Timing gear considerations on 1978 Ford 460

Propane, Butane, LPG, GPL, C3H8, C4H10
evranch
Posts: 50
Joined: Thu Dec 13, 2018 11:11 am
Location: Saskatchewan, Canada

Re: Timing gear considerations on 1978 Ford 460

Post by evranch »

Any chance you found a source for a 1644 anywhere? I've got good use out of the truck and "decent" economy all summer considering the work I put it to. Hauling hay, stock trailers, equipment on big goosenecks. I put the mech advance back to stock, dialled base timing back to 15 and gave up on the vacuum can and the truck hauls hard up hills pulling a load with no knock. With more base it ran great unloaded, but wouldn't pull hard up hills.

I'm wondering if the reason I could never get the vac advance to work is because I don't have lean cruise due to my undersized stock gas valve. Vacuum advance is meant to compensate for a slow burning lean cruise mixture, right? So if my cruise mixture is actually rich, then adding advance will just cause knock, which is what happens.

I noticed when cruising with a strong tailwind I can smell rich propane in the cab quite strongly. There is a spot in the throttle curve at which the power suddenly comes on strong, if I keep it below this point I use much less fuel. I suspect this is the tip-over point from cruise to enrichment. Unfortunately this point represents poking the pedal with my toe just off of idle.

The mechanical secondaries are set on my throttle plate to come in immediately, making it effectively one large throttle plate. This is how they were set when I got the plate and mixer from a school bus with a significantly smaller engine. I'm thinking to change them to come in later, changing my throttle curve to give me less sensitivity at the low end as the truck really has only two throttle settings, idling and off like a rocket.

Tom68
Posts: 69
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: Timing gear considerations on 1978 Ford 460

Post by Tom68 »

evranch wrote:
Thu Nov 10, 2022 11:38 am
Any chance you found a source for a 1644 anywhere? I've got good use out of the truck and "decent" economy all summer considering the work I put it to. Hauling hay, stock trailers, equipment on big goosenecks. I put the mech advance back to stock, dialled base timing back to 15 and gave up on the vacuum can and the truck hauls hard up hills pulling a load with no knock. With more base it ran great unloaded, but wouldn't pull hard up hills.

I'm wondering if the reason I could never get the vac advance to work is because I don't have lean cruise due to my undersized stock gas valve. Vacuum advance is meant to compensate for a slow burning lean cruise mixture, right? So if my cruise mixture is actually rich, then adding advance will just cause knock, which is what happens.

I noticed when cruising with a strong tailwind I can smell rich propane in the cab quite strongly. There is a spot in the throttle curve at which the power suddenly comes on strong, if I keep it below this point I use much less fuel. I suspect this is the tip-over point from cruise to enrichment. Unfortunately this point represents poking the pedal with my toe just off of idle.

The mechanical secondaries are set on my throttle plate to come in immediately, making it effectively one large throttle plate. This is how they were set when I got the plate and mixer from a school bus with a significantly smaller engine. I'm thinking to change them to come in later, changing my throttle curve to give me less sensitivity at the low end as the truck really has only two throttle settings, idling and off like a rocket.
So it would like vac advance when it's running with manifold Vac.

In what way couldn't you get vac advance to work ? It's not for lean cruise, it's for cruise, the cylinder isn't full so an earlier ignition point gives peak cylinder pressure just after TDC. Rich or lean doesn't cause knock, they can both burn valves if the timing isn't advanced to suit.

Needs some needle work maybe.

Worth a try.

C3H8
Posts: 1111
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: Timing gear considerations on 1978 Ford 460

Post by C3H8 »

Vacuum advance is exactly what it means. Normally if the engine vacuum is above 8" the advance is working. The higher the vacuum the more advance. However, once the vacuum drops below 8", which happens quickly on medium duty trucks, there is no vacuum advance at all. 60 and 70 Chevy C06 and C70 366 engines didn't even bother with vacuum advance.

The older Fords actually had an adjustment to change the vacuum advance setting. An allen key inserted into the vacuum advance opening allowed the spring pressure to be changed. As for the secondaries they were normally tied to the primaries because that was required on propane. The F600, F700, etc had governed 2V or 4V holleys. When the mixer was added to the 4V the secondaries became disabled, so they were mechanically tied to the primary linkage, or they just flopped around. This meant locking them closed or fixing them to operate at the same time as the primaries. Obviously closed would be no good for power.

The 1644 was used on these medium duty trucks to control the point at which the full power mixtures came in. Generally, you have to be into the throttle 80 to 90% before the valve will lift to the power point. However, the full throttle mixture is controllable at that point by using the power valve on the mixer. I'm not sure about your comment on the propane smell. You should never smell raw propane. That indicates a leak, failing regulator, worn hose, etc.

Lpg466
Posts: 5
Joined: Mon Nov 14, 2022 3:10 pm

Re: Timing gear considerations on 1978 Ford 460

Post by Lpg466 »

You are heading on the right path with your propane 460, i'm in saskatchewan also so feel your pain of trying to do road tests lol, I have a 466 built specifically for propane and am up around 16mpg with it as long as i'm not fighting a famous sask head wind, I likely have all the parts you could want to upgrade as you mentioned

evranch
Posts: 50
Joined: Thu Dec 13, 2018 11:11 am
Location: Saskatchewan, Canada

Re: Timing gear considerations on 1978 Ford 460

Post by evranch »

By can't get vac advance to work, I mean I can't get it to improve either driveability or economy. Already turned the allen key so it would provide the minimum amount of vacuum advance available. When I bought the truck the previous owner had vac advance disabled as well.

