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| Brian Evans (Bevans6)
Registered Member Username: Bevans6 Post Number: 82 Registered: 5-2009 Posted From: 67.71.36.165 Rating: |
Converting a Military/NATO 8V-71T for use in a Bus Re-power Brian Evans October 8, 2011 When I was looking at what to do to fix my worn out 8V-71 in my 1980 MCI MC-5C, one big question I had was could I use one of those surplus military 8V71T’s that seem to come and go on the market. I got a lot of advice, mostly don’t do it, funny things go on with those engines. Well, I bought a NOS surplus engine that I thought at the time was an industrial engine for a pump application, and installed it in my bus. Late in the game I found out that the engine number I have, 7083-7395, is indeed a NATO military engine used in that or very similar specification, in self propelled howitzers, troop carriers, tenders, and recovery vehicles among other things. Having done the job and completed it just recently, I thought I would document the differences and challenges that I had to overcome to get this thing into the bus and running. This article focuses on the engine and the differences that had to be overcome to make it a bus engine. What is a Military/NATO Engine? Mine is a 8V-71 turbocharged engine with these specifications, from the manual for an M-110 self Propelled Howitzer: ENGINE 8V-71T 7083-7395 Manufacturer Detroit Diesel Engine Division, GMC V-8, compression-ignition, liquid cooled Type Turbocharged, two-cycle diesel Model (7083-7398) or (7083-7395) 8V71T Weight, Dry (as installed) 2,442 lb (1,107.7 kg) Number of Cylinders 8 Displacement 568 cu in. (9,308 cm3) Bore 4.25 in. (10.8 cm) Stroke 5.0 in (12.7 cm) Compression Ratio 17:1 N-80 Injectors DW-LS governor Horsepower, Gross Brake (at 2,300 rpm) 405 (302 kW) Horsepower, Net Brake 345 (257 kW) Maximum rpm. No Load (governed) 2,450 rpm Idle Speed 650-700 rpm On the face of it, an ideal candidate for a bus transplant. Mine was a factory rebuild that had been sold as surplus and stored in various sheds and barns, well sealed. It was perfect inside, some storage rust on the outside. There are quite a few differences between it and an MCI bus engine, all in the ancillaries that bolt on to the basic engine. How hard could it be? About 200 or 300 hours and $6200 hard… over and above the cost of the engine. I used normal hand tools, a three foot breaker bar, my 700 ft-lb torque wrench and a 250 ft lb torque wrench, and various pullers. Nothing outrageous. I built the engine dolly to remove and roll the engine around on, an engine stand system that consisted of four legs that bolt to the side of the engine block, and an A-frame crane that I built to take a 4,000 lb chain hoist. I used Permatex Aviation #3 gasket sealer, a brush-on liquid sealer, on all gaskets. I didn’t use any silicone anywhere. I bought a Detroit Diesel gasket set, and several extra seals and such for various things. I did all the work by myself, with no helpers. Rear of Engine The NATO engine had an aluminium bell-housing and a flat flywheel that would not take a clutch. The bell-housing size was a fair bit smaller than the bus SAE bell housing that the Spicer gearbox bolts to, and needed to come off and be changed to the bus bell housing. Same with the flywheel and clutch. The NATO engine has no accessory drives at all on the back. Installing the accessory drives for the power steering pump, air compressor and alternator meant that the engine plate had to come off. That meant that the gear train - idler gear, two cam gears and the blower drive gear - had to come off, along with the blower drive. Taking all that off the bus engine, stripping down the NATO engine, cleaning and re-installing all the extremely dirty bus engine parts was around a 100 hour task. Much of that was simply cleaning the bus parts so they could be painted and reinstalled. I rebuilt the clutch and installed a new pilot bearing in the bus flywheel. The main difficulty is not the complexity of the work, it’s the weight of the parts. You need a hoist to install the bell-housing and the flywheel, although you can install the clutch by hand. Accessory drives The NATO engine has no accessory drives at all. The bus engine uses the right hand cam (looking from the back of the engine towards the front) to drive the alternator pulley, the left hand cam to drive the air compressor, and an accessory drive in the far left position for the power steering pump. You have to install the power steering pump drive on to the engine plate before you install the plate itself. The cam drives are internally splined steel plates about ½” thick that bolt onto the cam gears after they are installed and timed. Top of engine Moving forward, the NATO engine had an engine pre-heat system installed. It injected a mist of diesel fuel under high pressure directly into the air box beneath the blower, and ignited it with a spark plug. It was removed and tossed, and various holes plugged. The injection mechanism is in the same port on the block that is used for the water plumbing on an after-cooled Turbo engine, as a point of interest, so the block on the NATO engine is compatible with after-cooling. The blower on the NATO engine is non-bypass, and according to Don Fairchild the turbo is an old design low pressure turbo. Front of engine At the front of the engine, the MCI engine cradle system uses a large round boss on the front gear cover as the front engine mount. The thermostat