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Camshaft Phasing For Dummies (Like Me)

Posted By Tedster 2 Weeks Ago
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Tedster
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Do any of you guys fall prey to what I call "mission creep"? It goes something like this. Say you've decided that new valve stem umbrella seals are needed. You get in there, and wanting to do a good job, start measuring stuff. And other stuff too. Naturally it's all out of spec. And .... before you know it, a $20 set of umbrella seals turns out to be new valves, retainers, guides, springs, shims, machine work to install hardened stellite seats yadda yadda. And, those Aluminum Mummert heads are looking kind of tempting...Hm.

So I've seen this movie before. I've got to stay focused. I've convinced myself the need to replace the timing set in my otherwise stock 292. I can trust that a stock cam in a stock engine with a stock replacement timing chain and gears, should offer a noticeable improvement. "But as long as you're in there ..."

I can see where this is going. I don't have a degree wheel or a dial indicator with fixtures. But, "I gots to know!!" right? So I said to my self, "Self, you just know there's got to be a good ole' boy way to do this." In other words, a compromise or middle way between doing nothing and hoping for the best, and, spending a week waiting for more tools, immersing myself in a crash course on the finer points of valve overlap and lobe separation. Like here:

http://www.eatonbalancing.com/2015/09/24/degreeing-in-the-camshaft-part-i-finding-tdc/#more-907

These are GREAT articles, I love reading stuff like this.

This is of course the way to do it. Though I'm not building a high performance engine, OCD means I'd like to ensure at least that any tolerance stackup is towards the "advanced" side of things. This begs the question, why isn't the cam already advanced? Or is it? Why don't they grind them that way in the first place, and compensate for inevitable chain stretch in the first place? As always those of us not spinning 6000 RPM kind of have to read between the lines on some of this stuff.

It DOES look like one way to achieve a rough measurement on valve overlap would be to measure this way taken from the Iskenderian website, without using any special tools or equipment. It might be interesting to see what it is right now, before timing set replacement with what I estimate is significant chain stretch or wear, and then afterwards.

CHECKING VALVE OVERLAP WITHOUT DEGREE WHEEL OR DIAL INDICATOR
When installing a camshaft, or when an occasion arises where it is necessary to make a check on valve timing and no appropriate instruments are available, the recommended Isky procedure is as follows:

Insert the camshaft and mesh the timing gears on the stock marks. Do not as yet install the timing gear cover.

Adjust the valve lash of the intake and exhaust valves of the No. 1 cylinder.
Using a long wrench or lever, turn the engine over in the normal running direction. Use enough leverage to get an even, steady movement instead of a jerky motion. Rotate until the intake and exhaust valves of No. 1 cylinder are in the overlap position (both valves opened slightly). Stop exactly on T.D.C., which is marked on the harmonic damper.

Now loosen and back off the rocker arm adjusting screws until the intake and exhaust valves are just barely closed. Lock the adjustment screws so that the intake and exhaust valves are at exactly zero clearance.

Now turn the engine over exactly one revolution of the crankshaft to T.D.C. on the harmonic damper. You are now at T.D.C. on the compression or firing stroke.

Take Notice! Now there is a large space between the rockers and valve stem tips. The space indicates the actual amount the valves were open at T.D.C. of the overlap period (less valve lash, of course).

We will measure this gap space by probing with common feeler gauges of various thicknesses combined until we determine the gap space. After computing the gap, record the figures for both intake and exhaust in your notebook. If the amount of gap on intake and exhaust is exactly the same, you have a perfect split overlap.

AN EXAMPLE USING AN RPM 300 CAM

Advanced Cam Position: If your intake happens to come out with .100 gap, and the exhaust with say .080 gap, your cam is in an advanced position. In this position, the came will produce more low-speed power or torque. However, there might be a slight loss of power at high RPM.

Retarded Cam Position: If, on the other hand, the intake came out with .080 gap, and the exhaust at .100, your cam is in a retarded position. In this position, there will be some loss in low-speed torque and power, and probably some subsequent gain in high-speed power.

Split Overlap: If the intake and exhaust gap read out exactly even, or within .005 of each other, you have a split overlap. Generally speaking, all racing cams run best in the split overlap position. While there are exceptions to this rule, it is usually best for overall performance.
_______________________________

Ted, fellow Y-blockers, etc any thoughts on this method or other factors to consider? Would a few degrees of camshaft advance generally be adviseable for a stock 8-1 compression 64 292. I see that offset woodruff keys are available.




