1940 V8 Cam / valve timing

bcatcmc

bcatcmc

Member
Hi at the Ford Barn,

First time post here, just sharing some of my story trying to track down a miss coming off idle of my newly rebuilt 1940 truck engine. Having spent a lot of time on both ignition and carbs. I decided to do a partial tear down looking for potential valve problems . The valve lash was pretty spot on, however I noticed I could easily rotate some of the valve springs with my fingers when the valves were closed indicating to me weak valve spring pressure. ( spring tester on the way ).

As I had the valve gear removed I decided to check Cam / valve timing , being unable to find much info in doing that on a flathead I set up a dummy valve guide and pushrod for a dial indicator off the lifter ( big mistake ) got a set of readings about 35 - 40 degrees from the Ford specs. I checked and rechecked a few times the fired off an email to the company that reground the stock cam ( profile 58 ) asking for assistance , I ended up calling him , a cordial discussion followed him saying he could not understand my figures and maybe I was out of my depth ( I didn`t argue with that ) I did however get some usefull info ( the fully open intake numbers after TDC and fully open exhaust numbers before TDC ) which when applied were spot on.

My error was not putting the indicator on the valve head, the 35-40 degrees being the lash. ( nice if the cam guy had picked up on that ). Now my method ( the cam guy didn`t seem impressed with this also. ).

I had fitted a 307 Chev. harmonic balancer on the engine prior with an accurate TDC mark engraved. I then devided the circumference by 360 degrees giving me a mm / degree figure to work with. I used a paper tape starting and finishing at TDC held by button magnets and rotated the crankshaft CW marking the tape off TDC pointer when indicator showed opening and closing valves. Removing tape and multiplying measurements by mm/ degree figure proved very accurate ( 1-2 degees )

All this proving I don`t have to buy a degree wheel or find a camshaft guru in my area. ( as suggested ) Sorry for the long winded manuscript.

Regards to all, John
 
You actually did a very good job. The lash mistake is an honest one, and is not uncommon especially if someone doesn't do this for a living. Making your own timing tape and using a damper you have on hand is commendable. Now you know where your timing events are and can proceed with the diagnosis. Well done!
 
What distributor are you using? If it is a stock helmet, are you using a Haney rebuilt coil? If you are using an adapter with a round coil make sure it is not a really high secondary voltage one. A stock flathead doesn't need spark voltage above say 30k and if you do have a "hot" coil and resistance plug wires you could be forcing the spark to jump to the shaft the rotor is on THROUGH the rotor instead of going out to the plugs. This is just one possible cause of a miss. Good luck finding the problem, sometimes it takes a while.
 
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I've degreed a lot of cams . . . on flatheads, overheads, overhead cams, etc.. I'm not sure who you were talking to at the cam manufacturer, but every set of cam specs I've ever worked with specify that the timing specifications are checked with zero lash. So, unless this cam manufacturer recommends degreeing the cam with lash, then I'm not in agreement with the process. (Edit: See below - you have to know the specified "checking clearance").

I typically use the "intake centerline" method to figure out if the cam is advanced or retarded (then I adjust as needed). This is what most engine builders do - and the process is pretty straight forward. Once I have the cam where it should be, then I check the timing events at .050.


Here are some links and some examples from folks like CompCams (the following is not specific to any one type of engine - though it obviously is talking about overheads):


Adjust the rocker arms to their suggested clearance. If the camshaft you are checking uses hydraulic lifters, you must temporarily use solid lifters in their place. Hydraulic lifters bleed down and would provide a false measurement. Once the hydraulic lifters are replaced with solid lifters, adjust the lash to “zero.” Be sure not to pre-load the valve spring. Be sure to reinstall the hydraulic lifters before starting the engine​


Link to a basic article:

https://www.motortrend.com/how-to/0704-ht-how-to-degree-camshafts/
 
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Okay - time to eat a bit of crow and extend the conversation and technical details a bit. A very knowledgeable friend of mine and I discussed the issue of "checking clearance".

This is something that only the cam grinder can tell you --> basically it is "at what lash/clearance were the cam timing events taken at". He let me know that a lot of older flathead grinds used a "clearance/lash" amount as part of their timing specification. While I've seen almost all OHV cams specify that their timing-tag numbers are at 0 lash, that is not the case with some of the flathead grinds. So, John's scenario makes total sense if the camshaft numbers for his cam are based on having lash - or not.

If you think about it, many timing tags tell you the valve events noted are at .050 lift. Is this the RAW lift on the cam itself (no lash) . . . or AFTER a certain amount of lash is taken up? You can imagine that the timing events will be VERY different depending on the answer to this important question.

In the end, you have to know where the timing numbers came from - in order to know how to understand the readings you get with your degree wheel.

