Detroit 4-71 runaway and diesel in air box

[Pralhad Birdi]

Hi all,

I’ve got a Detroit 4-71 which I retro-fitted into an IH TD-14A bulldozer. Ran great for a couple of weeks, before it started over-revving again immediately upon startup, and sending diesel into the sump.
I assumed initially that the run away was caused by the level of oil rising due to the diesel, but when I took off the air intake cover I found oil on the rotors. Took the blower off and apart, replaced the seals with genuine GM parts, replaced the fuel pump (I was suspecting a leaky fuel pump seal might be sending diesel into the crankcase), and re-installed blower. The air box drains were also blocked, so I cleared those out and made sure they were open.
Started it up on the bench today, and it ran okay for about 5 minutes or so, before the revs started going progressively higher again, to the point where pulling on the stop governor was making no difference at all. Had to flip the emergency stop flap to get it to shut off. Took off the air intake cover, but the rotors are now completely dry, so it’s not taking oil in from there. The air box drain dripped a diesel/oil (mostly diesel) mixture for about 10 minutes after shut off (nearly 3 litres), and the sump oil level has risen slightly, indicating diesel still making its way into the sump. The fuel pump drain cock is open, so if it was a leaky seal, surely the diesel should be able to leak out from there rather than forcing it’s way into the engine? Also, using SAE 40 oil, not the multi grade stuff.
So I’d really be open to any ideas about where this diesel is coming from, and whether it’s the most likely culprit causing the run-away symptoms.
Cheers

 

[Mcrafty1]

No answers, replying to sub this post.

 

[BillG]

I'm going to try the easy way here. Pull off the rocker cover and start the engine. Watch for any fuel leakage around the fuel pipes and injectors. Fuel being a lower viscosity than oil will find it's way past the piston rings and cause the uncontrollable speed that you are experiencing.

 

[Pralhad Birdi]

I'm going to try the easy way here. Pull off the rocker cover and start the engine. Watch for any fuel leakage around the fuel pipes and injectors. Fuel being a lower viscosity than oil will find it's way past the piston rings and cause the uncontrollable speed that you are experiencing.

I’ll try that out first thing in the morning.

 

[Pralhad Birdi]

Update:
Took off the valve cover, cleaned it all up, and bled out the fuel system to start it. Just before starting it, I noticed clean diesel dripping out of the air box drain next to the flywheel. Started it up, no obvious diesel leakages at the injectors or pipes.
Where would the diesel be finding it’s way into the air box drain from before the engine is even running? Because that’s probably then the cause for the run-away as well.

 

[Mcrafty1]

Does the engine run smooth when you start it before it runs away? no skipping?

 

[Pralhad Birdi]

Y

Does the engine run smooth when you start it before it runs away? no skipping?

It runs fairly smoothly, but with a decent amount of white smoke.

 

[Pralhad Birdi]

I think we seem to have pinpointed the issue though. Took off the air box inspection covers, barred the engine over, and found No. 2 piston crown full of diesel. Going to take out the injector now, and swap it out for another one and see if it helps.

 

[Mcrafty1]

I think we seem to have pinpointed the issue though. Took off the air box inspection covers, barred the engine over, and found No. 2 piston crown full of diesel. Going to take out the injector now, and swap it out for another one and see if it helps.

I think your onto it.

 

[Vetech63]

Oh, those pesky Detroits. Let us know how this comes out.

 

[Simon C]

Your governor buffer screw is not screwed in a hair too much by any chance. Back it off and when it starts the engine will hunt up and down. Turn it in ever so slowly till you hear the engine go up only 10 -15 rpm. That could be causing your run away. Fuel cross-over lines commonly leak at the cylinder head spikes. If you hook up a Carter fuel pump to the secondary filter housing inlet fitting and pressurize fuel through the head back to tank you can usually find which cross-over line end is leaking. I have done this in the past and found the leak. Helps if you wipe around all the fuel spikes to be able to see the leak. Hope this helps.
Simon C

 

[Pralhad Birdi]

So we’ve changed the injector, just started it up, and she’s running like a dream. No more diesel out of the exhaust or air box or air box drains. Just need to sort out a few oil leakages (or at least try to) and stick it back in the dozer. Thanks guys!

 

[Pralhad Birdi]

Your governor buffer screw is not screwed in a hair too much by any chance. Back it off and when it starts the engine will hunt up and down. Turn it in ever so slowly till you hear the engine go up only 10 -15 rpm. That could be causing your run away. Fuel cross-over lines commonly leak at the cylinder head spikes. If you hook up a Carter fuel pump to the secondary filter housing inlet fitting and pressurize fuel through the head back to tank you can usually find which cross-over line end is leaking. I have done this in the past and found the leak. Helps if you wipe around all the fuel spikes to be able to see the leak. Hope this helps.
Simon C

So now it’s idling pretty well, so I didn’t touch the adjustment on the governor. If it does bring issues again in future, I’ll be sure to keep this mind. Thanks!

 

[Pralhad Birdi]

Oh, those pesky Detroits. Let us know how this comes out.

Tell me about it…we’re running a 6-71 in a D-740 Champion grader, this one in the TD-14A and a 4-53 in an Ingersoll-Rand roller. They keep us pretty busy

 

[Mcrafty1]

If oil leaks in your two stroke Detroits are going to be a problem you'll never run out of things to work on, it was always a running joke that oil leaks were how we changed the oil in a Detroit. Lol, Glad to hear you got the overspeed problem sorted out.

 

[DMiller]

There is a reason they are no longer produced and most shops do not any longer work on them. I swore at and off them years ago.

 

[Vetech63]

I still see those precious oil leaking bastards!

 

[DMiller]

So do I, then I about face and RUN Away!!!

 

[Pralhad Birdi]

If oil leaks in your two stroke Detroits are going to be a problem you'll never run out of things to work on, it was always a running joke that oil leaks were how we changed the oil in a Detroit. Lol, Glad to hear you got the overspeed problem sorted out.

If there’s no oil under them, there’s no oil in them!

 

[fast_st]

Bus grease monkey is a pretty cool customer while fixing the green leakers.