Timing... What, How, Why? Answers - and very long.

[Power Wagon]

Ok. . I won't claim this is going to be the best post on the matter. I wrote this down in text form recently. I was asked for it, but, instead, I lost the darn thing when my hard drive got corrupted, including the email address of the guy I was to send it to. So, if you were expecting this by email, I'm sorry, I lost your name and address.

Further, I just got an email asking me to answer the questions asked in another thread. I started a new one so it could easily be found.

First, I'll briefly explain some pump theory and operation, and then the affects of timing and injector changes on engine operation.

Your first gens all have a Bosch VE pump on them. This pump injects fuel by a single, rotating plunger that is forced up by a set of rollers held inside a cage, riding up and down a cam plate. This cam plate is round, and the surface is fluted, so that there are six positions for the rollers to be raised, and six valleys. When the drive shaft spins the cam plate, the rollers then literally walk, in a set of four, up and down the outside edges of the flutes (in reality, the cam plate moves up and down and the rollers stay fixed, but I'm only talking about relative motion here). In one rotation of the drive shaft, the rollers climb and fall six times. The plunger rides on top of the cam plate, and a little pin in a slot makes the pumping plunger rotate at the same speed, and in a fixed location with, the drive shaft. Two sets of very strong springs push the plunger down onto the cam plate, so that it returns to the low part, even at speed. It makes an up-and-down cycle 3 times for each engine rotation. The pump is geared to 1/2 engine speed.

The 'cage' that holds the set of rollers sort of 'floats' in place, but is rotated against the direction of the drive shaft by hydraulic pressure - that generated by the internal vane-type supply pump. By moving against drive shaft rotation, the rollers contact the raised lobes sooner, raising the pumping plunger sooner and voila!, advanced injection timing.

When the pump is first assembled, fuel is flowed through a specific port in the pump at low pressure, and the drive shaft slowly rotated until the ports close - cutting off the flow. The distance from the bottom of the lobes to the cut-off point is then measured, and then set, by means of a spacer, so that every pump has the same distance (plus or minus a small variation) for the plunger to travel before the ports close.

When in operation, the moment the ports close, the fuel is instantly displaced by the upward moving plunger (the ports allowed bleed off until closure) and the high-pressure fuel is then forced out the only opening left - the registered openings between the plunger and the outlet to the injector. Since we know how far the plunger travelled before the ports physically closed, we now have a set spot we can measure with a mechanical device that tells us when the hydraulic event takes place.

Cummins and Bosch have worked out a graph (one I am not privy to) that details how many degrees movement is related to the amount of lift. As with any U curve, the lift starts slow, and acclerates until it reaches some point, where it then decelerates to a stop and reverses course back to the valley.

So, when the engine is assembled, the TDC point is (theoretically) set where the pin locks the cam gear (in real life, we've found this varies, sometimes by several degrees engine rotation) and the pump is also locked at a specific measurement of plunger lift from the valley of the cam plate (or 0 point). This somewhat complicated procedure has been worked out by the engineers to achieve the desired initial injection timing, the rpm related advance, to achieve the desired effects (this is not, of course, necessarily the point of best performance or economy).

When I timed the engine, I used a custom made tool that screwed into the #1 injector hole and created a postive piston stop. I then rotated the engine (by hand, using a wrench) forwards until the piston touched the tool and stopped, whereupon, I marked the dampner and set a magnetic pointer to that exact spot. Then, using the alternator pulley, I rotated the engine backwards (with a wrench, slowly and gently) until the piston again touched the tool poking down the injector hole. Marking the spot, I could then measure the distance between the two marks and divide by half. The center point between the two is true TDC.

By rotating the engine around until the TDC pin will push in, we can then compare the "true" to the "set" TDC points. If they are not the same, we can loosen the pin's two mounting screws and rotate the engine to the true point and tighten the pin holder back up.

The pump is, by using a dial indicator, set to a specific "lift" point, locked by a provided set screw against the drive shaft, and then installed on the engine.

After it is fully tight, the locking screw is loosened, the TDC pin is pulled, and the engine can then be rotated.

Since this is going long... I'll address timing effects on the engine in the next post.


------------------
ICQ 3807791 Power Wagon
www.my2kcity.com/powerwagon
Mark Koskenmaki, General Diesel Moderator

 

[Power Wagon]

Timing effects on the engine are often thought of as as mystery or some sort of black art, but in reality, it's really sort of simple in theory, but not nearly as easy to know just precisely where you are at the process.

