Tech Tips 2020 no. 2
Steve Turchet dives into what is ailing your military vehicle
BIG HOLES
I have a 1944 Willys MB that is a daily driver. The engine needed a complete rebuild so I pulled it out and took it to a shop that does classic cars. The mechanic said they would have to bore the cylinders .080 oversize.
My grandfather warned me that this is too much and the engine will overheat because the cylinder walls will be too thin. He had this happen with a 1946 Ford pickup.
The engine in my MB is original with the correct serial number for this Jeep so I hate to replace the block. They can sleeve the cylinders but that is too much for my budget.
Do you think it is safe to just have them bored to .080?
Your grandfather may indeed have had a bad experience with a Ford flathead V-8. Boring these engines over .060 did sometimes create overheating problems. This would also happen with many newer engines having thinner cylinder walls.
However, it’s been my experience that L-head Jeep engines have sufficient cylinder wall thickness to tolerate being bored .080, so overheating shouldn’t be a problem. Of course, since your Jeep has its original engine, you may want to pay the extra expense of having the cylinders sleeved.
THE SMELL OF RUBBER IN THE MORNING
My M151A1 has started having a strange problem. When I go out on the road in the morning the engine makes a squeaky noise and sometimes I can smell burning rubber.
This happens when I step on the gas but it goes away when I back off. The engine temperature and oil pressure are normal, and the engine doesn’t misfire or lose any power.
I have checked to find where the burning smell is coming from but I can’t find anything. Any suggestions?
My first suggestion would be to check the fan belt or belts. Loose or glazed belts will make a squealing or squeaking sound at higher RPMs and when the engine is revved. Loose belts will also give off a burning-rubber smell. Look for a lot of black dust around the front of the engine. This indicates that belts have been slipping. If the belts are lightly glazed on their inner surfaces, you can sand them with fine sandpaper, but badly glazed or worn belts should be replaced.
Also check to see if the water pump and/or the generator bearings aren’t binding up and about to seize, or if they feel rough. The pulleys should spin smoothly and freely when turned by hand. If they seem okay, you still may want to sand the pulleys if they’re also glazed. Hopefully, your MUTT’s fan belts simply need to be tightened.
HOW HOT IS IT?
My 1958 M37B1’s exhaust manifold seems to get very hot. It turns a light gray overall with a pinkish tan where the two exhaust ports are next to each other.
The motor has been completely rebuilt with hardened seats and valves. It has about 500 miles on it. The distributor is advancing about 20 degrees. I set the timing, plugged the vacuum line going to the fuel pump for the wipers, and checked the intake manifold for vacuum leaks.
I tested the fuel pressure, 3.5 PSI at idle and 4.25 PSI at high RPM going down the road. I adjusted the idle screw and installed a new muffler and exhaust system.
I drove down the road at 35-40 mph for 2 miles, shut the motor off and coasted into the driveway. I pulled #1 and #6 spark plugs to read them: outer rings were black, porcelain clean, electrodes light gray to tan.
I have built many motors and am 99 percent sure this one is together properly including valve clearance. Do you think valve clearance too tight would cause this problem? What other things could I check?—Dan
Sooooo, what makes you think your M37’s exhaust manifold is getting too hot? If you painted it after rebuilding the engine, it’s normal for the paint to burn off and usually leave the colors you described.
Does it seem to be getting hotter now after the engine rebuild than before? This might be due to the engine having more power than before.
Gasoline engine exhaust can get hot enough to melt lead, but this usually means that the engine itself is running hot, which would be indicated by the temperature gauge, and/or a boiling radiator. Assuming the cooling system is in good condition, the usual things that can cause an engine to run hotter than normal are lugging, hauling a heavy load or climbing a steep grade, restrictions in the exhaust system such as a crushed pipe or the wrong (too small) muffler, a hot environment, too lean a fuel mixture at high speeds (sometimes caused by a vacuum leak) and/or improper engine timing.
Retarded timing, for example, can make an engine run hot. So can timing that’s too far advanced, though you would usually hear an ignition knock. Improper valve clearance shouldn’t make the engine run hot, but if the valves are set too tight they may burn. Another thing to check is if the butterfly valve in the exhaust manifold — the one for warm-up — is opening all the way after warm up.
Check these things and, please, let us know what you find.
CRACKING WISE
You helped me diagnose an engine problem with my 1945 GPW that turned out to be a cracked block allowing coolant to leak into the oil and cylinder. The crack was possibly caused by having the cylinder sleeved a few years ago, causing stresses that the cast iron could not stand.
Since then, I have checked out my two spare old engines. One seems to be able to be bored and rebuilt (waiting for word from the shop) and the other had enough corrosion to need to sleeve one cylinder.
When I had sorted though my options I talked with “Lock and Stitch” about repairing the first engine and they told me that these old blocks have problems with being sleeved, as the forces tend to crack the block, as I experienced. They suggested that these old cast-iron blocks need to have sleeves installed with less-than-normal clearance, and that they needed to be glued somehow.
