Timing quandry

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Derdenker-
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Timing quandry

Post #1 by Derdenker- » Mon Jul 16, 2018 2:51 pm

I've got a rebuilt '78 300 with '87 head and split exhaust. Offenhauser 4bbl intake, Holley 600 4bbl, a mild CompCams 252H, new distributor. I can't get better than 15inches manifold vacuum (CompCams says I should be getting 18-20). This low vacuum and the fact that I do get a mild exhaust pop when decelerating tells me I have late (retarded) ignition timing. BUT !! The timing is advanced as far as it will go and the engine still start and run. I also feel that my lower end torque is suffering. With just an empty trailer hooked up a have to use granny low to get off the line (I'm accustomed to driving these old 4 speeds like a 3 speed, ignoring 1st gear until it's really needed.) It does idle perfect 800 RPM (except for the low vacuum) and runs mid range just great. Any ideas?

guhfluh
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Re: Timing quandry

Post #2 by guhfluh » Mon Jul 16, 2018 10:11 pm

Um....check the timing?
1967 F-250 Crew Cab 2wd, 300 6cyl, T-170/RTS/TOD 4-speed overdrive
240 head, Offy C, EFI exhaust manifolds, Comp 268H, mandrel 2.5-3" exhaust, Edelbrock 500, Pertronix ignitor and coil, recurved dizzy. 200whp/300wtq

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GPGoverMPG
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Re: Timing quandry

Post #3 by GPGoverMPG » Tue Jul 17, 2018 7:29 am

I am guessing it's a vacuum secondary carb. There is a screw under the secondary throttle stop than can be adjusted (in very small amounts) to remove airflow through the secondarys. This will probably help idle vacuum. My truck likes 18 initial and 18 mechanical timing settings. The low end pull may be helped by checking and adjusting the accelerator pump. The screw with the spring on it atop the pump lever. As soon as the throttle moves it should squirt fuel. Best of luck
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72 F250 4x4 4speed 300 I6
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WorldChampGramp
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Re: Timing quandry

Post #4 by WorldChampGramp » Tue Jul 17, 2018 8:03 am

Derdenker- wrote:I've got a rebuilt '78 300 with '87 head and split exhaust. Offenhauser 4bbl intake, Holley 600 4bbl, a mild CompCams 252H, new distributor. I can't get better than 15inches manifold vacuum (CompCams says I should be getting 18-20). This low vacuum and the fact that I do get a mild exhaust pop when decelerating tells me I have late (retarded) ignition timing. BUT !! The timing is advanced as far as it will go and the engine still start and run. I also feel that my lower end torque is suffering. With just an empty trailer hooked up a have to use granny low to get off the line (I'm accustomed to driving these old 4 speeds like a 3 speed, ignoring 1st gear until it's really needed.) It does idle perfect 800 RPM (except for the low vacuum) and runs mid range just great. Any ideas?


Derdenker: Verify Top Dead center, FIRST. Make sure the engine won't start on its own while you bump it over to get #1 piston at what you think is TDC. Remove #1 sparkplug use a Phillips head screwdriver and see if the piston dome is where it’s supposed to be--- at or near TDC. A small LED flashlight may also help you with spotting the "its dark in there" piston.
Go fetch a beer or your favorite beverage and also one of those 'we all have too many' wire coat hangers and a longish skinny rubber band. Cut the entire straight section of the hanger and insert into one end into the spark plug hole as far as it will go. Now use the rubber band as a self-made tensioning device. By putting one loop end around the hanger and attach the other loop end to the closest valve cover hold down ¼ x20 bolt. Hint back out the selected cover bolt a few threads and hook rubber band aroud as instructed. Walla, eureka, out of sight, etc. you have just created the worlds cheapest most accurate TDC verification tool on the planet. A few tips from Gramps, it is easier to rock the piston back and forth in small increments with all the plugs removed and someone else on the business end of the damper with a deep ½” drive socket and a long breaker bar. For all the dial indicator using forum members that frequent this site using this field method will get you within .0001 field tested by Gramps, many times in my mis-spent youth.

Last thought and I will go away… Promise. For the “got to use the positive stop method” which guarantees 100% accuracy forum members you can Get a piece of readily available 18MM threaded rod and make yourself a new addition to your tool box with a knurled nut to dial that sucker in depth wise. Makes a great verification process and the KISS principal applies to this in particular.
Good luck I will shoot a text to the very knowledgeable colleague of mine Dr. PMuller9 for the “rest of the story” on why you may have the dreaded (But I used the stock Ford crankshaft timing gear, cause it looked so great) debacle. The Ford factory crank gear has a 4 or 5 degree retard, built in, which can screw up your seemingly good choice of components for a new punch when you nail it. In your case, if my above cam timing suspicion is correct you have what I use to refer to as the deep throated baritone sound when you get on it that goes nowhere in hurry. Have a great week. Bruce Sizemore

Derdenker-
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Re: Timing quandry

Post #5 by Derdenker- » Tue Jul 17, 2018 9:48 am

GPgoverMPG that secondary throttle stop idea has been tickling the back of my mind and I'm going to try it. THANKS.

Derdenker-
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Re: Timing quandry

Post #6 by Derdenker- » Tue Jul 17, 2018 9:59 am

WORLDCHAMPGRAMP you're dead on about TDC and that's something I've checked several times. Your comment about the Ford factory cam drive gear being 4-5 degree retarded kinda surprised me. I know that advancing the cam timing will give an added punch in the low end and have thought about pulling the cam out a ways and advancing it a couple of teeth but have been kinda nervous about it. I'd even thought of getting one of those special cam drives that you can install advanced on purpose (which I'm less nervous about)-I guess there are 3 notches for the woodruff key so it can be standard advanced or retarded. And you're spot on about that deep throated baritone sound that doesn't seem to do anything but make noise. THANKS for the input.

