IP Timing Confusion

[andyritter]

Hi everyone.
I hope someone can help me figure out this situation. I have an Avant built 6.2 with timing gears. The engine has 70k+ miles and runs pretty good but not perfect. I recently acquired a Snap-on MT480 timing meter and used it to check the timing. With the mark just a bit toward advance from TDC the meter indicated -3.5 degrees. I adjusted it further advanced - in fact as far as it would go - checked it again and got a reading of -5.5 degrees. So as I try to advance the pump timing it is actually retarding. I'm wondering what is going on here. I have used the meter to check another 6.2 and it showed TDC and the marks were exactly aligned, so I believe the meter is accurate.
Any insight would be appreciated. I'm not looking forward to opening up the front end to inspect the gears but don't know of anything else to do.
Thanks.

Andy

[More Power]

I'm not familiar with the operation of the Snap-On timing meter. However, negative numbers you're seeing probably mean before TDC. For example, a -3.5 reading probably means the injection event is occuring 3.5 degrees before TDC. :)

Jim

[andyritter]

I should have made that clear, but negative values are ATDC. Hence my confusion. Moving the pump in the advance direction, to the drivers side, caused further retardation.

Andy

[More Power]

Moving the top of the pump toward the driver's side advances injection timing....

Jim

[andyritter]

Right, but in this case the result was 2 degrees more of retardation.
The pump is now positioned as far toward advance as it will physically go - to the ends of the 3 slots - and the meter tells me the timing is 5.5 degrees ATDC.
I am wondering if my timing gears could be off by a tooth. If my math is correct that would amount to about a 7 degree cam timing error. Would the engine run somewhat "normally" under such a condition? For 70k+ miles? Seems unlikely to me but I really don't know.
Maybe I should rotate the pump back towards the passenger side and see what effect that has.
There is an inconsistency in this situation that I can't understand.
Thanks for your insight Jim.

Andy

[NH2112]

Do the MT480 instructions specify that - is ATDC and + is BTDC? I have an MT480 but it's not where I can get to it now to check. In any case, I'd think that a - reading is BTDC and + is ATDC since TDC - 5* = 355* (5* BTDC), and TDC + 5* = 5* (5* ATDC.)

[andyritter]

Phil, the meter display has the - values on the scale indicated as ATDC.
Do you have any idea what might be going on with my timing?
Thanks.

Andy

[NH2112]

Do the aftermarket gear drives for the 6.2l/6.5l use idler gears, or is the cam gear driven directly by the crank gear? If the latter is the case, then the effect of turning the IP will be opposite that of an engine with stock timing set because the IP drive gear will be turning the opposite direction from stock.

[DmaxMaverick]

Do the aftermarket gear drives for the 6.2l/6.5l use idler gears, or is the cam gear driven directly by the crank gear? If the latter is the case, then the effect of turning the IP will be opposite that of an engine with stock timing set because the IP drive gear will be turning the opposite direction from stock.
Yes. They use idler gear(s). It wouldn't work otherwise. A direct drive would require a cam and IP designed to turn backwards.

Keep in mind, the IP will rotate oposite of the crank and cam. The IP is driven directly (no idler or chain) off of the cam, with a gear in front of the cam/timing gear.

Also, if you have a serpentine belt, the fan (water pump) will rotate oposite the engine rotation. This means the fan will rotate the same direction as the IP. If you have V-belts, the only thing rotating oposite is the IP.

[More Power]

The idler gears (small intermediate gears) between the crank gear and the cam gear used by DSG maintain the correct rotation of the timing set.

What happens to the diesel engine combustion rattle when moving the IP?

Jim

[BobND]

Do the aftermarket gear drives for the 6.2l/6.5l use idler gears, or is the cam gear driven directly by the crank gear? If the latter is the case, then the effect of turning the IP will be opposite that of an engine with stock timing set because the IP drive gear will be turning the opposite direction from stock.

