Cams and Timing

[Jeff Rosansky CLC #28373]

First of all, I am going to ask this-- If you would not have used this cam, please don't say so here.  This engine situation has been quite long and drawn out.  I just don't want to hear any more "I told you so's" (I'm already married )

As some of you may have already read, I had the engine rebuilt and things did not go as smoothly as expected.  As a result, I have lost the conversation relationship with the shop. I have nobody to ask--- Except all of you! 
Where would you set the timing on this engine?  It is set to spec now but does not idle well but it runs along OK.  I admit I need to adjust the carb.  Have about 450 miles on the engine and trying for more but the winter salt isn't helping me much. 
I will try to download the sheet, but here are the specs.

The engine is a 472, 30 over.  The following cam was put in--Erson Cam part #E520101. Grind RV10H. Lobe Separation Angle 112 (111 is handwritten next to it).
Overlap 56, Intake Opens 28.0, Intake closes 72.0, Exhaust opens 72.0 and Exhaust closes 28.0. Running clearance 0.00, valve lift (int/exh) 0.462, duration (int/exh)280.
Checking figures @.050 tappet rise
Overlap-16.0, Intake Opens -8.0, Intake closes 36.0, exhaust opens 36.0, exhaust closes -8.0 duration intake 208.0, lobe lift intake 0.280, Lobe lift exhaust 0.28, intake center line 112, rocker arm ratio 1.65. 
No "I told you so's please!"
Thanks All,
Jeff

[Jon S]

Jeff -

I am far from a cam expert, but when you go to a higher duration cam the timing should be set more advanced than Spec.  That being said, I would experiment in 3 - 4 degree advances and see how the idle feels and take it for a test drive at each change.  I "believe" 10 - 15 degrees advanced is where you will end up.  As you note, get the carb adjusted as best you can - a vacuum gauge is most helpful.

Realize that the engine will never be as smooth at idle as the stock one was, so don't try to duplicate that . . . it will not happen.

Good luck and keep us posted!

["Cadillac Kid" Greg Surfas 15364]

Jeff,
You seem to have a "Torque" cam which should improve low speed performance. Assuming you are running a stock distributor 10 degrees initial with the vacuum advance disconnected would be a good start.  Then connect the vacuum advance and work on the carb for the idle.  This cam should not give you a rough idle, so look elsewhere. Again assuming you are running at least 93 octane you can safely run a maximum of about 32 degrees total advance.
Greg Surfas

[savemy67]

Jeff,

If you have the shop manual for the year of your engine, you may be able to find the valve opening/closing and lift spec's for the stock cam.  Compare these spec's with the spec's of the cam that is currently in your engine so you have an initial basis from which to judge performance.

I have a 429 and the factory cam spec's for opening/closing are measured with .001" ramp lift.  Your post indicates your values were taken with .050" ramp lift.  Do you have a degree wheel and pointer?  Consider measuring the cam in the engine using the same reference point as indicated in the shop manual.  If the opening/closing, lift, and duration are relatively close to the stock spec's, then you may have only a minor issue with timing, and more of a carb (or other) issue.  If the installed cam's spec's are significantly different than stock, then you will need to experiment with timing, and tune the carb for the installed cam.

I concur with Jon that you will probably wind up with more advance than stock, and that you should use a vacuum gauge.  When using the gauge, observe both the value (in inches of Hg) and whether the needle is steady or unsteady.  Also, use a tachometer in conjunction with the timing light and vacuum gauge.  And, as Jon said, if the installed cam's spec's do differ significantly from the stock spec's, you are unlikely to achieve a stock idle.

Respectfully,

Christopher Winter

[Scot Minesinger]

Jeff,

I'm going with vacuum leak instead of cam.  Two likely sources:

1.  I have found the single most common mistake on the 472/500 engine rebuild that results in rough idle is failing to seal the intake manifold.  It also can result difficult timing set up.  The instructions on the intake manifold gasket are to use an RTV around just the 8 intake ports.  This does not suffice.  The entire gasket must be sealed especially the four corners where that rubber piece, block, heads and manifold all meet.

