Originally Posted by qwerty (Post 3054634)

A-B lights use a reference point at 15 ATDC which corresponds to an actual start-of-delivery at 24 BTDC.

Originally Posted by Brian Carlton (Post 3054687)

No, it doesn't. The one drop per second just occurs at 9 degrees early.

Originally Posted by Brian Carlton (Post 3054687)

See, I can also confuse the forum and post irrelevant info for no good reason.

Originally Posted by qwerty (Post 3054868)

If you choose to use the term "timing," I would submit that you need to specifty the specific event being described. In the absence of any qualification, I suspect that the typical reader would infer that you are referencing start-of-delivery.

Originally Posted by vstech (Post 3054564)

oh, I think I see. the a-b light measures to the ATDC setting, which lines up perfectly with the pulse of BTDC... I get it.

Originally Posted by Army (Post 3054644)

I'm interested to hear if you've got a reference for the difference between the start of delivery and the point of delivery when the injector lets go; at engine revolutions below the interaction of the timing device.

I've been trying to find one for ages.

Originally Posted by Brian Carlton (Post 3055231)

You and I have spoken on this exact subject in the past and the information was provided to you at that time.

Either you have forgotten it or dismissed it..........

Originally Posted by Army (Post 3055333)

But nevertheless I still am at a loss to understand why the FSM would talk about "dynamic timing" and even go so far as to include another section describing how to set up the position of the tachometer probe on the front of the OM617 so that that too can be used in the process of "dynamic timing"; and yet not supply the basic data that says it should happen at XX degrees BTDC at XXX rpm.

It has got to be written some where => that's what I want to find!

Originally Posted by Brian Carlton (Post 3055388)

At the time the vehicles were developed, I sincerely doubt that the equipment was available to economically measure a pressure pulse from one of the injection lines.

The M/B reference to dynamic timing is interesting, however, I don't believe they were referring to the type of system that uses a clamp to one of the injector lines.

If you can find it, I'd sure be interested to see it, but I don't have a lot of confidence in that. Remember that M/B developed the A-B light in 1984 to eliminate the problems with the drip timing approach. If they had another method, why bother?

Originally Posted by Army (Post 3055392)

...the method detailed in chapter 7-108 is what I guess has caused the confusion! (Well certainly my confusion!) This is a dynamic method but it is still using the A-B timing functionality and not a clamped on the injector line sensor.

I'm guessing that somewhere this information exists as the A-B light method is pretty much out of date - I can imagine that most diesel garages would be using sensors on injector lines... I'm going to see if the dealer will tell me! Perhaps there is something in WIS. If I find it I'll let you know.

(This kind of information isn't by any chance available for more modern engines is it?)

Originally Posted by Brian Carlton (Post 3055394)

I believe you're referring to the "RIV" method of checking IP timing. That method requires another piece of expensive equipment and I'm not real clear on exactly how it functions.

I'm fairly sure the A-B light has become the standard for any independent shop. It's very fast and relatively cheap. The only problem is for vehicles that were built before 1984. In reality, they are getting to be a very small fraction of the business of an independent (an non-existent for a dealer).

Originally Posted by Army (Post 3055392)

Thanks for your response Brian. I spent a bit of time this morning combing my way through the FSM.

From what I can gather together there are two ways of using the A-B timing light method:- in the OM617 turbo part of the FSM there's the static way described in chapter 07 -111 and 07-116 => this is essentially turning the crank by hand until you get the desired position annotated by the A-B light box. But there's also chapter 07-108 where you do the begin of delivery check with the engine running...

...the method detailed in chapter 7-108 is what I guess has caused the confusion! (Well certainly my confusion!) This is a dynamic method but it is still using the A-B timing functionality and not a clamped on the injector line sensor.

I'm guessing that somewhere this information exists as the A-B light method is pretty much out of date - I can imagine that most diesel garages would be using sensors on injector lines... I'm going to see if the dealer will tell me! Perhaps there is something in WIS. If I find it I'll let you know.

(This kind of information isn't by any chance available for more modern engines is it?)

Originally Posted by Army (Post 3055455)

Perhaps another dimension of confusion is that the FSM uses the term RIV in each of the titles of the three chapters to which I referred?

As far as I can make out the additional bit of expensive equipment is a glorified tachometer that also monitors the position of the IP. There is a section in chapter 07-010 going on about RIV which means "Reference Impulse Verification" apparently.

In all of these RIV tests they seem to depend upon the IP being set up correctly in the first place. Much like the lug on the front of the crankshaft {that is used by the tachometer} another lug is fitted to the IP governor. This box of tricks just calculates the "chronological distance between the two pulses" (see chapter 07 - 010 again). So it is possible, for example in the situation of wear or poor adjustment, for begin of delivery to be happening at a different time - no matter what them there lights of the box of tricks says.

A "point of release" measurement seems to me to be a more desirable method of measuring.

Originally Posted by Diesel911 (Post 3055702)

Yes, the A&B Light, the RIV Method and the Timing Locking Pin all reference a projection on the Camshaft and assume the rest of the IP is timed correctly. There is no compensation for wear that would change the begin of Injection.

On the other Hand the Drip Method or any Impulse Method that clamps on to the Injection Hard Line only references the #1 Element.
It is sort of assumes that the Tappets, Rollers and Camshaft that move the other Elements are worn the same as the #1 and of course that may not be the case.

None of the Methods is perfect.

In the Manual you can check one of the other Elements to see if it drips the proper amount when it is supposed to. I am guessing you can only do one other Element because the degree markings do not go all the way around the Crank Damper. Otherwise it would be possible to check all of them.

Then there is the issue if #1 is OK and the others are not what do you do about it?

Originally Posted by Codifex Maximus (Post 3055768)

Yeah, yeah, I used to use acoustic timing on many of my old gasser cars. Loosen the distributor lock down bolt, turn the distributor until the engine sounded strong and lock it down.

Static timing on old VW's.

Timing lights are for sissies.:P