Mdixon300f100
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Re: Timing quandry

Post #7 by Mdixon300f100 » Tue Jul 17, 2018 12:05 pm

Wasn't 87 the first year for the fast burn EFI head? May be a problem with a carb setup and lack of power.

Derdenker-
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Re: Timing quandry

Post #8 by Derdenker- » Tue Jul 17, 2018 12:21 pm

Mdixon yes '87 was the first year for EFI on the 300. I don't know...I've farted around with the carb so much I don't want to see another one LOL.

rwhistles
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Re: Timing quandry

Post #9 by rwhistles » Tue Jul 17, 2018 1:23 pm

so is it the cam gear or the crank gear that is retarded and does this apply to after market replacement gear sets?
66 F350 300 6 NP435 84 Dana 70 3.73
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Lazy JW
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Re: Timing quandry

Post #10 by Lazy JW » Tue Jul 17, 2018 1:47 pm

[quote="Derdenker-"] ... BUT !! The timing is advanced as far as it will go and the engine still start and run... [quote]

If you are using a stock DuraSpark 2 ignition, verify that the ignition is receiving the signal to retard the ignition while cranking to start. IIRC it is the white wire that needs to have 12 volts during cranking; this retards the spark ≈ 5° for easier cranking.
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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Derdenker-
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Re: Timing quandry

Post #11 by Derdenker- » Tue Jul 17, 2018 2:08 pm

rwhistles it's the camshaft gear. You can buy them with the standard OEM setting or get one that's variable ( 4 retarded - straight up- or 4 advanced) But it is a pain in the arse to change one out. I'm almost convinced to do it, but wonder if I couldn't just rotate the cam a few teeth and achieve the same result. Probably better off to get the new gear.

Derdenker-
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Re: Timing quandry

Post #12 by Derdenker- » Tue Jul 17, 2018 2:17 pm

Lazy JW wrote:
Derdenker- wrote: ... BUT !! The timing is advanced as far as it will go and the engine still start and run...

If you are using a stock DuraSpark 2 ignition, verify that the ignition is receiving the signal to retard the ignition while cranking to start. IIRC it is the white wire that needs to have 12 volts during cranking; this retards the spark ≈ 5° for easier cranking.


I'll do that, but how does that make it retarded while running? I get an exhaust pop on deceleration. Also, if I advance it anymore while idling it "chokes out" and dies.

pmuller9
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Re: Timing quandry

Post #13 by pmuller9 » Tue Jul 17, 2018 2:44 pm

With the vacuum advance disconnected, what is the initial timing at idle and total timing at 2500 rpm?

Cloyes no longer makes the multi keyway timing gear set.
Each tooth on the cam and crank gears changes the cam timing by 12.4 degrees of crankshaft rotation which is way too much.

Lazy JW
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Re: Timing quandry

Post #14 by Lazy JW » Wed Jul 18, 2018 12:12 pm

[/quote]...I'll do that, but how does that make it retarded while running? ...[/quote]

It doesn't. But it will allow you to advance the timing and still be able to start it.
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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Derdenker-
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Re: Timing quandry

Post #15 by Derdenker- » Wed Jul 18, 2018 1:24 pm

Lazy JW wrote:
...I'll do that, but how does that make it retarded while running? ...[/quote]

It doesn't. But it will allow you to advance the timing and still be able to start it.[/quote]

Oh. Okay

Derdenker-
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Re: Timing quandry

Post #16 by Derdenker- » Wed Jul 18, 2018 4:33 pm

Derdenker- wrote:
Lazy JW wrote:
...I'll do that, but how does that make it retarded while running? ...


It doesn't. But it will allow you to advance the timing and still be able to start it.[/quote]

Oh. Okay[/quote
Well here's the thing- it starts just fine where it's at. Instant start as soon as you even touch the key ( I mean absolutely no hesitation at all, I swear you could just breath on the switch and it will start). If I advance it just a little bit of a squeak it will choke and die at idle. So retarding it for starting doesn't help me because it won't run otherwise. It runs great at mid range but I do get that exhaust pop on deceleration, I can't figure how it can be retarded when I'm advanced as far as I can go...AURGH

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Re: Timing quandry

Post #17 by pmuller9 » Wed Jul 18, 2018 5:04 pm

What does the timing light show for timing with the vacuum advance line disconnected?

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Re: Timing quandry

Post #18 by Lazy JW » Thu Jul 19, 2018 2:42 pm

About 10+ years ago the mechanical advance mechanism in the distributor on my White Ox malfunctioned. When I pulled it apart, the rusted parts just fell out. A new (rebuilt) distributor solved that problem.

I would be opening that distributor up and verifying that both the centrifugal advance and the vacuum advance mechanisms are functioning properly.
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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Derdenker-
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Re: Timing quandry

Post #19 by Derdenker- » Thu Jul 19, 2018 2:51 pm

Lazy JW wrote:About 10+ years ago the mechanical advance mechanism in the distributor on my White Ox malfunctioned. When I pulled it apart, the rusted parts just fell out. A new (rebuilt) distributor solved that problem.

I would be opening that distributor up and verifying that both the centrifugal advance and the vacuum advance mechanisms are functioning properly.


I'll be doing that when I start over from scratch with valve train adjustment, leak down tests and all new upper gaskets. The distributor is actually new, I replaced the old one when I put in the rebuilt engine (but I'm not going to discount the possibility that it's bad).

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