Ignition leads

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CaptB
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Ignition leads

Unread post by CaptB » October 16th, 2019, 7:54 am

Ok guys bear with me here. I have had my mutt for a year and a half now and have been replacing parts a long the way and gradually improving the overall performance and reliability. The engine was completely rebuilt before I bought it and since then I have fitted new leads, plugs, carburetor, fuel pump, filters. However I was still not happy with the way it ran especially at low speeds, so I got myself a timing light and decided to check the timing. I could not get the timing marks to line up, in fact couldn't even see the pulley mark under the light. Thinking it must be me I gave up for the time being. However after this I could not get the engine to idle it keeps reving up then cuts back and eventually cuts out. A few days later my refurbished distributor arrived so I decided to fit it. It is fitted with a Prestonlite type solid state unlike the points on my exsisting. So fitted it and could not start the engine, so fitted the old one back on, nothing. For 2 days I have checked everything I could think of, nothing. At the back of my mind there was something about the way the plug leads had been previously connected, so finding an old photo I had taken (see attached) I checked sure enough they were connected different. Looking down on the distributor starting at 1 o'clock 4 clockwise 2, 1 then 3. When fitting the new distributor I had fitted 1, 3, 4 then 2. Changed back and the engine started. After thinking about this, when I was trying to check the timing I would have been getting the firing sequence for 4 not 1 so could not see the timing mark on the pulley. So, what is going on with this engine, is it ok to run like this. Oh the engine started but will not idle and for info when I set the timing marks up tdc for cylinder 1 it lines up however obviously I will be firing on 4 due to the way they are connected.
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Re: Ignition leads

Unread post by Surveyor » October 16th, 2019, 8:17 am

Reversed firing order? Have you checked to see if the notched shaft under the distributor to the oil pump is in backwards? Possible the oil pump was put in backwards?
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Hambone
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Re: Ignition leads

Unread post by Hambone » October 16th, 2019, 8:56 am

Sounds like pump may be out of time, get #1 on compression stroke, set at top dead center, look where the pointer is aimed in distributor, start there with #1 and wire accordingly, I think firing is 1-3-4-2, of you can retime.

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Re: Ignition leads

Unread post by CaptB » October 16th, 2019, 11:40 am

Tdc on no 1 cylinder lines up as it should

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Re: Ignition leads

Unread post by Hambone » October 16th, 2019, 1:13 pm

So at TDC your rotor is pointing at #1 which should be top right wire? Have you ran any sandpaper around your pulley to expose your marks?

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Re: Ignition leads

Unread post by Cobra5 » October 16th, 2019, 2:30 pm

You need to make sure the #1 piston is TDC on the compression stroke.

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Re: Ignition leads

Unread post by CaptB » October 16th, 2019, 9:07 pm

I haven't run sand paper around but I can see and feel a small notch in the pulley which lines up with #1 tdc

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Re: Ignition leads

Unread post by Mark » October 16th, 2019, 11:32 pm

I put a touch of white paint on it.I think the notch is actually 6 degrees btdc
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Re: Ignition leads

Unread post by Hambone » October 17th, 2019, 7:18 am

From your picture, it isn't wired right, #1 is at the front of the motor, sounds like you have timing issues. Sounds like you need to pull distributor and see if oil pump notch is parallel to the engine block.
https://g838.org/viewtopic.php?f=3&t=11 ... ng#p100593

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Re: Ignition leads

Unread post by Mark » October 17th, 2019, 8:16 am

The wires positions on the cap is how I have mine(#1 is at top right corner,1o'clock pos)
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Re: Ignition leads

Unread post by m3a1 » October 18th, 2019, 11:20 am

Have you any old photos of your ignition wires? I'm assuming you don't but if you do, see what the set up used to be. Don't mean to be Captain Obvious but sometimes the easy answers get overlooked. You only made one significant change so you don't need to go looking under every nut and bolt for causality.

As for the following, will someone please correct me immediately if I'm wrong?

If the engine is 180 degrees out your #1 cylinder wire would now be directly opposite where it would correctly be. So, instead of #1 being at the top right point on the distributor, it is now going to be at the bottom left. That starting point being established, the rest of the sequence follows. Easy peasy. There are more sure-fire ways (sorry, I couldn't resist the pun) to figure out when #1 is at TDC on your motor but checking out the 180 degree scenario would be an exceptionally good way to start.

If you are still having trouble, well, it's only four cylinders. Fix yourself a favorite beverage and roll up your sleeves.

