The Novak's M715 Military Truck
The M715 makes an excellent, rugged and reliable truck when repowered with a Chevrolet Small Block or Big Block V8 engine. The conversion is extremely straightforward as there is ample room in the engine compartment.
The best choice of engine is probably the 350 CID Chevy V8. A large number of these engines were produced in a two-throat carburetor version and these engines give relatively good mileage and excellent torque in a useable RPM range. Throttle Body and TPI engines make great choices as well. Swapping these engines is not as hard as some presume, especially when you are well informed about fuel injection.
The Novak #C715 conversion kit will also work with all other Chevy small block V8's (283, 305, 307, 327, 400) but because the truck weighs 6,000 pounds empty, it should have a least a 300 cubic inch or larger engine. A 383 stroker will really make things exciting.
The engine being installed must be of the standard shift configuration. That is, it must have a Chevy flywheel, clutch and bellhousing. The clutch release bearing should be the correct one for the Chevy clutch being used. There are several clutches and six different length release bearings. Refer to our clutch information section.
When retaining the T98 with your Novak adapter, you can leave your transmission and transfer case in the same position.
The M715 uses a Borg Warner T98 four-speed transmission which has several differences from its civilian counterpart. These are—that it is mounted remote from the transfer case, it has a 1" shorter input gear, and does not use the adapter plate found on civilian models. Because of these features it requires a different adapter kit than the civilian J-series models with the 230 OHC engine and T98 4-speed. The proper adapter kit is our #C715.
The GM retainer is supplied bolted to the adapter it is used on—it does not go on the T98 transmission. The original T98 retainer will still be used in the role of retaining the transmission front input bearing. This retainer must be shortened enough to clear the GM retainer bolted to the front of the adapter. 1" will be enough, but NOT more than 1¼". There are special internal grooves in this retainer for oil control and if shortened too much it may leak oil. It is suggested that 1" wide masking tape be wrapped around the end of the retainer as guide for sawing. A hand hacksaw can be used to make the cut, followed by a deburring of the fresh edge.
It is advisable to use an 11" diameter clutch. We have found the 11" diaphragm type to work well and still have a very comfortable pedal pressure, provided that linkage modifications are made per the enclosed info. If a 10½" clutch is used it should be of the Borg & Beck™ type. Use of a special Chevy release arm (see our catalog #RAGM). The input gear on the M715 T98 transmission fits a standard 1-1/8"-10 spline Chevy clutch hub.
Install the new pilot bushing in the Chevy crankshaft. It's fairly soft—be careful not to damage it by hammering directly on it. Use a wood block to hammer on. Sometimes, a section of broomstick makes a good drift. In the event that the fit is too tight, you can drop the pilot bushing in the freezer for and hour and before assembly, very lightly heat the end of the crankshaft with a torch.
With the clutch installed on the flywheel (use an aligning tool or the transmission gear to align the disc with the pilot bushing) temporarily install the bellhousing, release arm, release bearing and adapter to check clutch arm "stickout" angle. If angle is not correct, it must be made so—refer to clutch info. Do not assemble adapter to engine until clutch angle is correct.
Before getting too far into the clutch system, you should definitely read our Guide to Clutches, Linkages & Bellhousings. The correct release bearing is chosen based on this clutch info.
You will install the special pilot bushing supplied with our kit in the engine crankshaft. Refer tobellhousing alignment and pilot bushing information, here.
We have found the following modifications to the clutch linkage work very well on this conversion.
A bracket must be made to support the inner end of the clutch cross shaft. Cut a piece of ¼x2" flat steel 6" long. Drill two 15/32" holes to match the holes in the side of the Chevy engine (5-1/8" centers). Cut the bent part of the Jeep clutch bracket off 2¼" in front of the pivot stud hole. This will be turned 90 degrees and welded to the ¼x2" piece to end up with a piece shaped like the enclosed sketch. If the engine block you are using does not have both ½-13 holes, a couple of tabs will have to be added to the plate to mount in the two bellhousing bolts above and below the bellhousing dowel pin.
Shorten the cross shaft (tube) 1½". Draw a line on the tube lengthwise before cutting. This will allow the two halves to be realigned so as to keep the original relationship of the arms. Clamp the two halves in a piece of angle iron when welding together. Note that the holes in these arms, as well as the pin on the upper pushrod end are often quite worn. We welded up the worn hole and redrilled it. We also replaced the worn end on the pushrod with a self-aligning rod end bearing (see catalog).
