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Classic Military Automotive » Jeep Flathead Engine Rebuild

Jeep Flathead Engine Rebuild


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WHAT TO DO, OR DON’T DO, WHEN REBUILDING THE L-BLOCK 134 FLATHEAD JEEP ENGINE

PART 1:

1) The first thing you should take into consideration is the warranty of the work performed on your L-block motor. Does the warranty start after the machine shop says to come pick it up or does it begin after you start it up for the first time? Also, how long does the warranty last? Most machine shops are good about giving you some leeway on this question but it’s still an important one to have clarified before you start any engine work.

2) It’s always best to start the motor project last because, having it done early, only delays the inevitable. If you put the motor in and there is a problem, you want to know that the warranty is intact. If possible, have your motor pre-run on an engine test stand for a period of at least 12 to 30 hours and run at various RPM’s. This should give you a good overview of any problems that may come up. If a test stand is not an option, then put the motor into the vehicle but leave as much of the front clip off of the vehicle as possible.
Some of the common problems are usually improper or defective oil pump or oil pump installation. We have found that some, if not most, of today’s oil pumps need to be taken apart and checked for slight malfunctions where by you need to make small modifications to prevent the pump from seizing up during your run-in period. INSTALLATIONS IN RELATION TO THE PROPER TIMING OF YOUR DISTRIBUTOR, REAR MAIN SEAL LEAKAGE AND IMPROPER VALVE ADJUSTMENT are also common mistake-prone areas.

PART 2:

SAVING MONEY IS ALWAYS IMPORTANT!!!

1) Before bringing your short block over to the machine shop, it’s always best to break down as much of the motor as you can by removing the following components:
a) Bell housing clutch and flywheel
b) Head and head studs
c) Manifold and studs
d) Timing cover plate and timing plate studs followed by removing the timing gear sprocket and chain or gear (CJ style)
e) Freeze plugs
f) Cam and cam bushing.
g) Oil pan, bearing caps and crank
h) Valve cover, valve springs and valves (Leave the guides to for the machine shop)
i) Piston rods and separate the piston heads from the rods
j) Oil pump
k) If you can, try and remove the valve guides with the proper tool. These should be pressed out on a press and not hammered out by hand. (Leave them for the machine shop if you don’t feel comfortable about this procedure)

2) By removing and or breaking down as much of the block, this will save you plenty of money in the long run. Be careful not to break or damage any of the studs or GUIDE HOLES as this will only cost you money. If anything is tight or unforgiving leave it for the machinist. Bring your machinist everything related to the basic short block. A large painters bucket is always handy when bringing all of your engine parts to your machinist. Make sure to mark in felt pen the serial number of your motor on the surface of the bucket so that they won’t confuse your parts with someone else’s, while they inspect every component for ware or damage.
Tell them that you don’t want the motor to be more than 30 over on the cylinder holes. It’s always best to consider re-sleeving the cylinders back to factory standards when ever possible.

3) Be prepared to replace tappets, piston rods and piston heads. Many engine re builders will try to re-use your old parts in order to save time and money. Used parts are usually the reason for motor break- down within the first 5,000 miles.

4) Take close attention to your engine head thickness. The factory head thickness from the flat spot above the valves to the gasket surface was approximately .500. Preferably, one should not go below .275 as this may cause problems when test running you’re freshly rebuilt engine. Too much metal taken off the head can and/or will cause higher compression which in this case, is not a good thing. The 6-volt system lacks the power to turn the motor over when higher compression is evident. Your valve clearance is also an issue when over shaving the head surface. Take a moment to ask your re builder if they think the stud hole threads look strong enough. Sometime it is wise to have the thread holes re welded and re drilled then tapped for extra strength. Most machine shops think helical coils work well enough but if you ever have to remove a stud later it may cause a problem with a helical coiled hole. Note: Head shims are available through Classic Military Automotive if you need to bring the thickness up to an acceptable specification.

PART 3: Assembly and Prep of Motor and Motor Components

1) Machine shops do not usually paint your basic engine block however they do bake and clean most engines. The cleaning process is fairly thorough however residual metal shavings can be found in the oil galley’s and small passageways. The best way to remove these excess materials is by performing a simple high-pressure steam wash by using any conventional and portable, high-pressure washer. Place your nozzle firmly up to all of the orifices and blast any debris and grinding oils out of each hidden passageways wherever possible. This will lessen any chances of material damaging your crank bearings during the break in period.
At this point, your cast block will begin to lightly rust. Simply wire wheel your blocks outer surface off as best as you can and then apply a strong primer base. (CMA suggests the DP Concept 40 LF or 50LF catalyst primer). After the primer is thoroughly dry apply whatever color best fits your factory color. The DP 40 gray primer is very close to the Ford GPW gray and should not need any additional gray topcoat. DP is sufficiently strong enough and the color will last a long time.

2) Your original head studs are usually not a good replacement for effective head torque and extended use. If you plan on driving your vehicle often, original factory marked bolts may look good but they can also start to leak coolant. The best engine stud is one without the hex head. It is better to use a headless stud (preferably temper coated studs) because when torquing it only puts pressure on top of the head and does not tend to pull up on the machined threads in the top of the block. A high temperature sealer is also a good product to use on your threaded studs. Toyota makes a high-strength black sealer called Seal Packaging 102 (fipg). Use of this product will lesson you chances of coolant leakage around the base of the stud. Wipe away any residual when using this product. Use gloves with this product for it will stain your hands and the wife may tell you to go away for a few years before she lets you touch her ever again!

3) Make sure your manifold is thoroughly restored and resurfaced before reassembling it to your motor. Improperly rebuilt manifolds will cause vacuum leaks and your engine will not run to its optimum potential. Use of the DP primer is also good for items like manifolds because of its high resistance to heat. Your timing chain cover, pulley wheel, valve cover, water pump, oil pump, thermostat housing, bell housing, throttle body etc. may also be coated with DP for extended surface life.
Installing as much of the bolt on components before installing your motor will be easier on the bench. Take the time to save your back!

PART 4:THE BREAKING-IN PERIOD

1) Now that your motor is assembled, you can begin starting your engine. Make sure your radiator is full of water and your engine has the required amount of oil. When breaking in a fresh motor, it’s always good to use good quality motor oil. CMA suggests using the Chevron Delo 400 for your breaking in period.

2) After staring your engine keep the idol up to around 2,000 rpm for about 8 to 10 minutes. This will help seat the rings in the cylinders. Lower your idol down to about where you’re idol position should be and check your fuel mixture and proper idol range. Sometimes “L” block motors have a distinct miss after the warm up period. This can be due to your fuel mixture and the fact that your valves have not seated totally or your distributor is insufficient or worn out.

3) Driving your jeep for about 500 or more miles may cure most of the miss however the W/O Carter carburetor is usually the main reason for extended ruff idol. If the distributor is found to be the problem then a Pertronic’s electronic rebuild kit may help this problem. These kits allow for a hotter spark resulting in better ignition.

NOTE: PROPER DISTRIBUTOR AND CARBURETOR REBUILDING MAY BE NECESSARY FOR YOUR MOTOR TO RUN AT ITS OPTIMUM LEVEL.

Thank you for your interest in Classic Military Automotive, a division of CMA North Bay. If you have any questions, comments, or just want to drop us a line, please feel free to e-mail Terry at gpajeep@yahoo.com. Prefer talking to someone instead of typing? Give us a call at (707) 542-4353. We are typically around seven days a week, so don’t hesitate to call to make an appointment.