Someone else did the valve job on my red Cadillac and they did not seal the corners (just the 8 intake ports w/RTV), as a result the car idled rough and when setting timing there was a slight fluctuation.  MTS told me about this nuance, and it is critical.  Fortunately I corrected this.  Now the car idles nice and smooth.

If you have any fluctuation in timing mark on pulley when trying to set it this is an indication, as no vacuum leaks it is steady as a rock.  While running you could spray carb cleaner on corners to see if there is a difference in idle.

If you find this to be true, a new intake gasket and RTV for under $40 and an afternoon of your time will cure the problem.  Figure if you can take out an engine, you can remove and re-install the intake manifold. 

2.  BTW, check the torque on the carb to intake manifold bolts, those tend to lose their setting after the first 100 miles and they should be re-checked.   

[INTMD8]

The cam is very mild for that displacement so it shouldn't be hard to get a nice smooth idle out of it.

For comparison I'm running a 212/212 @.050, 114lsa in my 390. Initial timing is close to 20 and mechanical advance was limited so it peaks in the mid 30's.

Increased idle airflow and it idles nice and smooth at 600rpm.  (was not smooth at factory idle speed which I believe is 480).

So, keep in mind you will likely need a bit more idle speed than stock and as mentioned and getting the carb set correctly is necessary.

[Bobby B]

Jeff,
Hi. All good info posted above. As far as the cam specs go, that cam is well within range of a good low-mid torque street-able grind, and the duration of 208@ .050 should make this type of grind idle pretty smoothly with good low end grunt. Why they changed the separation angle from 112 from 111 is odd. It would only increase the overlap, making it just slightly rougher at idle, most likely not noticeable if the car is well tuned. We used to run cars in the 106-108 range with 230-240 duration when gas was available. The increase in overlap is what gives the engine that lumpy idle like it wants to stall. This is due to both valves being open longer at the top of the stroke.  All in all, the cam grind is perfect for the application, and I would start looking elsewhere before getting upset. Vacuum gauge would be a good starting point. Remember that the engine is freshly rebuilt and is "tight". I don't know your specific engine/ valve train geometry, but have you checked to make sure everything mechanically in the valve train looks like it's opening and closing properly? Timing, Carburetor, Ignition, etc. all have to be in tip-top shape if you're looking for a dead smooth idle, and as Jon pointed out, it's not going to be the way it left the factory due to today's fuel grade. You have to compensate by experimenting with the timing, doing plug chops, etc. This is where all the fine tuning and trial/error take place. To me, your problem sounds as simple as the carburetor not being up to spec. After doing carbs for years, I found someone that really knows their trade, and I've been using him exclusively. Doesn't pay for me to do it for what he charges, and when I get it back, I bolt it on and go. No matter how many carbs he's done for me, I've never been disappointed. Idle speed adjustment is all that's been needed. You'd be surprised at the difference of having the carb done by someone who does it for a living. He's a one man shop and that's what I like about it. The only thing they could have done was to install the cam slightly retarded which would hurt your low end a bit. If the car feels good while driving under load in all ranges, the idle issue will most likely be something simpler than you think. Worst case scenario is that you need to degree the cam to check it. Keep us posted and Good Luck!         
                                                               Bobby

[Jeff Rosansky CLC #28373]

I plan to have someone look at the carb this weekend as it will be the first in a month + that we have not had snow. Should be far enough after they salted and we had rain so i will drive it. Will have 500 miles on it this weekend. I did not want to mess with the carb at first because i wanted to avoid it just idling during the adjustment as i want the cam to properly break in.
How do i check the timing once it is past 10? I think that is the nax on the pointer. Should i put the timing light on another cylinder or manually index the pulley and make a mark?

[Scot Minesinger]

If you can't find the mark on the pulley with timing light on # 1 cylinder and rotating distributor back and fourth, then your distributor is installed off a tooth or two and that is the problem or part of the problem.  On my 1970 you can easily tell when it is 10'.

