compression? This engine died several years ago. Owner never had time to find out why, but suspects a fuel issue. Now I'm trying to get it running. Even with a constant spray of starting fluid, one of the cylinders might fire just once after 10-15 seconds of cranking. I'll deal with fuel system problems later, but I know it's getting some fuel. When I crack open injector lines, small amounts of fuel pulse out of each line. After a few seconds cranking, white diesel smoke starts coming out of the exhaust. But again, I'm using starting fluid just to make sure the engine has the right conditions to run at all.

For any diesel compression test, be sure to use a Diesel Compression Gauge - it sounds like you have one. A diesel gauge normally goes to 1000 psi - much more than you can hold by hand. A gauge for a gas engine will not go high enough. In any compression test, test each cylinder by cranking the engine as close as you can to the same number of times, and with the throttle shut.

This is a general compression test procedure good for all diesels, but procedure 2,4,& 5 are specific to diesel motors that have pre-combustion chambers for indirect injection, and in which these pre-combustion chambers are held in place by the injector body. Not all diesels have indirect injection, but a lot of late model medium and small modern diesels do use indirect injection. In these there is a possibility that the pre-combustion chamber can come loose during a compression test if the right adapter isn't used.

This is the best desciption of compression test that I've ever found. It was originally given to mechanics at their factory school way back, but still good today.
Note that the graph shows the different pressures that can be expected with differing cranking rpm.
Luck,
rScotty

 

[Shawn T. W.]

Also when you got it apart ... Check for out of round cylinders and bent rods ...

 

[thepumpguysc]

I’ve seen small diesels run at 290 psi but not lower.. & they needed really long crank times.
To check the fuel system.. a quick and dirty way is to hang the injectors outside the engine and crank the engine.. see if the injectors fire..
DO NOT get near the spray.!!
U can set up some cardboard in front of the injector tips, to see if they’re firing.

 

[Frxdy]

Stop so much starter fluid! It's washing the oil from the cylinder walls.

 

[Fxfymn413]

Oil based WD-40 will fire a diesel when sprayed into the intake without causing damage.

 

[redmt]

Use more starting fluid. If it does fire it will disassemble itself. Does it have glow plugs? Starting fluid and working glow plugs will ensure a catastrophic disassembly.

 

[Bob435]

I have several Kubota engines various equipment some with several thousand hours on it. My skid loader has the V1702 engine. Only had to rebuild one - an eBay special Onan genset due to overheating.

First make sure valves adjusted to spec.

If you are using proper compression (injector/glow plug) adapter and getting these pressure results 200, 230, 230, 250PSI. Most likely cylinder bore, rings and piston worn out. If you pressurized a cylinder with compress air, you should heard air leaking into the crank case.

How many hours on the engine? If the air filter failed or no filter - it will wear out the cylinder bore (taper), rings (excessive ring gap), piston (excessive piston/bore clearance). Possible overheated at some time thus scored piston/bore.

Do all the testing first before you start tearing into engine.

Some of the USB borescopes have a very small camera may take a peek inside.

Not sure of your abilities in engine repairs but will know cause after pulling the head off.

Let us know what you find out.

Bob G.

 

[AnotherBueller]

Stop so much starter fluid! It's washing the oil from the cylinder walls.

In a compression ignition engine WITH a GLOW PLUG, using ether AKA starting fluid, is asking for damage to to the piston, valves and the head. NEVER EVER do it.

 

[AnotherBueller]

I have several Kubota engines various equipment some with several thousand hours on it. My skid loader has the V1702 engine. Only had to rebuild one - an eBay special Onan genset due to overheating.

First make sure valves adjusted to spec.

If you are using proper compression (injector/glow plug) adapter and getting these pressure results 200, 230, 230, 250PSI. Most likely cylinder bore, rings and piston worn out. If you pressurized a cylinder with compress air, you should heard air leaking into the crank case.

