1993 mechanial db2 timing

[HGM]

Good day, I have a GMC 6.5TD extra cab. Runs well with a new Standadyne IP which I have timed by ear. It runs well. Good mileage and power. I have come across a Snap on MT480 lumosity timing meter and utilized it and it says 8 degrees ATDC. Does anyone have any experience with this type of meter. I have done a search on mechanical IP timing via Diesel Page and the internet and have found little info on timing these engines or the use of this MT480. thanks for any info in the future. HGM

[Robyn]

Hi there.

I have used these units years ago on a couple 6.9 Fords but not on a GM engine.

The 8 after TDC makes me wonder.

The unit I have used, come to think about it had the pulse sensor on the number one injection line and not the Lumi probe.

Here is the long and short of it.

If the cold starts are good and clean and the thing runs good, your probably right in the sweet spot.

If the timing is too far retarded the engine will smoke a lot at idle, even when warm.

The lumi probe has to sense light (ignition flame) to trigger.

Does your fresh IP have a reference mark on the housing??? and if so does it come close to the original mark on the timng cover.

Generally the only timing reference is to line up the marks on the IP and the cover.

I have a 93 book and it does not say anything about the IP timing other than to line up the marks.

If the rattle is not nasty and the Exhaust gas temp is good, run it.

Every time I have done an IP on 6.2/6.5 with the DB2, I made sure the marks were clearly visible and had the IP rebuilt, so it was only a matter of aligning the marks.

Good luck

Missy

[Robyn]

Here is a link to an interesting article on using the Snap On meter to time the 6.2/6.5

Seems that you use #3 cylinder ???

Read the article and see whatcha can get from it. :)

http://www.oliverdiesel.com/tech/timing.htm

Good luck

Missy

[HGM]

Thank-you for response. I am bewildered. I have worked on cars my whole life professionally. Timing is probably one of the most integral portion of tuning a car. I have dial indicators for VWs, drip tubes for Mercedes and found a Snap on MT480 for this GMC. Talking to co-workers, other shops, looking the internet, pulling through mechanical books and data systems have really provided nothing. I did pull up the Oliver article quite a while ago and spoke with a friend who is a Snap on dealer and he said the MT 480 never worked consistently. It was replaced by the MT 1480 a digital version of the earlier MT 480 which met a similar fate. I have a good ear and know it runs well but I would really like to know how the factory set initial timing from the line. Anyone have an idea how or what is used. The best I can imagine is a pulse pick-up with a harmonic balancer timing pick-up over the timing mark. The IP has marks and it runs best 1/16 advanced on the marks. thank-you