To start out, let's review the diesel cycle engine:

Let's start out and the end of the previous engine cycle, where the piston is at the top of the exhaust cycle, and pressurized exhaust is mostly done being forced out the exhaust valve, and the intake's starting to open. As the piston travels downward, air is sucked into the cylinder through the open intake, getting about 70 - 80% filled - there will still be less air in the cylinder that it could have, if there were not resistance, both in getting the air through small passages and because of momentum (of course air has weight. Blow at your hand and stop suddenly. Notice that air continues movement briefly after you stop... )

Since this momentum thing keeps the air flowing even after there's not a vaccuum difference, the intake valve stays open for a little while after the piston starts back up. At cranking speed, this probably puffs a little bit of air back into the intake, lowering compression pressure a little, but it's not serious. At running speed, air is still going in until the valve closes. Unless, of course, you have boost, or higher-than-atmosphere pressure in the intake manifold, where you get more than a full cylinder of air.

As the piston is shoved upwards, it decreases the space the air is crammed into, increasing the pressure. By physical measurment, your mighty "B" ends up with the space being about 1/16 full volume by the time the piston reaches the top. By design, we're multiplying atmospheric pressure of roughly 15 PSI to well... a LOT more. This increase causes the air in that confined space to be heated. . heated to the point that when fuel is injected into it, it instantly combusts. Kinda like hairspray pointed at propane torch... WHOOF! Because of the heat, there's no need to ignite it by any other means. Just put it in, and BANG, it's burned.

Of course, the air is VERY hot, and we just injected fuel, which burned, and now we've got a LOT more pressure than we had before and a lot more heat. Now, think of this process in reverse - as the piston starts down, the space above the piston increases, the pressure falls, and by the laws of physics, the temperature falls. By the time the piston is not far from the bottom of the stroke, the pressure has fallen so much and the temperature dropped so far, that it no longer is effectively driving the piston, so the exhaust valve opens and the cycle finishes where we started this little rant - with the piston raising back up, exhaust valve open, forcing the remains of our little fire out the exhaust manifold to be tree and grass food (CO2 mostly, plus water and other unmentionable stuff - not visible if it burned well, but we all know what it SMELLS like #ad
)

Now, let's explore this event a bit more around the injection point.

The piston, of course, is connected to the crankshaft via the connecting rod. Now, for anyone who has bicycled, you know that when the pedal's at the very top, you just don't have any leverage, but at the middle, it moves so fast you can barely keep up with it. So, when you take off on yer bike, you put the pedal at around the 2:00 O'clock position so you have leverage enough to get started and can use the full stroke to jump start you enough to get the other foot off the ground and (if yer not like me) sprint off at warp speed down that mountain trail.

This same process occurs in your engine. At the very top, the piston slows down to a complete halt, and then acclerates back downward toward teh middle of the stroke where it begins decelerating down to the bottom where it stops and begins accelerating up... .

Now, when we inject that fuel in there on the power stroke of the piston (my apologies, ford robbed a mechanical term that's in every textbook on the 4 stroke engine), it burns - it sounds like a "BANG" to you... it's pretty fast. However, it does take time.

Also, the pump takes time to inject the fuel. Fuel does not flow from the nozzle the instant the ports close in the pump. The fuel begins to compress in the lines, the lines swell EVER so slightly and as the pressure rises, the needle valve in the finally snaps open as the hydraulic pressure finally overcomes the spring holding it shut, and the increased area of the needle exposed to high pressure now snaps it wide open and holds it until the injection stops.

By careful engineering, there is an optimum point we can find, where, if you could inject the fuel instantly, you could obtain the most work from it. It has to be, that the point where the most pressure combined with the most leverage occurs, where the most burn is taking place. AT some point after the piston has started back down, we have to reach maximum heat expansion.

If we do this too early: The piston will not have reached the compression point most conducive to igniting the fuel, so the fuel streams in a slightly cold cylinder, starting to burn, and that action suddenly heating things up and finishing the process. Can you say "smoke"? Sure you can #ad


Also; piston will be on it's way UP when the ignition occurs and the pressures spike way up. All that pressure has to be overcome and the piston forced back up to the top of the stroke by momentum and intense force against the rods and pistons and bearings and... . You get the picture. A harsh slamming of parts, compressing an explosion, generating extreme heat and loading.

By doing that, we are now forcing that fire into the smallest area, and then holding it there while the piston reaches decelerrates to the top, and begins accelerating downward. The piston, head, block, all absorb more heat than they should have, and the power stroke of the piston will be weaker than it could have been because there is no longer as much expansion going on and some cooling will have taken place.