Here's a photo:

http://ndtc3500.stellarnet.com/~blweltin/Bob/DSGtimingMARKS.jpg

[andyritter]

The rattle does not sound as "crisp" as I think it should, but with 3.5 or 5.5 degrees ATDC it is probably about right.
I have been cautioned not to attempt to move the IP while the engine is running, so moving it and listening in several positions is a time consuming process I have not yet done. But, I guess I will have to do some moving, listening , and meter checking in order to figure out what is happening. Maybe if I move it around a bit I'll find a spot where it will actually be the 2.5 to 3.5 degree BTDC setting I am looking for. I understand that there is a lack of precision in the process but am still mystified by 5.5 degree ATDC metering with the IP in "full advance" position.
Maybe if I can get this resolved I can seriously consider the rendezvous this year. We were on the way to the one at Missoula a few years ago when a wrist pin bushing failed. Never made it but got to spend a few days in Rapid City.

Andy

[85-m1028]

I might be stating the obvios but the timming gears have a 3 degree timing advance built in right?? and you have to readjust the timing marks on the harmonic balancer

[andyritter]

I'm not aware of the 3 degree advance with the gears. That would change the cam and IP timing, right? That also means my timing is 3 degrees advanced of what the meter shows, right?

[NH2112]

One thing I forgot is that since the MT480 triggers off the actual combustion event, it's not unheard of to get an ATDC reading at idle. Testing with engine speed around 1400rpm should see you around 0* or maybe a few degrees BTDC. You may also want to try timing off #3 and using the 99* offset instead of #1 and 9* because sometimes 9* isn't enough time for the meter to do its thing.

[andyritter]

Phil, the readings quoted in my previous posts (3.5 degrees ATDC and 5.5 ATDC) were using #3 and offset, and at 1300 rpms.
I have not had a chance to move the pump around and take more readings. Hope to do that soon.
Thanks.

Andy

[britannic]

What settings are you using on the MT480 meter?

[andyritter]

I am using the tach setting of 1400 and offset B (99.5 degrees).

[Yukon6.2]

Hi Andy
I was watching your post to see if any info came on timing. I also got some strange readings.The last time i used my meter i got these readings,line to line on pump and cover were 4 ATDC.Pump moved 1/8" to drivers side got me 1 BTDC.
I used the snap on gauge to check the pointer on the cover by the balancer.
My balacer looked in good shape,i'm thinking that the outer ring may have turned on the rubber,even though it looks like new.
I'm going to pull #1 injector and verify exactly were #1 top dead center is in relation to the mark on the balancer.
Hopefully getting this post on top will get some more responses

[andyritter]

Yukon, I still plan to "play" with the IP position and see what kind of readings I can get. Just have not had time lately. When I do I'll post the results. I'm interested to hear what you find.

Andy

[andyritter]

I finally took a little time to move the IP around and got a few timing meter readings.
First, I adjusted the meter, getting the timing needle to the far left of the scale with all leads disconnected.
Next I checked the timing before moving the pump. The pump mark was aligned about 1/16" towards the drivers side (advance). The meter read 5 degrees ATDC at 1400 rpms. This is consistant with the previous reading within 1/2 degree.
Next I moved the IP so that the two marks were lined up (TDC position) and the meter reading was 7.5 degrees ATDC at 1400 rpms.
Next I moved the IP so that the pump mark was about 1/16" towards the passenger side (retard). The meter reading was 15 degrees ATDC.
Next I moved the IP so that the pump mark was about 1/8" toward the driver side. The meter reading was 7 degrees ATDC which is not logical at all. That's as far as I could move the IP in that direction and that's where I left it.
This exercise did not reveal anything new and I am still confused about the situation. The meter could be inaccurate I guess, but I really don't think so. The engine does not have a crisp diesel rattle. I am back to thinking I am off by a tooth in the timing gear setup. Anybody had any experience with such a problem?
I would appreciate hearing from anyone with some diagnostic input.
Thanks.

