Don Terrill’s Speed-Talk

I am having problems degreeing in this solid roller cam in a 406 sbc.

The engine is a Dart SHP block,Scat 4340 crank and rods,SRP pistons.ALL NEW.

My cam is a custom billet roller made by a local cam guy about 6 years ago and it calls for 0.162" @ the lifter @ TDC. The lobe centreline is 104deg inlet and 110deg exhaust. Cam timing @ .050" is 30deg inlet and 58 deg exhaust.

I have verified TDC with a piston stop and i am certain it is correct.I have a new Rollmaster timing set which i first installed with the cam marker facing the O tooth on the crank sprocket.Set straight up like this i get: 0.115"@ TDC with a 112 deg centreline.
The degree wheel shows it is 12 deg retarded.

I advance the crank sprocket 8 deg (which is all it has got) and i get: 0.144"@TDC and the centreline moves to 106 deg.According to the degree wheel,it is still 3.5-4 deg retarded to what the cam maker has called for.

I don't get it. I have checked everything at least 50 times over the past month. I am verifying true TDC each time i make a change and checking it to the balancer. I have checked four other lobes and they are all the same. I have tried 2 different timing sets.Everything is new on the engine accept for the cam and balancer. I degreed this cam in my 383 about 6 years ago and i don't remember having any problems like this then and it made good power.

I am no expert,but i think i understand how to degree a sbc. Or am i completely wrong?

The only reliable measurement to degree in a cam is the .050" lifter rise open and close specs for intake and exhaust.

The cam must not be bent or worn. The roller lifter must not be worn or sloppy. The cam and lifter and bore must be clean. The dial indicator stem must be on the same X Y Z plane as the lifter. Any offset/angle of the dial indicator will induce geometric errors. If the dial indicator it self is fubared,, well.......

Turn the crankshaft in one direction only to get all the timing specs.

Degree the cam in using this method to determine the in and ex "duration @.050" and wether the cam is "advanced or "retarded" LSA and intake C/L is based on the .050" open close events.

Most cams are asymmetrical (the opening side is not the same as the closing side) and the calculated lobe center line may/Will shift when the cam is measured at different lift heights other than .050"

What is the .050" lifter rise timing event specs?. Intake opening, intake closing, exhaust opening, exhaust closing.
You need these numbers to know if the cam is advanced or... and by how much.
The .050" timing events should check within 1 deg.

Measured .050" specs VS cam card design specs. If the measuring lifter roller wheel diameter is different than the design roller wheel diameter, the cam will check a bit different than spec. If the cam lobe base circle is different than the design base circle the cam will check different in the motor.
Does the measured lobe lift check out?

The pin on the cam was probably put in the wrong place. The cam grinder starts with a semi finished cam core, where the lobes are already roughed in, and he can't move the centerlines much from where they're roughed in.
Just advance it one touth, and retard it to get the TDC lift the cam grinder recommends.

How are you doing the true TDC positioning?

I got an SBC Crane roller in the 70's for a 292 inch F/G Corvette with the intake lobes ground on the exhaust and the exhaust on the intake. After spending a day checking & rechecking I called them and was told I didnt know what I was doing. Fortunately I lived 10 miles from them. I took it in and they checked it. An hour later they came out with a new cam and an appology. Chit & disgruntled employees happens

Basically what the others have said plus: Trust your numbers. Pay no attention to the dowel pins, sprocket holes, crank keys, or timing marks. Those are only there so the factory people don't screw up too badly. You only need accurate TDC, an indicator, and degree wheel. Do what you need to do to get the cam lobes in the right place. If you don't do it that way, you are relying on the possible mistakes of others.

Put the crank at TDC. Put the intake at the right angle at .050". Stand back and see what needs to be where to make that happen. If it takes moving the sprocket a tooth and adding an offset bushing, so be it. You only need be concerned with results, not what it takes to get them or what markings are on the parts. Check your work and the cam numbers before you put it back together.

Couple of things don't add up

I degreed this cam in my 383 about 6 years ago and i don't remember having any problems like this then and it made good power.

If this is true, then you're missing something obvious. Maybe it is time to call in a consultant who'll take a fresh look at it.

I have checked everything at least 50 times over the past month. . . . I have tried 2 different timing sets

Second, SBC cams are cheap. If the cam were to be really that far off, then I wouldn't want a lash-up like that in my engine. The hours you've spent fighting this problem, you could have bought a newer, probably better cam from Mike and spent a couple of weekends on the strip.

jack vines

Thankyou all for the replies.
The measured lobe lift is correct (.430) and i checked it on all lobes.Also the cam timing @ .050 numbers were all retarded.
I tend to agree with Cam King and Kirk, that the dowel is in the wrong place and i should forget marks and do whatever it takes to get the cam to where the sheet says it should be. This time i will write it down so i will remember.

Also,why is measuring intake lifter rise not the prefered way of checking? It seems to be the easiest way to check.

