Published by Ted Eaton on 02 Dec 2015
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Published by Ted Eaton on 02 Dec 2015
Just click on the topic you’d like to view.
Published by Ted Eaton on 24 Sep 2015
Part of the blueprinting process during any engine buildup will include degreeing in the camshaft. This operation is performed to insure the camshaft is phased or installed at the desired position in relation to the piston sitting at TDC. While degreeing in the camshaft during its installation may seem to be an activity reserved just for the race engines, the fact remains that it’s just as important on the daily driver applications as it is for high performance engines. A camshaft being off just a few degrees can lead to tuning and performance issues as well as poor fuel economy. The more serious cam phasing problems can include a lack of compression or the complete opposite where detonation issues come to the forefront and must be dealt with. If problems with engine performance are present once the engine is up and running and the camshaft has not been degreed in, then this is an area that becomes a question mark and may have to be revisited. Degreeing in the camshaft during the initial engine build process is much easier on the engine stand than having to perform the operation after the engine has been installed in the vehicle.
Manufacturing variances are why the camshaft must be degreed in. The crankshaft key slot, the camshaft snout key or dowel pin, the crank gear keyway, and the camshaft gear keyway or dowel hole all have a given amount of variability during their manufacture. Added to this are the variances in lobe grinding on the camshaft itself that can also occur. While some of the manufacturing variances will have both positives and negatives involved thus cancelling out some of those variances, stack-ups are where the real problems begin. Stack-ups are when those variances are all positive or negative in nature. These simply add together creating a significant number of degrees in which the camshaft phasing can be ‘off’. While it’s unusual to see engines with as much as eighteen degrees of camshaft error with the gear timing marks giving every indication that all is ‘good’, it does happen. And this is assuming that the camshaft lobes themselves are all ground consistently and as stated on the camshaft specification sheet. That’s another subject that will be touched upon much later.
Before getting into the mechanics of what is actually involved in the cam degreeing process, the terminology must be clarified. Here are some of the common terms.
Lobe centerline angle – This is the total number of degrees between intake and exhaust lobe centers divided by two. This value is controlled by the cam grinder and may also be referred to as the ‘as ground lobe centerline angle’.
Intake lobe centerline angle – This is the number of degrees from the center of the intake lobe to piston TDC. This value is dictated by the variables that occur during the installation process. It is the deviation of this number from the as ground lobe centerline angle number that is most often used to describe the amount of advance or retard in which a camshaft is installed.
Exhaust lobe centerline angle – This is the number of degrees from the center of the exhaust lobe to TDC. This value changes inversely to the intake lobe centerline angle as the camshaft is being installed. The exhaust lobe centerline and intake lobe centerline numbers added together and divided by two will always equal the ‘as ground lobe centerline angle’.
Straight up – This refers to installing the camshaft on the ‘as ground’ lobe centerline angle. The number of measured degrees between the center of the exhaust and intake lobes will be equal. Simply aligning the reference marks on the timing set does not dictate that the camshaft is installed straight up nor does it indicate exactly the number of degrees that the camshaft is installed either advanced or retarded in relation to TDC. The gear timing marks being aligned simply indicates aligned timing marks and does not give any information regarding where the camshaft is actually installed.
Advanced – This is where the camshaft is installed so the timing events occur earlier than if the camshaft is installed straight up. If a camshaft is advanced, the number of degrees between TDC and the intake lobe centerline will be less than the number of degrees between TDC and the exhaust lobe centerline. These two values added together and divided by two will still add up to the advertised lobe centerline angle though.
Retarded – This is the opposite of the advanced scenario and is where the camshaft is installed so the timing events occur later rather than earlier.
TDC – Top Dead Center – This is where the piston is at the top of the bore. This doesn’t have to necessarily be the #1 piston but that is the piston that’s normally referenced during the camshaft degreeing in process. Keep in mind that a piston will sit at TDC for several degrees due to the rock in the connecting rod when it’s at full arm extension. More on how to find ‘exact TDC’ will be covered later.
The bare minimum of tools necessary to degree in a camshaft will include a degree wheel and a dial indicator capable of measuring up to 1.000”. The dial indicator ideally needs an extension on it that’s long enough to reach the lifters. A fixture or strap of steel for use as a piston stop can also be beneficial depending upon the methodology being used for determining exact TDC. For the dial indicator, some form of magnetic stand or fixture will be necessary to hold the dial indicator perpendicular to the valve lifter and/or piston.
