CUMMINS 6CTA8.3

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Repowered 745-C

Sooner or later, if you have a bunch of older equipment the time comes when you have to to junk it or repower it. We managed to buy ourselves a Fiat Allis 745C sight unseen for reasons that we are too embarrassed to mention publicly. Anyhow the iron dealer assured us it was in good condition and we sort of believed him. We had a clue of a problem when the trucker complained that it took extra time to load the machine because it had to be pushed on the lowboy because it wouldn't run. We actually got it running, enough to convince ourselves that the machine was fairly sound but for the bad engine.

The Fiat Allis 745C has a AC 11000 engine in it which commonly appeared in the HD11 dozer, and which was turned up to 195 HP for use in the 745C. It is the same basic engine that was also in the TL30. At this time (2002), engine parts for the AC11000 remain available, but the last one we repaired (in the other 745C that we owned didn't come out too well so we flinched and trying to fix this one. Then along came an opportunity to acquire a Cummins 6CTA 8.3 engine.

The Cummins 8.3 is an extremely popular mid range equipment engine marketed in all sorts of construction equipment with horsepower requirements from 150 to 300 HP. At 503 Cu. in 250-280 hp @2200) and 1360 lbs. it is a nice sized engine for a variety of applications. You will find it under the hood in Volvo road graders (formerly Champion), Army 5 ton trucks, and numerous other applications.

For repowering applications, it is pleasant to work with because it is physically smaller than many engines in this HP class. Indeed when we were done we found the front motor mount exactly 1 inch shorter than the AC11000 and the fan ended up about 6 inches further away from the radiator, but I am getting ahead of myself.

Torque and Horsepower

When you undertake a repower, there are a host of things that have to be considered. The first thing we looked at was the power and the torque. The particular engine we acquired was set at 240 HP with 750 ftlbs of torque at 1500 RPM. This was a bit stronger than the 195 HP engine we were removing which gave us some pause. As nearly as we could tell these Bosch systems are not easily derated (unlike the old Cummins PT systems) so we had to make a go / no go decision. We decided to go with it, because the limiting factor on a front end loader is usually traction, so if you are over powered instead of twisting things apart you ususally just spin the wheels. Also our experience with the 745C suggested to us that it was under powered likely because the old technology engine wouldn't put out more.

Bell housing and Flywheel

Once we decided the engine was usable from an output standpoint, then we set about seeing if it would fit physically. There is more to this than meets the eye. First there is the bell housing. The 745C has an out of production Allison transmission and is joined by a standard ASE bellhousing. Fortunately they were the same SAE number and they would 'bolt up', though we had to get some metric bolts as the Cummins engine is all metric. That is not the whole issue however. There is the transmission/engine physical connection. The Allison connection on this model is via a pilot on the front of the transmission that sticks into the flywheel, and a flex plate. The flex plate is bolted solid to the transmission shaft, and bolts to the flywheel, with a series of 12 bolts which come through from the front of the flywheel and screw into threaded pieces on the flex plate. This was our major problem. Cummins doesn't offer that kind of a flywheel. The flywheel we had was a conventional type designed to have things bolted on the back of it.

We finally tracked down the design specs for what the flywheel should look like and determined that we could machine the flywheel we had to do the job. So we faced it down as required by the specifications and drilled and counter bored bolt holes through it to allow the flex plate to be bolted to it. The Cummins bell housing is equipped with a 'hole' on the left front side of the bell housing where you can access the bolt circle. We had enough machine shop to do the machining of the flywheel. We found our JET 14x40 up to the job with the gap removed. We chucked up the flyweel, and then ran a long bolt through the headstock and cinched the flywheel up on the chuck to make sure the flywheel didn't get pried off the chuck jaws which really only could clamp inside the crankshaft recess.

Once machined we farmed out to a machine shop with the proper equipment, the job of rebalancing the flywheel -- something that you should do if you machine a flywheel.

The Oil pan

With that done, we could make the mechanical connection between the engine and the transmission, but there were other issues. Overall the engine that we removed was larger so there were not a lot of conflicts except on the bottom. The oil pan on the Cummins conflicted with the rear axle assembly on the 745C. Wtih some research, and a lot of help from Cummins Northwest, our friendly local Cummins dealer we found another oil pan. The standard oil pan is a 'front sump' or 'rear sump' oil pan (it is reversible) but overall it was about an inch and a half too deep to fit. That oil pan holds 5 gallons of oil and will allow the engine to be tilted 45 degrees in any direction and still pickup oil. We discovered that Cummins makes a "marine oil pan" that has a full length but shallower sump. It still holds 5 gallons but doesn't have to be as deep since it is full length. Its limitation is that it provides pickup at only 30 degrees end to end and 45 degrees side to side. We decided that as with a boat if a front end loader is pitched more than 30 degrees front to rear you have more problems than a loss of oil pressure so this 'mod' was good to go. We bought a new pick up pipe and oil pan. With this pan we had more clearance over the cross members and rear axle than did the take out engine-- more than 1 inch. With the engine being quite a bit narrower, there was actually good clearance between the air tanks that sit inside the frame on each side of the engine, and you can get to the oil pan drain plug---more than I could say about the OEM engine.

