what makes a detroit run away?

[JDOFMEMI]

Great old detroit stories.

I remember one of the mechanics telling me of an 8V-71 that ran away. He tripped the blower doors shut, but it already had a head of steam built up. It was spinning so hard it swallowed the blower doors, and proceeded to run to destruction.

I also remember a 6V-71 on the rear of a TS-24 when the trans stuck in first gear. On the return haul road, they were getting 6th gear wide open on that job. I was driving the haul road when I seen a strange piece of debris lying there. I stopped and picked it up, and discovered it was what was left of a connecting rod. Further up the road, I picked up 2 more of them. Then I followed the oil trail to the dead scraper. It had 2 new windows on one side of the block, and one on the other. 3 rods left completely, and a 4th was hanging. When we pulled it out, you could reach all the way through.

 

[busman]

Hello all, Busman here, newbie to this forum
Have an Austral Tourmaster ex touring coach converting to a motorhome with a DD 6V92 in the rear
We have a hydroponic farm (no not that sort, real food) and one of the workers did some work on the vehicle. One of the things he did was replace the shutdown cable (which was showing signs of age) with an electric solenoid, and also fitted one at the same time for fast idle. Of course these sit on top of the governer box anld I strongly suspect he has been playing with both the Jake switch adjustment and the governer screw in the rear of the box. Can't ask him, he isn't here anymore, probably good thing as you will agree as you read on................

Getting near the end of this build, yesterday we replaced coolant, power steer oil, fuel filters, oil filter and did an oil change

Turned the key and boom, she was running at 20,000 rpm (at least sounded like it). Got to the back prety quickly (yups the panic set in and I didn't think about switching the fuel shutdown switch at the driving position) First thought was to manually pull the fuel shutoff solenoid back to shut the fuel off. I couldn't move it (or was that the panic level was increasing and I was pushing in the wrong direction, dunno ?) At this stage haven't even tried activating it to see if it works (was checked and working, but not with motor running after install)

First thought was to starve the thing of fuel so unscrewed the primary filter, faltered then back up to full revs again, so unscrewed the secondary as well and it eventually died. The silence was unbloody belivable !!

I would like to ask any more experienced members of this forum for their advice on where to go from here. I need to know correct positioning of both of these as I am not sure if they have been touched before I even look at things like the shutdown solenoid. (this was checked when installed and was working but not checked with motor running)

Also need to know if Detroits need bleeding at the injectors if they have run dry of fuel

As you may appreciate something like this dents your confidence in your equipment and yourself, would not recommend it to those with weak tickers

Any thoughts ?

 

[Willis Bushogin]

Brings back old nightmares
Yes to the question about bleeding the injectors, just crack the outlet line on each injector and crank over until you see good fuel, then go to the next one beside it and on and on
Im not real familiar, with the governor on your setup, but Im sure it has a buffer screw, if your guy turned it all the way it, it could cause it to do this
If you have a stuck injector, it will cause this, check to see if the fuel rack is free, when you manually rotate it
I have never worked on a Detroit with jake brake, but I can tell you you need someone that knows what they are doing on this engine. Its not many young guys out there with 92 & 71 experience, look for and old timer, like me and Atco Willie

 

[willie59]

Yep, panic is a good way to describe that busman. And like Willis said, a number of things can cause that, and it's not possible for us to guess just what the cause is as we have no way of knowing what former wrench bender tinkered with, and if he monkeyed around with the governor adjustments, oh boy, fun getting everything back in order. Think I would do what Willis suggested, remove valve covers and check for free movement of fuel racks, would also consider disconnecting the installed shut down and high idle solenoids until you get things sorted out. Lastly, before you attempt to fire it off again, clamp some vise grips on rack control arm under valve cover. Don't start from driver seat 40 ft ahead of you, rig up a remote starter button to connect to starter, then you can crank it right there at engine, control engine speed and shutdown with vise grip on control arm, until you get things sorted out. Hope that helps.

