Won't start

Post by **wesk** » Fri Jul 15, 2011 1:08 am

Ok, now's a good time to slow down and smell the roses.

The distributor is not as complicated as it looks. But it only takes a second and one dumb move and it can cost you a bundle.

First lets try to remember that the main switch on the dash when turned on is feeding 24 volts to the coil. If the points happen to be closed this 24 volts is then grounded, completing the circuit and if the engine is not running the coil will overheat and cost you $80 to $100 for a Prestolite replacement or $50 for a Turkish no name replacement that doesn't hold up well. Left on long enough the points will also overheat and destroy themselves. So never turn the main switch on for troubleshooting unless you have confirmed the points are open or you have disconnected wire # 12 from the distributor.

You should use a simple 1, 2, 3, 4 and etc step by step approach to distributor servicing.

1-Check for power at the distributor connector for wire # 12 with it disconnected.

2- Find # 1 plug wire in the cap and make a crayon mark on the side of the distributor body for it. Remove the cap and inspect the interior and it's components.

a-Inspect the inner cap for carbon buildup, flashover and tracking indications and any cracks or loose or burnt contacts. Check the carbon contact.

b-Grasp the rotor and confirm the centrifugal advance is free and allows the shaft to rotate about 10 degrees and springs right back. Inspect the rotor for cracks, burned contacts and looseness on shaft. Make sure inner cap mount screws are tight.

c- Remove the rotor and inspect the wires for bare spots and overall condition. Make sure terminals are clean and tight. Make sure condenser is mounted tight.

d-While maintaining pressure on fan belts and watching your timing marks turn the fan to rotate the crank in it's normal direction until your timing marks are at 5 degrees BTDC and the rotor is pointing at # 1 spark plug mark on the side of the housing. Rotate the engine ever so slightly to set the points relative to the cam so that they are at their widest opening.

e-Now inspect the contact's surfaces. If they need cleaning use only a regular metal point file. Clean them with a shot of contact cleaner and some compressed air. Now set the point gap to 0.020".

3-Now with the # 12 wire connector disconnected, disconnect the coil's negative wire that goes to the points. Using a digital ohm meter check the coil's Plus terminal to ground (primary circuit) and you should read 0.5 to 1.0 Ohms. Now check the high tension contact to ground (secondary circuit) and you should read between 6,000 and 12,000 Ohms. A zero primary reading means a shorted coil, a primary Open indication means a failed coil. A very low or very high secondary reading means a bad coil.

4- Now's a good time to make a quick timing check. Rotate the crank backwards slightly until the points close. Insert a small piece of paper in between the contacts. Now while maintaining a slight pull on the paper slowly turn the crank forward until the instant the paper comes free. If you are not on your 5 deg BTDC mark go ahead and set the crank at 5 deg BTDC and insert the paper between the contacts again and rotate the distributor slightly until the paper slips out and tighten the distributor hold down up.

Let us know where you are now.

Oldsalt · Post by **Oldsalt** » Fri Jul 15, 2011 7:00 am

Interesting picture of the test adapters. I've seen the sparkplug adapter discussed many times but never knew about the other adapters. Are they available anywhere? I looked on a few vendors sites and didn't find anything.

Post by **wesk** » Fri Jul 15, 2011 8:44 am

Occasionally they show up but they are always available in the kit which if you shop carefully you can find between $50 and $100.

DFoley · Post by **DFoley** » Sat Jul 16, 2011 2:35 pm

Ok...I think I can handle this. However, I have one question. My M38 is one of the more earlier vehicles (MC19598 May/1951). And as such does not have the time marks on the flywheel cover plate. However, my engine crankshaft pulley does have the small timing mark hole. What "mark" am I supposed to line the timing hole up with to adjust the timing?

Post by **wesk** » Sat Jul 16, 2011 9:29 pm

If you have the early engine with the bell housing adapter plate with the window above the starter then use it. Bring #1 TDC on compression and align the 5 deg BTDC mark in the center of the opening. Now look at the front pulley. Is the hole in the pulley aligned with any mark on the timing cover?

DFoley · Post by **DFoley** » Mon Jul 18, 2011 2:20 pm

OK...every time I play with my M38 I learn something new about it. While my vehicle SN is MC-19598 my engine SN is MC-95489. Because there was no "R" before the engine serial number I have always assumed this was the original engine for this jeep. However, while looking for the timing hole on the bell housing to engine plate I noticed a painted over tag attached to the engine block directly under the starter. After cleaning most of the paint off I noticed it is an engine rebuild tag. Which states that the cylinders have been bored to .020 and a date of "7-50". OK...even though the engine number above the water pump does not indicate an "R" according to the rebuilder tag the engine apparently has been rebuilt. This seems important when I could not find the timing hole on the bell housing to engine plate. It turns out I have the newer style engine (10 bolt pattern) with the newer style plate without the timing inspection hole. I drove myself crazy trying to find that inspection port only to discover my engine does not have it. So now I have learned that my cam cover plate is of the earlier style with not timing makes AND my bell housing to engine plate is of the newer style also with no timing inspection port. So now my question is obvious...how should I best set the timing with no timing marks at either location?

Cacti_Ken · Post by **Cacti_Ken** » Mon Jul 18, 2011 2:45 pm

My engine also had a remanufacture plate on it. It did not have RMC in the serial number only MCxxxxxx. I'm assuming it is the original engine yet rebuilt.

DFoley · Post by **DFoley** » Mon Jul 18, 2011 3:30 pm

Yea...I would like to think I have the original engine that came win my body but what confuses me is my engine number is pretty high...95498. A quick review of Wes's serial number table seems to indicate that most jeeps with that high of an engine number were put in M38's towards the end of their run. I know that vehicle and engine numbers were not the same but it seem to reason that earlier engine numbers went in earlier vehicles. Another thing that has me confused is that my engine rebuild tag indicates it was rebuilt in July of 1950! How could an engine that may have been manufactured in 1952 have been rebuilt in 1950! Maybe my jeep was part of some experimental time machine:)

Post by **wesk** » Mon Jul 18, 2011 4:19 pm

An original engine would have an MCXXXXX serial within 4000 of your jeep's serial in 1950/51 moving out to about with 12000 in 1951/52.

The RMCXXXXX serial only comes on a factory new replacement engine.

An Army rebuilt MCXXXXX will not get an R ahead of the serial. It will get an Army rebuild plate.

To determine placement of a timing mark the most accurate method is to remove the head and check piston travel with # 1 TDC using a dial indicator.

Alternatively you can find TDC # 1 on compression with a fabricated wiggler. A small bent rod that you can slip into the spark plug hole and set one end on top of the piston and then bring #1 piston slowly to the topand when movement of the wiggler stops make a reference ink mark on the cover aligned with the hole in your pulley. Now continue moving the crank in the same direction until you feel the wiggler start to move again (going down away from TDC) and make a second mark the same way you did the first. TDC is now 1/2 the distance between those two marks. So make a TDC mark at the mid point. Now rotate the crank backwards 5 degrees (use a round degree wheel held on the front of pulley). Now make a 5 Deg BTDC mark and you are done.