Rear Motor Mounts

Both the Cummins and the AC had a 4 bolt pattern on the sides of the bell housing for the rear motor mounts. The Cummins as 3 inches narrower and a slightly different pattern. We fabbed a couple 1.5 inch thick adapter plates to bolt in the space. We made them like an 'I-beam' --- made a plate with 4 bolt holes for mount side and another for the bell housing side, and then welded a 'spacer between them. The front mount was designed to sit on a 'cross bar' and bolt down with 2 bolts. The gauge of the holes was different but since the Cummins was 1 inch shorter at this point we welded a strip on the back of the cross bar with two holes drilled in it and bolted the front of the engine down.

Wet Bell housing

Opps! I'm ahead of myself again. The Allsion transmission requires a 'wet bellhousing' which implies that the bell housing will have some oil in it. Part of the "mod package" that Cummins Northwest fixed me up with was a conversion package from the Dry to wet. This consisted of a pipe plug to screw in the bottom of the bell housing, a seal to fit behind the bell housing, and a heavy steel plate with a gasket to cover the 'bolt port' where you access the flex plate bolts.

Fan Height

Another issue in a repower is getting the fan the right height to match the radiator (and the old shroud etc). In years past the fan and water pump tended to be an 'item' but not on this model Cummins. The water pump is mounted on separately and driven off the serpentine belt, allowing the fan hub to be a simple 4 bolt-bolt on bracket. It supports I believe a total of 6 vertical positions or more. The hub center is 1 inch offset vertically from the 4 bolt pattern, so if you turn the hub over and bolt it on other side up it will change the fan height by 2 inches. There are 4 bolt holes in the front of the head and 4 bolt holes in the front of the block, and I believe it will also bridge the block and head for a center choice as well. The 'standard' mount is on the block, but to emulate my takeout engine I had to move the hub up and bolt it on the head, and I had to settle for an inch high or an inch low compared to the OEM configuration because I couldn't match exactly. Raising the fan meant a new mounting bracket for the serpentine belt tightner and a longer belt, neither of which was a big deal.

Retrofitting an Air compressor

Alas, I needed compressed air for the air over hydraulic brakes, and the engine I had acquired did not have air. Money fixes all things, and Cummins Northwest rose to the occasion. This model engine has a PTO opening on the back of the front plate below the injector pump for an air compressor (and the air compressor in turn is capable of taking a power steering pump on the back of it if the application requires.)

Installing the air compressor kit was a bit of an experience. Cummins sorted out all the parts I would need, but I had to figure out which piece when where. The plumbing is something else. Never having done it before, or seen one with an air compressor on it, It took me about half a day to bolt and connect the air compressor and plumbing working from the parts book diagram.

Some changes are pretty subtle. You remove the cover plate from the back of the front plate of the engine, but you can't bolt on the compressor with cap screws, so you install two stud bolts and then mount the compressor, but first you have to replace one of the plugs in the oil gallery with a stubby 'allen head' plug for clearance because the long plug conflicts with the compressor body. Actually it didn't have a long plug in it--it had the oil line for the feed to the Bosch injector pump there--but I had to move that for clearance reasons. The oil line was happy in the next oil gallery hole back, but that had the oil pressure sender unit in it, so that got moved to the other side of the engine in front of the starter.

The air compressor is water cooled, and so the plumbing included to weirdly bent tubes to feed water to and from a couple plug holes in the side of the head. The compressor is fed air from the intake manifold via yet another weirdly bent tube that comes down from the intake manifold (which is integrated into the head). This was the one thing that I had to sort of innovate on. The cummins Kit stopped with a sort hose right outside an aluminum drive in expansion plug on the side of the head. After some head scratching, I decided that a short half inch pipe nipple needed to be added to the mix. I pried the aluminum plug out expecting to find threads behind it. There weren't--- just a smooth hole, but in measuring it, it was drilled the right size for a half inch pipe tap. The challenge here was to tap threads in the side of the intake manifold without getting cuttings into the inside of the engine. Fortunately there was a little lip inside because of a machining issue (the hole wasn't drilled all the way through). I tapped it for half inch pipe, carefully cleaned the cuttings out of my work, screwed in a short nipple, and slipped the provided hose over the protruding end of the nipple and clamped it down with the provided hose clamp.

By taking in air in this fashion from the manifold, the compressor gets fed pressurized air as 'pre compressed' by the turbocharger which gives the compressor an advantage over having to 'suck in'. It also implies that the compressor gets 'clean air' and doesn't need its own air cleaner. My total package of 'engine mods' mentioned here were about $1500 and of that the air compressor was around $1000 of it. Ouch. Boy do they see you coming on compressors. For an air governor we were able to simply move the one over from our takeout engine and it bolted right on the compressor in a standard way and did not require metric bolts.

Hooking up the Other things

Once you have the heavy lifting done on a repower, you still have some work to do. There are all the 'little things' to hook up:

Conclusion

A repower operation always turns out to be more work then you planned, but the results can be very satisfying. We turned a pile of yellow scrap iron into a very usable machine. We've got a few hours on the machine now and are so far really pleased with the results. This Cummins 8.3 is a really high compression engine, and starts readily without a starting aid in moderate temperatures (above freezing). It is also a model that has kicked the smoking habit. Even though this particular engine is a Nov.95 model made a couple of months before the requirements for EPA certification took effect, it is very close to visible emission free. You see a small puff of white smoke as it starts, but that has cleared by the time the engine is up to running speed, and you can't get it to smoke by tromping the throttle, or loading it down.

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