housings and the water plumbing are quite different as well. Rather than make new water plumbing and engine mounts I decided to change the front of the engine. That requires removing the water pump, the front cover, the balance cam pulley on the right hand cam (looking at the engine from the engine’s front, right is passenger side), the water pump drive gear on the left hand cam, and the front engine plate. You can now gain access to remove the left hand thermostat housing - the right hand one is right out there, very easy to change, but the left hand thermostat housing can’t be changed by a mortal unless the engine plate is off. Putting it back together is straight forward, just clean, paint and put the bus parts back on in the opposite order of taking off. One note is you can’t install the MCI engine cradle with the water pump in place. Fuel System The NATO engine had a different plumbing installation for the fuel lines compared to the bus engine. I changed over to the MCI system - fuel into the heads at the front on both sides, a cross-over from the left head to the right head at the front, and fuel out from a restrictor fitting at the back of the right hand head. The NATO engine had the cross-over at the back of the heads, and the restrictor fitting at the front of the right hand head.. I also used the MCI fuel filters and plumbing, which were spin-on type and mounted on the engine cradle. The NATO fuel filters were mounted on the front of the engine. The fuel pump was a slightly different model to the one on the bus engine - I am told it’s a high volume version and it has slightly different input and output port locations, so you need to adapt the fittings to suit. I installed an in-line electric priming pump, which worked beautifully when I started the engine for the first time. Several of the fuel injectors were very sticky, I pumped solvent through them for several hours and they freed up. The NATO fuel injection system includes an external starting aid and a throttle delay system. The mechanical governor is a fairly normal automotive LS-DW type. If you don’t have Jake brakes to install, it can be used as is. If you have Jake brakes, you need to install the valve bridges, the fuel pipes and the Jake units following the instructions for that. I took the fuel control tubes off the heads while doing this, so I did a complete rack set up after I put it all back together. If you didn’t disturb the rack, all you would have to do is go through it and check all the settings. Oil System. The oil system externals are quite different between the NATO engine and the bus engine. The NATO engine has a very large two row oil cooler designed to cool the hydraulic systems associated with the automatic transmission in the military vehicle. It also does not have an oil filter head, and the adaptor for the engine coolant into the block is different. All you do is take off all the oil cooler stuff off the bus engine, clean it, paint it, and install it on the NATO engine. The block is pre-drilled and tapped with all the holes you need, but as they are unused on the NATO engine you have to clean them and chase the threads. The 8V-71 block has several external oil line feeds. I used the front right hand block feed for the air compressor, the rear right hand block feed for the power steering pump drive, and the rear left hand side for the alternator and the turbo. The rear left hand side feed on the stock MCI setup was for the alternator and for the oil pressure gauge manifold. I drilled and tapped the oil filter head on the return side for an oil line to the oil pressure gauge manifold, so it now reads oil pressure directly after the filter. The oil pump on the MCI bus engine was the standard scroll type pump housed in the front engine cover over the crankshaft nose. The NATO engine uses a different type of pump similar to the one found in the 12V-71, according to my manual, and it is mounted on the main caps and gear driven. The oil pan is deeper to allow clearance for the oil pump drive gear, and the bus oil pan will not fit. I used the NATO engine pan will just worry about the lower pan height on the back of the bus, and not drive over large rocks or down steep grades. Intake/exhaust system. The NATO engine has a turbocharger mounted on the back of the engine just about exactly where the air compressor is on the bus engine, so it has to be moved regardless. Different bus installations will put the turbo in different places. If your bus can have an 8V92T installed, the best solution is to get the exhaust manifolds and blower top from an 8V92 and use that whole setup - it should bolt right on. The MC-5C has a very low engine bay height, so I mounted the turbo on the drivers side of the engine, fabricated a completely custom exhaust to the turbo and then to the muffler, and fabricated a new blower top to take the pressurized air from the turbo. The turbo needs both an oil feed line of pressurized oil, and an oil drain line down to the pan. The NATO oil pan has two large pipe-threaded ports that you can use to drain the oil back, or you could drain it into the front engine cover if you did a top mounted turbo. Summary Those are the basic differences between the NATO engine and the MCI bus engine. Basically, the way to look at is that except for both being 8V-71’s they are about as completely different as they can be. To do the change right and use the stock MCI engine mounts I had to strip the both engines down