The diesel shop that did the dynamic timing for me had set the timing mark retarded about 4* from the static timing mark. Milage dropped 33% and the engine ran hot so I've been trying to re-set the timing to the old setting, which was advanced, but the first problem is I didn't mark the old setting before I took the truck to the shop. To try to find the old setting I've been advancing it in 1 degree increments from the static mark and taking test drives. The second problem is I don't trust my bad hearing to help much with tuning the IP on my 7.3 turbo and I don't feel I've found her sweet spot yet. Power seems to be improving a little with each advance.

Last night I moved the adjustment to 4* advanced from the mark. She started and sounded just a little rough until she warmed up and then she seemed to be running really smooth but I couldn't decide what I was hearing when I put her on the highway for a test drive so I turned around and parked her. I've read about guys claiming to have their timing set 6* advanced but I relize that doesn't make it safe. If the static mark is 3 1/2 degrees ATDC +/- then advancing 4 degrees from the mark should set the timing to somewhere around TDC to 1* BTDC which would seem to be safe but I sure don't want to be buying another engine.

1. What is the maximum amount the timing can be advanced from the static timing mark before there is a risk of power stroking the pistons?
2. At factory settings how many degrees does the timing advance going from idle to maximum rpms?
2. What are the maximum safe degrees BTDC these engines can operate at and not risk power stroking the pistons and does this number vary with the engine rpms?

Thanks!

Don

 

Here's an update. I went to set the timing back to 3* this evening (the last smooth running setting) and found that instead of having it advanced from 3 to 4 degrees yesterday I had jumped the advance to 5. What likely happened was that I set the dial calipers to .o6o to mark 4 degrees of advance and didn't lock the set screw which allowed it to open up while I was making the adjustment and then didn't recheck the setting when I was done. With a good caliper and a big magnifying glass I feel the timing can be set accurate to +/- about 1/4 degree.

This evening I reset the timing to 4 degrees advanced from the static timing marks and made the test run. She seems to have excellent power and sounds and feels really smooth but the low speed idle has climbed from 650 rpm to 700. I'm still hoping someone with experience or book knowledge will comment on this post.

 

Back when I worked at a gm dealership and the 5.7 diesel was alive, we had a service school on that engine, anyhow on the higher milage engines (if they made it) they recommended to advance the timing the width of the allignmemt marks to offset wear on the gears, whenever I did that it made a noticeable difference. I dont have the acess to the International technical material to answer your questions but someone will be by soon

 

I haven't measured the width of the marks on the 7.3 but I would guess that to be about 1/2 degree. They are wide enough that with my magnifying glass I can easily see when the edge of the caliper jaw is centered on the mark. I use the magnifying glass because don't have a close enough focal length on my reading glasses.

The timing marks on these 7.3 IP's isn't an accurate indicator of the true timing which is part of why dynamic timing is recommended. I have a note of the margin of my Haynes manual that states the static timing is 3.5* ATDC +/- 2* but I didn't list the source of the information and I don't recall where it came from. With a 4 degree range the static timing marks are only a starting point for setting timing. They are in the range that will get any 6.9 or 7.3 running but they aren't the optimum setting unless a person just gets lucky.

The assumption I'm making, based on my initial setting and the results of advancing 1 degree at a time, is that the timing on my engine was on the retarded end of the scale. ie 5 1/2* ATDC which means the 4*advance I'm set at has resulted in a true setting of 1 1/2* ATDC which is the other end of the timing range.

I can't prove that setting but the information I'm looking for would help me understand the risks associated with my method of timing. If I'm off by even 1 degree am I at risk of doing major damage to my engine or is there an acceptable margin of error? Is advancing the timing in 1 degree increments too much or should I be using 1/2 degree increments? What affect does adding the turbo have if any? Has anyone visiting the forum succeeded in achieving optimum performance using this method?

Lots of questions. Even just a couple of answers would help.

 

I am running about 7 to 8 degrees BTDC.
When the cold timing advance and high idle is on, I have a PS rattle sound to the engine. Once it kicks off the rattle is gone.

Power is good, which is more important to me than fuel mileage is.
The engine is very smooth through the entire RPM range.

I am using 93 or 94 IDI turbo fuel system parts on my 6.9. So the timing is set by the late model method, not the luminosity probe method.

 

Thanks Dave! That rattle when the cold timing advance is on sounds like it may be what I was observing at the 5 degree static setting. She was running smooth but sounded different at the higher rpms and my hearing isn't good enough to identify what was going on.

What rpm are you running when you set your timing and do you have an estimate of how much the timing may have advanced from the static setting at those rpms?

 

Warm idle 650 RPM
Cold idle is 800 RPM

Cold advance is 2 degrees

 

My search for information on timing advance has uncovered some important information for anyone wanting to mess with static timing. I knew there were some risks involved buy I didn't understand their magnitude. I'd like to share what I've learned with anyone else wanting to play with their timing.

1. The original stamp on these pumps and the housing was placed after the engine has been tuned. The factory tuning was usually conservative but most importantly the stamp was intended to only be a starting point for resetting the timing if the pump was removed for any reason. This stamp can also be used as a starting point if the pump is replaced but the stamp on a replacement pump and the stamp on your engine housing are 2 separate stamps and they were never intended to match.

2. Even if the same pump is going back on and the marks are set back to perfect alignment. one test found that the timing can vary by as much as 5 degrees anytime the bolts are loosened and the pump is jiggled. This probably explains the earlier information I had about the static mark haveing +/- 2* accuracy. 5 degrees is a really significant margin of error for a person trying to advance or retard the timing a given number of degrees by using the static timing mark as a reference point.

3. If you are good it's probably safer to time by ear than by measuring advance from the static timing marks but even those with a talent for using this method have listed variances of 2* in their settings. For a recreational mechanic with bad hearing and/or no ear for engine performance, dynamic timing like the guru's recommend is the way to go.

 

Pay a little now, or a lot later.

I have been around diesels for 40 years, and I have timed mine by ear many times before.
But like you my hearing is going somewhere I am not at.
The tenitis crickets are getting so loud I have a hard time hearing a phone ring and people talking.

I probably should get my engine dynamically timed when I get it back together, because I don't trust my ears any more either.