AS you can imagine, this combination is not good for any part of this engine. It over-stresses every moving part involved, and makes less power doing it.

Now, let's imagine you inject fuel late, instead of early. The piston has begun to fall, heat has been absorbed, and pressures falling... Now, we put the fuel into the cylinder. It's too cool to ignite well, and some of the fuel never really does burn all the way. Instead of generating a lot of pressure in a confined space, the explosion takes place in a rapidly expanding chamber. The pressures never reach that high, the pressure against the piston, when it's at the best point of leverage vs rate of movement is past, and we're still burning the fuel as the exhaust is opening, dumping the pressure, lowering the heat, and the fire goes out.

Now, in between those two points, is a point of best efficiency. But, being mechanical in nature, and limted by physics, we cannot inject the fuel in an instant. Instead, it comes in at an accelerating rate as the engine speed and quantity are increased, and the engine moves farther and farther along during this breif period where the pump is building pressure and opening the injector.

So, we compromise. We start it a little bit early, so that the best we can do is injection some early, some late and hopefully fast enough and well enough mixed with the air to be reasonably efficient.

Now along comes some men from the government, and discover that if we generate heat beyond a certain temperature inside that engine, compounds in the air itself, as well as combustion by-products actually burn too, creating emissions that aren't desired. So, to prevent that from happening, we purposely move the timing a little on the late side, thereby lowering the pressure spike just a wee bit, which lowers the maximum temperature just a wee bit (I'm being deliberately vague here, this is a very complex science - beyond mere mortal's ability to implement), and perhaps even helping the start and beginning of burn a little bit by making them closer the optimum point of ignition.

Now, put in the big-hole lucas nozzles, and you increase the RATE of injection. This means the fuel goes in quicker, almost like injecting sooner, except that it all gets in during less travel of the piston, for a given amount fuel. But, conversely, you have forced teh fuel through bigger holes at lower pressures, so it's not quite as well "shattered" as I like to say. It then may very well take more time to burn it, and some of it might not burn as completely, because it didn't mix with air as well.

Oh, wait, you noticed that belch of smoke you stomped the pedal? Hey, now you know how it happens - you're putting in more fuel faster and you don't have the air being shoved in by the turbo to burn it all.

Now, start thinking about this: When you put the fuel faster, it can be timed closer to the optimum point and still not over-stress your engine due to being too early or be too late to have much effect on creating power. Also, remember when you force fuel in over a period of time, you eventually have burned the oxygen in the path of the fuel, but it's still being inhected. . smoke and waste.

One last note: Why do the injectors increase the power without adjusting the pump?

The Bosch VE pump has the ability to generate a maximum amount of pressure. If you exceed that, you do two things: You exceed the mechanical design limits of the pump mechanism, and you increase the amount of leakage past the high-precision plunger and head assembly. The maximum pressure is merely a function of the holes in the nozze of the injector combining to act as an orofice, the speed of the plunger moving upwards (the faster it moves, the higher the pressure spikes, given a fixed orofice size), and the flow characteristics of the fuel itself. So, when you put in bigger nozzle injectors - you lower the pressure spike, meaning more fuel flows between the time the ports close at the beginning of injection and the time the ports open again, dumping most of the pressure that has been built up and re-seating the nozzle. No matter how far you crank that screw, once you reach the pump's capacity in pressure, you can only inject LONGER, not faster. So, by putting in the bigger hole nozzles, you increase efficiency of pumping AND burning at higher speeds. Now, of course, Cummins, with an eye on the EPA, has chosen a timing point that is, to them, the best they can do and meet emissions with a target safety margin.

The very same engine, when used in an off-road application, will have considerably different timing specs. This is due to them not having to meet quite the same standards of emissions. Those engines will put out more power, use less fuel doing it, and generally last just as long or longer doing it. So, by emulating the specs of the more efficient engines, we increase the efficiency and power and probably do no harm at all to the longevity.

I hope this feeble attempt to explain the why's of what's going on helps and not confuses...



------------------
ICQ 3807791 Power Wagon
www.my2kcity.com/powerwagon
Mark Koskenmaki, General Diesel Moderator

 

[Case500D]

Power Wagon,

Thanks for the wonderful amount of knowledge you have shared with us. I now have a much better understanding about pump timing and fuel delivery. What do you believe is the optimal pump timing for stock injectors versus higher flow injectors such as the PW injectors? Also, where did you get/make your special TDC tool? Do you like it better than a dial indicator? Once again thanks for all of the help.

