Initial Problem
Our 1998 John Deere 7810 was having poor engine performance and experiencing rough idle. With approximately 7000 hours, we initially suspected bad injectors. The old injectors were pulled and tested and showed they needed replacement. We replaced all six but there was only minor improvement in engine performance. We speculated that there were problems with the injector pump and planned to fix the issue after early season plowing and planting was complete. We unfortunately were forced to face the issue earlier than we had hoped.
During our spring planting season, the tractor continued to run poor with lower than normal power, higher engine temperatures and rough idle. At one point while pulling a disc, the engine abruptly shutdown and would not restart. The engine would not turn over and seemed to be “locked up” with trapped compression in the cylinders. The issue appeared to be most likely related to timing.
After removing the injector pump front timing gear cover, we found that it was not possible to correctly time the injector pump. We were not able to align the timing marks as shown in the fuel system repair manual which requires that when the number one cylinder is at top-dead-center (TDC), the marks on the crankshaft, camshaft and injector pump must be aligned. We speculated that the cam or crankshaft gears had spun or there were major problems with the camshaft. The injection pump gear appeared to be off by about one tooth which caused some initial confusion. We expected a more drastic error if the gears had spun on the cam.
We continued removal of the front engine timing covers and inspected the gears on the end of the camshaft. The key in the front end of the cam shaft appeared damaged and slightly sheared off; although not a major “spin”, it was still clearly enough to cause the engine and fuel system to be out of time.
Continuing our inspection of the gears we found that the injection pump drive gear was missing a significant portion of one of its teeth; we found the broken piece near where the timing cover and oil pan meet. Still curious as to what the overall cause of failure was, we inspected the injection pump drive and found loose and missing components. Our best explanation of the cause of failure is that the hardware holding the pointer on the injection pump loosened and pieces went through the timing gears. This failure lead to the shearing of the key on the camshaft due to increased resistance in the drive. Initially the damage was not enough to cause the engine to stop running, but it caused poor engine performance due to being out of time. During our spring plowing and planting the tractor labored under heavy load and the gears eventually slipped on the cam until it was out of time far enough to stop running. We eventually replaced the injection pump with a good quality used pump from bootheeltractorparts.com.
Body and Front end Disassembly
We decided to leave the engine in the frame of the tractor and attempt to do the work without complete removal of the engine. This required a significant amount of disassembly of the front of the tractor. We removed the hood, exhaust, air cleaner, front body panels and radiator in order to access the timing cover on the front of the tractor. We also removed engine accessories like the fan, idler wheels, alternator and AC pump. Eventually we removed the turbo, muffler, intake and exhaust manifolds.
Removal of Harmonic Dampener – Built Puller
In order to remove the front timing cover, we also had to pull the harmonic dampener from the crankshaft. There is a John Deere puller designed for this application, but we did not own one so we fabricated one from a piece of steel plate and four metric bolts. There are different dampeners on John Deere 8.1L engines; however, ours used 22mm bolts.
Removing the Head and Top-End Disassembly
The head was removed so we could inspect the cylinders since the engine locked up and with 7000 hours it gave us a chance to do a valve job. We dropped the head off at a local engine shop for the valve work and head inspection. Upon inspection of the cylinders we found no excess wear or scoring and all the cylinder honing was intact; therefore, no additional engine disassembly appeared necessary. We left the engine with the #1 cylinder at top-dead-center.
Magnet Holders for In-Frame Work
In the engine repair manual, it mentions “D15001NU magnetic holding set” for performing in-frame cam work. We searched for these holders on the internet and asked a John Deere supplier, but was not able to find them for purchase. It became evident that having the correct holder for keeping the cam followers in place while the cam was removed was very important. If one of these followers were dropped, it would cause significantly more work to recover it and reinstall it. If this portion of our work failed, our in-frame fix may be over and the block may have needed to be removed. Many shops would have removed the block and put it on a stand so the engine could be turned over to keep the cam followers in place. We were not going to remove the engine from the tractor, so we needed a strong and reliable way to hold the followers while the engine was upright.
We decided to build a set of magnetic holders from D78-N52 magnets ordered from KJ Magnets and attached them to 1/4” SCH40 aluminum handles. The magnets were 7/16” in diameter and 1/2” long and rated at 14.30 lb axial pulling force and felt very strong. The magnets are not machinable and needed to be attached to a handle without drilling or mechanical modification. The inside diameter of 1/4” SCH 40 pipe is 0.364”; therefore, we chose to machine the inside ends of the pipe, 1/4” deep, to an ID of just over 7/16” to accommodate the magnets. We performed this work on a mill, but a lathe would probably be a better tool or it could have likely been done with a 7/16” drill bit in a drill press. We chose to use aluminum handles to concentrate the magnetism on the followers and to avoid the handle from falsely sticking to a different component of the engine.
