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Old 06-09-2004, 09:11 AM
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Valve timing: What's the purpose of degreeing a cam?

Folks-

What is the purpose of "degreeing" a cam? I have never done it, and my cams work fine. I usually spend a few minutes finding TDC, and install the cam strait up. Unless you're using a keyway to adjust your valve timing, the closest you're goign to get to "exact" timing is the closest tooth on the timing chain. If it were off one tooth, you would be able to see that without using any tools.

I guess I never understood the point of degreeing a cam. As long as its manufactured properly, you shouldn't have a problem with just lining up the timing marks, correct? Specifically I'm talking SBC here, but I know its similar throughout makers.

Can somebody enlighten me as to why I would degree a cam? Is it just to make sure the cam is ground properly?

K

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Old 06-09-2004, 09:15 AM
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Same here, never really understood it too well. Always just lined up the holes, cam at 6 crank at 12, I trust the manufactures specs.

I would guess it has many different uses, maybe to degree a cam for a custom grind?
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Old 06-09-2004, 09:16 AM
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After the first two dial-ins I don't do it anymore either, unless you want to accomplish something specific theres really no need.

Looks good in a magazine however!
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Old 06-09-2004, 09:31 AM
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VALVE TIMING.

There are plenty of reasons to spend the time to degree every cam that you install. There are so many things that can happen during the manufacturing process. By degreeing the cam you can know for sure that you have the right cam.... that it's Installed at the proper centerline ect,,,, I have seen timing chains move the cam to 6 degrees retarded when the marks are aligned at zero.... I have gotten cams that the duration at .050 was off from what the card stated and so on. Most of the time if you use top quality parts none of this is an issue, But while the motors on the stand why not take the time and do it right????? Plus when you decide to build a killer motor and you "need" to do it right you allready have the experience.....

keith
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Old 06-09-2004, 09:37 AM
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basically what you are saying is degreeing a cam tells you if you have to send it back or no, correct?

K
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Old 06-09-2004, 10:16 AM
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Degreeing a cam is like following the recipe for a proven end result. Not degreeing your taking your chances. More often it will be okay, but it's not exactly what it was meant to be.

Engine parts are not perfect. A camshaft can be off, timing chain can be off, crank key can be off, lifter bores can be off a few degrees, all of this affects cam timing.

For the street guy, dot to dot will get you in the game, but if any of the above is off, your hours of labor may be in vane and then you go chasing ignition, fuel and other things if the engine doesn't run right. So I suggest to all, degree the cam and always have that in correctly to eliminate it as a problem for poor performance.

Professional built engines for competition must be degreed in. An engine builders rep is on the line and the engine must perform.

Proper phasing of the valve events to let air and fuel in and out of an engine can be big power gains. An engine is nothing more then a pump, so if the everything is working together, the pump is very effiecent and that makes a great engine.

Chris
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Old 06-09-2004, 11:05 AM
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or just plain ol' peace of mind that all is what it should be!
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Old 06-09-2004, 11:06 AM
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A cam is ground using the offset pin as the driver on the grinding machine. Grinding it incorrectly is impossible, the sprockets however have a good possibility of having the keyway misaligned.

Mainly, it looks good in a magazine folks.
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Old 06-09-2004, 11:12 AM
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degreeing

I've only done 1, I thought I was finding out where exact t.d.c. was. By the way , the first time it was (the cam) ground 2 degrees out, ran find but didn't have any lop. ( esk 505c) The second cam was right ,but the mark on the damper was 3/16 off, so I took a hacksaw blade and marked it right. While I had the degree wheel on the damper I mark it at 38 degrees cause thats where I was told total advance was to be. When I timed the engine, I would stab it and watch the timing , and move the dis. until it hit the 38 mark. Oh yea I have to go total centrif. advance cause I lost my vacuum. First 350 I built in 68
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Old 06-09-2004, 11:16 AM
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cam

4 jaw,
I agree to some extent about the grinding process, but i have been a machinist for 20 years and there is always the chance of something being machined wrong. In a situtation where you have operators just loading and un-loading machines anything can happen. I have noticed a pattern also by degreeing all my cams. there are some companys that the numbers are always spot on, and others that it's a mystery how they get things to run. All in all even the bad cams are close enough for the motor to run ,but in the high performance line close is not right....

killer,

It's not always the case where you need to send the cam back. If you buy a cam that has a number @ .050 of 255 and you check it and find it only to be 250 you probably will not send the cam back. If the key ways on the chainn are marked wrong you can just set the proper center line and go with out returning the chain, but when a pattern develops then you start knowing where to buy the parts from and where not to.

Keith
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