Curious about the term, "ground in advance" when referring to camshafts.

What does that mean, and how do you tell there is additional advance ground
into the cam by looking at the cam card?

I've seen a couple of posts recently that state something about the above.

When I dial-in a camshaft, I use the intake centerline method. I can also
check my IVO, IVC, EVO, etc. @ 0.050" using the cam card.

Where does this 'advance' come into play...and how do you read that from
the specs?

 

The dowel pin is located so that the intake centerline is advanced. Usually something like 4 degrees for Comp for instance. The intake centerline they recommend you install it on is usually built into the cam and is not supposed to require you to use offset dowel bushings or keyways. On a custom Comp cam you may specify where you want it and the grind number will end with the advance, such as +4 or +6.

 

Cool thanks!

 

I've found sometimes it's ground in sometimes it's not! Makes degreeing in those puppies fun.

 

First off, have not ever seen in person, cam lobes being ground. It was my reasoning, the cam lobes were ground using the drive dowel to locate from. Thus if any advance/retard were to be 'ground in', it would be programmed in, or done with an indexing head would rotate the shaft, via the drive dowel. Now I've been led to believe the cam shaft lobes are ground the same without any regards to lobe centerline. IOW, NOT 'ground in'. Any advance/retard built into camshaft, is done after the fact, via locating/drilling drive dowel location in predetermined location, to establish the amount of advance/retard. Anyone know for a fact, which way the cam is manufactured? The mindless wants to know.

EDIT: If it is the latter, I can understand how screwups occasionally materialize.

 

I don't know for a fact...but I'm going to take a wild stab and say the dowel is positioned after the profiling.

From a production point of view, the same cam profile could be ordered with
several advance/retard settings.

Good question Arnie.

 

I believe the cam is indexed off the locating holes on the rear of the cam. The bolt holes and dowel pin are drilled in accordance to intake centerline. The core allows for a limited amount of lobe seperation variance, so they pick a core with the correct lobe spacing for the intended grind. Cam grinds have a wide range of intake centerlines from say 98 degrees to 112 or higher. It would be impractical to cast and machine such a wide variety of cores that were already indexed for a particular centerline when installed "heads up". The drive indexing must be done as part of the grinding operation.

 

Bret,

My Comp book addresses this very thing. The 306S for instance mentions the advance is not ground in. Page 10.

 

Who would have thought such a simple question would lead to this?
What does the core look like before cutting? I always thought it would be a
square length of alloy before it hit a CNC lathe?

Here's some good reading on camshaft processing. Don't say I've never given
you guys anything!

http://www.mmsonline.com/articles/120402.html

http://www.deltacam.com/camshaftgrinding.php?p=2

http://www.manufacturingcenter.com/t...04grinding.asp

http://www.landisgardner.com/products/cam.htm

 

Flat tappet and many hydraulic roller cams are cast iron and have lumpy looking lobe masses on them before the are ground.
90% of your billet cam cores come from Crane, no matter who grinds the finished cam. While some of what Crane receives may be bar stock I think that some are forged into a rough shape. You can special order a non-relieved cam that has 4 lobes all touching each other for strength, but those are nearly double the price of a standard cam. If you notice the newer 4/7 swap cams are a bit more money because they require a lower volume dedicated core.

 

Yeah problem with the LT motors is that it throws off the timing if they are not ground to the advance spec you have to adjust for it in the tuning because the opti is based of the cam dowel pin... fun.

Yeah the 4/7 swap cams add about $40-$50 to the price of the cams.
Hell that's better than the -0 cores cost!

Mark, you would be suprised what the new high end flat tappet cores are now. Still not cheap but doesn't take as much work as the hard welded crap.

Bret

 

Just slightly off topic, but related:

What is the process to break-in/set a roller cam (hydraulic, or roller).

Many say a break-in is not required for roller, but I find that a little odd.

Wouldn't you need to give the valve train some sort of conditioning before
beating on the motor?

 

Cast (iron) cores are cast in a "near net shape" so very little material is removed from the round portions. Steel or "billet" cams are machined from a round bar of stock, with all of the finished surfaces machined to .010 to maybe .050 of finished size. The areas not to be hardened are copper plated to prevent carbon infusion, and the blank is carburized, or heated to the 1600F range in a rich carbon atmosphere for hours. Carbon infuses into the outer surface of the exposed surfaces to allow them to become hard when the cam is quenched, or rapidly cooled. It is them tempered, or heated at a much lower temperature (400F or so) to adjust the final surface hardness and relieve many of the heat treating stresses.

A cam company usually buys "cores" which are completely finished except for the "non-round parts"...the lobes and perhaps the fuel pump eccentric. For example: a selection of SBC or LT1 cores with unground, but hardened lobes with diferent centelines and sizes are available. When the lobe profiles and LSA and ground in advance are chosen, the best core configuration is chosen and the lobes are ground on a dedicated cam grinder.

The old way was to use metal "master lobes" and have the rotating camshaft move in and out with respect to the grinding wheel. Yes, the cam is indexed to the drive pin. There could be cases where building in advance pushed the desired lobe too far toward one side of the lobe on the core, so the desired advance can't be ground in with the chosen lobes and LSA on an available core.

Modern CNC cam grinding machines store the lobe profiles digitally, and after the appropriate core is loaded into the machine, lobe profiles, LSA and advance are keyed in, and all lobes are ground within about 12 minutes.

FWIW, Nextel Cup cam cores are MUCH more complex and very costly. Traditionally they involve building up the lobe surfaces by welding on tough stuff like stellite, then a few heat treatings and final grinding. That's how some aftermarket cams for things like some Porsche engines are made because aftermarket cores are not available.

GM sells Ecotec cam cores with unground lobes. They WANT the aftermarket to produce different cams.

 

Maybe at the most heat cycle the valve springs.... Other than that... nothing. Rollers are nice because you can beat on the motor very soon so that you don't glaze the cylinders.

Bret

 

Not to sidetrack the discussion, but while we're talking camshaft tech...

We've got some poor fool on the RX-7 forum (in the general discussion area) trying to prove that a 750 horsepower V8 is losing 200+ horsepower to valvetrain friction because of the spring pressures involved. He's gone through calculating spring pressure at the cam lobes (multiplying "average" spring pressure by the rocker ratio) and says that there could be 8,000 lbs. of pressure involved in one rotation of the camshaft.

I asked, if that's the case, why you can turn an engine over with a standard 1/2" ratchet on the crankshaft snout with very little effort.

I also mentioned that given engine and chassis dyno numbers, that it was pretty easy to prove that a 750 horsepower V8 was only losing ~100 horsepower rotating the entire drivetrain, so why would the valvetrain consume 200?

Any comments I can share with this bozo? Of course, he's trying to prove why the valve-less rotary engine is superior...