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Old 07-06-2008, 09:39 PM
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Cam Timing

OK cam guru's I need some assistance. The card below is the spec's on the current cam I have in my car. When I checked the numbers against the crank balancer I think that the cam is indexed incorrectly. If it is, I did it, so no one else to blame. According to my calculations the 8" balancer should get a degree for every .07". My cam spec's indicate that the exhaust should open at 48 degrees after TDC. Multiplying the .07 X 48 I get 3.36" after TDC. I pulled the valve cover and cranked the engine to the point where the exhaust started to open. I put a piece of masking tape at that point and marked it at 0 degrees with the timing cover. I then took a flexible tape and measured out to 3.36" (approximately) from exhaust opening point to TDC mark. The TDC mark was at least another inch (4.36") away. Will the engine run being that far off? And am I going about this the correct way to try to determine whether or not the cam is indexed incorrectly. Any help is appreciated.

Steve


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Old 07-06-2008, 10:15 PM
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I can appreciate your math and measurements but when you installed the cam, how did you do that? What type crank sprocket was used? Was it a multiple keyway set?
Quote:
am I going about this the correct way
Well, if it all worked out you could justify, but since you have the cam installed and are now trying to 'see' where it is, no. Your cam card specifies timing events @.050, measured at the lifter. You are eyeballing the valve when it moves, not .050 as measured at the lifter. You cannot do this and expect anything to jive. How is your cam installed now (strainght up, adv or retarded)? Or do you know at all? You have some work ahead of you if not.
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Old 07-06-2008, 10:18 PM
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Suprisingly they will run pretty good 15* retarded (one tooth on the timing gear) or even one advanced, which can make the valves hit the pistons.

You need to follow the entire procedure for degreeing a cam, which starts at determining the exact TDC and making sure your damper is not slipped and is reading correctly. All readings will be taken off of the degree wheel tool.

Check the knowledge base for info. This has been covered several times on this board I'm sure.
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Old 07-07-2008, 02:01 AM
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First of all, you have to find the circumference of the damper by multiplying the diameter times 3.14159. This will give you a damper circumference of 25.132". Dividing 25.132 by 360 will give you 0.0698" per degree.

You can't eyeball the rocker and tell when the lifter is at 0.050" lift. You might be able to get close by mounting a dial indicator on the edge of the retainer. Multipling 0.050" by 1.5 or whatever your rocker ratio is (0.075" for a 1.5 rocker) and observing 0.075" lift on the dial indicator will, like I say, get you close to 0.050" tappet lift, depending on the validity of the rocker ratio.

While you're messin' with it, here's a tutorial for finding exact top dead center on your inertia ring....
http://www.crankshaftcoalition.com/w...op_dead_center
Best piston stop to use is the Crane. It has a hole drilled in it to allow cylinder pressure and vacuum to escape so that the motor turns over easier.....
http://store.summitracing.com/partde...5&autoview=sku

Last edited by techinspector1; 07-07-2008 at 02:31 PM.
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Old 07-07-2008, 06:38 AM
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Thanks for the replies. I have already verified that the crank pulley has "not" slipped. I have a TDC locator and performed that check yesterday. The TDC mark is right on 0 at the timing tab.

I understand that if I were setting this up technically I would need to check at .050" of lift. However, as I understand physics the opening of the valve should not change from the initial timing spec. that it was ground to. So if the exhaust valve is supposed to open at 48 degrees after TDC, then no matter how you install the cam the exhaust valve will aways open at 48 degrees after what "should" be TDC. The cam profile cannot change from the orginal grind.

I really should not have to worry about the timing a .050 of lift in doing what I am doing. If the cam was ground correctly by Engle when it was manufactured, all I should have to do is to make sure that the cam is installed correctly in correlation to the crank. Whatever the grind is will take care of itself since I cannot change its characteristics.

When I installed the cam I used a double roller chain and gear set. I thought I had set the cam dot at 6 o'clock with the crank dot at 12 o'clock. I do not remember buying a sprocket set with the offset capability but I could be mistaken on that. I put this thing in a long time ago and it has never run quite right. Now it will barely run at all.

This setup does not have that many miles (10,000 at most) on it that I would have to worry about the chain jumping a cog. The only thing I can think of is that I installed the gears and chain incorrectly.

Steve
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Old 07-07-2008, 09:11 AM
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Quote:
Originally Posted by techinspector1
First of all, you have to find the circumference of the damper by multiplying the diameter times 3.14159. This will give you a damper circumference of 25.132". Dividing 25.132 by 360 will give you 0.0698" per degree (or, right at seven thousandths, not seventy thousandths).
Hello techinspector1, It must have been early morning when you made the above post. Either that or your keyboard "mis spoke" , as .0698 is only .0002 ( two ten thousands) away from .070 (seventy thousands) and .0628 away from .007 (seven thousands)

Just having some fun being 'picky, picky, picky'. Must be my old age.

To reflog, since you think you may have installed the cam incorrectly it would be best to remove the timing cover and the related parts to check how you have the cam installed. Both Crane and Comp cams have excellent info and photos showing how to install a cam as well as how to 'degree' the cam. You could also do a search on this site as both have been covered here extensively.

Here is a link to INSTALLING a flat tappet cam and here is another link to DEGREEING the cam. Both are from the Crane Cam site.

Last edited by Frisco; 07-07-2008 at 09:45 AM. Reason: added two links
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Old 07-07-2008, 12:22 PM
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Quote:
no matter how you install the cam the exhaust valve will aways open at 48 degrees...

I really should not have to worry about the timing a .050...

If the cam was ground correctly by Engle when it was manufactured, all I should have to do is to make sure that the cam is installed correctly

Whatever the grind is will take care of itself since I cannot change its characteristics
WOW! Never heard this stuff before...

