What are "symtoms" of incorrect a push rod length?
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What are "symtoms" of incorrect a push rod length? I may have an incorret push rod length when we did heads/cam...we will be measuring next week after the holidays...what are possible indications if using a 7.4 and it should be 7.35 or something else?
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Originally Posted by MadBill
One would be rapid guide wear, due to excessive side loads from rocker tip scrub.
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Originally Posted by Macon
Thanks any sounds...like intermittent valve noise? Ex sounds great until warm or sounds noisy cold and better when warm?
Last edited by MadBill; Nov 25, 2005 at 02:11 PM.
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Too short and you will have the pushrod 'bouncing' up and down. Too long and you have too much preload, won't get compression. Unless it is a proven combo that you have confidence in I would always use an adjustable pushrod to determine correct pushrod length. Especially if using aftermarket rockers/lifters.
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Interesting stuff...AFR says we need to use a 20lb test spring too in order not to affect lifters. All this inquiry since I have intermittent valve tick...real odd. Push rod length is probably not the culprit, but we'll check everything carefully.
Install a test spring, color the valve tip black with a marker, re-install rocker arm, then roll the motor over several times by hand. When you remove the rocker, there will be a line across the valve tip where the rocker was riding. That line should be in the center of the valve. Any line to the bottom side is to long, anything to the top side is to short.
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Pushrod length does not determine wipe, only preload. Proper preload is about one turn or about .040. If you are at 1 3/4 or 2 turns preload is too much and lifters can pump up. Wipe is determined by shimming the rockers.
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I thought one turn on stock rockers is .060 being that each quarter turn is .015.
Regardless, I can say different length pushrods DO make different noises. A 7.325 was much louder than my current 7.350. IMHO.
Regardless, I can say different length pushrods DO make different noises. A 7.325 was much louder than my current 7.350. IMHO.
Originally Posted by bigdsz
Pushrod length does not determine wipe, only preload. Proper preload is about one turn or about .040. If you are at 1 3/4 or 2 turns preload is too much and lifters can pump up. Wipe is determined by shimming the rockers.
John
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Bump thanks - seriously we will be pulling valve covers off Sunday or Monday and checking over retorquing and trying all these great suggestions. BTW to be more specific...
AFR 205 (#1510 Heads)
FMS FM13 114 Cam
7.4 .080 Futral Hardened Push Rods
Manley Nextek Springs (380 lbs?)(Whatever Futral sells)
The Titanium Retainers that were on the AFR heads (1.8")
Stock 1.7 Roller Fulcrum solid tip Rockers
AFR 205 (#1510 Heads)
FMS FM13 114 Cam
7.4 .080 Futral Hardened Push Rods
Manley Nextek Springs (380 lbs?)(Whatever Futral sells)
The Titanium Retainers that were on the AFR heads (1.8")
Stock 1.7 Roller Fulcrum solid tip Rockers
Originally Posted by John02SS
You sure about that buddy? I'm pretty sure it is the other way around. Get the swipe looking right with pr's and then adjust preload with shims.
John
John
With non-adjustable rockers, it's a little different because (without shims) your geometry is set if you torque the rockers according to spec (i.e. the relationship of the rocker to the valve stem is set). Changing the length of the pushrod will only change the preload on the lifter. Now, once you introduce shims, the geometry changes.
What does it mean? My guess is that the stock geometry from GM with the NA rockers is fine. If you buy a set of aftermarket heads, you hope that they engineered them and installed the correct valve stem lengths to keep the geometry correct when using a stock setup. If it isn't, then you must use shims to get the geometry correct (by using the wipe method at 0 lash). After that, you break out the dial indicator with a pushrod checker and start playing with preloads for your specific lifters.
Since I switched to adjustable rockers, all this is a lot easier. With a felt tip pen and a dial indicator, I can set the wipe and preload to anything I want.
If I could only find the sweet spot for these damn Comp 850 lifters...
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Originally Posted by Byter
Setting the wipe is used to find the correct VT geometry and should be done at ZERO LASH. You use the pushrod checker to set different lengths until you get the correct wipe (basically in the middle of the valve stem). Once that is done, you go about setting the preload.
With non-adjustable rockers, it's a little different because (without shims) your geometry is set if you torque the rockers according to spec (i.e. the relationship of the rocker to the valve stem is set). Changing the length of the pushrod will only change the preload on the lifter. Now, once you introduce shims, the geometry changes.
What does it mean? My guess is that the stock geometry from GM with the NA rockers is fine. If you buy a set of aftermarket heads, you hope that they engineered them and installed the correct valve stem lengths to keep the geometry correct when using a stock setup. If it isn't, then you must use shims to get the geometry correct (by using the wipe method at 0 lash). After that, you break out the dial indicator with a pushrod checker and start playing with preloads for your specific lifters.
Since I switched to adjustable rockers, all this is a lot easier. With a felt tip pen and a dial indicator, I can set the wipe and preload to anything I want.
If I could only find the sweet spot for these damn Comp 850 lifters...
With non-adjustable rockers, it's a little different because (without shims) your geometry is set if you torque the rockers according to spec (i.e. the relationship of the rocker to the valve stem is set). Changing the length of the pushrod will only change the preload on the lifter. Now, once you introduce shims, the geometry changes.
What does it mean? My guess is that the stock geometry from GM with the NA rockers is fine. If you buy a set of aftermarket heads, you hope that they engineered them and installed the correct valve stem lengths to keep the geometry correct when using a stock setup. If it isn't, then you must use shims to get the geometry correct (by using the wipe method at 0 lash). After that, you break out the dial indicator with a pushrod checker and start playing with preloads for your specific lifters.
Since I switched to adjustable rockers, all this is a lot easier. With a felt tip pen and a dial indicator, I can set the wipe and preload to anything I want.
If I could only find the sweet spot for these damn Comp 850 lifters...
.) 
Originally Posted by John02SS
You sure about that buddy? I'm pretty sure it is the other way around. Get the swipe looking right with pr's and then adjust preload with shims.
John
John
Man I already gave you lessons. You musta failed though