I use the 'intake centerline' method of installing cams on most engines in that I know I cannot change the grind (and associated events) - I can only change whether or not the cam is advanced or retarded . . . and the intake centerline method is a reliable way to determine this. With this method, you're working with the lifter/cam toward the top of its travel (both sides of the lobe) - usually .050 on either side of peak lift.

Once I know whether or not I need to advance or retard the cam (on a flathead), I use my mill and rotary table to drill a new set of holes to set the timing where I want it. Then I remark the timing gear for a NEW index to the crank.

So, make sure you know the checking clearance if you're degreeing in a cam and are looking at the valve timing events. In the end, it is a good idea to check BOTH the intake centerline as well as the timing events - kind of a good "cross check" to validate what you're seeing.

Best of luck!
 
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Thanks for your informative comments B&S,

Early in my build I had the cam between centers in the lathe showing variations in dimensions, also had some slight galling on a couple of lobes so I decided to get it cleaned up to the original spec. The cam grinder listed the same cam on his web site ( stamped # on the cam nose ). Given that it was a stock regrind no spec sheet from him was supplied, meaning when I decided to check it out recently I was flying blind, when the figures were so out of whack I thought I must have stuffed the gear alignment so off came the timing gear cover, no problem there however.

Initially it was all a bit frustrating but I am now confident that is not now part of my problem. As they say you learn by experience.
 
In reply to Deuce Roadster

I think a reply regarding ignition might stray from the cam topic and get lost so if you can hang out for a few days I will start a new thread regards ignition ( Mallory breakerless )
 
Good perspective John!

One thing I know is that camshafts (and their specs) get a lot of folks quite confused and the only real way to become comfortable with them is to spend a bit of time with a dial-indicator and a degree wheel. When you see with your own eyes the relationship between the timing numbers and the degree wheel - it all starts to make sense. I always have a big pad of paper with me when I do this - writing down all the events, calculating duration at .020 duration at .050 etc..

Great that you stuck with it!
B&S
 
Great post. I used this article, http://www.muzzys.com/articles/lobe_centers.html when I determined and changed the advance on my XS650 motorcycle. The link no longer works nor is it available via the Internet Archives. I have attached a copy from my records

"One of the least understood topics and regarding engine tuning and building
continues to be the concept of cam timing and “lobe centers”. The opening and
closing process of an inlet or exhaust valve as controlled by a cam lobe
constitutes a complete “event” in the cycle of the engine. Like any event, it
has a beginning and an end. Naturally, then it also has a middle or center. The
location of this center in relation to the rotational position of the crankshaft
is known as the lobe center.

The process of “degreeing” cams allows the engine
builder to place the lobe center of a cam in the correct orientation with
reference to the crankshaft. The opening and closing points and resultant
figures of the cam, although important, are very difficult to reference to set
cam timing and are, after all, the result of where the lobe center is placed.
Therefore the lobe center is used to reference cam timing. The difficulty in
measuring the opening and closing points is the result of the very shallow and
gradual starting and stopping of the valve motion. How do you tell just when the
valve motion starts and stops? If you pick a specific amount of lift at some
height beyond the initial gradual motion and always use that amount as a marker
for the beginning and end of the motion, the center will always be halfway
between these points. Therefore, the lobe center is computed from a timing
number derived at a specific valve lift. Any lift could be used to compute this,
but in the Japanese motorcycle industry 1mm or .040” is traditional. U.S.
(automotive) cam grinders have used .050”. This “checking height” must be used
to minimize the effect of the shallow opening and closing ramps on the cam lobe.
Without this, each builder’s subjective notion of when movement starts would be
the defining factor of timing."


543984
 

Attachments

Here is a reference to CompCams and how they describe the 'Intake Centerline' method of checking a cam's location (advance/retard). This is basically what I do - though the individual steps will vary depending on the type of engine and the type of timing system. This was written for an OHV engine with rocker arms - though you can easily "translate" it to a flathead type process.

======================

Intake Centerline Method
There are several accepted ways to degree a camshaft. COMP Cams® suggests the intake centerline method as the easiest and most accurate. This method of cam degreeing is very practical and indifferent to design characteristics. It simply involves positioning the center, or point of maximum
lift, of the #1 intake lobe with Top Dead Center of the #1 piston. The intake centerline method still requires accuracy to be correct, but it is somewhat forgiving.

Once you have degreed a camshaft using this method, you will be surprised at its ease. We also recommend positioning the dial indicator on the #1 intake retainer because lift measurements will include any deflection that may occur in the pushrod and rocker arm. This makes the degreeing process as accurate as possible in relation to what actually goes on inside the engine.

Step 1: The camshaft and timing set have been installed. Make sure that the timing marks on both the cam gear and crank gear are aligned properly per the cam installation instructions. Use chalk or similar marker to better define the marks.