["Cadillac Kid" Greg Surfas 15364]

Jeff,
10 degrees initial with the vacuum advance disconnected is where you want to be.  The vacuum when re connected will help with part throttle cruise, and with a stock distributor you should be right in the ball park. Checking actual total advance is properly done with a "dial back"
timing light.
Greg Surfas

[Bobby B]

Jeff,
If you are unsure about the timing being correct, and you don't have a dial back light, you can either measure the pulley diameter and go down to your local speed shop and get some degreed timing tape, or you could just make a temporary one out of tape. No reason to go above/below 40 degrees. Take the diameter of your pulley, use this formula, and you could make one and stick it on to check. Ex. 6" pulley diameter x PI/360 =0.0523 per degree. Take a divider and maybe double that so you have it marked in 2 degree increments and stick it on the pulley obviously starting with your factory 10 degree mark as a base. This will at least let you know if your distributor is off, the timing is set incorrectly, your vacuum advance unit is stuck, leaking, broken, etc.  Going further you can use the tape to set TDC with piston  stop tool in the #1 Spark plug hole to see if that's correct also. Again, not as accurate as a degree wheel, but will point you in the right direction. If you have a hand vacuum pump, you could also check your vacuum advance unit. They are always problematic due to age, frozen, etc. Don't trust the aftermarket on these things because I have gotten bad ones right out of the box. I think you have enough input here from everyone to get started. I have a feeling that you have a very simple problem going on which is not as complicated as you think. Could be as simple as a bad vacuum line. Good Luck!
                                                                                                                                                                                    Bobby

[savemy67]

Jeff,

Regarding your question about what to do past 10 degrees, you may find this article by a GM engineer useful and or informative.

http://www.crankshaftcoalition.com/wiki/Determining_top_dead_center#Getting_started

Christopher Winter

[Jeff Rosansky CLC #28373]

Thanks guys.  I hope to work on it this weekend if time permits.  I figured to advance but wasn't sure about how much.  I am pretty sure the timing is indexed correctly.  The timing was pretty solid when I checked it just after I got her running (didn't waiver around when it was set).  I will also advance the idle speed a bit to help out.  She is smoother with a little more idle but I wasn't sure if it would hurt the transmission,etc with an extra 150 or so idle.   
The local QT has 93 octane fuel.  I will advance the timing a bit and see what happens.  I can just create a linear scale to figure where the timing is.  Will just advance it until she likes to run, start easily and doesn't ping then back it off a bit. 
Thanks,
Jeff

[Jeff Rosansky CLC #28373]

And as far as the advancing timing light goes, I had one in hi school. I got rid of it because once I had a "newer" car, I was never again going to have an old car........ If we only knew.

[Bobby B]

Jeff,
   Confucius say….."Never Sell Tools"     
                                                      Bobby

["Cadillac Kid" Greg Surfas 15364]

I personally think anyone that would sell ANY tool or not buy one they might use "sometime" later should be banned from this or any other forum. It's sacrilegious.
Greg Surfas

[Scot Minesinger]

Glad I'm not alone in the buy a tool I might use later or never throw away a tool that may seem obsolete crowd.  The buy a tool I might need later is about an 80% hit rate, not including the tools I do buy while in the middle of a project that are needed to finish it.  Still have my Grandfather's 3' pipe wrench from when he was working gas rigs in Ohio circa 1915 (now fossil fuels are back in the Midwest 100 years later), that has the good case hardened steel teeth and nothing says no to it.   

[Bobby B]

I personally think anyone that would sell ANY tool or not buy one they might use "sometime" later should be banned from this or any other forum. It's sacrilegious.
Greg Surfas

Glad I'm not alone in the buy a tool I might use later or never throw away a tool that may seem obsolete crowd.  The buy a tool I might need later is about an 80% hit rate, not including the tools I do buy while in the middle of a project that are needed to finish it.  Still have my Grandfather's 3' pipe wrench from when he was working gas rigs in Ohio circa 1915 (now fossil fuels are back in the Midwest 100 years later), that has the good case hardened steel teeth and nothing says no to it.   

Tools/Cars (Men) = Shoes/Pocketbooks (Women)
Don't try to figure it out………...
                                                Bobby

[Jeff Rosansky CLC #28373]

I agree. I have several now but you see, i made $3/hr back then. I was rich and cocky. I would never again need to work on an "old" car........ What can i say. Youth is wasted on the young!