Since I don’t want to see otherwise usable blocks go to waste, what do you know about the best techniques to sleeve a cylinder without causing a crack? —David Voit
This is like finding the right specialist for a major operation: you should have long conversations with people at different engine shops who have done this kind of work, especially on vintage engines. Get a feel for their experience and if they sound like they know what they’re talking about, and if they’re willing to stand behind their work.
By the way, I’m not a big fan of “Lock and Stitch.” Their motto seems to be: “If you can’t blind ’em with brilliance, baffle ’em with BS.
GRIND ME A POUND
I just bought a 1957 M38A1. The transmission always grinds when I downshift to first gear and usually when I put it in first after backing up. Does this mean that the clutch needs to be adjusted?—Alan Roth
It might, and you should check for proper clutch pedal free play. However, most M38A1s had Warner T90 transmissions with synchromesh second and third gears but no synchromesh in first. It can be hard to shift into first after using reverse, when at a complete stop, or moving faster than a walk, unless you learn to double-clutch.
NEW DADDY
As a new and proud owner of a 1967 M35A2, there are a couple of issues with which I need help. First, the front axle will not engage or operate in an off-road situation. Is this operator error (or ignorance), or can you suggest a troubleshoot procedure?
Second, this truck is multi-fuel: can you suggest a source to inform me of limitations for fuel used?
Congratulations on your new M35A2! You should get manuals for your truck.
Most M35s of that era had automatic engagement of the front axle via a sprag-type clutch in the front of the transfer case, though many were later retrofitted with manual air shifts. I assume you’ve checked for obvious things, such as a missing front drive shaft, missing or stripped drive flanges on the front wheels, or a broken front differential?
Assuming your truck has the automatic all-wheel-drive engagement, it’s possible that the sprag unit has failed. To check, jack the truck’s front end off the ground so one of the wheels can be turned by hand. With the engine off, put the transmission in reverse and try to turn the front wheel. It should turn backward easily but should not turn forward. Then shift to first gear: the wheel should then turn forward but not backward.
If your M35 fails this test, you may have transfer case problems and the truck should not be driven until the trouble is diagnosed and fixed. Aside from getting manuals, you might want to contact Memphis Equipment Company (an advertiser in this magazine) for more advice. They have decades of experience with M35s.
If your truck does have an air shift, you should check to make sure the shift mechanism is working. As for fuel, #2 diesel is the best — and preferred — fuel to use in the multi-fuel engine.
GAS GUZZLER?
What kind of fuel mileage should I be getting from my 1942 GPW if I drive it mostly on the road?
It’s hard to say what to expect in the way of fuel mileage from a 60-plus-year-old vehicle, because many components such as carburetors, distributors, timing gears and chains, camshafts, wheel bearings, drive line and valve train parts are probably worn and/or have been replaced or rebuilt.
For your Jeep, cruising about 45 mph on level highway, I’d say somewhere between 15 and 20 mpg. Interestingly, in these days when many new cars are being praised for getting 30 mph, it seems to have been forgotten that one model of 1942 Willys automobiles was advertised as getting 30 mpg!
SAVE THE FINS!
According to the U.S. Army, one of the best ways to ensure that your HMMWV’s engine, coolant and fluids stay cool is to keep the fins of the cooling stack components clean and straight. These fins are often bent during repair and maintenance, and when enough fins are bent the reduced air flow through the radiator and cooling stack leads to engine and transmission overheating.
To help prevent this, make a fin shield from a piece of plywood. Cut the wood to the necessary dimensions to fit the HMMWV’s cooling stack over the lifting rings. Also round off the edges. Then paint the shield so it looks like something more important than just a piece of plywood, and stencil it with NO STEP.
To use the shield, remove the lifting ring seals and slip it over the rings. Then lay it flat on the oil cooler frame. The rings prevent the shield from sliding off. Don’t run the engine with the shield in place: it will block air flow and lead to engine overheating...just what your nifty new shield is designed to prevent!
After using the shield, replace the lifting ring seals. And, even though the shield should have protected the fins, check for bent fins anyway. If necessary, use the official fin-straightening tool (NSN 5120-00-157-2180). Also clean the cooling stack frequently, especially if your HMMWV is driven off-road, using low pressure compressed air or a low pressure water stream.
WHICH WINCH?
The 9,000-lb. winch is no longer available for the M998/A1 HMMWV. Instead, use NSN 2590-01-456-7879 to get a 10,500-lb. winch kit that replaces the old one. Easy-to-follow installation instructions come with the package.
WHERE’S THE SPARE?
Use NSN 2590-01-525-1995 to get a spare tire carrier for ONLY these HMMWV vehicles with an airlift rear bumper: M1113 expanded capacity HMMWVs (not carrying a shelter), M1114 up-armored armament carriers, M1025A2 armament carriers, and M1097, M1097A1 and M1097A2 heavy variant cargo/troop carriers.
WIRED?
I’m rebuilding my Jeep’s Spicer 18 transfer case. I see that the shift fork bolts are drilled for lock wires. Is this factory, and should I install new wires when I put it back together?—Doug Gardener
A: Yes and yes.