The cross shaft and new mounting plate can now be installed. Bolt the rod end bearing of the pushrod to the cross shaft arm.
Make a new lower pushrod from a piece of ¼" pipe. Weld a ½" diameter bearing ball to one end and a 3/8-24 bolt to the other end. This should end up 7¼" long.
Screw a 3/8-24 nut and self-aligning rod end bearing on the threads.
Attach a light spring to the hole in the end of the release fork. Connect the other end to a wire loop around the cross shaft. This will keep the ball end of the pushrod from falling out of the release fork. Use the proper fork only (see catalog #RAGM).
If this was all done properly, you should end up with free play when the clutch is engaged (foot off the pedal) and about .030 to .040 air gap between the disc and flywheel when the clutch is fully released. Adjust for air gap—not free play. The amount of free play is not important as long as the release bearing is clear of the clutch fingers (or spring, if diaphragm type) when the clutch is engaged (foot off the pedal). Also, do not try to adjust where the clutch starts to engage in relation to the floorboard—this doesn't matter either. What does matter is that you have air gap (full release) and release bearing to clutch clearance (fully engaged). If the correct fork stickout angle was obtained per the clutch information, the clutch will work, as well as, or better than it did originally.
For many, the most difficult part of any 24 volt equipped military vehicle conversion will be the wiring. There are two basic approaches—keep it 24 volt or convert to 12 volts. To keep it 24 volt, a bracket to adapt the military generator to the Chevy engine will have to be fabricated. The pulley won't be the right width or diameter for the Chevy belt but a Chevy thin single crank pulley could probably be adapted. The Chevy starter will operate on 24 volts but it's a little rough on the drive pinion when it engages. Use a separate 12 volt solenoid and control button to operate the starter. An alternative would be to use two 12 volt batteries in series for 24 volts and tap off of one for 12 volts to the starter. Regular coil type 12 volt GM ignition systems require 7.2 volts to operate. This is obtained by the use of a resistor or special resistance type coil wire. The resistors are available in any parts store, they are usually referred to as ballast resistors. The 1975 and later "electronic" distributors take the full 12 volts.
Converting to 12 volts for the entire vehicle will allow the use of lower priced, more readily available electrical system parts. When this type of electrical conversion is done on a military vehicle it is usually simpler to completely remove the military wiring, switches, etc. and completely rewire. Our "Basic 12 volt wiring diagram" is suitable for use in completely rewiring the vehicle.
Trying to convert the military system to 12 volts is tricky if you are unfamiliar with DC automotive wiring systems. We've put together our guide to electrical conversions in Jeeps to assist you. This will help greatly and your efforts will be worth it.
The front axle on the M715 is a Spicer model 60, and rear is a model 70. Ratios available, other than original, are 4.88, 4.56, 4.10, and 3.73. Ratios higher (smaller number) than 4.56 will require a change of differential carrier in addition to the ring and pinion change.
With the stock 36" diameter military tire and 5.89 gear ratio, the engine will be turning 3,000 RPM at 55 MPH. This is considered excessive. 4.88 and 4.56 gears are recommended for a good balance of on/off-roadability. See our gearing calculator to help you ascertain your situation and make calculations.
The New Process Model 200 transfer case is quite adequate for a truck rated at 5/4 tons. It has all the strength required for even the strongest V8's. Like its well known progeny, the NP 205, the Model 200 is all gear driven, dual range transfer case with a 1.96:1 low gear.
The Novak #MMX Engine Mounts
Our M715 mounts are designed to allow a Small Block Chevy V8 to be welded to the existing frame brackets in an M715. They offer a good range of adjustability if required and add to the elegant simplicity and non-invasive nature of the Chevrolet conversion in these trucks. Note that these mounts are designed to be used with a point type distributor. If an H.E.I. distributor is used, it may be necessary to indent the firewall for distributor cap clearance.
The following will be based on the assumption that the back of the engine has been prepared per the prior adapter assembly instructions and the engine is ready to install into the vehicle.
Tack weld (at this stage) the provided steel channel plates to the Jeep frame brackets. Support the engine for safety and test fit the motor. Because the mounts are telescoping and offer some height adjustment, you can move your engine into the best location for your situation.
