distributor and timing issues

[M151A2 MUTT]

I have a 1973 M151-A2. The engine ran pretty well at idle, but struggled to provide power required when accelerating and did not sound very good. Someone removed the electronic distributor some time ago in order to try a mechanical distributor from another older M151-A2 engine. This experiment offered no improvement. The electronic distributor was re-installed and the engine backfired when attempting to start. Troubleshooting began on ignition timing not only as a possible cause of the drop in power when accelerating, but now for the more severe problem of back firing when trying to start. The valve cover was removed. Top dead center of piston #1 (closest to front of vehicle) at the end of the compression stroke was found by rotating the crank shaft pulley clockwise when facing the engine from front of vehicle, until piston #1 stopped moving up and both valves were closed (fully upward). At this position, the distributor rotor was about ¼ inch past piston #2 contact, instead of the expected alignment with piston #1. As expected, after removing the distributor to rotate the shaft to align the rotor with piston #1, the distributor shaft could not be re-installed. It can only be installed with the rotor positioned 180 degrees from the original location, which would put the rotor pointing just past piston #3 contact.

How could this occur? Now here, how can we recover? How can the distributor be installed so that the rotor is at least near piston #1 contact when piston #1 is at TDC?

[Rickf]

You do not rotate the shaft, you rotate the distributor. There is a bolt on the bottom of the disrtibutor body that you loosen and turn the body of the distributor to time it with a timinglight.
A good rule of thumb istwo fingers between the oil filter and the power feed on the distributor. That will get you started.

Rick

[Fil Bonica]

The distributor shaft position is determined by the placement of the oil pump gear in to the camshaft gear.
If at some time it was replaced improperly timing the engine can be near to impossible.
To confirm this it is necessary to remove the distributor and the intermediate shaft and observe the position of the slot on the top of the oil pump.
At TDC it should be parallel to the engine block.
Anything other than that position could mean you will have to remove the engine and relocate the oil pump properly to achieve proper mechanical timing. The -34 manual spells out how to set up things properly.
If you decide that this is the problem it would be wise to confirm that the cam shaft and crank are properly aligned .
You can confirm this by uncovering the camshaft cover and locating the dots on both shafts. When they are rotated they should line up with one another.
Hope that this whole treatise makes sense and helps you find the problem.
Fil Bonica

[Rickf]

The distributor shaft position is determined by the placement of the oil pump gear in to the camshaft gear.
If at some time it was replaced improperly timing the engine can be near to impossible.
To confirm this it is necessary to remove the distributor and the intermediate shaft and observe the position of the slot on the top of the oil pump.
At TDC it should be parallel to the engine block.
Anything other than that position could mean you will have to remove the engine and relocate the oil pump properly to achieve proper mechanical timing. The -34 manual spells out how to set up things properly.
If you decide that this is the problem it would be wise to confirm that the cam shaft and crank are properly aligned .
You can confirm this by uncovering the camshaft cover and locating the dots on both shafts. When they are rotated they should line up with one another.
Hope that this whole treatise makes sense and helps you find the problem.
Fil Bonica

I think what Fil meant to say was "Replaced improperly, timing the motor can be near impossible". A missed apostrophe means everything!

[Ed Schommer]

I'm wondering if, when the point type distributor was removed to reinstall the electonic distributor, the intermediate shaft was lifted from the oil pump gear and was reinstalled 180 degrees out-of-time? The intermediate shaft can be installed incorrectly....the tab on the shaft on the bottom of the distributor is off center and the top of the intermediate shaft that it mates with is the same...off center. But the tab on the bottom of the intermediate shaft can be engaged in the oil pump either way. Try reinstalling the intermediate shaft.

Also: rule of thumb from auto electric technicians: Before you remove a distributor from an engine block ALWAYS first remove the distributor cap to see where the rotor is pointing. Another rule of thumb, crank the engine until the rotor points to a 12 o'clock position as you see it...you can always remember that. Now remove the distibutor from the block. When you reinstall or install another distributor, if the rotor will not point to the 12 o'clock position something is wrong. And, don't ever crank the engine when the distributor is removed.

Use a timing light...rotate the distributor until the mark on the pulley aligns with the pointer. {I always advance the timing a couple of degrees beyond the factory preset of 6 dgreees BTDC...more responsive acceleration].

Also, the problem you describe would appear to be a carburetor problem, or engine badly out of time. Have you adjusted the valve clearance?

[Kurt Lesser]

I helped a guy out that had a similar problem and what he'd done was to reinstall the plug wires 1 hole off when he reinstalled the distributor. Couldn't figure out why he couldn't rotate the distributor far enough to get things to line up properly. Removing the cap and checking the position of the rotor is always a good idea but making sure the plug wires go back the way they were is equally important.

Kurt