How many hours on the engine? If the air filter failed or no filter - it will wear out the cylinder bore (taper), rings (excessive ring gap), piston (excessive piston/bore clearance). Possible overheated at some time thus scored piston/bore.

Do all the testing first before you start tearing into engine.

Some of the USB borescopes have a very small camera may take a peek inside.

Not sure of your abilities in engine repairs but will know cause after pulling the head off.

Let us know what you find out.

Bob G.

While you are doing everything above listen for air leaks in the adjoining cylinders. This can help diagnose head gasket issues.

 

[TORQUIN]

A trick for starting a diesel without starting fluid, is a gas-soaked rag over the intake. This is safer than starting fluid as all that gets to the cylinder the gasoline vapor. Just make sure you don't let the rag get sucked into the intake. I have used this trick instead of starting fluid for diesels that ran out of fuel, to get them running enough to re-prime their fuel systems.

Chris

 

[DieselBound]

I never trust numbers, for numbers sake, from a compression test as there are many things that can affect them: a cheap tester, temperatures and so on. What matters most, however, is whether the numbers fall within an acceptable delta- highest and lowest are within a PERCENTAGE spec which is usually no more than about 10%. In your case a high of 250 and a low of 200 gives a 50 psi difference which is a 20% delta and that's just too high. BUT...

One needs to do a WET compression test to determine whether it's the rings or the valves. I suppose there's also a chance of a head gasket issue and that should probably be assessed as well.

I now that engines wear but it's pretty rare to get one to wear down across the board to the point of "failure." Usually it's one or two cylinders that for some reason or another are responsible for the condemnation of the engine (rebuild or replace).

 

[AnotherBueller]

A trick for starting a diesel without starting fluid, is a gas-soaked rag over the intake. This is safer than starting fluid as all that gets to the cylinder the gasoline vapor. Just make sure you don't let the rag get sucked into the intake. I have used this trick instead of starting fluid for diesels that ran out of fuel, to get them running enough to re-prime their fuel systems.

Chris

Problem is that IF your engine has a GLOW PLUG even gasoline WILL detonate well before TDC, leading to the same issues as using ether. Although it may not be as big a problem. The best practice is to use WD-40 which is a very light oil. This has been the way to for more years than I can remember. I learned it in the military in the 70s. Of coarse if it does NOT have glow plugs ether is the choice.

 

[etpm]

Of coarse if it does NOT have glow plugs ether is the choice.

My Yanmar 2310 does not have glow plugs but I have been told many times to never use starting fluid in my engine.

 

[TORQUIN]

Problem is that IF your engine has a GLOW PLUG even gasoline WILL detonate well before TDC, leading to the same issues as using ether. Although it may not be as big a problem. The best practice is to use WD-40 which is a very light oil. This has been the way to for more years than I can remember. I learned it in the military in the 70s. Of coarse if it does NOT have glow plugs ether is the choice.

The trick to that is to wait until the glow plugs cool off. For instance, if your ignition has a separate position, to the left, for glow plugs, don't use it when adding "starting assistance chemicals". If your ignition uses a timer for glow plugs, wait for a few seconds after the glow plug light turns off before you crank it. Once the glow plugs cool, no problem. You must be aware of exactly how your glow plugs cycle, though.

Chris

 

[Dennis Mohn]

Compression is 200, 230, 230, 250PSI. I know this is lower than ideal (350PSI?), but shouldn't it still run at this compression? This engine died several years ago. Owner never had time to find out why, but suspects a fuel issue. Now I'm trying to get it running. Even with a constant spray of starting fluid, one of the cylinders might fire just once after 10-15 seconds of cranking. I'll deal with fuel system problems later, but I know it's getting some fuel. When I crack open injector lines, small amounts of fuel pulse out of each line. After a few seconds cranking, white diesel smoke starts coming out of the exhaust. But again, I'm using starting fluid just to make sure the engine has the right conditions to run at all.

If you haven't gotten the engine running yet send me a picture of the injection pump. I recently had a little starting trouble and may be able to help. But first I need to know what pump your engine is running