Timing, 6.6 mm LIFT!

['956Wheel]

First let me post the specs and modifications:



1995, 3500 5 speed, TST # 8 (stock position) AFC housing 1/16" from all the way forward, boost elbow (with the plate).



I put the plate in to help towing up grades, noticed heavy knocking up grades with load. Suspected timing.



Upon checking the chart in the D. C. manual I see 12. 5 BTDC (stock for my CPL) is obtained by setting pump lift to 4. 2mm.

Checking the timing I find that the pump lift is 6. 6mm. I set it to 4. 4mm (13. 5 BTDC). Idles nice but when RPMs are raised (no load) BIG smoke screen... . I mean BIG. WITH NO LOAD.



I turn the star wheel AWAY from engine 30 clicks and get approx a 40% reduction in smoke. Turn the wheel to 50 total clicks (same direction) some smoke but a lot less, these adjustments are all done with just "driveway conditions". A test drive shows a lot of smoke, at take off and loaded up acceleration, some at reving with no load, pre turb EGT seems to max out at 1100.



Before getting into checking and changing the timing the truck would run like a cheetah with its butt on fire, with a limited range (RPM) of power... . 1300 to 2000 approx. Now it runs with power that is "softer" what I mean by that is the former would rev like it had no flywheel.



Now the question (s) :



On timing 4. 2mm lift =12. 5 BTDC and every 1/10mm more increases the timing by 1/2 a degree so what would 6. 6mm equate to in BTDC. If I figure right that would be 12 degrees advanced beyond stock! 24. 5 degrees BTDC



IS THIS POSSIBLE?



Would it run as described as above



Should I keep tightening the star wheel (away from engine)?



Why would it smoke just gunning it in the driveway??



The mileage (combo, city hwy, empty) was 19, what should I expect now?



Mike

 

[Smoker]

Yeah, it will run at 24. 5 easily. I ran at 28 this summer. I may bump up to about 31 or 32 this coming summer.

 

['956Wheel]

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[Evan A. Beck]

That is awfully far advanced... I don't like to set them much past 17-18 degrees... Get up near 25 you can get hard starting problems, and excessive white smoke...

 

[JohnE]

Mike Adams of Mike's Custom Truck told me he has flow advanced into the 20's on hot trucks. It helps control EGTs when heavy fueling.



Evan;

White smoke? Is that from advanced timing or retarded timing? I read you state both. I see it mostly from cold temperatures around here.



-John

 

[HoleshotHolset]

32*BTDC worth of timing!!?? :--)

Matt

 

[Evan A. Beck]

John,



White smoke can come from both retarded and advanced timing. Basically, white smoke is just unburned fuel... So bad timing in wither direction can cause it. Typically, retarded timing has a bit of blue smoke to it as well, not to mention low power.

 

['956Wheel]

need to know

In the initial post I mentioned going from 6. 6mm lift (24. 5 BTDC) to 4. 4 (13. 5 BTDC) due to knocking when loaded (truck not me). This is a daily driver and thrashing it is not in my best interest. Lots of smoke now, even with no load. Should I turn the star wheel away from the engine more? Is there any downside in doing so?



Info needed,

Thanks Mike

 

[Smoker]

'956,

The knock you were hearing could have been what some call a "spark knock". When you get into 20's and 30's, they do develop a slight knock from the high timing. Evan is right about hard starting and white smoke. At 28*, mine takes quite a bit of cranking and it does shoot out a lot of white smoke until it gets warm in the cylinders. The only reason I time mine so high is for truck pulling. I can see no benefit for street driving at all for this kind of timing. High timing does better for high rpm's. When I take out of the line, I start out at 4500 rpm. It defuels down to about 3800 when I get going. Once I get the gov. springs shimmed solid, I should be able to hold 4500 all the way unless the motor runs away. I have been told that I run the chance of that happening if I shim the governor solid. If it does hold around 4500, my high timing should prove very beneficial. Other guys I pull with are running timing around 40*. To do this you really need a good cam in the truck.

 

['956Wheel]

Star wheel?

Smoker, When you advance your timing to the 20's do you make adjustments to the star wheel?? I am just trying to figure if I should turn the wheel more (away from engine) as there is too much smoke. I am going from the 20's to 13. 5/14 BTDC.



Mike

 

[Don M]

Mike,



Do you still have the stock AFC spring in the housing?

If you are getting lots of black smoke you and I both know its from too much low end fuel going in before the turbo boost is brought up.