------------------
Jeremy Sweeten 1992 Dodge W-250 4x4 Cummins Diesel, Intercooled,LE Package, 166K, AT, Warner Hubs, Dana 60HD 4,060 lb. front axle and Dana 70 6,084 lb. limited slip rear axle with 3. 54 gears, NPG 205 transfer case, 3. 5" Banks exhaust with straight pipe and 4" tip, K&N air filter. Tekonsha Voyager XP electric brake controller.
http://home.earthlink.net/~sweeten1/index.htm

 

[Power Wagon]

The stop tool I had was made from an old injector. One of the guys in the shop drilled a damaged body all the way through, threaded it, and then we put in some redi-rod (rod that's threaded like a bolt... this came in 3 foot long chunks). It fit just like an injector, tight in the hole, and with a locknut holding the protruding rod tight.

There are more means than only that of finding true TDC. Someone suggested a dial indicator to show piston movement, with a long probe down the injector opening, and some pull the rocker off, take the valve spring loose (while the piston is at the top, ONLY) and measure the valve stem height as it rides the piston.

Now, the dial indicator for the pump:

The center bolt in the head is removed (it's only a plug), and an adapter is screwed in that holds a dial indicator. By turning the engine back and forth, you can find the lowest part of the plunger travel, set it to 0, and then rotate the engine to TDC. If the lift is not what you want at TDC, you then loosen the pump and rotate it until you do have the desired lift.

As for the best timing... It is difficult to compare engine to engine, as there could be mechanical differences in the cam plate profile (I don't know, I have never looked them all up to see if they are the same part number), but the lift specs at TDC range from a low of 1. 20 or 1. 25 to 2. 1mm. You'll recognize the lowest as belonging to the engines in the pickups. . that's the least advanced timing spec.

User's reports have been that going to 1. 4 or so will lower EGT, smoke and make more power. Some have tried higher lift settings, and most have said it smoked more without any particular gain in power.

For some reason that's not clear to me, the non-intercooled engines seem to like a little bit more advance than the rest.

------------------
ICQ 3807791 Power Wagon
www.my2kcity.com/powerwagon
Mark Koskenmaki, General Diesel Moderator

 

[boatpuller]

#ad
#ad
THANKS #ad
#ad
Mark #ad
#ad


------------------
1993 LE W250 4x4 CC,Auto,3. 5's,LS. . Diamondplate,PowerWagon injectors,K&N,Egt,Boost,trans temp VDO Vision series, BD 3 1/2" Exhaust, 16cm housing,Mag Hytec Diff+ Trans pans,Transgo TFOD shift kit,Roadmaster Active Suspension.

Caleb Reese (per forum guidelines)

 

[R.E. Miller]

Thank you Power Wagon for the info, I am slowly getting the hang of things that make the fire under the hood. I found your point about off road engines most interesting, this emissions business is going to distroy all that makes diesel engines diesel in the end adios longevity #ad
. Anyway this clears-up a lot, thank you, and I am off to perform much less complicated procedures. . . 3. 5" jardine straight set-up he he he #ad
.

------------------
1992 W-350 Club Cab Dually (All quiet for now)
1992 W-350 8' contractors dump with 3. 5"BD exhaust, 16cm^2 housing, DI pyro&boost
Russell

 

[Wirenut]

Mark, your the man. I heard that I can get a different camplate for the VE44, is this true? I want more power still. Do I have to do all that crazy stuff with TDC and dial calipers just to time the pump? What HP difference would you say (approx) timing would have.

------------------

• '93 250 LE 4x4 5spd 4:10 Loaded,dual 5" chrome stacks,12cm² turbo(37psi),PW injectors,K&N,pyro/boost,US Gear E-Brake,tool box,CB,10" AR rims, 285/75/16 Bf goodrich. "wirenut_21529" on Yahoo Messenger
• '97 Ford B-Series school bus (5. 9 Cummins!)I'm gonna Bomb it!
• '94 GMC 2500 6. 5L Turbo

PICTURES.

 

[Case500D]

Power Wagon,

I have dropped a valve down on top of number one piston before and used a dial indicator to find TDC. I was wondering if you could provide an explanation of spill port timing? Currently the timing on my truck is 1. 25 mm and I am thinking about advancing it to between 1. 37 to 1. 40 mm. Thanks for wealth of information.

------------------
Jeremy Sweeten 1992 Dodge W-250 4x4 Cummins Diesel, Intercooled,LE Package, 166K, AT, Warner Hubs, Dana 60HD 4,060 lb. front axle and Dana 70 6,084 lb. limited slip rear axle with 3. 54 gears, NPG 205 transfer case, 3. 5" Banks exhaust with straight pipe and 4" tip, K&N air filter. Tekonsha Voyager XP electric brake controller.
http://home.earthlink.net/~sweeten1/index.htm

 

[Matt S]

Does turning the diaphram affect the timing in that there is more fuel sooner?

