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351M "straight up cam timing"

 
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Old 10-14-2003, 01:03 PM
palmrose2
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351M "straight up cam timing"

What is it? How do I accomplish it?

This winter when I have more time, I will be changing the timing chain and mabey just pulling the engine to replace worn items and generally tighten things up. I keep hearing about the retarded cam timing on these engines and figured while I was at it I would like to put my timing "straight up". I understand what retarded cam timing is, but how am I supposed to figure what is straight up?
 
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Old 10-18-2003, 08:18 PM
palmrose2
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BTT

Is straight up when you set your cam to start opening the intake valve @ TDC.

C-mon now. Whazzup?
 
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Old 10-18-2003, 09:39 PM
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Depending on your cam the intake valve can open before TDC. I take it that 'straight up' is Zero degrees. Zero degrees means neither advanced (early) or retarded (late). The factory setting on some motors is retarded. This was done to reduce pollutants. It also affects power. This was done by moving the keyway in the crank sprocket. If you install an aftermarket timing set like a Cloyes double roller set, the crank gear will have a keyway for zero degrees as well as one for retarded and one for advanced. Use the zero degee keyway and select a cam for the performance that you want.
 
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Old 10-19-2003, 12:47 AM
Brian S
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Camshaft Q & A

Comp cams and a few other online cam companies have a tutorial section on their sites. I have an camshaft article on my site that does a good job of explaining cam terminology. It would be best to get some backround info 1st and ask questions if you have a problem understanding anything.
 
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Old 10-19-2003, 11:43 AM
powerram50
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didnt they stop retarding it after a sertain year?when i replaced my chain two years ago it was strait up.was this stock or did a previes owner do this?it is a 79 351m.
(ps i love this moter it has good power much more just couses tickets)
 
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Old 10-19-2003, 09:23 PM
palmrose2
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Re: Camshaft Q & A

Originally posted by Brian S
Comp cams and a few other online cam companies have a tutorial section on their sites. I have an camshaft article on my site that does a good job of explaining cam terminology. It would be best to get some backround info 1st and ask questions if you have a problem understanding anything.
I have a problem understanding "my site". I looked in your profile and saw no mention of it.

Thanks for info gentlemen.
 
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Old 10-19-2003, 11:29 PM
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Straight Up

Palmrose,

Straight up for your engine can be accomplished by getting a timing gear set for a 1970 or 1971 351C. It should fit your 351M no problem. In 1972 Ford started retarding by 4 deg. When you install the pre-1972 timing set, or any aftermarket timing set for that matter, just make sure you get the dot on the cam gear at 6 0'clock and the dot or zero on the crank gear at 12 o'clock.

If you already know this, sorry for over simplifying.

Steve
 
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Old 10-20-2003, 08:14 AM
palmrose2
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Well there you go. I never thought that Ford would leave the marks and rotate the cam so that the marks wouldn't match. Or am I still wrong? Mabey a cam set for a 79 351M will be retarded if the marks are lined up..

Don't ever be sorry for enlightening your fellow man Steve.
 
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Old 10-20-2003, 08:24 AM
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If the marks are lined up, the cam timing will still be retarded, because the keyway is rotated and the crank is not at TDC when the marks are lined up.

You could install the set with the crank at TDC and the cam dot at 6 o'clock and ignore the crank dot.
 
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Old 10-20-2003, 11:24 AM
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Danlee is right on. If you install a post-1971 stock timing set, Ford built in the 4 deg retard with everything lined up at 6 o'clock and 12 o'clock. That's why you have to get a pre-1971 timing set. If you get an after market set, I have installed both the edelbrock and the comp cams (current set) and each one has a three-keyway crank timing gear. For straight up you find the zero mark or whatever code they use and put the crank at that position. The cam stays at 6 o'clock no matter what. I had a shop that just rebuilt my engine install my cam 4 teeth advanced and it caused a lot of damage and problems. Needless to say, all the profit they made was erased when they had to fix several bent intake valves. Just 4 teeth on the cam gear was worth nearly 40 deg crank timing. So make sure the cam spot is at 6 o'clock and make your timing decision +4, 0, -4 deg on the crank timing gear.

The edelbrock timing set came with some pretty good instructions. The comp cams website has a good tutorial as said in one of the posts above.

Steve
 
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Old 10-22-2003, 02:08 AM
willd
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Unless I am forgetting basic engine building you could put the cam straight up with the factory retarded gears. By putting the keyway in the correct alignment with the cam gear you would effectively do away with their retard. Assuming of course that you could get the links and teeth lined up. This would require a degree wheel to be sure everything was kosher, but it makes me wonder if it could be done.
 
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Old 10-23-2003, 02:29 AM
jdon88
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I just installed an Edelbrock timing set on my 1980 351M and it looked to me like the stock set was about straight up. There was so much slop in the original chain that it was hard to tell. It looks like the difference between straight up and 4 advanced or retarded is just a fraction of an inch rotation of the crank, is that correct? Either way I hope to see a difference over my old timing set that had 1 of the nylon teeth broken off and a few others cracked.
 
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Old 10-23-2003, 07:35 AM
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I think that it is the cam that is retarded 4 degrees. Since the crank turns 720 degrees to the cam turning 360, then the crank will be 8 degrees off. Eight degrees is 1/45 of one rotation, or not very much. The slop in the timing chain could retard the cam another 4 degrees. I suppose the symptom of a stretched timing chain is loss of low speed torque.
 
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Old 10-23-2003, 12:51 PM
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Cam timing is always specified relative to crankshaft position. So cam timing is "advanced" or "retarded" in relation to crankshaft position.

For example, cam timing retarded 4 degrees means that the cam (valve) events occur after 4 degrees more crankshaft rotation than they would if the cam timing was "straight up." Cam timing advanced 4 degrees means that the cam (valve) events occur with 4 degrees less crankshaft rotation than they would if the cam timing was "straight up."

So-called "straight up" cam timing is the cam position relative to the crankshaft that the cam manufacturer specified in the cam's design. It is called "straight up" because the crankshaft keyway points straight up toward the cam when the index teeth on the cam and crank sprockets (or gears) are aligned.

Cam timing (advanced, "straight up," or retarded) is determined by the timing set, which locates the crankshaft keyway in relation to the index tooth on the crankshaft sprocket or gear.

With an OEM-type retarded cam timing set, the crankshaft sprocket keyway is located so as to alter the position of the crankshaft's keyway (relative to the index tooth) so that it is not "straight up."

The only way to change the alignment (and cam timing) would be to cut another keyway in the crankshaft sprocket. That's why the aftermarket timing sets that allow multiple +/- cam timing have multiple keyways in the crank sprocket.
 
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Old 10-23-2003, 03:13 PM
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Bubba, would you recommend cutting another keyway into the crankshaft sprocked or would it be easier to install a new aftermarket sprocket?
 

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