57RancheroJim
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I recently thought the same thing about chain stretch. I helped a friend who had a small leak at the timing cover to repair it, this engine only had about 5000 miles on it and I was amazed at how much stretch there was. He had used a Cloyes OEM type chain on the build. This was a stock 292 daily driver and the difference was never really felt that he could tell. A few years back another friend with a Tbird tried both advancing 2 degrees and retarting 2 degrees and as far as just driving it never could tell a real difference. I'm my street engines I just install straight up as is and drive them..
But if you feel you need to go through all the degee work on a stock street motor in a truck I would rather use a timing set with keyed sprockets rather then an of set key. But mine is only one of many opinions...
Ted
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You degree in the camshafts due to machining variances in the various parts.  Stack ups are your enemy as that's when all the variances align with all being positive or all being negative.  In many instances those stack ups cancel each other out but like playing the lottery, sometimes you have a winner.  In this case, you have a loser.  I've found several engines now (all makes and brands) with the cam timing off as much as 18 degrees.  They all crank and run.  Some have detonation issues from being too far advanced while others are just sluggish due to being too far retarded.  As a general rule, it takes about a four degree change to be noticeable in the seat of the pants.  On the dyno, I can pick up differences with two degrees of change.  If the camshaft has symmetrical lobes, then measuring the lifter rise off of the base circle of the camshaft at overlap can give a good idea of advance or retard at TDC,   When being installed 'straight up', the exhaust and intake lifters will be the same distance off of the base circle of the camshaft.  This is an easy check on an assembled engine as a straight edge can be put across both the intake and exhaust valve retainers or roller rocker arms and when they are both level with each other, then look at the damper and see how many degrees from TDC you are at.  This is not as exact as doing the degree wheel method but it is close enough when looking for some serious discrepancies.  If the camshaft is simply being installed with the link count or alignment of the timing marks, that is not necessarily being installed straight up.  In those instances, the camshaft is simply installed and you do not know exactly where the lobes are in relation to TDC.

Lorena, Texas (South of Waco)


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57RancheroJim (8/11/2019)
But if you feel you need to go through all the degee work on a stock street motor in a truck I would rather use a timing set with keyed sprockets rather than a set key. But mine is only one of many opinions...




Yeah no like I said I didn't want to get tooinvolved. Too late for that, ha ha! It looks to me that there is 8° or 9° of stretch in this example, by carefull turning crank and observing rotor movement. Forgetting any potential stackup errors for the moment, that seems like a lot to retard to the cam? So I was looking to see that the centerline is at least on the "advanced" side of the crankshaft.

Does camshaft phasing affect cylinder compression testing? This engine measures 145-150 pounds cold across all cylinders, burns no oil, doesn't smoke etc. Heck it doesn't even leak, much. I see from reading forums some people advocate advancing or retarding a cam for best compression. This sounded promising to me, but I don't think it works that way. Is there a definite peak that is found as the cam phasing advances, and then it starts to fall off?

I assume, maybe wrongly, that engine manifold vacuum specifications listed in the manual are to be observed at factory idle ignition timing. In this instance say, 6° BTDC. TDC has been verified. I can get a nice steady 18" to 20" Hg. and smooth idle, but only by advancing the distributor timing by quite a lot. This has had me puzzled a bit, which isn't difficult. So that and other symptoms kind of led me to chain stretch. It kind of fits. I've played around with the mechanical advance and springs and such and it just seems to be a little anemic. When I replaced a fuel pump I noticed the chain looked old and was awfully loosey goosey on the slack side. I've heard the Cloyes sets are supplied with tighter tolerances, and the imported el-cheapos are to be avoided, but that's not news.
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Ted (8/11/2019)
When being installed 'straight up', the exhaust and intake lifters will be the same distance off of the base circle of the camshaft.  This is an easy check on an assembled engine as a straight edge can be put across both the intake and exhaust valve retainers or roller rocker arms and when they are both level with each other, then look at the damper and see how many degrees from TDC you are at.  This is not as exact as doing the degree wheel method but it is close enough when looking for some serious discrepancies.  If the camshaft is simply being installed with the link count or alignment of the timing marks, that is not necessarily being installed straight up.  In those instances, the camshaft is simply installed and you do not know exactly where the lobes are in relation to TDC.