It will be necessary to dent the firewall for clearance at the passenger side cylinder head and exhaust manifold. This will be at the "corner" of the firewall where the toe board meets the indented area that the 6 cylinder engine sat in. It doesn't take much—don't get carried away! It is entirely possibly to make this look stock. Be careful.
On the drivers side at approximately the same area, there is a stiffener that sticks straight forward about a ½". Bend about 2" of this flat against the firewall to provide for manifold clearance.
Once you are content with all your clearances, you can pull the engine back out and do a final weld on the frame brackets and bolt up as per the provided instructions.
Install the engine in the M715. We have found it easier to have the transmission in the vehicle and adapters assembled to the engine. If the clutch was assembled with an alignment shaft, the two will slip together with no problem. If they do not—do not try to pull together with the bolts—something will surely be damaged or break!
After the transmission and adapter mate up and the bolts are tightened, lower the engine so the ears on the mount cushions go over the tube on the mount plates. Put the 7/16 x 4" bolts through the ears and tubes and lower the engine on the mounts.
This engine installation will be centered in the frame. The center of the crank should be 15" from each side of the frame. The mounts have enough "give" to allow side to side shift to center the engine. The four mounting plate to frame bracket bolts can now be tightened. Tighten the nuts on the 4" long bolts and run the jam nuts on these using two wrenches.
At final assembly of the mounts, do not over-tighten the bolts that go through the urethane insulator cushions. Note that we have provided a step in the isolators to lock them onto the new frame brackets. When properly tightened, the mounts will provide a very secure fit. The bolts should be tightened enough to keep the engine from moving but no so tight as to squash the urethane cushions. Over-tightening will cause excessive engine-to-frame vibration as well as early failure of the cushions. After the first nut has been properly tightened, put the second nut on and tighten it as a jam nut against the first, using two wrenches.
You may wish to follow up with a sandblasting or wire brushing of the frame and mounts, followed by a good priming and paint.
A tight fitting, block hugging style manifold or header is recommended for clearance of steering components. Fenderwell exit headers are a solution, but sometimes a sloppy one - not to mention the vortex of exhaust fumes that they often cause to swirl into the Jeep. It is best to run the exhaust through a Y-Pipe and run it out the back of the Jeep along the inner side of the passenger's side frame rail. Leave clearance for brake and electrical lines.
Speaking of manifolds, we advise using the older style Chevy "rams horn" type with the outlets that point straight down. Perhaps even better (and more readily available) are our #CC158 headers. These will give maximum clearance at all areas and they have excellent flow (low backpressure) characteristics.
Rams horn manifolds will fit any Chevy small block cylinder head through 1979. In 1980 some small block heads use an offset bolt hole on the right front port only. Rams horn manifolds can be used with these heads also by using a spacer/adapter kit available from most engine rebuilding shops. There is a series of rams horn manifolds that have a rearward turn to the exhaust pipe flange. This type will work fine on the passenger side but will require a tight turn of the head pipe to clear the clutch linkage on the drivers side.
V8 conversions usually require a larger radiator. Read our cooling guide for detailed information and theory. Some of our customers claim to be able to use the factory radiator once the outlets are changed to the proper locations. Others require the addition of an extra row, or the fitment of another radiator.
The throttle "linkage" is most easily accomplished by using a cable and pedal assembly from nearly any GM car built after 1970. While the pedal itself may vary, all brackets and cables are very similar and are widely adaptable to nearly any GM engine conversion application.
Steering can remain unchanged, but Saginaw power steering is desirable. This will require a car or truck power steering box. You must use a lengenthed pitman arm. These should be available through Boyce equipment ( www.boyceequipment.com )
While reading through these instructions, and especially while performing the engine swap, it is often recognized that it is not the swap itself that provides the greatest difficulty, but in the ancillary things like linkages, mounts, clearances, and the like. Any good installation should consider all the points in this article and also allow for time, energy and funds for the dozens of variations in drive train conversions that cannot be anticipated. With a little clear thinking, ambition and ingenuity, the GM engine conversion can be a strong and reliable one.
We strongly suggest that you keep these instructions and the following, associated parts list for future reference. For questions concerning your conversion, contact your 4wd retailer or technician. If you bought your conversion kit directly from us, contact us and we'll make every effort at answering your questions.