You can still adjust all the spring pre-load you want (out or in) the AFC spring with no harmful side effects. Cutting the fuel back wont hurt anything.



Do you have 370 injectors or something like that?



Finally, the AFC housing being slid forward is not letting the link contact the rocker arm as fast as it would with the AFC in the stock position. This is gonna cause ya some more low end (before spool-up) smoke.



And of course the timing getting rolled back from the high side will increase low smoke too.



I dont think that the MM of lift is linear because the cam exibits differning rates of lift as it turns from the bottom of its base circle. As the plunger moves up the cam profile the lift is rising but it does so at a non linear rate. So, 4. 2mm of lift is 12. 5, but it may not always be 1/10=x amount of degrees.



I would recommned you put the AFC in the stock position, set timing to 15. 5 max and roll the AFC spring away from the engine a bit more (tightin' it up a bit). Since you tow a trailer and dont race around town in the truck its seems the best solution to your troubles. Remember once the boost builds up you will have the AFC link outta the way of the rocker anyway for top end power. Your mileage will suffer with the AFC slid forward too. 15. 5 degrees of timing seems to be a good 'mileage' setting as well.



Good luck.



Don~

 

[Rammin On]

Mike ...



Have you had this truck since new? What is the info on the pump data plate? Could be possible that a replacement pump was installed on the engine ..... get me the data plate info and I'll cross reference the #'s for you... ..... Also... what is the CPL # on the engine. (I'll guess 1968 but without the pump info ... Hmmmm)



First fundamental ... . find out what you have installed!! Let me know your #'s and we can go from there.



Keith

 

['956Wheel]

Don,

Thanks for all the info.



As for stock position on the afc, I know I slid it to the front as per TST directions... . now I have to find out where stock is. Well maybe a close exam of the paint and such will show that.



You are right on the linear movement not being in direct ratio of rotation, makes sense. With the timing set at 13. 5/14 BTDC it seems the bad knock is gone however it appears it may have cost some low end power. I think the next move will be to get that afc back a tad.



thanks again,

Mike



Rammin, I have not had the truck since new, so there may be some "history". The CPL is 1550 and the number, only one I can find, on the pump is on the top of the AFC and is "Bosch 2 425 209 158. Any info is GREATLY appreciated.

 

[Smoker]

'956,

When I set my timing that high in the summer, I take the AFC housing off and I pull everything out of it. I don't worry about smoke, just max power. I need my truck to dump all the fuel when I pull.

 

[Rammin On]

956 . .



I'll check on the life settings for a 1550 ...



The pump data plate is on the drivers side of the pump between #2 and #3 ... should have three lines of #'s ...



1. serial #

2. part #

3. designation code



Keith

 

[Rammin On]

956 ...



Check your private message



Keith

 

['956Wheel]

Rammin,

Well that dental mirror came in handy here is the #'s just below BOSCH PES69120A120RS7275. The gearcase plate shows CPL #1550 along with 12. 5 BTDC which is 4. 2mm lift... if the pump has not been changed! I set the timing to 13. 5/14 (tad over 4. 4mm).



Mike

 

[Rammin On]

956 . .



Call me ... your lift settings are wrong . . I sent you a private message with my phone #



Keith

 

[Don M]

Hey Mike, the lift setting for 12. 5 degrees should be a 5. 7mm for the CPL of 1550.



5. 8=13.

5. 9= 13. 5

6. 0= 14

6. 1= 14. 5

6. 2=15. 0





It looks linear from the chart I have, but the chart stops at 15 degrees. Your timing was very high 6. 6 though.



Where you have your timing now is below 9 degrees because at 5. 15 lift the timing is at 9. 5 degrees. Ooops!



No wonder she smokes. I would set it at 6 flat. That would 14 and very conservative.



Don~

 

['956Wheel]

THANKS!

So after all this the truck runs better than ever! Thanks to Rammin and Don M I got the real numbers. Now, why does D. C. publish a big green book of bad info?... that costs a small fortune.



I talked to Kieth (Rammin) on the phone and got the numbers at the same time Don M was posting them! Turns out Kieth is on the opposite coast as me and he has a sis 1/2 block away from me! I went out on a test drive after setting the lift to 6. tad and bought a lotto ticket! Its gotta be a winner!



THANKS AGAIN!



Mike



Oh, I turned (loosened) the star wheel back 50 of the 57 clicks that I had tightened it to try to get the smoke out. . touch of smoke on take off... fine!