Cam timing

narfire · Post by **narfire** » Tue May 15, 2012 8:43 am

maytag wrote:the adjustable cam pulleys from Miller Mule don't have timing marks on them

My adjustables,from Millers', had the holes on the backside that I lined up with the raised ribs on the cam towers.

baltobernie · Post by **baltobernie** » Tue May 15, 2012 3:13 pm

The whole point of adjustable cam wheels is to allow the builder to align the camshafts with the crankshaft, regardless of dimensional changes which may have been made during machining of the various components. I'd recommend setting the cam timing to the specifications provided by the camshaft vendor. After the engine is performing its best with those numbers, you can then experiment with different opening, closing, and overlap times (if you want).

maytag · Post by **maytag** » Tue May 15, 2012 4:33 pm

baltobernie wrote:The whole point of adjustable cam wheels is to allow the builder to align the camshafts with the crankshaft, regardless of dimensional changes which may have been made during machining of the various components. I'd recommend setting the cam timing to the specifications provided by the camshaft vendor. After the engine is performing its best with those numbers, you can then experiment with different opening, closing, and overlap times (if you want).

Precisely.
but that is my question: when he tells me "3 degrees advanced": advanced from WHAT? I need to get the cams dialed-in to ZERO, so I can then advance them from there, yes? But my question is WHAT IS ZERO?
Or does that "3 degrees advanced" refer to when the cam should begin opening, expressed in crank degrees of rotation? I time the cam so it begins opening the valve 3 degrees before the piston reaches TDC?

what am I missing here?

lanciahf · Post by **lanciahf** » Tue May 15, 2012 4:58 pm

You need to get the specs from the cam builder/seller than read and re-read Guy Croft's excellent write up on how to properly time cams. But you need to find the specs.

http://www.guy-croft.com/viewtopic.php?t=14

maytag · Post by **maytag** » Tue May 15, 2012 5:30 pm

but even after reading the link you sent, these #'s mean little to me.

Somebody please show me what my malfunction is? cuz I'm seriously blocked here.
If I follow Guy's math, I'm great. But he states: "The cam degree setting at tdc, relative to cam full lift, will be ½ the crank degrees at which you want full lift."

Ok.
But the statement "at which you want full lift" is what's throwing me.
He's got the math showing where he comes-up with that 110degrees, and I'm great with that, but it is based on advertised cam-timing numbers. (40/80)

How do I determine cam-timing numbers from the cam specs I've got above, for instance?

All I really need to know is: at what crank-degrees are the stock cams at full-lift? (with Full-lift as defined by GC: midway through the dwell-time that the valve is open all the way)

engineerted · Post by **engineerted** » Tue May 15, 2012 9:51 pm

Here read this, you need to degree the cams and mark them to the cam boxes, that way you will know where to put them when timing them to the crank.

http://www.guy-croft.com/viewtopic.php?f=3&t=213

maytag · Post by **maytag** » Tue May 15, 2012 10:19 pm

engineerted wrote:Here read this, you need to degree the cams and mark them to the cam boxes, that way you will know where to put them when timing them to the crank.

http://www.guy-croft.com/viewtopic.php?f=3&t=213

Thanks Ted. But that is mostly a regurgitation of the guy-croft tutorial referenced several posts above, which I also read.
So I still have the main question, which nobody seems to understand. let me try again:

Guy says (in the tutorial you just referenced) "If the spec for the inlet cam is full lift at 100deg, this means that the inlet valves should be fully open at 100 crank degrees after tdc".

great. I'm all for that.

But how does that equate to the cam specs I have posted above? How do I determine at what point I want full lift? Should my cam supplier have supplied me with this cam-timing information? Because so far my cam supplier is telling me to time it same as the stock cams, and then advance the intake 3d from there. I have no way of telling what that stock cam-timing was.... surely somebody must know?

Please understand that this is not a question of tools, or knowing how to use them. I could go out right now and plot-out the lobe and its centerline, and every other detail about that cam using degree wheels and dial indicators and fixtures galore. But without some way of relating that to a similarly degree'd crank: what good does it do me? I need to know how to determine that starting point.

Really? Does nobody know what the factory timed the cams to? or am I so dense I'm missing it somehow?

engineerted · Post by **engineerted** » Tue May 15, 2012 10:47 pm

Ok, I will try to clarify.

I degree the cam by just using the cam, cam box and one shim and bucket. Clamp the cam box to the table or to a metal plate so the dial gauge has something to mount to. Put the shim & bucket in #1 bore and place the indicator inside the buck so you can read the cam lobe lift with the dial indicator as you rotate the cam. Now with a degree wheel mounted to the cam pulley find the true FL of the cam lobe. I use 0.050" lift on either side of the lobe and note the degree reading at each one then divide degree difference in half this will put you at the true FL point on the cam. Now mark the camshaft and cam box so you can come back to this position any time you need.

