Preload Noise :( Pushrod length
10-15-2010, 12:11 PM
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Preload Noise :( Pushrod length Hey guys ..
The goal was to achieve the maximum street manners, Patrick G spec'ed 222/226 115lsa with EPS lobes and the result was great ; it idles like stock ! but I'm having preload noise!
I installed this cam on my LS1 346cid with stock crank and forged rods & pistons, set of PRC 5.3 stg 2.5 milled to 59cc, Comtic head gaskets 0.040, replacement comp lifters .. I used 7.4000 pushrods ..
I don't know what would be the correct pushrod. I know I should measure but I'm not living in US , and the order will take two weeks to be recieved here
The goal was to achieve the maximum street manners, Patrick G spec'ed 222/226 115lsa with EPS lobes and the result was great ; it idles like stock ! but I'm having preload noise!
I installed this cam on my LS1 346cid with stock crank and forged rods & pistons, set of PRC 5.3 stg 2.5 milled to 59cc, Comtic head gaskets 0.040, replacement comp lifters .. I used 7.4000 pushrods ..
I don't know what would be the correct pushrod. I know I should measure but I'm not living in US , and the order will take two weeks to be recieved here
10-15-2010, 12:16 PM
#2
You milled the heads, used thinner gaskets, and are still using 7.40" PRs? Your PRs are way too long. You probably have your lifter plungers bottomed out. How many turns past zero lash are you?
What springs are you using? That can make a significant difference in valve train noise.
What springs are you using? That can make a significant difference in valve train noise.
10-15-2010, 03:50 PM
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I have stock 853 heads & gaskets just like they came from the factory. No milling or anything like that, & I ended up going with 7.375" pushrods with my cam for .065 preload.
I started off with 7.425" & went to the dyno & realized that I had lost a bunch of HP. Took out the pushrods & remeasured & realized 7.425" was way too long. I & E valves were staying open at the same time & I wasn't building any compression.
So, if you have cometics & milled heads, I can almost guarantee you need shorter pushrods. That said, MEASURE, MEASURE, MEASURE to make sure!
I started off with 7.425" & went to the dyno & realized that I had lost a bunch of HP. Took out the pushrods & remeasured & realized 7.425" was way too long. I & E valves were staying open at the same time & I wasn't building any compression.
So, if you have cometics & milled heads, I can almost guarantee you need shorter pushrods. That said, MEASURE, MEASURE, MEASURE to make sure!
Last edited by osuhog; 10-17-2010 at 08:27 PM.
10-15-2010, 04:37 PM
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not trying to 
. but exactly what are you guys measuring? the pushrod itself or from cam to a "close" rocker tip? just trying to clear things up.
edited: nevermind i caught up. do you guys think he could maybe loosen up the rocker a lil to help the valves seal up?
. but exactly what are you guys measuring? the pushrod itself or from cam to a "close" rocker tip? just trying to clear things up.edited: nevermind i caught up. do you guys think he could maybe loosen up the rocker a lil to help the valves seal up?
Last edited by defdaboss; 10-15-2010 at 04:45 PM.
10-15-2010, 05:00 PM
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Well, I found about a dozen ways to check for correct pushrod length in all my searching. I ended up using 2 different ways to double check my #'s.
1. Get a lifter on the base circle of the cam by using the EO/IC method (Exhaust Opening/Intake Closing. When exhaust valve is opening for any given cylinder, the intake lifter is on the base circle of the cam. When the intake valve is closing back up, the exhaust lifter is on the base circle of the cam).
Now set an adjustable pushrod to 7.25" & insert it on the base circle lifter. Now tighten the rocker arm down where it's snug against the rocker pedestal (no need to torque all the way to 22 lbs./ft/). Now reach in and adjust the adjustable pushrod until there is no play from the rocker arm between the pushrod & valve spring at all. This is zero lash. Now pull it apart & check the length on your adjustable pushrod & add your desired preload from there. My adjustable pushrod came out right at 7.310", so I ordered 7.375" pushrods for .065 preload.
2. Insert a known length pushrod on the base circle lifter (stock 7.385" pushrods worked great for me here since they were essentially still the correct size for me). Hand tighten the rocker arm until you achieve zero lash, the point where there is no play from the rocker arm between the pushrod & spring. Now get out your torque wrench & torque the rocker arm down to 22 lbs./ft. & count the turns of the bolt. I marked the socket with a sharpie & that worked great. Each full turn of the rocker bolt is .047", so generally you would want about 1.25-1.75 turns of the bolt from zero lash to fully torqued if you have the correct length pushrod inserted. If you have less than 1.25 turns, you need a longer pushrod, more than 1.75 turns & you would need a shorter pushrod.
Anyway, hope this makes sense. There are many other threads that explain these methods better than I probably just did.
1. Get a lifter on the base circle of the cam by using the EO/IC method (Exhaust Opening/Intake Closing. When exhaust valve is opening for any given cylinder, the intake lifter is on the base circle of the cam. When the intake valve is closing back up, the exhaust lifter is on the base circle of the cam).
Now set an adjustable pushrod to 7.25" & insert it on the base circle lifter. Now tighten the rocker arm down where it's snug against the rocker pedestal (no need to torque all the way to 22 lbs./ft/). Now reach in and adjust the adjustable pushrod until there is no play from the rocker arm between the pushrod & valve spring at all. This is zero lash. Now pull it apart & check the length on your adjustable pushrod & add your desired preload from there. My adjustable pushrod came out right at 7.310", so I ordered 7.375" pushrods for .065 preload.
2. Insert a known length pushrod on the base circle lifter (stock 7.385" pushrods worked great for me here since they were essentially still the correct size for me). Hand tighten the rocker arm until you achieve zero lash, the point where there is no play from the rocker arm between the pushrod & spring. Now get out your torque wrench & torque the rocker arm down to 22 lbs./ft. & count the turns of the bolt. I marked the socket with a sharpie & that worked great. Each full turn of the rocker bolt is .047", so generally you would want about 1.25-1.75 turns of the bolt from zero lash to fully torqued if you have the correct length pushrod inserted. If you have less than 1.25 turns, you need a longer pushrod, more than 1.75 turns & you would need a shorter pushrod.
Anyway, hope this makes sense. There are many other threads that explain these methods better than I probably just did.
Last edited by osuhog; 10-16-2010 at 10:27 AM.
