"Dot to Dot" Valvetrain Tech

[1sicklx]

Pulled from Flowtech Induction.

Originally Posted by Ed Curtis

“I installed it dot to dot.”

This is one of the most popular comments I hear after less than ideal results are seen when a camshaft installation is completed. Just the mentioning of this sends chills down my spine.

The proper installation of a camshaft and its peripheral valvetrain is one of the most important jobs an installer must do when maximizing the performance of any engine combination. Any short cuts or miscues in this regard, and the overall success of the project, and its ulimate performance, will definitely suffer.

How can something so simple be so problematic?

Let’s start with the basic premise that everyone can have a bad day at work. Who’s to say the crankshaft keyway was machined absolutely “dead on” when the machinist set it up? I mean, even a slight error of a degree or two is no big deal considering the thousands and thousands of engines out in the world. They run, don't they? Maybe it wasn’t even a bad day but something that is machined off the mean number but still within manufacturing tolerances. What's a degree or two among friends?

Now we have the next piece of the tolerance puzzle, the timing set. There are a series of variables that can occur with this component. The relationship of the keyway to the crankshaft sprocket teeth, the location of the cam dowel hole to the cam sprocket teeth and then there’s always the possibility of “both” items being off. Why worry? Well, if each facet is off in the same direction, it is a cummulative error that will change the engine's dynamics. That's why verifying the intake ceterline as it relates to top dead center is very important.

When you're installing these two pieces to the engine, who’s to say they are so perfect, there’s no reason to check them?

Nothing is further from the truth. You'll never hear a professional engine builder say this. At least not one that knows the hows and whys of valvetrain importance. This is the type of attention to detail that separates the engine assemblers from the engine builders.

No camshaft should be just installed “dot to dot” if the installer is a professional!

Now the novice or the weekend mechanic might be able to justify doing a camshaft installation in this manner just because the tools required are not something a newbie has put the investment in. It's "almost" forgivable when this is spoken. However, when I hear his “dot to dot” comment from a shop that just charged a customer a lot of money to do the install, well, it definitely crosses the line and takes them off the referral list.

Take your time and verify everything. If you don't have the time, tools or talent to do it yourself, find a professional to do it for you. It's worth the effort!

[1sicklx]

Instructive article from Ford Muscle on degreeing a camshaft.

http://www.fordmuscle.com/fundamentals/camdegreeing/

It's definitely worth a look if you're interested in dialing in your bump stick for optimal performance.

[coupe]

For a custom grind, or high-end cam...definitely degree it in for max performance.

However, many of the cheaper cams (Alphabet cams, trick-flows, cheaper cranes, etc...) are all a few degrees off from one lobe to another, so degreeing one of them from say, TDC of cylinder number 1, might yield something totally different for the other cylinders.

Generally, for these cams, putting it in dot-to-dot is sufficient. Mine runs like a raped-ape and it's never had a degree wheel on it.

[Craig K.]

I had a "B" cam which I had checked with a wheel and it was nearly dead on, I had actually checked it across three cylinders and it was right on for each.
This was when I worked at a machine shop as part of a school project. The owner taught me the how to's on this one.

This was the only time I degreed a cam.
On a "race" motor I would spend the time/money to do it.
On a street car that sees redline rev's only sometimes, I wouldn't bother with it.

[Blown 5.0]

The last cam i got from Comp, Was 8 degrees off on # 4 cylinder. If you have a cam with close piston to valve clearnce, It is very wise to check EVERY cylinder. P.S. The guy at Comp said that that does not happen often, Thats when i found out they offer a race grind in every cam, Yes i does cost more, But in my opinion worth every penny.

[coupe]

What does their "race grind" offer? Is there a cam-doctor sheet with a mathematical representation of the lobe geometry? That is truly the best way to measure one. Plot the lobes out.

[Blown 5.0]

What i understood about their race grind, It is ground on a more closely kept in spec machine, that by the way is mounted on rubber,( seems there is a rail yard behind Comp that has played a part in some mis ground cams in the past) The cam is basically a blue printed cam, I'm not sure about a cam doctor sheet, You would have to ask that from comp. I do have a buddy in the machine shop business that does have a cam doctor, If you ever need a cam spec ted out.

[coupe]

Thanks for the info. Knowing the details and having them confirmed on a cam-doctor really means alot for the serious builder.

I have access to a cam-doctor as well. Definitely gonna "double-check" mine when it comes in.