Andy

[Yukon6.2]

Andy
Do you have the Snap on guage to check the position of the holder by the harmonic balancer?Mine is a red plastic piece,it slips in the round holder,and has a pointer that you aline with the pointers next to the balancer.With it you can verify that the timing marks are in the right place.
havn't had a chance to pull #1 yet to see what i can find.
good luck on your quest

[andyritter]

Yukon, I did not know that device existed. Do you have any info as to how I could locate/buy one? I'll check the Snap On web site.
If I have this situation pictured correctly in my mind that tool would not show if my gears were or were not correctly aligned. Right? I could still be off by a tooth on the top gear.
Thanks for the input.

Andy

[john8662]

Timing is a bit of a confusion on these engines!!!

I too was playing with the MT480 timing meter borrowed from a fellow member. Small movements did not net me much results, I finally got the engine to 2.5* BTDC and left it alone. It's a powerstroke in the morning with the cold advance on.

My timing at the marks was 1.5* BTDC
Timing towards the passengers side 1* BTDC
Timing towards the drivers side 2.5 BTDC

Each movement was one line's width either way.

Moving the pump back to the 1.5* BTCD did not change the powerstroke rattle I get in the morning...

There are other possibilties, the internal timing inside the injection pump is off, which is what I'm leaning to on my engine.

When using two different kinds of meters, a Standayne Tach 'N Time and an MT480, I get different readings.

Both meters measure timing differently. The MT480 uses the lumy probe, the Standadyne unit uses an inductive type probe (measures pulses in the injection lines).

When using the MT480 I got the 1.5* BTDC
When using the Standadyne unit I got 8.5* BTDC

Why the varying timing?!?!

Should be the same right? Or close, not that far off!

That's what leads me to think it's a pump internal timing issue, the engine still fires given the fuel, so the MT480 can see that in relation to crankshaft position and RPM. The Stanadyne unit can see that the injection pump is injecting fuel early by the pulse of the injection line to that cylinder, then in relation to the crankshaft position and rpm.

I'll post the Snap On P/N for the little adjustment tang for the front cover, it's somewhat important. I say somewhat because the probe mainly senses how fast you're turning the engine by the notch on the cover making contact with it (or close to it magnetically).

So, in conclusion, just giving you another possibility.

Could be tooth off
Could be IP
Could possibly be adjustment on front timing cover (needing to be set #1 at TDC with head off).

I hope to get my MT1480 meter working soon (calling the Snap On Guy this week), I need to order ~$175 worth of parts! Keep getting outbid on the older MT480's on ebay... So, I might as well spend the same money and use the one I already got (digital).

[BobND]

I think it would be very unusual for the pump to fail internally stuck in the advanced position. Usually, due to wear, timing gets later, and when the advance piston bore wears and scores, timing gets REALLY late.

With the clamp-on Stanadyne piezoelectric pickup, have you tried observing the differance in indicated timing when the clamp-on probe is as near the IP as possible, vs. as near the the injector as possible?

I wonder what the real figures are for timing variation of picking up the pulse at the IP, vs. at the injector, vs. observing the actual light-off of the fuel with the lumy probe?

[arveetek]

After playing around with timing meters and such, I've come to the conclusion that timing is best set by ear on these engines. Unless the timing tab on the front cover has been perfectly set in relation to TDC, timing with a meter is really useless. The timing tab has slotted holes to allow for adjustment, so who knows if it's been set properly? That's why there is such confusion and controversy on what numbers to go by.

Set the timing by ear and by EGT guage, and you can't go wrong.

It's very unlikely that the timing gears are off...that would throw off the camshaft timing as well....so much so that I doubt it would even run.

Casey

[john8662]

Bob,

With the S Unit (tired to spelling out) We set the probe as close as possible to the injector, which I believe is how the instructions tell you to do so.

