Come inside Cam Gurus
This is a discussion on Come inside Cam Gurus within the Internal Engine forums, part of the LSx Technical Help Section category; This is a continuation of my Magic Stick 3 Saga and need some verification. I have a Magic stick 3 ...
11-22-2012, 05:55 AM #1
Come inside Cam Gurus
This is a continuation of my Magic Stick 3 Saga and need some verification. I have a Magic stick 3 cam 238/241 605/610 lift cam on a 114 LSA from TSP back in 07. Toasted the LS1 I installed it in, Exhaust valves hit. Currently I'm building another with the same cam, it made it out alive suprisingly. Started putting it together and have contact between the exhaust valve and piston. Started calling Texas speed and Comp cams to try to resolve the issue, both say the lift and duration shouldn't be hitting. Had the cam profiled at Comp cams (they're local for me) which showed the specs to be correct save for one, LSA and advance. It's a 114.2 LSA but has an additional 1.380 of advance ground in. According to Texas speed I have to install the camshaft advanced not dot to dot. I'm confused now though. If the cam already has additional advance ground in, would you not retard the cam or am I reading into that backwards? I'm really getting tired of this saga and I'm ready to get this car back running. I don't know if I should trust installing an improperly ground cam, have it reground, or just get a new one (which I realllllly don't want to do). Any advice and clarification on this would be helpful.
11-22-2012, 06:52 AM #2
When you have advance that is ground into the camshaft, they are talking about the intake centerline in relation to the lobe seperation.
So if you have exactly 114.2 lobe seperation, and you have exactly 1.380 of advance ground in,,,then your intake centerline is 112.82.
Your cam card will show both of these specs (or should).
So if you install the camshaft "dot to dot" it means it will be installed on this 112.82 intake centerline and will already have a slight advance ground into the lobes.
However I always degree the camshafts because even at "dot to dot" on the timing gears doesn't always mean it's exactly at the intake centerline that the camshaft manufactures want. There are sometimes variations in the keyways of the crank and camshaft, and sometimes variations in the keyways of the timing gears, and sometimes there is chain stretch that also affects the advancement of the camshaft.
So bottom line is that it needs to be degreed all the time, every time, to make sure these variables are checked and the camshaft is exactly where it's supposed to be. If it is not, there are advance/retard bushings that can be used on the cam gear, adjustable timing gears, etc...
11-22-2012, 07:17 AM #3
Thanks. OK so I have a degree kit and adjustible timing set on the way which way do I start with the cam advancing it or retarding it? How would you do it 1 degree at a time until it clears?
11-22-2012, 07:37 AM #4
First thing I'd do is install the cam degreed exactly how the cam card or manufacture wants it in there. Sounds like basically they have 1 degree of advance ground into the camshaft, that's where I would start. See if it comes in at 112 or 113 ICL and go from there.
Advancing the camshaft moves the intake valve closer to the piston, retarding does the opposite.
If you have exhaust valves hitting my guess is that the cam went in retarded (even though you lined up the dots) because like I said there are variances from one engine to the next in regard to crank keyways, cam keyways, crank gear and cam gear keyways, timing chain stretch etc. that can vary the install position of the camshaft a few degrees in either direction...which might explain why it worked in one engine and not the other engine.
This is especially critical when you are playing with a camshaft that has very minimal valve to piston clearances. A general rule is to have about .100" clearance for exhaust valves and .080" for intake valves. Some push this even further when building an engine so you can see how close things get.
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