After the aluminum handles were modified to fit the magnets, we applied a liberal amount of JB Weld to the inside of the pipe and inserted a magnet into each of the 12 handles. It was critical to obtain a strong bond so that we would be assured that the cam followers would not be dropped.
The length of our shop built magnetic holders were right at 10 inches long which was adequate for holding the followers in the block with the head removed. In the case that someone would have left the head in place, the handles would have needed to be considerably longer to account for the thickness of the head.
We measured the depth from the top of the block to the followers when they were engaged on the top of a lobe and when not engaged. The difference was about a half an inch and we marked each magnetic holder with a marker at these depths. This allowed us to visually determine if we were holding the follower off the cam assuming we had a good magnetic bond on them.
After the magnetic holders were placed in the push rod holes and we felt them magnetize to the followers, we pulled them up to our bottom mark and held them in place with Anvil brand spring clamps from Home Depot.
Removing Weight Stack to Clear the Cam
The only obstacle preventing us from removing the cam was the front end weight stack. It did not appear that the gear on the end of the cam was going to clear the weight stack and hanger so we chose to remove them. There is some amount of movement possible in the end of the cam to allow clearing but we did not want to risk bumping a follower and losing one into the lower end of the engine.
Removing the Cam
With the weights removed, the cam was pulled straight out but had to be turned slowly to navigate the lobes through the journals. We slid in a 2.25” diameter piece of aluminum tubing for added insurance in case a follower became dislodged or magnetic holders failed. It was very important to us to prevent losing a follower into the engine.
Cam Gears Removal and Reinstall with Press and Press Plate
With the cam removed we were able to press off the inner and outer gears in our 20 ton hydraulic press without special tools or plates. After inspecting the cam, we applied Loctite LB 8012 (part no 234227) to the end of the cam and replaced the damaged key keeper. We then proceeded with reinstalling the gears with the 20 ton press.
For reinstalling the cam gears, we built a plate that fit around the cam lobe nearest to the gears. This was done so we knew we had solid support before pressing the gears back on.
Reinstalling the Cam in the Engine
With the #1 piston still at TDC, we thoroughly inspected the positions of the magnetic holders and made sure none had slid and that all were still held up by the clamps. Once we were confident they were all in place, we carefully removed the aluminum tubing and began installing the cam. The cam was slowly re-inserted and rotated as required to navigate the lobes through the journal carriers. We lubricated each cam journal with 10W-30 as recommended in the John Deere Technical manual CTM86 as we made progress.
Once the cam was nearly fully inserted, we took a moment to check the timing mark on the end of the cam. With the cam riding on the journals but without its gears engaged with the crankshaft, we rotated to align the timing marks and then fully inserted the cam.
Injection Pump Gear and Timing
With the cam installed and the #1 piston at TDC, the injection pump also needed to be timed. We proceeded with mounting the pump on the engine and making sure the fuel solenoid linkage could be connected. In order to be certain the injection pump was timed correctly we looked through the viewing hole on the right side of the casting and made sure the pump drive wheel's timing mark was aligned with the visible tab on the pump. We then inserted the used gear we purchased to replace our damaged R504089 and loosely arranged it so the bolt holes and timing hole aligned with the pump drive wheel. We then torqued the Torx head cap screws on the injection drive gear to 45 ft-lb per CTM243.
Cleaning Off Old Gasket Material
With the repaired cam in place and the magnetic holders removed, we were able to clean off the old head gasket material. We did not want to clean the block with the magnetic holders in place because we did not want to bump one and lose a follower into the engine. We took adeqaute time to clean all the old material and make sure that we avoided losing debris into the cylinders and water jacket or push rod holes. All the cleaning was done by hand with a Shopvac running to suck material as it was scraped off.
Notes About New Gaskets and Where to Order Parts
With the exception of the head and valve job being done by a local shop, we sourced all our parts online. It became evident that it was important to use a reputable source when the first head gasket we ordered from Amazon ended up being a Cummins head gasket in John Deere packaging. We returned that item and ordered all the other gaskets and head bolts from GreenPartstore.com.
Head and Top-End Reassembly
We utilized our shop hoist and a short chain to set the head back on the block while taking care to make sure the head gasket did not move or become damaged. Once the head was in place we installed the new head bolt kit RG24026 while applying clean 10W-30 to the threads of each bolt. It was necessary to install new head bolts because these engines require torque to yield head bolts; thus, the bolts are not reusable.