------------------
90 W250, 5-speed, isspro gauges, 16 cm2, K&N, Borgeson shaft, JRE 3" exhaust, Banks Intercooler, Lucas injectors

 

[Power Wagon]

Originally posted by Wirenut:
Mark, your the man. I heard that I can get a different camplate for the VE44, is this true? I want more power still. Do I have to do all that crazy stuff with TDC and dial calipers just to time the pump? What HP difference would you say (approx) timing would have.

The VP44 is the pump off the ISB. It works by an entirely different set of controls, and is different internally.

------------------
ICQ 3807791 Power Wagon
www.my2kcity.com/powerwagon
Mark Koskenmaki, General Diesel Moderator

 

[Power Wagon]

Originally posted by Case500D:
Power Wagon,

I have dropped a valve down on top of number one piston before and used a dial indicator to find TDC. I was wondering if you could provide an explanation of spill port timing? Currently the timing on my truck is 1. 25 mm and I am thinking about advancing it to between 1. 37 to 1. 40 mm. Thanks for wealth of information.

"spill port timing" is the process described above, where the plunger lift to the point of port closure is set. It sets the pump itself... After that, you just move the pump on the engine to achieve the plunger travel at TDC you desire.

------------------
ICQ 3807791 Power Wagon
www.my2kcity.com/powerwagon
Mark Koskenmaki, General Diesel Moderator

 

[Power Wagon]

Originally posted by Matt S:
Does turning the diaphram affect the timing in that there is more fuel sooner?

For all practical purposes... no. It does change the amount (and as described above, the duration) of injection, but it does not advance or retard the pump itself. In the case of the VE pump, it delays the end of injection to get more fuel.

 

[Wirenut]

The VP44 is the pump off the ISB. It works by an entirely different set of controls, and is different internally.

vEEEEEEE 44 pump. The rotary 1st. gen. pump! Not vPPPPPPPPP.

 

[Power Wagon]

Never heard of a VE 44. That doesn't look like a good model number for a VE pump.

The "model" numbers of the VE pump for the 6B always start with VE6 and a string of numbers and letters. That "6" means 6 cylinders or 6 outlets. Any VE4* designation would mean a 4 cylinder.

As far as changing cam plates, I'm loath to suggest you put any part except that which Bosch put in those things to begin with. A steeper ramped cam plate would add even more stress on the pump than it has now, and I consider it very marginal now. That cam plate is the most common mechanical failure next to the return springs that hold the rollers and cam plate against each other and return the plunger to the bottom of the stroke. If you're determined to get a lot more horsepower than you can get by cranking the fuel screw and changing to big injectors, then you're going to have to switch to the inline pump - the P7100.


[This message has been edited by Power Wagon (edited 02-24-2001). ]

 

[Wirenut]

Somebody must have fibbed to me on some letters and numbers and all that junk PW, but your right on about the p7100 deal! I got one on the Ford bus but I can't seem to find the guts to jump under the hoods and switch 'em! It looks like a pretty big project but just may be my next move. And the $$$ isn't in my wallet now so I'm stuck with trying to kill that VEP44-6P716-9er or what ever the heck that old pump is on my '93 #ad


------------------

• '93 250 LE 4x4 5spd 4:10 Loaded,dual 5" chrome stacks,12cm² turbo(37psi),PW injectors,K&N,pyro/boost,US Gear E-Brake,tool box,CB,10" AR rims, 285/75/16 Bf goodrich. "wirenut_21529" on Yahoo Messenger
• '97 Ford B-Series school bus (5. 9 Cummins!)I'm gonna Bomb it!
• '94 GMC 2500 6. 5L Turbo

PICTURES.

 

[mark93]

Hi PW!

Your injectors were the best thing I've put on my truck. Out accelerated a late '80's Firebird/Camaro the other day in fourth gear-not by much but hey 6800 lbs and same size engines!!

Hope all is well.

------------------
'93 W350 Club Cab, Bright White, 5 sp. , 136K, Factory Options: LE package, 4. 10 Limited Slip, 7600 lb. rear springs, tachometer, front stabilizer bar. Mods: Banks stinger plus, Linex bedliner, 25,000 lb gooseneck ball, 10,000 lb receiver, Tekonsha brake controller, POWER WAGON injectors-WAY faster than stock!.