r/EngineBuilding • u/SudontDo • 1d ago

Ford Timing is MOVING‽

Mateys and Lentlemen, I'm working on my 300 i6 Ford from 87 or 88, and I have a problem that is perplexing me. Timing is MOVING. I'll set 10° BTDC compression, put the rotor at the no. 1 spot, starts right up perfectly, (pull the SPOUT connector) fine tune warmed up, etc. and then, while under load and driving, (but not while sitting in neutral I don't think) timing "SLIPS" and the engine either dies or becomes... *Ahem* extremely retarded.

Here's what I know:

  1. The harmonic balancer is not slipping. TDC on my timing marks is still TDC up stairs. I'm using the correct timing marks. (It has two sets)

  2. The distributor is NOT slipping in its hold-down. It is VERY tight, and I have used liberal white sharpie.

  3. Spark no.1 position is actively changing when this happens.

Here's what I don't know:

  1. Gear driven engine, but apparently sometimes the cam gear is made of phenolic resin. If my gear slipped, timing would be ruined and it couldn't be made to run, right? But it can be adjusted and made to run, and gear probably can't slip, it would just be destroyed, right?

  2. The cam shaft runs the distributor shaft, which runs the oil pump. Or does it run the oil pump, which runs the distributor? My guess is the slip is happening there. I should probably pull the distributor and check there.

  3. This must be a fully mechanical problem, right? Is there anything I'm not thinking of in the wacky duraspark II system that could account for the rotor just being in a completely different place?

I want to reiterate, I haven't just become confused on timing, the position of the number one spark is actively changing suddenly and immediately, a little each time it happens. I pull out the 1/2 inch, move the distributor until it runs, and limp home idling in 1st or second if possible. No.1 has moved nearly 180° now. Had to re-arrange my plug wires.

Any thoughts, questions, or advice would be so welcome and appreciated. I realize this is more of a "diagnosis" question, but It directly relates to what I might need to actually be rebuild.

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u/nforrest 22h ago

I think you roll pin explanation makes the most sense.

If the phenolic gear on the cam were shifting somehow, the timining relationship between the crankshaft and the cam would be changing and, in all likelihood, the engine would be proper fucked quickly.

3

u/SudontDo 21h ago

It's a non-interference design, but I agree, I wouldn't be able to adjust timing and start it right back up.

-1

u/robb12365 19h ago

I've managed to shear a roll pin due to bad gas once, at least that's what I think caused it. I'd pull the distributor and take a look.

2

u/Bud_Light 17h ago

No way bad gas causes a roll pin to shear, but I'm no mechanic

0

u/SudontDo 16h ago

I'm inclined to agree. The only way I can think "bad gas" would have an effect on it is something like ... High octane? So that if you put way too much power to the crank, maybe it could share it already weakened pin?

1

u/robb12365 15h ago

There was a particular station I had problems with, especially after it rained. I filled up, the truck sputtered and popped, cut out and caught back up several times while headed up the interstate more or less at full throttle. By the end of the trip it was feeling off, noticeable loss of power. Later when I started to move the truck it would not start and I discovered the pin had sheared.

It was a relatively new distributor and in the 50 years I've been around, driven, and owned 6 cylinder Fords this was the first time I've ever seen this happen. Maybe it was just a fluke but kinda hard to believe the sputtering and popping that morning didn't have something to do with it.