We followed the torque sequence described on page 102 of CTM86 which required 4 steps to reach final torque values. Step 1 requires following the torque sequence while tightening each head bolt to 65 ft-lb with a torque wrench. We then went through all 26 bolts and marked the tops with a soapstone line parallel to the crankshaft. Step 2 of torquing required turning each head bolt ¼ turn (90 degrees) following the sequence shown in the manual. This was repeated two more times until the head bolts had been turned 270 degrees in ¼ turn increments after the initial torque to 65 ft-lb.
When we were ready to place the rocker arm assembly back in the head we found that the springs made it difficult to line up the indexing pin and hole. We used zip ties as shown in the photo to hold the rocker arms away from the journals. This made it much easier to be certain the indexing pin and hole were correctly aligned at that the assembly was properly seated in its carriers before tightening it down.
Once the rocker assembly was in place and the hold-down bolts torqued, we proceeded to set the valves per the procedure described in section 02-021-03 (page 111) of John Deere Technical Manual CTM86. The procedure requires the use of two John Deere tools; JDE81-1 or JDG820 Flywheel Turning Tool and JDE81-4 Timing Pin as shown in the photos.
The timing pin falls into a hole in the flywheel when the engine is at #1 top-dead-center (TDC) and when it is at #6 TDC. These are the two positions the engine needs to be in to set valve clearance. The flywheel turning tool is used to turn the engine over with a wrench to reach the required positions for adjustment.
When the engine is at #1 TDC the manual requires that the number 1, 3 and 5 exhaust and 1, 2 and 4 intake valves are set with a feeler gauge. Then with the engine turned to the #6 TDC position the number 2, 4 and 6 exhaust and 3, 5 and 6 intake valves can be set.
The manual requires that exhaust valves be set between 0.026 – 0.030 in and intake set in the 0.016 – 0.020 in range. We used a 0.028 inch for the exhaust and 0.018 inch for the intake bent feeler gauge to set the valve clearance.
Injectors and Fuel Lines
We removed the injectors to have the valve job done and had to reinstall them. We applied anti-seize to each one and torqued them to approximately 65 ft-lb with return nozzle port facing out. There is a special tool shown in the fuel system manual CTM243 referenced as tool JDE92 that would make proper positioning and torquing much easier, however we did not purchase one. We used a 12 point 24mm metric socket and end wrench to install and position each injector. We did modify one end wrench so that it could be used to access the injectors in difficult positions and allow exposure of the upper portion of the injector so that the return fuel port could be positioned correctly. Flare nut end wrenches were used for all the fuel lines to avoid damaging the connections. In some cases it would not have been possible to use a different tool due to clearance issues.
Re-Installation of Harmonic Dampener
The factory bolt for holding the dampener on the end of the crankshaft is not long enough to reach the threads without the dampener in its final position. We used a longer bolt that engaged an adequate amount of threads to seat it close to its final position, then installed the bolt we removed during disassembly. With the flywheel pin in place we torqued the dampener bolt to 170 ft-lb as specified in the manual.
Belt Idler
During our disassembly, we found that the idler wheel near the AC pump was seized up and not rotating correctly. We looked at the available replacement parts through John Deere and they offered the entire wheel and bearing assembly, RE505265 for $135. We found some aftermarket nylon idler wheels with bearings for $40, but chose to purchase replacement bearings instead. We disassembled the idler by removing the snap rings and found 2 bearings with the part number NTN 6203LU. The bearings were not offered through John Deere, but we found that they were available elsewhere on the internet for $13.75 each. We chose to press out the old bearings and install new bearings so we could keep the John Deere cast idler wheel rather than replacing it with an aftermarket nylon wheel.
Radiator and Coolant lines
We had a brief moment of confusion regarding the overflow tank and associated small diameter coolant lines but soon figured out the problem. In addition to the overflow tube from the radiator cap to the overflow tank, there is another small line that leads from the plastic tank near the top of the radiator to the barbed fitting on the top of the head near the front of the engine.
Start Up
With the hood and body panels off, but all the critical components hooked up, we performed our start up. We did an oil change and checked the coolant level. We primed the fuel system with the manual pump on the injection pump and operated it by hand until some resistance was felt in the system. We then opened the number 6, 5 and 1 injector line at the top of the pump to bleed air and turned the starter for a few seconds. We then re-tightened the injector lines at the pump and cracked the #6 fuel line at the injector and cranked for a few seconds. The tractor began to fire and run so we shut it off and re-tightened the cracked line and then re-started the engine. After checking for leaks, we re-installed the remaining body panels and began giving our shop a much needed clean up.
References
John Deere Technical Manual CTM86 for 8.1L PowerTech Engines
John Deere Component Techincal Manual CTM243 for PowerTech 8.1L Diesel Engines with Mechanical Fuel Systems.
Fred Kunz and Kris Kunz
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