Cheers,
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Re: Ignition leads

Unread post by rickf » October 18th, 2019, 4:52 pm

He says it runs with the wires at 180 out so my guess is that either the intermediate shaft under the distributor is backwards or the oil pump was put in wrong. What I would do is to reverse the intermediate shaft and that will bring number one back to it's proper position. But, while the distributor is out be sure to check the oil pump drive to see if it is right or 180 out.
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Re: Ignition leads

Unread post by CaptB » October 19th, 2019, 5:33 am

I have checked and the oil pump has been installed the wrong way round. So my question is this, it has been running like this for a year and a half, do I need to change it. If so, can the oil pan be removed with the engine still in if up on an inspection ramp

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Re: Ignition leads

Unread post by rickf » October 19th, 2019, 8:49 am

If you can get the timing mark to line up with the wires in the 180 out position then running it there is fine. The engine has no idea what position the wires are in as long as the spark gets to the plug at the prescribed time. The only ways to get the oil pan off is to pull the power pak out or drop the front suspension. In my opinion pulling the powerpak is easier than disconnecting the brake line and steering linkages and shaft, rolling the whole thing out and then still working on your back under the vehicle. Remember, on this vehicle you do not need to drain the radiator to pull the powerpak, it comes out as a complete running unit.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Re: Ignition leads

Unread post by m3a1 » October 19th, 2019, 2:08 pm

For those of you who might be following along and wondering about an engine being assembled with the timing 180 degrees out, I offer this grossly oversimplified explanation.

When we discuss degrees, we are talking about one full rotation of the bottom half of the engine. For a visual representation of 360 degrees of rotation, if you made a mark on the pulley of the crank (front of the engine) or the flywheel (and again, these are all connected to the crank) if you turned it one full rotation your mark would come back to where you started and that would be 360 degrees.

So, with that said, there already happens to be a timing mark and that mark typically represents TDC or, "top dead center" where the number one piston is fully up into its cylinder. (Author's note: As Rick will add in a later post in this thread, on the M151 the mark represents perfect timing for the ignition on this engine rather than TDC.) But, for purposes of this discussion, this is merely the starting point from which we will get the lower half of the engine to be in sync with the upper half of the engine (valves) and the ignition system. If you have an engine apart there are usually other marks inside the engine that serve this purpose for reassembly. Now, I say TDC is the starting point because we know that most engines actually runs better at some point other than TDC.

"Timing" on our engine is a matter of getting two other systems to do certain things at certain times in cooperation with the bottom half of the engine during its full 360 degree rotation. As you already know, one system is the upper half of the engine and that would be the matter of intake and exhaust...feeding the engine's cylinders fuel and air and removing the exhaust gases through a system of valves which open and close. In this case, "timing" is ensuring that they do that at the correct time. The valves act like little trap doors at the top of the cylinders. Now, imagine they are opening and closing at absolutely the wrong time! If our little trap doors are open when the bottom half of the engine sends the piston upward on a compression stroke, no compression is taking place and....you guessed it....you have and engine that just won't run.

The other system is ignition. Insofar as ignition goes on our engines, to achieve proper timing (cooperation with the other two systems), its mechanical link to the lower half of the engine happens to be piggybacked to the oil pump. Out of nothing more than convenience and simplicity of design, the oil pump just happens to be a mechanical link between the lower half of the engine and the ignition distributor. So, when the oil pump rotates to pump the oil, it also turns the distributor. Oil pressure doesn't turn the distributor. It is the mechanical movement of the oil pump while it's doing it's job that also turns the distributor. So how can it be 180 degrees out of sync?

Well, first, think of the link between the distributor and the oil pump as being like a flat-head screwdriver and a flat head screw. If you put that screw driver into the screw's head there are only two ways it can go in and yes, that screw can turn 360 degrees but again, only two ways for that screwdriver to go in. One way represents zero degrees or, you can turn that screwdriver around 180 degrees and put it back into the screw head and that is almost exactly the matter being discussed in this thread but not quite. Now, what if the slot in our screw were located, offset, so that it is just a little bit off the centerline of that screw....

Our engine's oil pump has a slot and yup...it's eccentric, meaning it's located just a bit off center and, the blade of the distributor is also just a bit off center. So, there is only one way for them to couple together. Why? Well, so the distributor can never be 180 degrees out of alignment with the oil pump. Which is to say, the eccentricity of the slot, there is only ONE way for the distributor to mate with the pump so it will never be improperly aligned with the oil pump. Some genius thought that up....probably all by himself.

So, right about now, I'm betting you're tearing your hair out and saying, "Now wait just one darned minute! You said the timing WAS 180 degrees off! How is THAT possible?"

Well, the genius who worked on the design of the coupling between the oil pump and the distributor apparently wasn't the same "genius" who designed the oil pump itself or the manner in which the oil pump couples to the lower half of our engine and there's the rub. The oil pump can be installed 180 degrees out of sync and in this particular case, it was.... and because it was, the dominos begin to fall, taking proper orientation of the distributor to the rest of the engine with it. The design would ultimately have been better if they had just put that slot and blade dead center. Mess up your installation and all that is left to do it pull the distributor, rotate it 180 degrees and stick it back in and you'd be done.

Ok, so that explains our friend's troubles. His oil pump is installed 180 degrees out of proper orientation and thus, his distributor is disoriented and 180 degrees out of line with what is "normal" for most of our engines. In my opinion the issue is a minor one and easily resolved. All he has to do is move the distributor wires around two spaces thus, relocating them 180 degrees from what is "normal" and the engine will run without any complaints whatsoever because, as Rick put so well, the engine doesn't care where those wires are, just as long as things happen when they're supposed to happen and that, dear reader, is what timing is all about; keeping the bottom half and the top half and the ignition working happily together, in sync.

Cheers,
TJ
Last edited by m3a1 on October 31st, 2019, 11:47 am, edited 3 times in total.

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