Diesel Injection pump

[Marqus]

I am about to set the timing on my injection pump, and the instructions I have are not all that clear, so I have a rather basic question regarding the internals of injection pumps.

Diesel injection pump - rotary style (being Bosch VE, but question is generic).

My engine, a 3-cyl four stroke diesel. Each fuel injector squirts once every two full rotations of the crankshaft.
(For a 3-cyl, this ends up being once every 240 degrees of crankshaft, but that's not so important).

"If" the injection pump were rotating at the same speed as the crankshaft, it will have to be smart enough to only inject three times every two rotations of its own shaft, instead of three times every single rotation of its own shaft (mechanically much simpler).

Question:
Are injection pumps that smart, or are they dumb and will simply squirt fuel 3 times per single pump-shaft revolution (for a 3-cyl pump). So it's up to the engine's gearing rations to ensure that the injection pump is driven at half the speed of the crankshaft ?

[a64pilot]

I have only seen injections pumps that are driven at half speed, just like a camshaft is. Only ones I have timed were stupid easy to time, IE install a lock pin in the hole in the block that went into the flywheel, open the "window" on the pump and install so the marks were lined up in the window or similar

[River Cruiser]

The magic is in the timing gears, 2 turns of the crank = 1 turn of the injection pump.

[Marqus]

Originally Posted by a64pilot

I have only seen injections pumps that are driven at half speed, just like a camshaft is. Only ones I have timed were stupid easy to time, IE install a lock pin in the hole in the block that went into the flywheel, open the "window" on the pump and install so the marks were lined up in the window or similar

Thanks.
This one seems a bit more involved. You're supposed to mount a dial indicator, then reverse the flywheel and find a "flat area" on the injection pump's cam plate. Then advance the flywheel closer to TDC and monitor how far the injection plunger is being pushed outwards.

If it is not per spec, I think you're supposed to "un-mesh" the injection pump's drive gear and advance it by a few teeth, then re-run the procedure to see if it's closer, etc.

[Marqus]

Does not seem that that it will be easy to set my injection timing as per spec (dial indicator procedure), mostly because I am doing it with the engine in the boat (can't extract it for the time being).

So, if I cannot get it on the money, which side is it better to err on: timing a handful degrees advanced, or a handful degrees degrees retarded?

I have read that advancing the timing too much can lead to knocking noises, while retarding timing can lead to elevated exhaust valve temperatures, but I don't really have expertise in this area.

If I can't get injection timing spot on, any opinions on which side it is better to err on?

[a64pilot]

I'd say slightly retarded. You are spot on in your observations too.

[hpeer]

You didn't remove the gears did you? The ones that connect the fly wheel to the pump shaft? Don't ask why I ask.

[Marqus]

Thanks A46pilot.

Originally Posted by hpeer

You didn't remove the gears did you? The ones that connect the fly wheel to the pump shaft? Don't ask why I ask.

No, only pulled the injection pump drive gear.

The intermediate gear that drives it was not moved, and since it also drives the camshaft gear, I think I get what you're saying about not disturbing the cam timing.

Actually, the reason I'm in this timing bind while the engine is inside the boat (difficult access), is because the injection drive gear actually fell off its shaft. Yes, hard to believe. The "nut" that holds it on the conical injection pump shaft, unscrewed itself during normal engine operations and fell off.

Fortunately, the only physical damage was to the shaft key, because the engine stopped pronto (no choice, if you think about it).

So, if I can get this injection pump timing more or less close, I'm wondering how to keep this freedom-fighter nut in place.

To use threadlocker (Loctite Blue) may create problems in future if the pump needs to be removed or timing needs to be adjusted (may need flame to undo it).

But what else can be done to stop this 1/2-inch nut unscrewing again.

Would using very high torque to set the nut (how high) alone be enough to keep it in place given the engine goes through heat up/cool down cycles?

[a64pilot]

You want to use either blue or green Loctite. It's the red (stud and bearing mount) that requires excessive force or heat to remove. Blue is good stuff and shouldn't be hard to remove. Not to sound condescending, but the way a bolt works when you tighten a nut is it actually stretches, like a rubber band. Excessive torque may over stretch the fastener and cause it to break in service. Can you get a star or regular spilt lock-washer under the nut?
Can you drill a hole through the nut and shaft and tap a roll pin in, or even safety wire? Sounds a little excessive, but it will hold the nut on.

[Marqus]

Originally Posted by a64pilot

but the way a bolt works when you tighten a nut is it actually stretches, like a rubber band. Excessive torque may over stretch the fastener and cause it to break in service.

Thanks A64pilot, clear you know what you're talking about.

The quote above is a bit of a worry, because before I read your e-mail, I had already installed the gear applying 50ft-lb torque and blue Loctite. I did not want this nut to drop off again, because it can wreck the timing and crackshaft gears in the process.

I did not really want to go in there and undo the nut again. So, does 50ft-lb on a 1/2inch nut means it is dangerously overtorqued and likely to fail in time?

Since the engine is in the boat and I'm working through a rear access plate, the position means its' hard to do anything like drilling in there.

[a64pilot]

It's done, so I wouldn't undo it. But to give you a truthful answer we would first have to know what is meant by 1/2" nut? Talking thread size or the size of tool used? If it's wrench size, then yes you put a LOT of torque on that shaft. It's what the shaft is made of, it's dimensions and the thread pitch used that would determine the "stretch" of the shaft. Fine threads will impart more pull per rotational force, think of a winch in low gear.
I'll bet it wasn't properly torqued to begin with and since you didn't wring it off, you'll get away with it

[Marqus]

Yes I should clarify - the thread is about 1/2inch at 13TPI, with the nut requiring a 3/4inch spanner.

In the attached a photo you can see the thread machined into the shaft of the injection pump. The threads were "lubricated" with blue Loctite when I applied the torque. Think it will survive around 55 ft-lb torque?

http://www.cruisersforum.com/forums/...1&d=1389491450

[a64pilot]

I think off the top of my head your fine. I want to think that .5" tq. value for a tension nut for aircraft is about 600 in/lb. You convert simply by dividing by 12, so if I'm right 600 div by 12 is 50 ft/lb. Plus all aircraft hardware is fine thread and I think that increases the pull put on a fastner. let me try to find a link to a tq. chart.

[a64pilot]

OK, here is a simple tq chart link.
http://mybearhawkpatrol.com/torque.htm people will point out, and they are right that this is for aircraft, but it ought to be close

[a64pilot]

I'd bet your real close to manufacturers spec for tq., and yes having the Loctitie act as a lube will increase applied force slightly, that's what is meant by wet tq., but still I'd bet lunch your fine, right in the ballpark is my guess.
Good thin you din't use German torque