Degree wheels are available in a multitude of diameters and degree readings. They all share a TDC and BDC but how they are numbered in between those two locations may differ. Using larger diameter degree wheels does allow for a greater degree of accuracy but wheels as small as nine inches in diameter can be used with a high level of confidence. It’s important that the locating hole in the center of the wheel be appropriately sized for the bolt that’s being used to attach it to the crankshaft snout. Having a hole that’s too large for the bolt can allow for some sloppiness and inaccuracy in the readings. Many degree wheels if purchased new will include bushings so that varying sizes of bolts can be used. In lieu of using bushings, the underside of a bolt head can be machined with a register so that the degree wheel hole matches the machined bolt head underside.
Click on pictures for larger image.
Also required will be a sleeve, nut, or other apparatus for the crankshaft snout so that the crankshaft can be turned without disturbing the degree wheel which is fastened to the front of the crankshaft. Use of a pipe wrench to turn the crankshaft at the unprotected snout is highly frowned upon. While slightly cumbersome, extended bolts in the flywheel flange of the crankshaft in conjunction with a long bar can be used to turn the crankshaft. It’s important that the engine be able to be turned over without disturbing the degree wheel. Using the bolt that fastens the degree wheel to the engine cannot be used to turn the engine over as that can unintentionally move the degree wheel once it has been set.
For the Ford Y-Block family of engines, the lifters, camshaft, and timing set needs to be already installed prior to attaching the degree wheel to the crankshaft. For other engines where the lifters can be top loaded, only the camshaft and timing set needs to be initially installed. This is so that the degree wheel is not disturbed by installing the camshaft and/or the timing set after the fact. For the Ford 292/312 family of engines, the chain is installed on the gears so that there are twelve pins between the gear dots and those pins will be on the oil filter side of the engine. For other engines, the dots on the gears are centered and aligned with each other through the centerline of the cam and crankshaft journals. If in doubt on how the timing gears are initially aligned, simply consult an engine manual for the particular engine being worked on.
It’s assumed at this point that the crankshaft and at least one piston assembly is installed within the block. That piston does not necessarily need the rings on it but the rings being already installed will help to keep the engine from turning over too easily. Most camshaft degreeing takes place with the engine short block already assembled. Ideally, once the camshaft with its corresponding timing set has been degreed in, then it should not be removed to eliminate the risk that the camshaft is reinstalled differently if not re-performing the cam degree in process again.
FINDING ‘Exact’ TDC.
Much emphasis is placed on getting the TDC on the degree wheel properly located. This is simply due to all other measurements being based off of this. Any error in locating exact TDC will be transferred as error in the camshaft degreeing in process.
There are several different methods in which to determine the exact TDC. I’ll be concentrating on those methods that have the cylinder heads off of the engine. Eyeballing the piston while it’s at the top of the bore is not one of these. With most methods, a degree wheel will be attached to the front of the crankshaft. In addition to this will be some form of pointer or indicator mounted to the front of the engine so that specific readings on the degree wheel can be identified. The pointer can be as simple as a piece of wire that’s bent appropriately or a more elaborate or specifically built piece that can be used repeatedly.
One method for finding exact TDC would be with a dial indicator. With the dial indicator set at zero and with the piston simply located at the top of the bore, the degree wheel is initially tightened so that the pointer is aligned with ‘TDC’ on the wheel. The piston is then moved a set amount in both directions and the wheel is adjusted so that the same number of degrees from TDC is indicated in both directions. The amount that the piston is moved in both directions simply needs to be the same but 0.100” works in most cases. As mentioned earlier, do not rotate the engine with the bolt that fastens the degree wheel to the crankshaft snout.