 

[Zed]

The jake brake switch on this engine is actully in the buffer screw, it hangs out the back of Governor housing, and has a full thread on it with lock nut. When adjusting the racks on these you need the buffer screw wound all the way out. The buffer is the last thing you adjust after everything else on a Detroit. it basically stops the engine hunting (smooths out idle). There should be 2 levers on governor housing, one is shutoff, the other should be throttle. Disconnect the solenoid and cable from shutoff and throttle, so you can move them backward/forwards by hand. Remove rocker covers. Now while looking at the racks, you should be able to pull the shutoff lever and the racks should move OUT, away from injectors. If they dont do this, there is something wrong! They should move a long way, maybe 1/4" from inside of head casting. If you don't know how far out the no fuel position is for the injectors, remove the governor to rack rod pin, at front of rack, then there should be 2 mounting bolts on either end of rack, you need a 1/4" socket, 1/4" drive to get these bolts out, dont drop them down drain holes into sump... After you remove the rack, move the injector control in and out. out is no fuel, in is full fuel. While you are looking under rocker cover, check all your rocker gear, valve bridges, for any damage.
It sounds like this needs a full tune up to get it sorted, but if this guy screwed the buffer in too far, the thing will rev and the shutoff wont do anything.
The buffer will overide the governor, so if its wound too far in, the governor wont pull it back. We used to check for full fuel on the dyno by using a tool that screwed into where the buffer was, and we could "dead rack" the injectors by pushing it all the way in, to make sure the governor was giving it full fuel.
You don't need to bleed injectors, in fact this is a bad idea because it can lead to fuel leaks at the injector lines, which will cause fuel dilution in the engine. These things will start on just a sniff of fuel, and all you have to do is take the fuel line off the secondary fuel filter and pump fuel through the heads. older engines have flared end fuel lines, newer engines have fuel lines with orings. There is a special tool for tensioning flared fuel lines.
There should be a tag on the governor housing that tells you what it is, yours should be a LS (limiting speed) for that application. Limiting speed governors only govern low idle and high idle.
Let us know how you go with this, if you need more help I can try to get hold of procedure for tune up.
I used to work for Detroit Diesel Australia, and have a fair bit of experience with the old 2 strokes.

 

[busman]

Hello guys and thanks for your replies, I have learnt a lot since this incident.
My suspicions have been proven correct, the buffer screw (with the Jake switch) was screwed in further than it should be as was the screw at the rear of the govenor box (which I think is to hold the racks slightly forward for easier starting?). Buggered if I know why he played with these, his brief was to mount 2 solenoids on top of the govenor box, 1 for shutdown, the other for fast idle.
Have a mate who has a similar coach (only couple of months apart) so I rang him and got him to measure the thread sticking past the locknut for each of the two. For instance, on the rear screw, I believe this is the one that did the deed from the above post, his had 9mm sticking out, mine had 2mm. So, just as a rough guide we had a starting place.
Backed off both screws to similar (bit further actually) amounts of free thread and hit the button, after filling both filters with dieso.
Spun over about 10 revs and boom, away she went, didn't have to bleed.
Funny thing is, motor is now quieter and sounds "sweeter" than before. Oil pressure is also slightly higher. Ran it until was hot and now have suspicion the temp sender is dud so new one on the way. I am mystified why the oil pressure is slightly higher, it was the first oil change so maybe was just the new oil ? or maybe there is a whole hea

 

[busman]

Ooops sent off above without finishing my post.

Seems was not runaway, but more wrong settings, at that level of noise and panic not much difference !

What I was about to say was, maybe there is a heap of crap scooped off the internals, that has filled the filter, maybe that accounts for the slight oil pressuer increase ?

Will wait till I have new sender unit and do a couple of oil/filter changes back to back to be certain. Have also sourced a tune procedure, as it is "sweet" at the moment will wait till unit is rego'd then find myself an old time DD mech to do first one while I look over his shoulder. Pity you are in Indonesia Jed !!

Cheers