The Cat “A” Model Pump and Governor - Diesel Truck Forum -
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post #1 of 1 (permalink) Old 08-26-2009, 03:05 AM Thread Starter
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The Cat “A” Model Pump and Governor

The Cat “A” Model Pump and Governor:

The “A” model pump is a standard scroll and rack pump that uses much smaller pump assemblies than the later and more efficient “B”. Peak pressure from the A governor is 11K psi, using, if I recall correctly, 9.8mm plungers. It times with the standard pin-in-cam plus TDC pin for “field” timing, or before the advent of the meter, dial indicated TDC with the pin in the pump for more accurate timing. Timing for the DI is still the standard 24* static, or 26* dynamic for the 14.5/1 pistons.

The A model governor is the latest governor based on that of the “D” series bulldozer and Ag/ Gen governor set from the sixties and seventies. It has the same basic housing set, the torsion drive gear to drive the flyweight gear that will drive the servo assembly, a bottom mount shut-off that sits in a dry housing, or the attachment for the manual shutoff, and the “fat” type air/fuel ratio that is the same as that on the 3208T.

The drive for the pump, or the timing advance, is the old style standard sliding weight type. Instead of the helix for advance being on the drive gear for the helical faced cam, it is in the advance itself with an angled outward slide of the advance weights. These are governed by two inner and outer springs that are designated RPM wise by the stiffness of the spring set. The advances were basically three degrees for the PC and five degrees for the DI.

Building and Repairing:

Removing the injection pump for complete overhauls can be done one of two ways. It can be removed by the drive nose by removing the timing advance and locating the four 3/8” bolts and square plate that holds the 15” drive “snorkel” to the front cover plate from the inside, the attached support bracket near the transfer pump under the nose, the fuel lines and linkage, the AF/C line (#4 AN instead of steel), and the shut-off components, depending on build. The other way is to remove the five 3/8” bolts in the front of the IP, facing the pump, and pulling it straight back from the geared drive. If pinned when removing, it will not need to be re-timed if using this method of disassembly, but will need the oil pressure o-ring two inches in on the shaft to be replaced for re-assembly (5H7370), and the 4N0813 gasket.

There is really no rebuilding of the snorkel drive. The front, behind the square cover and bolts, holds a roller bearing that I’ve never seen fail. The rear is supported by the gear type transfer pump on the bottom, and the tachometer drive by the top, there-by holding it centered to be inserted into the front of the pump cam. To remove the driveshaft, both the T-pump and tach drive must be removed, along with the bearing assy in the front.

The A pump is fairly straight forward for replacing pumps sets. The difference is the timing. To zero the rack, instead of a timing hole, there is a set of two aluminum pieces bolted together in the very front bottom directly in line with the rack and behind the tach drive. You must first remove the front tach drive ¼” bolt and retainer, then the two ¼” bolts from the block set. Once off, tap on table and they will split in half. Remove the gasket from the front piece with the nub sticking out, use two shorter bolts, and re-attach this piece to the front. That is the rack “zero”. The rest of the set-up is the same as the “B”, in which you will over-ride the shut-off in your own preferred method (if it is equipped with a Kysor or mechanical lever shut-off, nothing is required here, as it is in “dead state” already) then pull the throttle wide open. The rack is now zero’d. Remove all the bushings (7E5085) and pull the pumps (6N7829 pumps seem to be the new “all around” pump number) straight upward. Now comes a critical “A” part. When removing the shim washers from underneath the pumps for cleaning procedures, they must be kept in order, unlike the B and C. These shims are used for bench timing and are of different thicknesses. Once bench timed (factory timed), they will use the same washers every time afterwards. Re-assemble the same way as any other scroll pump. Set the scroll gear in line with the alignment notch in the barrel, drop it in straight, grease and install the 3D2992 o-ring, and then the bushing. Do all six, then torq to 155ftlbs. Start engine with a shutdown plate next to the open turbo front for safety, and button it up!!

The “A” governor is a different bear. The main reason for teardown and repair is the infamous loping-at-idle. This is caused by the torsion drive of the servo drive gear creating slop between its drive and the final output of turning the servo gear… There are two kinds of drives, both with the same problem, and to about the same degree of fault. The first, on the PC engines, is the “U” drive. This mechanism has a U shaped spring type torsion drive behind the drive gear. As the U spring gets worn, it creates slop between the two drive nubs. Simpler fix, in which you will just check to make sure the teeth are still good on the gears, then just replace the U spring and the lock. That’s it… Now, we have the second and most common assembly. This is the flat spring and yoke drive. In the center of the cam six inches in, is an 1/8” roll pin. This drives a yoke, pinned to a flat spring, pinned to a yoke and block, which is pressed into the gear at ninety degrees. The rest is the same in the mechanism of driving the servo gear. Here are the details of the governor repairs.

