engine timing

[gene]

MY M38a1 f134 distributor has to be turned all the way to the right against the block to get the best timing i can get,when i took the oil pump out for maint could i have put it back 180 off and the jeep still run, ant ideas would be appreciated, thanks Gene S.

[wesk]

With the civvy jeeps which have round distributors a little error in oil pump pre-alignment is not a problem. But with our oval distributors it becomes an issue.

This is one of the most common errors in ignition timing for the M38/M38A1/M170. And one that usually happens during engine rebuilding and final reassembly simply because of a lack of understanding of what drives what and which do we pre-align first.

1 - Get #1 piston TDC on compression. Not about TDC instead you want exactly TDC. A little know tool called a wiggler will let you know when piston travel actually reaches the top. It threads into the spark plug hole and helps you read actual movement of the piston. If you have a flywheel or front crank pulley timing mark you can now verify it's accuracy. If this is the first time for you with this engine setting timing I suggest you install a degree on your crank pulley. Align the 0 with your TDC mark. Now rotate the crank backwards until you are at 5 deg's BTDC.

2 - Properly index/orient the oil pump. You must remove the distributor to see the top of the oil pump drive shaft.



3 - Now you can install the distributor. With the distributor fully engaged with the oil pump drive the rotor should be pointing to the 5 o'clock position. This is where #1 plug wire should be. This is another common error area. Some manuals show the wrong clocking of the plug wires. The illustration below I took from the M38A1 service manual and corrected the wire numbering. The Army did publish an official change illustration but it was well after most original manuals were published. A good reason to insure you have copies of all changes for each of your manuals.



4 - Now you can proceed with the final detailed timing by rotating the distributor til the points just start to open and voila you have your timing correctly set 5 Deg's BTDC.

Some tools for the above tasks:






_________________
Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

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