A second method which is also my own preferred method, involves using a strap or piston stop that fastens across the bore. With the piston slightly down in the bore, a strap with a stop protruding down into the bore is bolted to the block deck using the threaded head bolt holes. If the engine is using pop up pistons or pistons that rise above the deck surface at TDC, then a simple flat plate or strap without a protruding stop will also work. The engine is then rotated so that the piston is against the stop. Once this is done, the degree wheel is turned so that the pointer is aligned with TDC on the wheel and lightly tightened. The engine is then rotated in the opposite direction until the piston once again rests on the piston stop. The number of degrees the piston is residing from TDC is noted and this number is divided by two. The degree wheel is then loosened and turned so the pointer is now indicating the new ‘divided by two’ number as degrees from TDC on the wheel. Rotating the engine back in the opposite direction and coming to rest at the piston stop should now have the degree wheel sitting at that same number on the opposite side of TDC. If the numbers are not the same, readjust the wheel and double check by insuring it’s the same value in the opposite direction. Once the numbers are the same, then it’s time to actually degree in the camshaft. This will be covered in Part II.
Until next issue, happy Y motoring. Ted Eaton.
This article was originally published in The Y-Block Magazine, Mar-Apr 2015, Issue #127.
Published by Ted Eaton on 24 Sep 2015
Part I of this article went into detail as how to find exact TDC. With that now behind us, the actual process of checking the camshaft and how it is currently phased within the engine can begin. For this, a 1.000” travel dial indicator will be required that can measure the up and down motion of the lifters. While the number one cylinder is customarily the cylinder of choice in which to check the camshaft, any cylinder can be used to degree in the camshaft once TDC has been found for that cylinder. In fact, later in this operation another cylinder will be checked in which to both verify the results obtained off of the first cylinder check and also insure that the camshaft is at least consistent in values on two different cylinders. For now, the number one cylinder will be used as a reference.
There are two basic methodologies in checking the camshaft phasing. One would be to check the opening and closing events of the intake and exhaust lobes and comparing those to the camshaft specification card. Most checks performed with this method for aftermarket cams will be done with the lobe opening and closing events being measured at 0.050” off the heel of the camshaft. For instance, lobe lift is measured at 0.050” after the lifter starts to rise and again at 0.050” before the lifter comes to a rest at the end of its closing event. Some of the older oem Ford grinds use 0.100” for the check so be sure to know what the spec card or manual calls for when checking a camshaft using the opening/closing specs methodology.
Because of manufacturing variances and/or excessive lubricant on the lobes and tappets themselves, there tends to be some error introduced into this checking method that can make it difficult to obtain accurate readings. Be aware that most high viscosity cam lube is to be used only on the tappet faces and the lobes and should never be used on the lifter stems or lifter bores; also do not use camshaft specific lube on the engine bearings. While working with lobes and lifters that are simply oiled would give more accurate results, doing it this way would require that the cam lobes and lifter faces be removed to properly lube them for the final engine assembly. Doing this then increases the risk of the camshaft being reinstalled incorrectly if not re-performing the degree in process again.
Another method which is also my method of choice involves checking the lobes as measured from their centerlines. This method works for a majority of the camshafts out there and only gives issues when the lobes are special ground to the point they are not symmetrical on the opening and closing ramps at the top of the lobes. The following detailed instructions will be using the lobe centerline methodology.
Lobe Centerline Methodolgy –
At this point the camshaft, lifters and timing set are already installed. If the crankshaft gear has multiple keyway slots, then use the ‘zero’ position slot as a starting point. Many camshafts already have a given amount of advance built into them and in most instances starting with the ‘zero’ slot will have the camshaft much closer to its desired installed position. Second guessing the camshaft and pre-adjusting the crank gear more often than not ends up having the camshaft being installed way off of the mark when performing that first check.
With the dial indicator firmly attached to the deck surface and so that its stem can contact the intake lifter for the number one cylinder, the engine is rotated until that lifter is at full lift as indicated on the dial indicator. Placing the indicator stem at the outer edge of the lifter rather than in the pushrod cup hole tends to also give more consistent readings. With the lobe at max lift, rotate or adjust the dial indicator dial so that it’s reading zero. Now rotate the engine backwards (CCW looking from the front) so the lifter falls back down ~0.060”. Then rotate the engine forward until the lifter rise is at 0.050” before the top of the lobe. The reasoning for going back to a point more than 0.050” from lift peak and then coming back to the 0.050” mark is to insure that any slack in the timing chain is compensated for by loading the chain in the direction that the engine normally turns. At this point, take a reading from the degree wheel as the number of degrees from TDC. In this instance, we’ll use 49° ATDC for the example.