Start by cleaning everything, like always, as best as possible with a Hotsy or brake-clean. Now remove everything you can that’s in the way like hoses, wires, the linkage, the AF/C line, etc… Now remove the ¾” nutted #6 AN line or the the #8AN (7/8") from the top bracket and push hose aside. Bracket and feed hose can be pulled backwards out of the way. If it has a shutoff, now is the time for that. The shut-off solenoid is located in the center of the bottom of the governor and is real fun to get at. The best part is that the retaining bolts go clear thru the housing and the ¼” nuts are on the rear. Hold the bolts, remove the nuts, pull out the bolts and let the assembly fall to the starter where it will sit until assembly (or cleaning). Now, tap on the front where the nuts were, and this piece will drop off also, as it is just the front (rear) shut-off cover. At this point go ahead and remove the ¼” bolt from the very top of the gov., removing the oblong cover from over the hi idle screw. This is not tight at all, so some are known to brake-clean the oily bolt and mark it with a marker or paint stick.

Now we tear into guts. First remove the air fuel ratio by removing the two 5/16” bolts at 1:30 and 7:30 from the rear. Pop the nose downward and out it comes. Now, under where the hi idle cover was, is a short 5/16” bolt. Remove that, along with the 4 longer 5/16” bolts below it in a square, and the last very short 5/16” in the bottom part of the backing plate. This cover should fall right off, but so will the housing in front of it. Tap the cover loose and pull it first, then pull the next housing by unhooking from the shut-off lever that is one-arm locked behind the “medallion” shaped steel thing with two screws. The one to the rear is the rack screw. This screw can be thrown away if desired, as it has no variable torq rise. The other screw is the retaining screw for the rack stop (medallion thing). Remove this screw with the same 7/64”(?) Allen that a B uses and pull rack stop off the end of the servo shaft, being careful not to lose the low idle buffer spring behind it.

Now we are at the main housing. Two bolts from the top in from the front, the next two down are Allen head 5/16”s, the bottoms are standards again. When all the bolts are removed from this housing, you will have to pry it off the locating dowels at 2:00 and 9:00. This sux, but just knock it around a little then pound in something sharp on both sides and pry it off. Just as the B disassembles, catch the spring and washer pile in your hand from the governor guide. Going back to the dozer stage, we have bend locks to contend with now. Bend the three tabs from the ¼” bolts holding the servo, remove the three bolts. Now remove the servo by turning it to unlock, just like a B. Next bend the tabs on the drive gear, but before loosening the bolts, rotate this gear back and forth to see just how much slop we are dealing with. Half inch is about as good as it gets without pulling the cam for the center drive pin for repair if drive assy is (mostly) tight already. Chances are you have 1.5” slop or more from the loose drive assy. This causes the low idle surge, and some power. Remove bolts, holding the sleeves and washers with it, and slide entire torsion assembly out the back. Set all components on the bench, to be rebuilt one by one.

We will start with the drive section, then the front housing, and work back to the end (start). The torsion set of this assembly, as afore-mentioned, consists of a 4N0627 drive pin, 2) 6D9953 roll pins (but get three cause you’ll launch one), the 4N2483 flat spring, and the 4N4051 drive yoke, which slides onto the 9F7882 roll pin in the cam that cannot be serviced without removing the cam, so that part will be left for someone to post a need to go that deep.

Assembling the drive group isn’t that hard, but have a bench and vice. Grab the front yoke and set in vice screwed down to hold the width of the piece in place, but not clamped, or about ¼” open. Insert flat spring into yoke and center by eye thru the pin hole for role pin. Use smallest needle nose you have and grab the first role pin which will shoot across the room. That’s the practice one. Now grab the second one directly in the center with the pliers, hold over hole, which has slight recesses in the fore and aft, and smack it good with your 32oz. hammer. Now drive it STRAIGHT in with your 1/8” punch. Just get it close to centered in the yoke. Perfect from side to side is not necessary. Now set your pin in the vice and repeat the process with the third role pin that you bought extra. Next, build it... Role your vice out to ½” open this time. BrakeClean the removed carrier for giggles and insert yoke-down in vice/ left loose. Bang it out with a hammer and whatever you want. Now set washed gear flat on the bench, empty yoke side up as removed. Bend newly assembled drive assy to 90* sideways, then in the hole of the gear, flat spring facing out at exactly 90* between rotating slots, and bang it with a hammer til it hits the bench on the other side. Drive is finished.