Your satatement in bold (above) says it all. If you had followed the @.050 degree in per the cam card it would be installed correctly and you wouldn't be here asking now would you? JMO
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Old 07-07-2008, 02:32 PM
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Quote:
Originally Posted by Frisco
Hello techinspector1, It must have been early morning when you made the above post. Either that or your keyboard "mis spoke" , as .0698 is only .0002 ( two ten thousands) away from .070 (seventy thousands) and .0628 away from .007 (seven thousands)

Just having some fun being 'picky, picky, picky'. Must be my old age.

To reflog, since you think you may have installed the cam incorrectly it would be best to remove the timing cover and the related parts to check how you have the cam installed. Both Crane and Comp cams have excellent info and photos showing how to install a cam as well as how to 'degree' the cam. You could also do a search on this site as both have been covered here extensively.

Here is a link to INSTALLING a flat tappet cam and here is another link to DEGREEING the cam. Both are from the Crane Cam site.
Yeaaaaahh, well......blame it on a senior moment.....
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Old 07-07-2008, 02:49 PM
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I wish everyone was here to put their foot up my you know what. Pulled the timing cover and appears cam was installed 1/2 round off. Had the dist. set on number one. Had the crank indexed to 0 degrees and the dot on the cam gear was located at 12:00 o'clock. I'll probably get new gears and chain as it looks like I had to force the old crank sprocket on. It is pretty well hammered. Also need a new key so will get that if I can find one.

Steve
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Old 07-07-2008, 04:41 PM
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Quote:
Originally Posted by reflog
Had the dist. set on number one. Had the crank indexed to 0 degrees and the dot on the cam gear was located at 12:00 o'clock. I'll probably get new gears and chain as it looks like I had to force the old crank sprocket on. It is pretty well hammered. Also need a new key so will get that if I can find one.

Steve
That actually sounds like it is correct.

If you did have the cam sprocket 180 degrees out the engine would not run at all.

With the distributor aimed at the #1 plug terminal in the cap and the #1 piston at TDC on the firing stroke (the timing mark on the crank (harmonic balancer) will be very close to the '0' mark, then the cam sprocket should be at the 12 o'clock position.

For small block Chevy engines, when you are doing the installation of the cam the key in the crank will be at approximately the 2 o'clock position and the '0' mark on the crankshaft sprocket will be at 12 o'clock. At this point the cam sprocket will be installed at the 6 o'clock position. The piston that is at TDC at this time is the #6 piston.

If the crank is then rotated until the #1 piston is at TDC on the firing stroke and the rotor in the distributor is pointing to the #1 plug terminal, the crankshaft sprocket will be at 12 o'clock and the cam sprocket will also be at 12 o'clock.

Confused yet? Most are but that's the way the engine was designed.
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Old 07-07-2008, 05:10 PM
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I could be wrong, but I think 48* makes for a very short power stroke.
I think the 48* is cam degrees and you have to double it to get the crankshaft degrees. Anyone else agree?
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Old 07-07-2008, 09:23 PM
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Quote:
Originally Posted by Frisco
That actually sounds like it is correct.

If you did have the cam sprocket 180 degrees out the engine would not run at all.

With the distributor aimed at the #1 plug terminal in the cap and the #1 piston at TDC on the firing stroke (the timing mark on the crank (harmonic balancer) will be very close to the '0' mark, then the cam sprocket should be at the 12 o'clock position.

For small block Chevy engines, when you are doing the installation of the cam the key in the crank will be at approximately the 2 o'clock position and the '0' mark on the crankshaft sprocket will be at 12 o'clock. At this point the cam sprocket will be installed at the 6 o'clock position. The piston that is at TDC at this time is the #6 piston.

If the crank is then rotated until the #1 piston is at TDC on the firing stroke and the rotor in the distributor is pointing to the #1 plug terminal, the crankshaft sprocket will be at 12 o'clock and the cam sprocket will also be at 12 o'clock.

Confused yet? Most are but that's the way the engine was designed.
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

OK!! I'll ask you the same question I asked on the CF. If I time the cam at 6:00 and the crank at 12:00 where do I install the distributor?? Would I then have to install it at the No 6 position??

Steve
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Old 07-08-2008, 08:38 AM
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Quote:
Originally Posted by reflog
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

OK!! I'll ask you the same question I asked on the CF. If I time the cam at 6:00 and the crank at 12:00 where do I install the distributor?? Would I then have to install it at the No 6 position??

Steve
Rotate the engine until the #1 piston is at TDC on the firing stroke. This is easily determined by simply placing a finger over the #1 sparkplug hole and slowly rotating the engine manually (this is best done with all sparkplugs removed) in a clockwise direction when looking from the front. As the #1 cylinder approaches TDC the compression in the cylinder will push your finger away from blocking the sparkplug hole. Continue slowly rotating the crankshaft until the timing mark is lined up with the '0' mark on the harmonic damper. That will be "close enough" to TDC to install the distributor. You can now install the distributor. When correctly installed the rotor will be pointing towards the #1 plug terminal in the distributor cap. You may have to rotate the oil pump shaft manually (a long screwdriver works well for this) to get the distributor to drop all the way down to engage the oil pump driveshaft and seat on the intake.

When you fire the engine up the timing will have to be adjusted to whatever specs you wish to use.
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Old 07-08-2008, 11:00 AM
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Since you guys have straightened me out on the timing I have another question.

How much cam walk should I get. I have installed the timing gears and chain. The cam gear seems to be in a little farther back than the crank gear. I assume this will take care of itself when the engine is started. Doesn't the cam walk forward in these units and that's the reason for a button?

Steve
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