Now rotate the engine in a forward direction (CW looking from the front) so that the lifter crests at full lift and continue rotating so that the lifter is now at 0.050” down on the other side of the lobe. At this point take another degree wheel reading as degrees from TDC. In this instance, we’ll use 157° ATDC for the example. Taking the sum of the 49 and 157 values and then dividing by two, the resulting value is 103. This would be the number of degrees that the intake lobe centerline is from TDC. Now looking at the cam spec card, look for the number of degrees that the camshaft is ground on. For this example, the card says the camshaft is ground on 108° lobe centers. With the measured intake lobe value being less than 108° and subsequently closer to TDC, then 108 minus 103 would have this camshaft being 5° advanced. Some cam cards will include the manufacturers recommended intake lobe centerline installation value which can be compared to your measured value. Our card has the recommended installation being at 104° degrees intake lobe centerline which has the camshaft as measured having one more additional degree of advance. Had the intake lobe centerline value been a number greater than the advertised lobe centerline value, then the camshaft would be that number of degrees retarded. If the measured intake lobe centerline equals the advertised ‘as ground’ lobe centerline value, then the camshaft is installed straight up (no advance, no retard).
Because of manufacturing variances, we are now going to go an extra step and check the exhaust lobe to get some real numbers on the camshaft and how it has been ground. This is being performed to both verify the checking procedure and also insure that the camshaft is ground as advertised at least for this particular cylinder. So with that in mind, move the dial indicator to the #1 exhaust lifter. Rotate the engine in a forward manner until maximum lobe lift is obtained on the dial indicator and then zero out the indicator dial. Rotate the engine backwards so that lifter falls back down approximately 0.060” and then forward so that the lifter is sitting at 0.050” before max lobe lift. Take a degree wheel reading as degrees from TDC. In this instance a 160° BTDC value is indicated on the degree wheel. Now rotate the engine forward (CW looking from the front) so that the lifter crests to max lift and continue forward until the lifter is sitting 0.050” down on the other side of the lobe. The reading on the degree wheel at this point is 64° BTDC. Taking the sum of 160 and 64 and dividing by two gets a value of 112° for the exhaust lobe centerline. Because we are now dealing with the exhaust lobe, any value greater than the advertised lobe centerline will also indicate degrees of advance. In this case, 112 minus 108 equals 4° of cam advance based on the advertised ‘as ground’ lobe centerline value on the spec card.
As determined by the individual lobe measurements, the intake is installed at 5° of advance and the exhaust lobe measurement says 4° of advance. Which is correct? To determine this, the two sets of degree wheel measurements must be combined. Add together the measured 112° exhaust lobe centerline and the measured 103° intake lobe centerline values obtained earlier and divide by two. 107½° is the revised or actual ‘as ground’ lobe centerline value rather than the 108° that is listed on the cam card. Revisiting the intake and/or exhaust lobe centerline values and recalculating using the actual ‘as ground’ lobe centerline, the camshaft is actually 4½° advanced instead of the 5° value that was determined earlier by only doing the intake lobe measurement.
SAME DRILL, DIFFERENT CYLINDER.
Because the #1 and #6 cylinders on most V8 engines share the same TDC on the degree wheel, the #6 cylinder will now be used to reaffirm both the checking procedure and any variances in the camshaft itself. (The Buick V8 Nail Head engines are a known exception to the cylinders 1 & 6 sharing the same TDC.) Because the #6 cylinder is being used for the double check, the degree wheel can remain as it was for the #1 cylinder check. Any other cylinder can be used for the recheck as long as exact TDC for that cylinder is found and the degree wheel is adjusted accordingly.
In this case, the dial indicator is simply moved to the #6 intake lifter and the same procedure as used for the #1 intake lobe is performed once again. In this instance, the intake lobe centerline measures to be 104°. The dial indicator is then moved to the #6 exhaust lifter and that ends up being installed at 113° lobe centerline. Adding the 104 and 113 values together and dividing by two gives us a 108½° ‘as ground’ lobe centerline for cylinder #6. Taking the 104 value and subtracting from the 108½ value leaves the intake on this cylinder being installed at 4½° of advance. The check for the #1 cylinder also had the actual amount of advance right at 4½° so in this instance, both are identical. In the event there was a difference, then averaging the values would give the advance value to be used for this particular engine.