Guess we should pop it in before the next stage. Take the new drive assy and wiggle it side to side holding the gear and end yoke. If there is play from assembly, lay it flat and smack it on the sides where the pins are, tight. Hold gear at 45* up, where drive will stay tight in place if done right, and put bolts in the bottom of the gear slots, washers on, and thru the reused lock tab. Slide bolt spacers onto bolts, drop to 95* so it all stays, and slide assy into cam. When you turn it to line up the bolts, it will also pop into the cam roll pin (or picture it vice versa, same thing) “drive ready”, and tighten/ torq bolts to 20ftlbs. Twist back and forth against the spring and check your play. This will be how much is gone off the cam pin. If it worbles (luv that word) more than ½”, pull it back out and slightly squeeze the input yoke, pop it in again, and see if it’s tighter. It may be all you get. I like less than 3/8” gear play myself. The #1 problem with the “A” governor is now solved. Moving on…

Now to build the front. With the torsion drive installed, re-install the servo assembly with the lock pounded flat again. There really is no wear to this part, just install, slide in lock, tighten bolts, bend locks over, done. The main housing itself is rather simple also. Check governor guide for wear on the top of the front and the bottom of the rear. If it has any sort of wear groove, it needs to be replaced. There is a Cat tool group for this, or make do with what you have. First, check to see if throttle shaft moves up and down in the housing, then remove throttle shaft, again by bending locks out and yanking bolts. If play was felt, replace bushing with a new one. Clean blank housing, set on front face, and using a 3/8” punch, drive out governor guide. Use a socket or any round thing that the new 8M8403 guide sets in fairly tight but protrudes one inch out, slide in the new guide, and with the locking tip fully protruding from the housing, use a ½” steel ball or whatever is handy and crimp/ smash it in place just as it was with the old one. Now install the new 8T2604 seal over the bushing, polish throttle shaft smooth to the very end, re-install as it was originally. Front section is now built. Set this aside for now.

Clean and scrape all other parts, and we will now build the shut-off section. This aluminum piece is simple, but a bich to build. Remove locks and bolts to remove shut-off shaft. Check for play and replace the 1S7984 bushings as needed (x2). Take pictures, lay in order, or just figure it out on assy where the flat sides and the round sides go. It only goes one way, and you can tell by the locks and washers which way the “arms” go. It is a two section piece. The inner is a “wet” housing, the outer, where the shut-off fork is located, is a dry housing. Polish the entire shut-off shaft, and pound out the two seals. Install the first 5P0796 seal facing oil side in, then install the other 5P seal in the outer section reversed, or seal facing out (dust seal). Grease shaft, re-install as removed, bend over flattened locks, and this piece is ready also. Next we will build the governor.

Install the front section with a new 6N9339 gasket just as you would a “B”. That is, install the spring guide, wavy’s and flats, and governor spring onto governor guide. Also note the convex washer to be installed on the end of the servo pin if it happened to fall off. Slide housing directly in place til seated against pump housing. You will now notice the nail end of the servo pin protruding thru the end of the guide hole. Install the retaining bolts to housing, torq to 24ftlbs (or just tight). Now flip the throttle lever back and forth (one time really) and feel the pop of the spring seating onto the guide and assy’s. If torq spring group was removed, re-install it, and for added power remove all shims above the plastic guide one (dropping the torq spring down further against the housing). As noted before, with the nail head of the servo protruding thru the guide hole will now be obvious. Trick number 34 (or whatever). Install low idle buffer spring, if it had one, onto the end of the servo pin, pull pin all the way out, bumping the spring trying to return it, and take some baby needle nose Vice-Grips and clamp them to the very front of the servo pin nail head. This will aid in installing the rack head and screw. Now take a screwdriver; slightly pry the afore-mentioned “medallion” rack head slot apart and on to pin nail head; insert stupidly small Allen screw, and tighten to 80inlbs. Yes, it will roll around and wobble. No worries, we aren’t there yet.

Next we assemble the stupid built stuff, and keep a “mechanics” eye out for assembly goofiness, as this is the weird part and I’m 16 beers deep doing this by memory. Take your newly re-built “center section” and the backing plate in hand. Insert the previously removed 2P8679 restriction strainer, place the 2P8697 rear housing gasket on the front, then role the single arm shut-off fork behind the “medallion” rack head. Insert the very top 5/16” bolt that is under the hi idle screw and screw into place, but not tight. Now take the backing plate, which you will notice has the ¼” horizontal pin, and, after rolling the rack head up so that the half cut hole is up, not the deeper slotted one, install the backing plate which will now hold the wobbling “medallion” rack head in position. Install all remaining 5/16” bolts in place. Wiggle the housing set to center so the pin is aligned with the rack head, and tighten all six bolts to 22ftlbs. Verifying the hi idle screw is in place, or where you want it (one turn = 80RPM), install hi idle cover with the new 5L8991 gasket.

Hard part is done. Take one of the two 8S5388 shut-off gaskets and install the cover, gasket and ¼” bolts from the rear. Install the second 8S gasket onto rear section over ¼” bolts. Slide either the Kysor air-over shut-off onto the front side (right in the middle of the housing base) and lock onto shut-off forks, or just the plain cover that is same as the rear (with a manual shut-off arm and cable). Tighten nuts. Now install the air/fuel ratio, of course the gasket being the easiest number, I forgot, and hook up line.

Guess what. We be done. Use the ever-so unused shut-off plate (anything to cover the turbo to starve for air on start up), hit the key, and run it. Rack screw (under AF/C) and ratio control are all variables. Settem where you want, make sure timing is right on, and off we go… As BlackDog so well puts it, carry on gentlemen
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