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Old 04-15-2013
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

More catching up to do...


Chapter 17: Injector Pump Redux

If you are expecting an explanation of how to rebuild the injector pump, you're gonna be disappointed. I let the pros tackle that job.

Now, getting it mounted and timed -- that's definitely something we can do.

FWIW, the pump in question is a CAV DPA hydraulically governed pump.



Mounting the pump can be a real pain in the rear. Access is pretty cramped, and the fastener configuration makes it a little tedious. Here are a few recommendations:

- If you have the Bowman h/x removed, mount the injector pump first during reassembly.

- Use gasket adhesive on the block side if the gasket only, and mount the gasket before you try to install the pump.

- Once you get the quill shaft of the injector pump aligned with the drive hub, move it forward only far enough to get the washers and nut started on the bottom stud. If you move it all the way forward to the block, you won't have enough room between the end of the stud and the injector pump to get the nut on.

- Get the nuts finger tight on the two studs before you try to get the cap screw started in the inner hole.

- For the cap screw, BUY A BALL END HEX WRENCH! (Seriously - you'll be happy you did.) Rotate the pump out (clockwise from the front of the engine) as far as you can, since that should give you a little more maneuvering room around the anti-stall device on the top of the pump.

Once you get the fasteners set up, you can time the pump to the engine.

There are three ways to skin this cat (well, four actually...)

The easiest way is to line up the indexing marks on the pump flange and the engine block -- and pray. Chances are that the engine will run, but it may not run at its best. Basically, you are betting that the external index marks accurately match what's going on internally. If the timing gears haven't been taken off, and the diesel shop has got the pump reassembled correctly, then you're gonna be really close to where you want to be.



But if the stars and planets aren't aligned, then more work is in order.

The next way to do it is using a special tool (which of course your average schmuck like me doesn't have, and oh by the way they don't make any more). What this tool does is let you dial in the external index marks. Since I don't have this tool I didn't waste a lot of brain cells trying to fully understand all the steps and settings to make this device do its stuff.

That leaves us with our last option -- physical measurement of the piston.

There are a couple of ways to do this. The first way is to take a direct measurement before the head is reinstalled on the block. Very simple, very accurate.


The second way is to use the piston drop method. Since I'd already installed the head, that's what I had to do. This is also the method most will use if they are timing the pump with the engine already installed in the boat, so it probably will be useful to other Perky-philes.

I pulled the rocker assembly off to get unfettered access to the valves on #1 cylinder. The workshop manual says to just move one of the rocker arms to one side, but after I looked at the situation for a second I realized that that just wasn't gonna work for me. There was no way I was going to be able to get a valve spring compressor into the game without removing the entire rocker assembly.

After making certain that the engine was at TDC (check the mark and/or the keyway on the crank pulley), I removed the springs from #1 intake valve. I put a piece of locking wire around the top of the valve stem just as a precaution against it dropping all the way into the cylinder if I went too far (the old o-ring groove in the intake stem is perfect for this.)

I set up the dial indicator with the probe on the very top of the valve stem, and rocked the crank back and forth to see exactly where the piston reached its highest point (i.e., TDC.)



Once I verified TDC, I rolled the crank counterclockwise about 30*, and then slowly brought it back up and stopped when the piston top was 0.108" below TDC. I made sure I was measuring on the upstroke (i.e., when turning the crank closkwise) to eliminate any backlash in between the idler gear and the pump drive gear. At that point, I pulled the inspection cover off of the pump to see the static timing marks. I lined up the external timing index marks on the pump flange and the engine block and tightened up the nuts and the cap head screw.



After loosening the three bolts on the drive gear, I used the rotated the hub until the stating timing mark inside the injector pump was aligned with the "A" mark and then retightened the gear bolts. I made new alignment marks on the gear and drive hub. (Alternatively I could have just rotated the pump, but I wanted to keep the external marks accurate just in case I ever need to pull the pump in the future.)

Another bit of "thinking ahead" came to mind: Why don't we add a couple of index marks on the timing case cover that shows both TDC and 18* BTDC? These are just temp marks with a Sharpie -- I've got to think about something a little more permanent...



Then it was just return the piston to TDC, remove the safety wire, and reinstall the valve springs and rocker arm assembly.

Done deal.
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