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Re: Cryptic Camshaft Specs......what do they mean?
Tracy - this is fairly typical of camshaft grinder specifications. The ATC and ABC refer to "After Top Center" (or After Top Dead Center) and After Bottom Center or Dead center respectively. So these degrees are relative to rotation past or before each dead center reference point. This is why you aren't seeing a tyical duration such as 242 degrees etc. I good camshaft book will go over these nuances. Not the specs are are 50 thousanths lift, which is also fairly typical. Other measurenents are often overlap and lobe centerline measurements.
I would personally us ARP brand break in lube. I have a Speed Pro CS185R solid lifter cam and plan to break it in with the ARP lube, I have always had great luck with it...Craig -
Re: Cryptic Camshaft Specs......what do they mean?
It has been a long tome since I dialed in a cam. Your assumptions are currect. The @0.050 means that at 10 degree before the piston reaches to dead center (as we used to call it), the intake lifter will lift .050 thousanths of an inch. The lower numbers are probably the older way of checking the timing at 0.006" lift. Either spec will do, although the 0.050 is the current method. This can be checked easily , by placing a dial indicater on the intake lifter or if the heads are installed, on the rocker arm exactly on top of the pushrod location (assuming that you have already extablished a true top dead center). You may need to get a degree tape for your vibration damper. It is also easyer to remove all of the spark plugs first. The lifter can also be checked that it reaches .050" again at 52 degrees after bottom dead center. The second set of numbers refers to the exhaust valve timing. The procedure is the same. If the timing is different by a few degrees, an offset cam button can be installed in the cam timing gear to change the cam timing to meet spec. You will need to drill the gear hole larger if a button is needed. Isky cams used to make these buttons. DO NOT FORGET TO CHECK THE VALVE TO PISTON CLEARANCE AFTER THE HEADS ARE INSTALLED. As you come up on top dead center with the intake valve opening, use a hand held tool to open the intake valve until it hits the piston. Retate the engine a couple of degrees and check it again. Do this until the clearance starts getting larger. Repet this process with the exhaust valve when it is closing and closest to the piston.
I always used Isky moly cam lube that came with thier cams. I would think any speed shop would have cam lube. It is alway a good idea to prepressureize the oiling system as previously discribed on this site a day or two ago.
Hope I did not confuse the issue. That is what we did when I made a living building race engines, A long-long time ago, in a distant galixy, I mean memory.Comment
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Re: Cryptic Camshaft Specs......what do they mean?
I just checked one last week for a friend,355,vortec heads,retro-fit
hydralic roller and it was 4 degrees off.
He said it wasn't needed since all parts were name brand high dollar parts
good double-row timing sets come with three keyways to adjust cam timing the easiest way.
A find anywhere great working cam/lifter break-in lube
a past buick mechanic/then machinist told me
STP oil treatment / friction additiveComment
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the best thing to use is GMs EOS for cams and
engine break in.Comment
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Re: Cryptic Camshaft Specs......what do they mean?
Inlet valve open, BTC - inlet valve close, ABC / exhaust valve open, BBC - exhaust valve close, ATC. These are the timing points at the specified lifts.
The @.050" lift timing points are off the base circle, so they include a lot of clearance ramp.
The SAE J604d timing points should be at .006" valve lift, however, the data listed by FM for this LT-1 cam clone are closer to the lash point timing numbers that I measured on an actual LT-1 cam.
The SAE J604d duration with clearance set to take up the lash at the top of the ramps with the measured 1.37:1 rocker ratio at the lash point are (based on my measurements)
26-71.5/83.5-29.5
Add the numbers on each side to 180 to get duration, which is 277.5/293.
The "centerlines" are halfway in between the opening and closing points which compute to 112.8 ATC for the inlet and 117.0 for the exhaust, however since the lobe is asymmetrical the centerlines and points of maximum lift are not the same. Points of maximum lift at 110 ATC and 122 BTC inlet/exhaust, respectively.
The "lobe center angle" is the spread (in cam degrees) between the centerlines of the lobe. Add the centers together and divide by two to get the result. In this case the lobe center angle is 114.9 degrees.
This, of course, is different than the angle between points of maximum lift which is 116 degrees.
See, cam specs are easy to deal with and perfectly clear.
DukeComment
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Re: Cryptic Camshaft Specs......what do they mean?
Here's a description of cam timing and info on specs.
Roger
#36316
http://www.compcams.com/Technical/TimingTutorial/Comment
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Re: Cryptic Camshaft Specs......what do they mean?
Sometime in the '50's there was a paperback book published that went into great detail on cam timing. It also explained in great detail the theory of ram tuning (this book predated the original Ramcharger car, maybe they read it). It was written so that an idiot like me could sit down and at least halfway understand camshafts. I had the book, but lost it in one of my moves. It would be great text for anyone wanting to understand the theory.Dick WhittingtonComment
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Re: Cryptic Camshaft Specs......what do they mean?
I recently saw a good article on cam theory on the magizene rack the other day. I did not buy it, but it was titled domething like tech tip of the years. It appeared to be published by car craft or chevy power as a year end deal. about $4.99.Comment
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Re: Thanks to all respondents!
the closest the piston to valve clearance will be is 10 degrees before TDC for the exhaust and 10 degrees after TDC for the intake. the quick way to check the piston to valve is to install light springs on the intake and exhaust valves in one cylinder. set your valve lash,then place a .100 thick shim between the rocker arm tip and the valve tip,then slowly turn the engine over with a bar. if you do not have any resistance to the turning of the crank you are good to go. if you use a feeler gauge stack to do the checking and and can very the thickness to see what you have.Comment
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Re: Thanks to all respondents!
Skip the timing tape,they are not degreed 360, only at the beginning,no marks at cam spec areas, get a degree wheel you can use on any engine,I put 1 1/2" masking tape on balancer while removed using degree wheel,I mark it 0 to 40 btdc then at 45 90 180 270 and at cam card specs at .050 and a little few degrees each way,after installed, find true tdc and adjust pointer.
Last weeks engine tdc was marked at 2 degrees retard on timing tab on cover!
It was a new balancer last year.Comment
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Sounds like excellent advice..thank you! *NM*
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