Dynahoe engine rpms really high

Hi,

I just purchased an old dynahoe it starts great the only problem I'm having is when it's not underload and it's in neutral the engine starts to rev way up and I can't shut it off the conventional way. Also when it's cold it doesn't do this until it warms up usually after about 5 minutes.

Any ideas?

Thanks,
Brad

my guess is a bad seal in the super charger and it is sucking in oil.

Edward

You say you can't shut it off the normal way, so how are you shutting it off? While it could be sucking some oil past the blower seals, they usually run completely away, and there's no controlling them when they do that. Typically the problem your describing has to do more with a stuck injector. When the load comes off of the engine the stuck injector/injectors don't respond to the movement of the rack caused by the governor so they keep fueling high even when they should be cutting back to a lower fuel position. Then, on shutdown they aren't going to the no fuel position to allow the engine to stop.

Dependent upon the design of the rack the one that's stuck might be the only one staying 'on' or it might be holding all of them partially 'on'. If it was me I'd check the injectors before I did anything else.

NCWayne nailed it.

Thanks Wayne,

I'm shutting it off by the emergency kill device. Any idea how I check the fuel injectors to see if one or several are sticking or is that best left for a professional?

You can check by pulling the valve cover and looking at the rack and plungers that slide in and out of each individual injector. They should all be in the same position relative to each other. In other words if one is all the way in all of them should be the same, and if all are out all of them should be out.

If I'm understanding right, in your case you say the problem seems to start when it gets hot so you might need to run the engine to get it hot and then shut it down and pull the valve cover. In most cases you can then restart the engine and watch the rack when you hit the shut down lever. It might spatter a little oil around with the cover off, but as long as you don't rev it up it usually won't make a mess. If all of the injectors don't go to the no fuel position when you hit the shutdown, then a stuck injector is your problem.

If that is your problem you can change that one injector, but I really wouldn't recommend it. Usually changing just one puts more load on that one cylinder than the others due to the injector being clean, etc, and that's not really a good thing. To change them isn't that difficult as long as you have the info needed to do the job. There is one special tool/guage that is nice to have, but it can be replace with a depth mike or a good set of calipers with the depth guage feature if you can't get your hands on the tool.

Ultimatly you need a bare minimum of a manual for the engine to do much of anything. If you don't feel like it's something you can handle then by all means call someone that knows what they are doing because the injectors have to be timed to each other (with the rack) properly, and timed for stroke (with the special guage) or the engine will not run properly. Too, it would be a good thing to have someone basically make sure all of the governor adjustments, etc are all good too, in other words give it a tune up. So, really, if you have to replace any injectors, etc, getting someone that knows the engines and has the tools probably wouldn't be a bad idea anyway.

Good luck and if you have any more questions feel free to ask. Wayne

Wayne,

First of all thanks for the quick response I really appreciate you taking time to help me out with this problem. I'm going to take off the valve cover this weekend and investigate what you have explained with the fuel injectors. Also I traced the stop switch line down to a device maybe the governor but not sure (also where the throttle appears to go to) and worked the levers back and forth no change. My question is shouldn't this device stop the flow of diesel to the injectors. Sorry if it's a dumb question I'm just trying to gain as much knowledge about what i'm getting myself into. Again thanks so much for your time and knowledge.

Brad

Not a problem. I was going to explain things a bit further to you, but check out the link below for a really good explination of Detroits mechanical fuel system. It tells you pretty much everything you could ever want to know about how it works along with pics so you can see it also.
Hope it helps you when you go to look at it this weekend.
Poke here