dynamic timing: ford vs navistar?

[siegler]

I was looking through the engine manual I have for the navistar 7.3 idi, and I noticed that navistar specifies that the engine be dynamically times to 3.5*+/- 2* before top dead center at 2000rpm. Ford specifies 8.5* +/-2* at 2000 rpm.

Both navistar and ford specify a kent-moore tach-n-time (j33300 it would appear) with the pulse adapter supplied on #1 or #4 injector, 20* offset and magnetic pick-up in the upper hole by the vibration dampener.

Why the different specs?

 

[icanfixall]

I bet the information you posted is confusing the pulse and lumi method of timing. When timing by the luminosity probe in the number 1 glow plug hole you rev to 1400 rpm and time to negative 1 or 2 degrees. I'm really no expert on lumi timing but it is very different from pulse timing. Pulse timing uses the clamp on number 1 hard line and the mag probe in the damper tab. Set the 20 degree offset and rev to 2000 rpm. Set to 8.5 plus or minus 2.5 degrees. This is also known as the clamp method of timing.

 

[siegler]

I bet the information you posted is confusing the pulse and lumi method of timing. When timing by the luminosity probe in the number 1 glow plug hole you rev to 1400 rpm and time to negative 1 or 2 degrees. I'm really no expert on lumi timing but it is very different from pulse timing. Pulse timing uses the clamp on number 1 hard line and the mag probe in the damper tab. Set the 20 degree offset and rev to 2000 rpm. Set to 8.5 plus or minus 2.5 degrees. This is also known as the clamp method of timing.

That's what I thought at first too. But the Navistar manual does specify 3.5* btdc via pulse method at 2000rpm. The procedure in the Navistar book is exactly the same as the ford procedure. Just different spec.

 

[riotwarrior]

Likely cause IH is detuned lower revving beast IMHO ...

 

[siegler]

Likely cause IH is detuned lower revving beast IMHO ...

specs say 170hp @ 3000 rpm for navistar vs 180hp @ 3300 rpm for ford in 1988.

Doesnt sound THAT detuned. Maybe if the navistar were allowed to rev to 3300 rpm it might make 180hp too?

 

[riotwarrior]

Governed to 2600 iirc....ours 3600...

So not sure...also woukdnt be as peppy likely and run up to rev as quick....

HP means crap....what is the TQ ratings...

 

[siegler]

no torque output listed in my specs. This does though:

http://www.arb.ca.gov/msprog/onroad/cert/mdehdehdv/1990/navistar_lhdd_a0040129_7d3_6d0-0d6.pdf

The A130, A155 and A170 are listed in my book. 332 ft/lbs @ 1600rpm for the A170

ford lists as having 345 ft/lbs @ 1400rpm.

That does make the navistar seem a little more gutless.

 

[riotwarrior]

@Agnem

Whats yer take on differences in timing?

 

[FORDF250HDXLT]

I was looking through the engine manual I have for the navistar 7.3 idi, and I noticed that navistar specifies that the engine be dynamically times to 3.5*+/- 2* before top dead center at 2000rpm. Ford specifies 8.5* +/-2* at 2000 rpm.

that's extremely difficult to believe that retarded as much as 1.5 BTDC could be within spec for a 7.3l idi engine.this is very interesting.could you scan the navistar page and post it for us please?
scan the book cover too would ya?

my very first inclination to your post was; this guy found a book with a typo error.

 

[FORDF250HDXLT]

I bet the information you posted is confusing the pulse and lumi method of timing. When timing by the luminosity probe in the number 1 glow plug hole you rev to 1400 rpm and time to negative 1 or 2 degrees.

Gary,i hope you don't mind but with all do respect,iv got to correct your statement.timing via the lumy method is actually around 4-7 degrees ATDC (depending on fuel cetane value and elevation)

the reason i wanted to correct you is because i too have read those low numerical numbers posted in older posts on various idi forums and found it very dangerous and harmful to set my truck at those numbers (back when i used to time via lumy) it was clearly far too advanced and i could tell by the sound it would damage the engine if left there for any amount of time.

here i'll attach a pic showing a chart that matches several charts found in various books from the era.

this isn't so important these days as there just aren't many folks around who time via the old school method anymore but, just in case someone picks up an old meter cheap and then stumbles upon this thread looking how to time with it,i just wanted to post the correction.

 

[siegler]

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[FORDF250HDXLT]

that's interesting as all get out.my guess is it's a typo error.the 3 was misread/misprinted/transferred incorrectly from an "8" to a "3".
even though i see the typo on 4 different pages.this is my best guess.

(i have seen both 8 +/- 2 degrees BTDC & 8.5 +/- 2 degrees BTDC before)


if im correct and it's a typo.i feel sorry for the owner of any of those medium duty trucks back in the day because if their mechanics set 'em to those spec............they must of been some slow crawling rigs up any ant hill.

thanks for sharing.very cool! hopefully others here have some other opinions,facts,views, or guesses too.

 

[icanfixall]

Gary,i hope you don't mind but with all do respect,iv got to correct your statement.timing via the lumy method is actually around 4-7 degrees ATDC (depending on fuel cetane value and elevation)

the reason i wanted to correct you is because i too have read those low numerical numbers posted in older posts on various idi forums and found it very dangerous and harmful to set my truck at those numbers (back when i used to time via lumy) it was clearly far too advanced and i could tell by the sound it would damage the engine if left there for any amount of time.

here i'll attach a pic showing a chart that matches several charts found in various books from the era.

this isn't so important these days as there just aren't many folks around who time via the old school method anymore but, just in case someone picks up an old meter cheap and then stumbles upon this thread looking how to time with it,i just wanted to post the correction.

No problem correcting me. I encourage this all the time. I really do not know enough about the lumi method of timing. What I find bothersome is reading any kind of misinformation about anything. In this case I have no idea why this particular publication printed this. It reminds me of the published information that the turbo idi block has main webbs that are 100,000 wider than the non turbo blocks... So where do these measurements come from. Having seen the insides of turbo and non turbo blocks I have no idea where to measure. Clearly it can't be a non machined area. BTW ALL idi engines take the same width main bearings as do the same with rod bearings. Makes it nice to be able to buy one part that fits every idi engine too..

 

[bbjordan]

Has anyone compared pulse to lumy timings?

 

[riotwarrior]

Has anyone compared pulse to lumy timings?

No however...send me a J33300 lumi Probe...and I will add it to th various timing threads I have....

Need 1 just fer that reason...

Comparred J33300 to J33300A to two timing lights...to timing tape on all 4......really lumi and the fox pulse adapter are all thats truly left for me to compare....locally there are 5 IDI i can set up to play time my truck.....


Jjst sayin