Once you have marked the cams FL, now rotate the camshaft CCW (intake cam) CW (exhaust cam) 55 degrees, mark the position on the cam and box. This is the position the camshaft needs to be when you install the timing belt and the engine is at tdc#1cylinder. The adjustable cam pullies makes this easy. Now both cams are time with Fl at 110 crank degrees. Now if you want you intake at 100 degree, rotate the camshaft 5 degrees CW while keeping the crank at TDC. You gotta love those adjustable pullies.

maytag · Post by **maytag** » Tue May 15, 2012 10:59 pm

thanks. Something you said jogged a cog for me, maybe it's that you also used the 110d figure that Guy Croft used in one of his examples. So are you telling me that the factory setting for stock cam-timing is 110-crank degrees for full-lift on the intake? or is that 110d just an arbitrary number, based on that 40/80 cam that is so popular?

I guess what I'm really getting at, is that I'm being told to advance my (regrind) intake cam 3d from stock, but I don't know where "stock" is. I need to establish that first.

we are all circling around this somehow, but no real answer yet. But I sure appreciate y'all help trying to make me understand it....

124JOE · Post by **124JOE** » Wed May 16, 2012 12:31 am

CAN I TAKE SOME PICS FOR YOU?
i have a set of stock cams still in them and gears on
if this will help let me know

engineerted · Post by **engineerted** » Wed May 16, 2012 8:25 am

Maytag,

Yes, the stock TC cam is 110degrees as set by the dowl position at the cam pully. Thus all advacing or retarding are from this position.

maytag · Post by **maytag** » Wed May 16, 2012 8:32 am

engineerted wrote:Maytag,

Yes, the stock TC cam is 110degrees as set by the dowl position at the cam pully. Thus all advacing or retarding are from this position.

Ted.... I think I love you! (but not in a weird way...

)

This is what I needed to know to be able to move forward. Can I assume the exhaust cam is the same? (110d BTDC?)

And 124Joe: thanks for the offer to take pics... it almost came to that!

majicwrench · Post by **majicwrench** » Wed May 16, 2012 12:57 pm

The factory marks/dowels are likely NOT going to be accurate enough to use for "advancing 3deg". Milled heads, all sorts of things effect that.Reallly need to establish TDC accurately (easy with head off, steel bar bolted across cylinder, some sort of stop so piston can't come all ways up, rotate both ways, mark where it stops, halfway tween is TDC)

Methinks when he say "advacne 3deg from stock" he means the "stock" numbers listed with the cams you bought, not "stock" as in OE.

Advancing 3 deg is a lot. Cams should run well set at their factory specs. Having to advacne them very far to get car to run right generally means they are too wild.
Keith

maytag · Post by **maytag** » Wed May 16, 2012 1:30 pm

majicwrench wrote:The factory marks/dowels are likely NOT going to be accurate enough to use for "advancing 3deg". Milled heads, all sorts of things effect that.Reallly need to establish TDC accurately (easy with head off, steel bar bolted across cylinder, some sort of stop so piston can't come all ways up, rotate both ways, mark where it stops, halfway tween is TDC)

Methinks when he say "advacne 3deg from stock" he means the "stock" numbers listed with the cams you bought, not "stock" as in OE.

Advancing 3 deg is a lot. Cams should run well set at their factory specs. Having to advacne them very far to get car to run right generally means they are too wild.
Keith

Keith, as usual, you're right-on with your comments... and I'll disagree with them anyway.

It's not just TDC that needs to be established accurately (which I've already done, by the way) but it's the Full-Lift location (relative to the crank location) that needs to be accurately established. this is where I tend to not trust the factory timing marks.
I've clarified with Daniel, and he is talking about advancing the Cam 3 degrees from the factory cam-timing (since these are regrinds of factory cams). You may notice in the "Purple Cam" thread that he has confimed I should b elooking for it to be timed at or near 104d (3 cam-degrees advanced form 110d)

and there is NO SUCH THING AS TOO WILD!!

majicwrench · Post by **majicwrench** » Wed May 16, 2012 1:50 pm

Ohh wild is good

But by advancing them 3 deg you are basicly making them milder.

And it's been a loooooong time since I degreed cams on race motors ( mostly Isky, good stuff, would really work with us), so help me out, but it wasn't full-lift we used for that purpose, it was a certain amount of lift off the base circle.
Always fun,
Keith

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