The injection pump is not old and tired, it was a NEW milspec pump.. Which leads me to think that maybe it's not calibrated properly. I think the wild timing advance I get cold is due to too much housing pressure, because once that's off, the engine sounds great, not too much rattle, etc.

Advance piston works, when in doubt get a long screw driver with the engine running and carefully push the lever attaching to the advance plunger and the engine should instantly get quieter.

The weird #'s that I got with both types of meters is what is confusing.

Casey,

I do think the engine would run one tooth off, but there would likely be some piston to valve interference with the cam timing off, especially on a stock C/R engine (which mine is).

I truely wonder really how much the tab in the front REALLY has to do with how the meter calculates timing. Almost worth taking a tamper-torx and moving it on an engine for a before and after w/o touching anything else.

EGT's on my rig are very nice. I can't get it to do more than 900* pre turbo, but I haven't pulled. Running empty on the h/w at 70 nets 500* temps, light truck. If the advance was really too much (mechanically) then i should see higher EGT's... Water temps on the other hand will swing rapidly depending on how much I'm on the go petal. Nothing hotter than 180 though... Just swings fast, but 100*F days already!

J

[NH2112]

When using the MT480 I got the 1.5* BTDC
When using the Standadyne unit I got 8.5* BTDC

Why the varying timing?!?!

Should be the same right? Or close, not that far off!




The injection pulse is advanced just like the spark is on a gasser. Your 7 degrees of crank rotation between injection pulse and combustion allow for the time it takes the pulse to get from pump to injector (almost instantaneous but not exactly), the time it takes the pintle to be forced open, and the fuel to spray out and combust. An engine with a lot of miles on it and lower compression will take longer to combust as well.

[john8662]

Not all the fuel charge in the line is expelled each cycle, but I'd think that the meter's display would account for any delay. Because the specification is the same for both.

There is a specification sheet that comes with the S meter, nothing with the MT480, other than what we can find in a GM manual.

[BobND]

I'd think that the meter's display would account for any delay. Because the specification is the same for both.

I have a Snap-On MT 1480 Digital Timing Meter, but I haven't had time to "play" with it much.

The display does NOT account for the difference between the various ways of observing the injection/"light-off" event.

I have had the timing "specs" around here somewhere, but can't put my finger on them at the moment... the timing figure IS different for the Lumy system, due to the observed "light-off" of th injected fuel vs. the actual time of the start of injection. The "spec's" are NOT in the booklet with the timing meter.

Here are some photos of the tool to set up the timing probe holder:

http://ndtc3500.stellarnet.com/~blweltin/Bob/Lumy1.JPG

http://ndtc3500.stellarnet.com/~blweltin/Bob/Lumy2.jpg

http://ndtc3500.stellarnet.com/~blweltin/Bob/Lumy3.jpg

[john8662]

Bob,

Put your finger on those timing figures, should be interesting.

The S meter said to time the engine to 3.5 - 4.5 BTDC.

Well, I'm dead in the water as usual. Found the Snap-On truck and we looked up the parts I need. They are not available any more. So... I won't be doing any more experimentation.

J

[andyritter]

I still have not solved the timing mystery but I wonder if I have an incorrect crankshaft pulley on my engine, and if so, could it cause the problem. Bear with me while I explain.
I noticed a while back when I needed to rotate the engine manually that there was no bolt head in the center of the pulley to use for cranking. I went to a dealership and had the parts guy look up the size of the bolt and then got one at the hardware store. It was too small, just wobbles around in the threaded hole. I e-mailed Jamie at Avant and he sent me a bolt. It was the same size as the one from the hardware store and likewise too small. I e-mailed Jamie again and explained and asked him to send me a correct pulley. He did not respond. I resent the e-mail several times and never received an answer.
So, the question is, could I have a pulley on my Avant built engine that is close in size but not the correct one and could that be causing the timing confusion?
Any help would be appreciated.

Andy