Timing adjustment methods
 

Hi all,

I have a question regarding injection timing adjustment methods. In the Haynes manual, it instructs to use the drip method. I talked to one of my friends who is a 3rd generation diesel mechanic (not a weekend mechanic like myself) and he was very much against the drip method, citing that it can be very inaccurate compared to using a diesel timing light. I always cross reference anything I hear or read regarding Mercedes diesels with this forum, so I am interested to hear what peoples' input is about the drip test vs. using a timing light.

Thanks!

Bryan

If you have a diesel timing light.. which I assume also involves the sensor which clamps onto the metal injection pump line ... go for it.
If not, the Factory Shop Manual shows using the drip method to set the IP.
Do not use the ' bubble up ' method... at least drip size has some basis in physics in order to standardize the procedure... ' bubbling up' does not.
All this stuff is well discussed in the archives also...

where can I get a factory shop manual? all I have is the Haynes, which is helpful, but I would like some more detail. My other vehicle is an 89 Dodge w250 diesel, and I have the two volume factory service manual for it, which is extremely helpful.

Gosh, I just time by ear and double-check my work with the butt dyno.
If I wanted to get real fancy I'd borrow a G-tech and fine tune some runs for optimal 0-60 times, but meh... it's not a race car.

The '85, unlike the older engines, has a port on the side of the IP to allow the use of the OE factory tool commonly known as the "A-B lights". This simple device has a pair of lights that signal when a reference point inside the IP reaches the probes and closes the circuit between the two lights. At this point, the IP is at a known position. This position should be 15° AFTER TDC on the crankshaft.

Random Thoughts:
I am not speaking about the A-B lights; but from what I have read about the generic Diesel Timing Lights You have to already have your Fuel Injection Pump timed correctly.
Hook up your Timing Light and see what it does.

Once you have the specs you can now use them the next time you use your Diesel Timing Light.

As far as Drip Timing not being accurate; at least in the past all most all inline Fuel Injection Pumps were Drip Timed (Flow Timed). The exception is where some companies use a Timing Pin (CAT does this).

When an inline Fuel Injection pump is rebuilt each one of the Elements is drip timed to the proper degrees of Fuel Injection Pump Camshaft rotation before the Pump is calibrated. The exception is where some companies specify a Dial Indicator or Depth Micrometer reading ad such-and-such Camshaft position (CAT does this) on the Element Plunger.



The inaccurate part of Drip Timing comes from the manuals not being entirely detailed about the procedure and not keeping a constant Fuel Supply pressure.

Also it requires a little understanding of what is going on inside the Fuel Injection Pump concerning the Begin of Injection how that is related to the x number of drips per second when you time it.

And, then there is that it may just take some practice.

I think another problem with doing a Drip Timing for the first time is that people simply rotate the Fuel Injection pump too far or turn it the wrong direction and sort of get lost for a while (put some reference marks before you rotate the Fuel Injection Pumps so you can get it back close to where you started).
Assuming that your Fuel Injection Pump is a few degrees late in timing due to Timing Chain/Gear/Stretch/Wear the Fuel Injection Pump only needs to be nudged a little bit in rotation to bring it back into timing.

Greg
The bubble method was described by the late Marshell Booth" as being "more accurate than it needs to be"

I agree with your whole post.. but this is really true. The FSM does not give a pressure needed or a way to get that pressure.. At one time we discussed putting a can of diesel a specified number of feet above the IP to try to standardize this procedure.

"The bubble method was described by the late Marshell Booth" as being "more accurate than it needs to be"----Stevo

Well Stevo, all I can say is that according to my analysis of the physics involved..And the fact that the people who MADE the car suggest the drip method...I am sorry he died holding onto that opinion..and sharing it with others..

The flow rate which causes similar viscosity fluids ( hopefully exactly the same grade diesel--- but temperature will have an effect also ) to form drips is way more accurate and reproducible in trying to duplicate the size of the opening in the IP than spill rate or bubbles bubbling up from a hole.

If that was true that that method produced ' excess' accuracy... then think how close to perfect we can get it using the FACTORY SHOP MANUAL APPROVED METHOD....

Another way to look at Drip Timing is that if done correctly it has a long history of being proved entirely adequate.

Drip timing has proved challenging enough to some that they have looked for easier methods to do the timing.

Which one of the timing methods is the most accurate is going to depend on how well the person who is doing the timing does the job.

So far no one has mentioned using the Fuel Injection Pump Locking Pin/Screw (if your Fuel Injection Pump is set-up to use that). If you are looking for the easiest way to time your IP it ought to be as accurate as the AB Light.

The A-B light is the most accurate.

Period.

Can you use this method on all OM616 and OM617 injector pumps?

EDIT - or are we talking about 60X engines?

Unfortunately, no.

1984 was the first year that the port was available on the side of the IP, to my knowledge. A few late '83s might also have it.

The OP has it and that should end all discussion for him. Anybody who has used both methods (few on this thread) would realize this.

Oh well that's me and the drip then - thanks!

Greg, I'm sure your "analysis of the physics involved" in the IP timing procedure is more accurate than that of Dr Booth's, but here is a copy of page one of his five page post on IP timing. Anyone with a spare IP can easily try this on the work bench. But of course if you believe nothing outside the FSM is valid...;)


Date: Wed, 03 Jul2002 12:36:38 -0400
From: Marshall Booth <mbooth+@pitt.edu>
Subject: Re: [DIESEL] IP Timing
Mike, Here are several ways to time the pump (its almost NEVER out of
time except by about 1/2 the amount of chain stretch you have and that
usually isn't any problem until the chain needs to be replaced). The
bubble method is the easiest!
I'll include all 3 WAYS that I know of to do it.
> Bubble method!
>>
On the subject of diesel timing. If you are replacing the pump or
> rebuil~in~ t~e engine. The si~plest ~nd.m.ost accurate. way of setting the
> pump IS. \R.!?connect the fuel line gOlng).Q!Qt.he.EumQfrC?mthe filter. ,
> Take the spring and plunger out of #1 delivery valve, put the delivery
> valve back in and snug it down, hold the the pump linkCjlgein the full
> open position. If you have the drip tube install it on the delivery
> valve, if not use the injector line in such a way that it is pointing
> away from the engine. It you don't mind the taste of diesel you can blow
> through the fuel line or use low air pressure. Put the open end of the
> injector line in a glass of water and watch the bubbles. Turn the engine
> slowly until the bubbles stop and check the timing mark. After
> tightening the pump recheck. This method is really more precise than it
> needs to be and although it may sound complicated it is very easy.

>
>

It is not unusual for people to run across someone they elevate to ' Guru ' status ...then accept what they say not matter what evidence is offered to the contrary.

Why did you not address the ' flaw ' in my description of the physics of being able to reproduce the flow rate on other IPs by utilizing the amazing uniformity of size of drops formed by the same viscosity fluid at different locations ?

Why would those people WHO MADE THE CAR risk their reputations by recommending in the FACTORY SHOP MANUAL the drip method IF some other easier more accurate method was so obvious ?

Does not compute.