Lucas CAV rotary injection pump math

[fitterski]

On a Cummins 5.9 12-valve currently in the shop I will have to take a close look inside the injectin pump as it is the last one in a long line of suspects for failure to accelarate. There is another engine just like it on youtube where you can see THAT operator also trying to coax the rpm's up with only a litle more success. These engines are usually started automatically and almost immediately drive to full power, I SUSPECT that their timing is OFF the typical automotive application for example. My use for it will be more like automotive or tractor (actually a snow blower, another thread).

Cummins firepump - YouTube

I've redone the injectors, inside everything is like new (supposedly 1300 hours and consistent with that #). The pump is a Lucas CAV



It is turned by a 73 tooth gear @ half crank speed. There are timing LETTERS in the view-window and a ref line. According to the plate the letter B should be at the timing line when the pump is installed with #1 cyl at TDC. The gear is keyed so it can only be installed one way but it may be turned together with the pump innards beforehand to change timing. Normally the inside drum is locked by a screw prior to removal at TDC and unlocked after reinstallation. So far so good.

The thing is that I like to understand things before I touch them. I have no idea what the other timing letters stand for or what the actual timing would be at the prescribed "Letter B". On the automotive 5.9 typical timing is 11 degrees before TDC, which would approximate about 5.5 degrees on the pump gear. If I turn the spool from the letter B to A it eats up 9 teeth, far too many degrees to be an 'an adjustment' thing, and backing just 5.5 degrees to take a wild guess at the actual injection point there is no mark to be found. I hate Cummins for not being much, *MUCH* more explicit in the manual! Maybe the letters are used for different engines with different numbers of cylinders.

At LEAST igf they had placarded timing as "The Letter B = 12 degrees" or something then I would have a point of reference. I want to know what I'm getting into before I open the pump up.

Any pump experts around with a few words of wisdom? TIA

Oh yeah, I can't delete the hi-res image to save on upload overhead, how do you do that? What's the use of a thumbnail as opposed to an inline image?

 

[thepumpguysc]

The timing is 5* advanced on the pump at letter B.. Hope this helps.. TPG

 

[fitterski]

The timing is 5* advanced on the pump at letter B.. Hope this helps.. TPG

It certainly DOES, thanks! From that I can start bracketing if need be 1/2 degree for every crank degree. I got a lot to learn about injection pumps. I had a similar pump on my Cat-426 go bad because of water in the fuel, my mechanic had it redone cause we had no time for puzzle games. If I remember correctly the flyweights didn't work and a spring was broken (due to rust through).

 

[fitterski]

Is it likely for the flyweight response to be poor on a 1300 hour engine?

Here's what I've done:

Pump timing verified on spec i.e. "On Letter B"

Stripped engine, the only problem found was valve lash being extrememly high (probably a misread of 0.100 instead of 0.010 by the last person doing it). Lash reverted to spec in-010/exh-020.

Smoke is gone, idle is very nice, otherwise little change. Entire pump body slewed to adjustment advance limit (clockwise seen from rear). Accelertation now also improved and I can now work my way up to 2100 but engine still misses if accelerating fast to or above about 1800.

Initially my hunch was that timing to spec "On letter B" must be a mistake but that would really require knowing what the added dynamic advance would be, which I don't. On the other hand if the dynamic timing has gone 'jamming or jammed' then that could be a possible culprit and would show similar symptoms. It 'seems' (maybe just wishful thinking) that exercising the pump is also improving the result. I'll exercise it some more and maybe crank the gear over a tooth for another 5 degrees of static advance, then look at the performance. If I get a good run with high static advance then that would pretty well point the finger at no dynamic advance I think.

http://trixtar.org/3/tinkerings/12valve208hp/barf2.mp4

 

[thepumpguysc]

Pump advance it based on rpm & internal pressure.. The faster the pump spins, the more internal pressure it creates, moving the advance piston.
The rate of movement can be changed by adding & removing shims.. located under the spring cap at the advance housing..
The spring cap is the one that has the small screw in the center of it..
Its SOP to replace the "pressure parts" inside the pump on a rebuild.. Liner & blades.. & the pump is checked/set for internal pressure & advance movement on the test stand..
We run the pump at a certain speed & set a pressure according to manuf. specs.. THEN run the pump at another speed & set the amount of advance required according to spec, by adding or removing shims..
The PRESSURE has to be there in order for the advance to move..

 

[fitterski]

Pump advance it based on rpm & internal pressure.....