With the numbers obtained from the #6 cam lobes check, the variability within the cam lobes between cylinders 1 & 6 can now be observed. The 108½° value on cylinder #6 is compared to the 107½° degree value that was obtained on the #1 cylinder and there is a 1° difference. That is your lobe centerline manufacturing variance for these two cylinders. This is assuming your cam checking methodology is both consistent and accurate. While 1° of variance would be my own upper limit of variability, there are those cam manufacturers that are comfortable with 2° or more of variability. In summary, the more accurately the cam lobes are ground, the more potential power an engine will make once that camshaft is installed at its optimum position. If so inclined, the camshaft lobes for all eight cylinders can be checked for a better feel for how the camshaft is ground. In this particular instance, the camshaft that was just checked will be left where it is and ran.
The scary part of all this is if you only check the lobe or lobes on the #1 cylinder, the variability within the camshaft is basically unknown. That variability can be an engine performance issue all by itself once the engine is in the vehicle and being operated. The caveat to checking a large number of cams from the different manufacturers gives the installer a good feel for which cam grinders do a consistently better job in keeping variances to a minimum; or said differently, which cam companies to stay clear of.
HOW MUCH ADVANCE OR RETARD?:
As a general rule, most camshaft installations prefer a given amount of advance when being installed. Examining the spec card will give the manufacturers recommended installation specs but if not given those values, then 4° of advance covers most installations. Why advance the camshaft rather than simply install the camshaft straight up? Because a timing chain has a given amount of elasticity, the camshaft retards as the rpm increases so this initial amount of cam advance helps to compensate for this. Also, as a timing chain wears it stretches and as a result, the camshaft is also being retarded over time. All out race engines will break many of these rules in that the camshaft is simply being installed for the best power numbers in a given rpm range. Long term wear or stretch in this instance is not being compensated for.
Here is a word of caution regarding moving the camshaft phasing around. As the camshaft is advanced or retarded, the intake and exhaust valve relationship to the piston at TDC is changed. Depending upon the engine and the piston design, the potential is there for a valve to contact the piston resulting in a catastrophic failure if valve to piston clearances are not being checked. As the camshaft is being advanced, the intake valve becomes closer to the piston; as the camshaft is being retarded, the exhaust valve becomes closer to the piston.
A general rule of thumb for flat tappet camshafts is for each 4° the camshaft is moved, the valve to piston clearance is altered roughly 0.025”. If the camshaft is advanced 4°, the intake valve becomes ~0.025” closer to the piston; if the camshaft is retarded 4°, the exhaust valve becomes ~0.025” closer to the piston.
While the first part of degreeing in the camshaft is simply checking to see where it is initially installed, the second phase of the operation is actually moving the camshaft so its relationship to TDC is altered. If the camshaft has been found to be off enough to necessitate a change, then the camshaft phasing in relation to TDC will need to be moved. On some engines, one degree of change may be critical while on others it may take four degrees to be significant. Changing the camshaft phasing on some engines can be performed at the camshaft gear by lieu of using an offset key or offset bushings. Where the crankshaft gear has multiple key slots, then the appropriate slot can be used to move the camshaft a given number of degrees in one direction or the other. Where the crankshaft gear has only a single slot, then an offset key can be used at the crankshaft with the direction of the offset that’s built into the key determining either advance or retard. Another option where the crank gear only has one key slot is broaching an additional slot at a new position in the gear to also move the camshaft in the desired direction and amount. Likewise, a new key way slot can be broached into the cam gear or a new dowel pin hole placed at the appropriate spot on the gear.
To advance a camshaft, then either the cam gear is turned more clockwise (looking at the front of the engine) or the crank gear is turned more counter clockwise in relation to the opposite gear not moving at all. To retard a camshaft it’s the opposite scenario where the cam gear is turned counter clock wise or the crank gear is moved clockwise. Advancing the camshaft simply has the cam timing events occurring sooner while retarding the camshaft has those same events occurring later.
While part II of this article ended up being more complicated than I envisioned, I trust it is laid out in such a manner that the cam degreeing in process has been simplified. Part III will go into the specifics of the Rollmaster timing set for the Ford Y-Block and the nuances in moving that particular crank sprocket to achieve the desired results. Until next issue, happy Y motoring. Ted Eaton.
This article was originally published in The Y-Block Magazine, May-Jun 2015, Issue #128.