to the block front and rear, and build it back up. As Clifford said when I started, it is a lot of work. But these engines are available new and as factory rebuilds, can be had way cheaper than an out-of-frame will cost, and you basically get to start with a brand new engine. Costs Here is the basic cost break-down of the project- note that I included the cost of fabricating the stands, the dolly and the crane I built to lift it with. It’s interesting that the engine cost was less than 25% of the total project cost. Also that the engine cost was less than the price of a good set of piston kits and liners. I bought the best gaskets, filters, etc, that I could buy, I replaced the air compressor while the engine was out, and yeah, I have now got a set of engine stands and a dolly for an 8V-71 that I sincerely hope I never have to use again - on my bus anyway! 8V-71T NATO engine $2,000 Gasket Kit $650 Bendix Tuflo 700 air compressor (rebuilt) $550 Pilot bearing $50 Throw-out bearing $125 Dolly (fabricated) $350 Stands (fabricated) $200 Crane/hoist (fabricated, chain host, trolley) $850 Fuel/air/oil lines and plumbing fittings $400 In-line fuel pump priming $65 Clutch springs and fittings $300 Seals and bits not included in gasket kit $100 Exhaust tubing/bends and fittings $850 Turbo flange and down-pipe to exhaust $200 Paint and cleaning supplies $100 Valve bridge machining $125 Oil and filters (oil, fuel, coolant) $250 Air filter and elbow, mounts $250 Throttle cable $325 Stuff I forgot $500 Total $8240 The end, for now… Next I have to drive it, and I figure sure as God made little green apples with a hundred more HP I’ll be upgrading the cooling system, there may be a different turbo in the future, and everyone says I need an intercooler… Brian Evans October 8, 2011 | ||
| Ralph Peters (Ralph7)
Registered Member Username: Ralph7 Post Number: 204 Registered: 3-2004 Posted From: 74.50.128.155 Rating: N/A |
Yes you need the aftercooler AND drive useing the temp guage! My 8-71TA gets warm at 65 on the level, and I need to lift, this is in a 77 TMC MC-8 with HT- 740 air trans cooler, and the rads are good. The reason I went with the engine I have is my old 8-71N was very tired and needed a rebuild, this engine only needed 2 injectors and IF I do not hurt it probley not need another, hope! | ||
| joe padberg (Joemc7ab)
Registered Member Username: Joemc7ab Post Number: 571 Registered: 6-2004 Posted From: 66.38.159.33 Rating: N/A |
Brian Congrats on getting it all back together and running.I am sure it has given you a great sense of satisfaction. After all busnuts get their hands dirty once and a while and have to spend some dollars to keep their beasts going. | ||
| John & Barb Tesser (Bigrigger)
Registered Member Username: Bigrigger Post Number: 558 Registered: 9-2007 Posted From: 97.91.68.252  Rating: N/A |
"You're a better man than I am Gunga Din". Well done and well blogged. I learned more in the 15 minutes I spent looking over your post than I knew in all the years I have owned 8 V 71 detroits in various vehicles. Thanks for sharing. John | ||
| marvin pack (Gomer)
Registered Member Username: Gomer Post Number: 1556 Registered: 3-2007 Posted From: 76.4.122.151  Rating: N/A |
I am glad you did this instead of me LOL GOOOOOODDDDD JOB and thanks for the post,learnt a lot from it also Gomer | ||
| Brian Evans (Bevans6)
Registered Member Username: Bevans6 Post Number: 83 Registered: 5-2009 Posted From: 67.71.36.165 Rating: N/A |
That was really just the "this is a NATO engine, this is a bus engine, shake hands, return to your corners and come out fighting" post. I am also writing a blog type post on the story behind the conversion, I'll post that in a day or so. I feel bad they are so long, though, I guess people can not read them if they don't want to! Brian | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 1287 Registered: 8-2006 Posted From: 184.10.185.251 Rating: N/A |
Brian,fwiw some MCI 8's and 9's with 8v71's had the oil pump in the pan not on the front of the engine.Derrick Thomas here has a 8v71 n/a in his MCI with the oil pump in the pan good luck (Message edited by luvrbus on October 09, 2011) | ||
| Ian Giffin (Admin)
Board Administrator Username: Admin Post Number: 1469 Registered: 7-1997 Posted From: 24.239.5.12  Rating: |
Hey Brian, Great posting! Would you consider donating this to BNO so everyone can reap benefit from it forever and ever? Thanks. Ian www.busnut.com | ||
| Brian Evans (Bevans6)
Registered Member Username: Bevans6 Post Number: 84 Registered: 5-2009 Posted From: 67.71.36.165 Rating: N/A |
Ian, that was what I hoped would happen, to be honest. Please use it as you can. I am preparing another document that is more the story of the build, rather than the bald things I changed on the engine outline. It has pictures in it. it will be in a WPS format as drafted. Can you do anything with it? Brian | ||
| Ian Giffin (Admin)
Board Administrator Username: Admin Post Number: 1470 Registered: 7-1997 Posted From: 24.239.11.34 Rating: N/A |
Hi Brian, If you can copy and paste it into a Wordpad or Notepad document and email it to me, that'd be great! If it's just as easy to create it in either of those two Windows programmes, then you could also copy and past it directly onto a message on this bbs. I would capture it and delete the message, then put it in the archives all formatted and looking pretty! If any of that makes sense to you, lemme know! Thanks so much! Ian www.busnut.com |