There's a man who sounds like he's seen a few pumps

Some of this is news to me, most of what I THINK I know comes from bits and pieces of CAV manuals found on the net plus this youtube video:

CAV Injection pump full strip down to re seal and stop fuel leaks - YouTube

Thanks for the info, I was under the impression that flyweights alone did the advance work. I'll try to get as prepared for opening the pump as I can over the next days. Could you expand on the location of that 'spring cap'? Also, what's a good source for decent rebuild kits? I don't mind buying chinese but good references are indispensable

In YOUR experience what is the probability of a 1300 hour pump developing a case of whooping-cough like this? It's a rhetorical question in a sense, I wasn't prepared to see valve lash at 1/5 of an inch either yet there it was ))

 

[thepumpguysc]

There are several parts that NEED to be replaced..
Kit> 7135-110
Liner> 7139-540
Blades> 7123-019 comes in a 2 pk..
IF its not leaking from the throttle shaft.. just pull the end plate, 4> 5/16 bolts & replace the liner & blades.. THAT can be done ON the machine.
TORQUE the bolts to 35-40 INLBS..
WATCH the video.. & determine if you want to tackle it..
The parts can be purchased online BUT if you go to a "local" diesel fuel injection shop.. it'll be cheaper.. about 25.00US

 

[fitterski]

There are several parts that NEED to be replaced..
Kit> 7135-110
Liner> 7139-540
Blades> 7123-019 comes in a 2 pk..
IF its not leaking from the throttle shaft.. just pull the end plate, 4> 5/16 bolts & replace the liner & blades.. THAT can be done ON the machine.
TORQUE the bolts to 35-40 INLBS..
WATCH the video.. & determine if you want to tackle it..
The parts can be purchased online BUT if you go to a "local" diesel fuel injection shop.. it'll be cheaper.. about 25.00US

I think I _will_ tackle it, even if it means removal, just did that twice so I now know it by heart )

I've just checked the check ball and it's not missing. In addition to this the Cummins manual also says that broken springs will cause too much advance and knocking while low pressure will cause retardation. Well, I do not have enough advance by the look of things so it's gotta be #2. I'm still surprised that a 1300 hour pump should be in such a state. We have a general diesel shop and a major auto parts stopre 50 kms away, I'll see tomorrow if I can get the goodies from them, if not I'll try on-line.

 

[thepumpguysc]

That check ball will give more trouble than its worth.. if its at all possible, try hooking up a straight pipe off the pump to catch the return, bypassing/removing the checkball return fitting & see if it doesn't cure your problems..
BTW> the springs in the advance DONT break..
Low pressure is caused by worn liner & blades which is a direct result of dirty fuel &/or, poor filter maintenance..
Have you checked the inlet pressure TO the pump.. what kind of condition is the lift pump in?? IF the lift pump is not working properly, that may be your entire problem..??

 

[fitterski]

That check ball will give more trouble than its worth.. if its at all possible, try hooking up a straight pipe off the pump to catch the return, bypassing/removing the checkball return fitting & see if it doesn't cure your problems..
BTW> the springs in the advance DONT break..
Low pressure is caused by worn liner & blades which is a direct result of dirty fuel &/or, poor filter maintenance..
Have you checked the inlet pressure TO the pump.. what kind of condition is the lift pump in?? IF the lift pump is not working properly, that may be your entire problem..??

I should have the liner/blade set tomorrow, the old one doesn't look too bad



I also opened the Advance fitting and eyeballed the piston, it's free to move with no sticking and has just a touch of staining in two spots.

BTW it's the Cummins manual that says that a missing check-ball will result in NO advance. By a straight pipe you mean to remove that fitting with the check-ball altogether and T a hose into the return-to-tank line? I think I should be able to rig that up too.

The filter is new and the lift pump seems like-new. During runs we did pump it manually in addition and vigoroulsy to see if it would make a difference, it did not. I'm not equipped to gauge output but I could try to rig something up. I do have a mobile electric lift pump that I could piggyback on it. I could also cannibalize the lift pump off my Ram-engine (it's a 175hp version in pieces, similar hours i.e. 130k kms).

I'm 80% convinced it's a dynamic advance problem because cranking in an additional 4-5 degrees of manual static advance seemed to help. If the new liner/blades don't fix it I think I will next crank in a lot more manual advance like maybe a whole tooth on the gear (5 degrees) plus the mounting screw slot good for another 4 to 5. If the result is even better than the last try then I'll be just about certain that it is a lack-of advance issue.