Cheers, Gary.

dat383, your question about why they don't also give lifter rise at TDC has been my question for years. When I install a cam, I keep notes on intake lifter rise @TDC. That is always my base point. I also try to put a scribe line on the flywheel at TDC referenced off the bottom of the block. That way, if the front and rear don't agree, you know you have a problem with something. Typically, I use white Dykem on the rear of the flywheel, and a 1/4" tool bit ground to a sharp edge for a scribe.

Always check .050 numbers, ICL/ECL & int lift@tdc.
Doing this proves the cam timing by more than one means and ensures you that you are correct.
if you come up with 12deg retarded after checking these then you have got to say you are right! Providing you are doing everything right, but to get the same reading using 3 methods sort of rules out 'doing it wrong'.

You are not stuck by the position on the timing set to correct the cam timing. How many teeth does the crank gear have on your timing set? 360 / (number of crank gear teeth) = degrees per tooth.
You will find that you can advance the crank gear 1 tooth from straight up then use the 2 deg keyways to fine tune the timing.

Normally, as Craig says, cross-referencing via two or more specs ensures that all is correct and the engine doesn't care where the dots are, as long as the cam is indexed correctly to the crank. In this case however I'd say several things don't add up re the numbers you quote:

o If the 0.050" IVO is to be 30° BTDC and the ICL 104°, then the intake duration must be 268°.

o If the EVO is 58° BBDC and the ECL is 110°, then the exhaust duration is 256°. Suspicious, in that such a 'reverse split' is unusual.

o You state: "Set straight up like this i get: 0.115"@ TDC with a 112 deg centreline. The degree wheel shows it is 12 deg retarded." This does not compute, as for the required 104° ICL it would represent only an 8° retard.

o If a lift of 0.144" @ TDC corresponds to an ICL of 106°, I'd be surprised if an additional 2° of rotation would produce the needed 0.018" more to match the 0.162" spec. Have you checked if it does?

o You state: "According to the degree wheel, it is still 3.5-4 deg retarded to what the cam maker has called for." but per the previous bullet point, it is actually only 2° R.

o The best advice is normally to "degree it in the way the manufacturer states", as non-symmetrical lobes will distort the relationship between 'centerlines' and valve open/close points, but in this case, there is a disconnect in the reported recommendations and this would not appear possible.

I suggest expanding on Craig's advice by checking 0.050" IVO/IVC and EVO/EVC and determining if max lift is exactly halfway between them. If it is, the lobes are symmetrical and you can with reasonable assurance set the ICL at 104° and forget everything else. If it is not, you'll have to decide which spec to follow and which to ignore. (BTW, obvious question: Have you tried contacting the grinder for clarification?)

Keep us posted re the resolution!

Great points Bill. Definetly verify ALL the cam specs to make sure that the cam is what it is supposed to be.
AND one that I'll admit to (im sure a couple other may have done this once or twice! Lol) is intending to check an intake and having set the exhaust up!! Then looking at the measurement taken and thinking WTF is going on?! Then realising, swearing then doing it properly! Lol
Anyway-enough of my stuff ups!
So, yes, verify all the cam specs, THEN set it up when you are 100% sure that all the numbers add up.

Thanks for the advice guys.This is what i have found.
I made a typo on the @.050 cam lift numbers it should be: (IN O- 30) (IN c- 58) (EX O- 69) (EX C- 29) Duration @50 is 268 inlet and 277 exhaust.

I believe i was not carefull enough with my earlier measurements of the intake ICL,because as you have pointed out the ICL and crank have not changed at the same rate.

Anyway,I advanced the cam 1 tooth (which gave me a lot of advance), and retarded the crank sprocket in 2 deg amounts (it is a 9 keyway rollmaster set), until the intake lifter rise at TDC was 0.162" . ICL was 102.5 deg ECL was 112 deg .
The cam card calls for ICL 104 ECL 110. So again the lobe separation figures don't exactly match the intake lifter numbers.

I will say,i believe i can measure the intake lifter rise more accurately than the ICL/ECL because the lobe seems to dwell at max lift for quite a few degrees of crank rotation and if i am not really carefull to stop exactly at the right point,it throws out the ICL/ECL findings. I hope i explained that correctly. Note that i am a mechanic, not an engine builder.
For me, measuring the intake lifter rise is very repeatable, so as i make timing adjustments i tend to trust those figures the most.

With the cam reading: intake lifter rise at TDC 0.162" . ICL 102.5 deg ECL 112 deg
The cam timing numbers at .050" are very close to advertised on the intake and exhaust.(again,maybe my inaccuracy).

Iam pretty happy with where those figures are and also piston to valve seems its best with the cam in this spot.

What do you think?

Cheers,Gary.

The problem is the crank gear and cam gear you got are not a matched set.

If you were to install a cam and crank gear SET from the same box, even a $20 stock replacement set, it would degree in exactly as the cam card within 1-2deg.
Your 9 key way crank gear and the cam gear are not a matched set.

I had this issue years ago on a 454 BBC.

Change the cam and crank gear, you'll see.

I think you might be moving the crank sprocket on the crank and using the same timing mark on the teeth, have a look at diagram 2. 3. 4.



http://www.romac.com.au/Std_&_Offset_Crank_Info.pdf