Step 2: For example, we have our cam card and it suggests we install the cam on 106 degree intake centerline. Install all the rocker arms and pushrods in the engine as normal. On #1 intake lobe, install the solid lifter in place of a hydraulic lifter. If a solid lifter or roller cam is being checked, use that respective lifter. Adjust the #1 intake lash to exactly zero. Do not pre-load the lifter. Next, adjust the #1 exhaust lash to zero. You should be able to turn both pushrods with your fingers easily.

Step 3: Attach the pointer to the block. Many people will make a pointer out of some sort of rigid, yet manageable wire. A stiff coat hanger wire works well.

Step 4: Attach the degree wheel to the balancer and install the assembly on the crankshaft. There are several ways to attach the degree wheel to the crankshaft. The crank may be rotated from either the front or from the flywheel end. Obviously, if the engine is in the car, you must rotate from the front.

Remember, the greater the leverage, the smoother the crank rotation, thus more accuracy. Note: Never use the starter to turn the engine while degreeing a cam.

Step 5: Before installing the piston stop, rotate the crankshaft to get the #1 piston in approximate TDC position with both the intake and exhaust valves closed. This can be a rough guess, but it can save you from making a mistake later. Adjust you pointer to zero or TDC on the degree wheel.

Step 6: Turn the crankshaft opposite the engine rotation approximately 15-20 degrees. This will lower the position enough to allow the TDC stop to be installed in the spark plug hole. Screw in the piston stop until it touches the piston. Continue to turn the engine in the same direction until the piston comes back up and touches the piston stop. Mark the degree wheel with a pen or pencil on the number the pointer is on. Turn the engine in the other direction, same as engine rotation, until the piston comes back up and touches the piston stop. Make a mark on the number the pointer is on.

Step 7: Remove the piston stop after marking the two points on you degree wheel. Rotate the crankshaft to the midpoint of the two marks. This point is TDC for cylinder #1. Without rotating the crankshaft, adjust the degree wheel to read 0 degrees at the pointer. You are now ready to locate the intake lobe centerline relative to TDC. If you are not absolutely sure that your 0 degree mark is set at TDC, repeat this procedure. This step by step is critical to proper cam alignment.

Step 8: Attach the dial indicator to the dial indicator mount. Position the dial indicator mount so the tip will contact the retainer of the intake valve. It is important that the indicator plunger be parallel to the valve stem. Any
variance in the angle of the indicator will introduce geometric errors into the lift readings.

Step 9: Rotate the engine in the normal direction of rotation until you reach maximum lift. The dial indicator will change direction at the point of maximum lift. At this point, set the dial to zero.

Step 10: Back the engine up (opposite normal rotation) until the indicator reads .100.” Next, turn the engine forward in the normal direction of rotation until the dial indicator reads .050” before maximum lift. Record the degree wheel reading.

Step 11: Continue to rotate the engine over in its normal direction of rotation until the indicator goes past zero to .050” on the closing side of maximum lift. Again, record the degree wheel reading.

Step 12: Add the 2 numbers together and dived by 2. That number will be the location of maximum lift of the intake lobe in relation to the crank and piston. This is the intake centerline.

For example: The first degree wheel reading was 96 degrees. The second reading was 116 degrees. These two numbers (96 + 116) added together will be 212. 212 divided by 2 will equal 106. Your actual intake centerline is 106 degrees. Reference back to your cam spec card and see what the recommended intake centerline is.

In the event that your camshaft did not degree in as per manufacturers’ specs, it will be necessary to either advance (move the cam ahead) or retard (move the cam back) the cam to meet the suggested intake centerline.

Depending on the engine application, there are several different ways for advancing or retarding the camshaft.

One common method is by use of a crank gear with multiple keyways-each
one being at a slightly different relationship to the gear teeth. A second method is to use offset bushings that fit on the cam pin and in the cam gear. The offset will advance or retard the cam depending on how the bushing is placed on the cam pin.

DHays: On a flathead, we usually redrill the camshaft gear (if bolt on), or change the location/indexing of the press-on gear. Some folks use "offset cam bushings" - I've never used them on a flathead.

Another method is by offset keys that fit into the crank gear keyway. A more elaborate system uses an adjustable timing gear. Contact COMP Cams® for the method best suited to your application.

Note: When degreeing a cam, remember to look at the degree wheel as a full 360 degrees no matter how the degree wheel you are using is marked. Many degree wheels are marked in 90 or 180 degree increments. On wheels that are marked in 90 degree increments, keep in mind that you must continue to count the number of degrees on past 90 degrees. Be sure all readings are taken from Top Dead Center.

Keep in mind that to advance the cam, you must lower the intake centerline. For example, if our cam has a lobe separation of 110 degrees. Moving the centerline to 106 degrees advances the cam 4 degrees. If we change the centerline to 112 degrees, this would be 2 degrees retarded.
 
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