When I have the vacuum advance can in play I always have too much advance except at idle, at least the way I drive this truck (with a light pedal when possible). Even if I remove most of that advance from the base timing, and if I remove too much then I don't have enough advance under load. Starting off, tip-in knock like mad. Climbing hills at moderate throttle, knock and loss of power. Cruising - fine - until I try to accelerate, then knock. So I decided just to not bother with vacuum advance as it's wasting my time, hurting my engine, and not giving me any results! At least I didn't blow an electrode off with all that knocking.

I will have to look at how the secondary linkage works but I suspect you are right C3H6, it is a governed Holley throttle plate which is a bit odd compared to a regular Holley. I probably only have tied together or no secondaries as options.

The propane smell is not anything leaking, it's coming out the exhaust. All hoses are new, regs functioning well, sniffed everything with a gas meter and there is no smell while sitting or at idle. I only smell it cruising with a tailwind. I got a buddy to follow me on a windless day and he confirmed it, it's unburnt fuel out the tailpipe at 1/4 throttle cruise. Must be super rich is all I can think, which is why I'm looking for ways to lean it out.

Lpg466
Posts: 5
Joined: Mon Nov 14, 2022 3:10 pm

Re: Timing gear considerations on 1978 Ford 460

Post by Lpg466 »

What is causing the knocking? Is the engine in bad shape? Worn rod bearings or broken piston skirts will make noise and kill power if too much timing is put in, sounds like you need to change the advance cam in the distributor, I run 30* total timing without vacuum advance and have it all in by 1500rpm, initial is 14*, vacuum advance gives me an extra 22* @ 15hg cruise vacuum, this is with 12:1 compression and a 205* thermostat, cranking compression is 215 psi, no ping or detonation even at wot.

Tom68
Posts: 69
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: Timing gear considerations on 1978 Ford 460

Post by Tom68 »

evranch wrote:
Wed Nov 16, 2022 11:58 pm
Even if I remove most of that advance from the base timing, and if I remove too much then I don't have enough advance under load. Starting off, tip-in knock like mad. Climbing hills at moderate throttle, knock and loss of power. Cruising - fine - until I try to accelerate, then knock. So I decided just to not bother with vacuum advance as it's wasting my time, hurting my engine, and not giving me any results! At least I didn't blow an electrode off with all that knocking.
Doesn't sound like vacuum advance, sounds like venturi advance, attach the vacuum advance hose to the manifold.

You don't reduce base timing or centrifugal timing to run vacuum advance, vacuum advance works when there's high vacuum, that's when your cylinder is almost full of nothing, that is unless you're pulling oil in the cylinder under vac, then when you touch the throttle it'll rattle its head off, some times literally.

evranch
Posts: 50
Joined: Thu Dec 13, 2018 11:11 am
Location: Saskatchewan, Canada

Re: Timing gear considerations on 1978 Ford 460

Post by evranch »

The knock isn't piston slap/rod knock, it just seems like classic spark knock. The engine is in good shape with even compression ~150psi cold, no oil consumption. In fact the knock is very quiet compared to knocks I've heard on gasoline engines and characterized more by power loss and a light clattering sound. But there is a LOT of power loss, and it seems adding more throttle doesn't help but just makes it bog and clatter louder. Which is strange, because getting on the pedal should wipe out the vacuum and take the advance out. I need to get my vacuum gauge permanently installed in the cab, it's sitting here beside my desk, just need to make a housing for it.

I wonder if the diaphragm is malfunctioning in the vacuum advance can, or if the vacuum hose I've teed into (which runs to the C6 transmission) is somehow ported or restricted and fails to drop when the manifold drops. It looks like it comes right off the manifold to me. Maybe I should run a hose from there into the cab to confirm what the vacuum can is seeing under load. As I mentioned the previous owner had the vacuum advance blocked off too when it was on gasoline so maybe there is something wrong with it. It seemed to work fine when tested with the hand vacuum pump, though.

Everything sounds similar to your setup there Lpg466, 15 base + 18 mech for around 32-34 all in, and around 20 from the vacuum advance. Yet it absolutely hates accelerating at mid throttle with the vacuum advance enabled. And as you say, you have a lot more heat and compression, and should be more susceptible to knock. Off topic, is that one of the 466 diesel conversions? Sounds like a neat setup.

Tom68
Posts: 69
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: Timing gear considerations on 1978 Ford 460

Post by Tom68 »

evranch wrote:
Mon Nov 28, 2022 7:32 pm
and it seems adding more throttle doesn't help but just makes it bog and clatter louder. Which is strange, because getting on the pedal should wipe out the vacuum and take the advance out.


When it starts clattering the vac advance is already out of the equation, more throttle and load is just more cylinder fill, so more clatter and hammered engine components.

Are you saying with the vac advance disconnected it doesn't do that ?

Teed in point should not be a problem, unless there is a small restricting hole at the vacuum connection in the manifold.

Had my old dual fuel at the same time 327 out the last couple of days, 34 odd degrees fixed timing (no mech) plus 15 degree manifold vac, struggles to restart hot with all that advance, same as its been for over 20 years. Needs a start retard, when it was a Petrol only motor 40 years ago it had an ignition cut, get it spinning then hit the ignition.

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