Author Topic: Injector Cam Timing  (Read 3730 times)

mcreeferson

  • Jr. Member
  • **
  • Posts: 53
    • View Profile
Injector Cam Timing
« on: March 08, 2017, 03:38:23 PM »
I didn't want to clutter up 38ac's WOK camshaft thread with too much more of my malarkey, so figured I'd start a new topic here with a question I have...

I am about to put all of the pieces together for my roller-cam build, and have come upon a stumbling block I had not considered in all of my thinking about valve timing. I have inspected the OEM camshaft and have found it to be straight and true, and it does not sound as if the injection cam lobe is normally considered a problematic item. 38ac's awesome write-up pretty much opened the door to me making this happen with his in depth explanation of what happens when, which events are most critical, and why, but the actual injector cam timing is never really detailed fully. I can see why of course, unless you are fabbing up an entirely new assembly, which is entirely unnecessary and frivolous, there is really no need to get into such menial details.

However, let's say some buffoon comes along who is foolish enough to waste his time engineering and building such a Rube Goldberg solution to a simple problem, he would probably at some point realize he is missing a piece of the puzzle. How would the in and ex valve timing be clocked in relation to the injector lobe on the camshaft? I can draw out a nice graph of the valve lift and timing curves, but can't seem to find any info on the same for the injector. Does such data exist out there, or do I need to essentially assemble the whole rig to the point of testing injector timing physically before I can properly locate my valve lobes in their ideal location?

What am I missing, and how much am I overthinking this? Should I just ballpark it, and rely on plunger adjustment?

dieselgman

  • Hero Member
  • *****
  • Posts: 3189
    • View Profile
    • Lister Parts
Re: Injector Cam Timing
« Reply #1 on: March 08, 2017, 08:20:53 PM »
I don't know if this will translate clearly, but here goes:

If I understand your question, the additional variable related to pump operation and injection timing will be the actual cam lobe profile and ramp in both lift and duration. I have not seen any specific discussions of this engineering factor for the Lister... The pump itself has a very specific and limited travel that the cam lobe will have to match (and/or vice versa), the injection timing will of course be adjusted for its starting point by length of its tappet (and to a much lesser degree the spring setting [opening pressure] in the injector), and its duration will be determined by the diameter (fluid volume) of its plunger - and (again to a lesser extent) the shape of the lobe ramp and performance of the pump and injector hydraulic relationship. You will see that most valve lobes have a fairly sharp "peak" at the top of travel and the fuel pump lobe will have a flat "peak" of quite some duration between equal ramps on either side. Perhaps a comparison of OEM Lister design vs the Indian copies could be made at some point to see if they are an accurate match or not. Really it is not that critical as far as I understand the overall system.

The critical point is that the injection event timing is mechanically controlled/adjusted by tappet length, its duration will be controlled by the hydrodynamics of the overall system components (plunger size and travel - thus pump volume, injector spring setting and nozzle orifice size/s), the end of the injection event occurs independently from the cam operation and should end somewhat before the cam lobe actually begins to return the pump plunger to its retracted position.

Valve lobes will be adjusted specific to piston travel, quite apart from the fuel injection event and that portion of the system.

dieselgman
« Last Edit: March 08, 2017, 08:25:37 PM by dieselgman »
ALL Things Lister/Petter - Americas
Lyons Kansas warehousing and rebuild operations

Thob

  • Sr. Member
  • ****
  • Posts: 255
    • View Profile
Re: Injector Cam Timing
« Reply #2 on: March 09, 2017, 01:49:27 AM »
I think you need someone with a dial indicator to remove the injection pump and find the point on the flywheel (in degrees relative to TDC) where the injection lobe is at the maximum, based on a "known good" cam.  It would be good to know the total lift (maximum minus minimum) as well.
Witte 98RC Gas burner - Kubota D600 w/ST7.5KW head.
I'm not afraid to take anything apart.
I am sometimes afraid I'm not going to get it back together.

dieselspanner

  • Hero Member
  • *****
  • Posts: 726
    • View Profile
Re: Injector Cam Timing
« Reply #3 on: March 09, 2017, 05:08:24 PM »
For what it's worth I was in the shed doing something else and I took a few minuets to look at the injector pump.

Rotating the flywheel I found the following, bearing in mind that this was done with the Mark One finger and the pump in place, the positions, in degrees, were derived from the marks I made on the fly wheel to set up the cam and rockers and not accurately taken off TDC, so I'm going to be a bit out either way.

The machine is a 6/l bitza but I've no reason to believe the camshaft - and most of the other bits - are not genuine Lister.

The follower started to lift around 75 degrees before TDC, (that doesn't mean it was in contact with the base of the pump)

The injector 'creaked' at 5 degrees before TDC.

The top of the cam felt like it was around 60 degrees after TDC.

I didn't look for the point where the follower came off the cam

Not at all what I'd have forecast. Sadly I'd no time to measure the 'lift' of the cam.

Don't know if that will help, but it seems to me there's a lot of latitude there, the ramp angle is probably most important.

Cheers Stef
Tighten 'til it strips, weld nut to chassis, peen stud, adjust with angle grinder.

dieselspanner

  • Hero Member
  • *****
  • Posts: 726
    • View Profile
Re: Injector Cam Timing
« Reply #4 on: March 09, 2017, 05:23:13 PM »
For what it's worth I was in the shed doing something else and I took a few minuets to look at the injector pump.

Rotating the flywheel I found the following, bearing in mind that this was done with the Mark One finger and the pump in place, the positions, in degrees, were derived from the marks I made on the fly wheel to set up the cam and rockers and not accurately taken off TDC, so I'm going to be a bit out either way.

The machine is a 6/l bitza but I've no reason to believe the camshaft - and most of the other bits - are not genuine Lister.

The follower started to lift around 75 degrees before TDC, (that doesn't mean it was in contact with the base of the pump)

The injector 'creaked' at 5 degrees before TDC.

The top of the cam felt like it was around 60 degrees after TDC.

I didn't look for the point where the follower came off the cam

Not at all what I'd have forecast. Sadly I'd no time to measure the 'lift' of the cam.

Don't know if that will help, but it seems to me there's a lot of latitude there, the ramp angle is probably most important.

Cheers Stef
Tighten 'til it strips, weld nut to chassis, peen stud, adjust with angle grinder.

dieselspanner

  • Hero Member
  • *****
  • Posts: 726
    • View Profile
Re: Injector Cam Timing
« Reply #5 on: March 09, 2017, 05:27:27 PM »
Oops, double post, could some one in admin delete one please?

Cheers Stef
Tighten 'til it strips, weld nut to chassis, peen stud, adjust with angle grinder.

mcreeferson

  • Jr. Member
  • **
  • Posts: 53
    • View Profile
Re: Injector Cam Timing
« Reply #6 on: March 17, 2017, 11:54:39 AM »
Thanks guys for the input. I think I was overthinking this a bit (once again). I was able to establish proper clocking using the old cam lobes to verify, and using 38ac's idler gear install method. That makes it sort of foolproof, but I am a pretty ingeneous fool...