In your article on camshaft degreeing I think you mentioned the relationship between #1 and #6 cylinders, I took it to mean that when #1 piston is at TDC compression, if the #6 valves are at overlap the camshaft and timing set is installed "straight up". It isn't that simple?

I'm a little unclear on this straightedge business, remember ya hafta dumb it down for us dummies. What do think of the Isky method using feeler gauges? If I can get this centerline business decidedly on the advanced side a little that would probably work for me and my OCD.
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Tedster [and others],

" I can get a nice steady 18" to 20" Hg. and smooth idle..."

We should all remember that gauge-measured vacuum will also generally vary depending on altitude (will show less with higher altitude); and, specifically can vary from time-to-time (hours, days, weeks, season) due to changing atmospheric pressure/weather/temperature/season: Our Atm. Press. ["Hg] here at my home, 1,200' Above Mean Sea Level, has varied from lows of 27" to highs of 31"; and, summer temps can be +100*F or more (rare) with winter down to -45*F or more (also rare) - this will affect "vacuum" readings similarly; so, if you keep records, also note the atmospheric pressure and other conditions at the time you take your reading - for comparison.  Just another little "tidbit" to keep in mind.

Regards, JLB

55 Ford Crown Victoria Steel Top
Tedster
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That's a good point, altitude particularly plays a big role. Someone who lives in Denver won't see 20", and it would be interesting to know the best an engine in Leadville could pull.

Can't recall what ignition timing setting I found achieves good manifold vacuum but I'm pretty sure it exceeds 12°, it shouldn't be required to advance the timing much beyond this to get in the zone? See where I'm goin' with that?

Engine starts reasonably well cold though I think not as snappy as it should. Could be way off base on this chain stretch, it shouldn't hurt anything.

The manual shows the 12 pins and dits oriented on the fuel pump side. I takenit this is with #1 at overlap and #6 at TDC?
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Camshaft phasing as you call it can create problems with aftermarket camshafts.  Ted and I recently found out that there is a problem with the industry standard for grinding camshafts for the Y Block Ford engine in that they are using the wrong lifter angle from bank to bank when custom grinding a camshaft.  If you use a camshaft from any company other than Isky, then they are using the industry manuals that list the degree for the Y Block, and it is wrong.  If you install the camshafts straight up, then the engine will run fine, but if you advance or retard the camshaft, then you run into problems (think phasing) with the bank angle causing one bank to be several degrees wrong, and will not perform as expected.  Last year I had a custom Comp Cam given to me for the EMC engine as a sponsorship, but we could not use the cam due to trying to advance it as suggested.  The lobes were all over the place in the 2* and 4* advanced position, causing us to go back to the Isky.  I recently had this confirmed when another brand of camshaft was custom ground for our EMC entry for this year, and straight up, it was Ok, but when we went to advance it, one bank was retarded, and the other was advanced, making it unusable.  I sent the camshaft back, and it was put on the Cam Doctor machine and confirmed that it had been ground wrong according to the industry standard information.  After obtaining the correct specifications for lifter bore angles, the camshaft has been reground and parkerized, and in on its way back to us for dyno testing.  Anything other than stock Ford or Iskendarian camshafts should be degreed if you are serious about performance gains without valve to piston, valve to cylinder wall, interference issues or degraded performance.  I am sure Ted will have enough material for a magazine article after we get through with this EMC dyno session dealing with double checking your performance camshaft installation.  Joe-JDC


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Interesting.  I know it will probably fall on def ears, but did you tell those companies that they are doing it wrong?  If they don't know, they can't fix it.


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charliemccraney (8/11/2019)
Interesting.  I know it will probably fall on def ears, but did you tell those companies that they are doing it wrong?  If they don't know, they can't fix it.

I was told that I was the first to bring up the issue, and yes, the owner of this company is now aware, and is also reworking two more camshafts that they custom ground for me earlier this year.  That makes three custom camshafts that he will personally make sure gets done correctly.  Can't ask for better customer service than that.  The listings in Howards Cams, Comp Cams, and several others is wrong, and unless someone goes to the trouble of degreeing all the lobes as Ted and I just did, they will never know that the camshafts are actually ground wrong.  Straight up is ok, but anything else will be off bank to bank.  Joe-JDC


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