Comp 918 springs with XR265 cam.. valvetrain noise
10-01-2008, 04:17 PM
#11
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Normal, it is a more aggressive cam, lobes then the stocker, no good on tightening the rockers more tq them to 22 ft and its all good... I wouldn't worry unless it is really loud, sounds out of pattern...
John
John
10-01-2008, 07:07 PM
#12
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did you torque them down correctly? did you use loc-tite? my 212/218 with LS6springs and stock pushrods did not make any noise...... make sure the rocker bolts have some loctite for sure cause they will loosen up.
10-02-2008, 06:59 AM
#14
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The stock pushrods are 7.395. Most go to 7.400. As for noise, if it bothers you put LS6 springs in it's place. The 918's create so much noise that even the knock sensor pick's it up as faulse KR*. They are fine when needed, but at your low lift they are excessive. I call it the sewing machine noise.
10-02-2008, 08:12 AM
#15
I am running patriot dual golds with my 218/224 high lift cam and the noise is there but not as loud as you're describing. Riddle me this...... How can a spring make noise when the coils themselves never contact eachother? I'm not saying you're wrong, I just have always wondered this. I can see on the spring seat (but minimal) and on the retainer (but very minimal as well). Once again, not saying you're wrong but can someone explain why A vs. B spring would have a different sound? Are their harmonics created from the quick compression and rebound of the spring that equates to a "snap" or "tap"? You hear of LSx guys hollaring about valvetrain noise all the time but I think the little bit of a tap or snap they hear is the valves slamming shut due to the modern day lobe profiles. That's what mine sounds like at least.
10-02-2008, 08:45 AM
#17
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Then for every full turn of the bolt it is .049" compression of the lifter plunger (this is your preload). Hopefully you already have your torque wrench set to 22 ft lbs so count how many revolutions it takes you to get to 22 ft lbs after you reach zero lash. For me it was 1 3/4 turns so this is .8575 lifter preload. You want your preload between .060 and .100 thousandths. .
10-02-2008, 09:03 AM
#18
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I don't know what the reason really is. If you slowly turn and engine over though you can hear a little snapping noise from the springs. I'm not sure if the main noise is a resonance or valves hitting the seats harder or what. I know that I've worked with many different types of valve springs and the stiffer they are, the noisier they are. I've even had a Silverado SS that we took the bigger cam out, put in the stock cam, and left in the 918's. That truck still sounded like a sewing machine with the stock cam.
10-02-2008, 10:32 AM
#19
I forgot to use parallel triangles in my math. The threads are 8mm X 1.25, so every turn is 1.25mm or 0.049". Using the rocker ratio (parallel triangles), you get every turn is 2.54/1.54 * 0.049" = 0.080". So if you had 1-3/8 turns should therefore be 0.110" or there abouts as an approximation. You really need to measure with a pushrod length checker to be accurate.
10-02-2008, 10:36 AM
#20
I don't know what the reason really is. If you slowly turn and engine over though you can hear a little snapping noise from the springs. I'm not sure if the main noise is a resonance or valves hitting the seats harder or what. I know that I've worked with many different types of valve springs and the stiffer they are, the noisier they are. I've even had a Silverado SS that we took the bigger cam out, put in the stock cam, and left in the 918's. That truck still sounded like a sewing machine with the stock cam.
After playing with my 4.8L on the engine stand, I grabbed a rocker that's at full rest and it wiggles from side to side. It clicks as there is side to side play from the needle bearings (naturally there has to be). I would think the 918's over the LS6 springs have a considerably higher amount of seat pressure at rest. This in fact is putting more stress on the rocker so you are going to hear that clack or side to side movement as the rocker leaves and returns back to its resting position. I believe it to be the nature of the beast. Maybe this is moreso heard than the initial theory I had of the valves slamming onto their seats.