"The Sewing Machine"
09-13-2007, 08:00 PM
#1
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"The Sewing Machine" Hey guys
I know many of you all suffer from the same annoyance that i suffer from, but what i want to know is what is there we can do to get rid of it?
After my cam swap and installing my patriot duals with 7.400 pushrods my car went from having an almost silent valvetrain to a VERY noisy valvetrain. I was wondering what is it that causes these dual springs to be so noisy? Some people have mentioned that going to a 7.425" pushrod will help alot, but i dont see how just a little longer pushrod should make up for it. I thought the larger lobes with a smaller base circle was supposed to equal out and allow the use of a stock size pushrod. Also after doing my cam swap i rotated the cam about 10 times and then retorqed the rocker-arm bolts. Should i have retorqued them after some driven miles?
Lets hear some ideas, and some personal experience from what people have done to get rid (or reduce) the sewing machine sounds they have.
I know many of you all suffer from the same annoyance that i suffer from, but what i want to know is what is there we can do to get rid of it?
After my cam swap and installing my patriot duals with 7.400 pushrods my car went from having an almost silent valvetrain to a VERY noisy valvetrain. I was wondering what is it that causes these dual springs to be so noisy? Some people have mentioned that going to a 7.425" pushrod will help alot, but i dont see how just a little longer pushrod should make up for it. I thought the larger lobes with a smaller base circle was supposed to equal out and allow the use of a stock size pushrod. Also after doing my cam swap i rotated the cam about 10 times and then retorqed the rocker-arm bolts. Should i have retorqued them after some driven miles?
Lets hear some ideas, and some personal experience from what people have done to get rid (or reduce) the sewing machine sounds they have.
09-13-2007, 08:07 PM
#2
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Rubber valve seats? 
Extreme lobe profiles let the valves land harder on the way down.
It's going to clatter more. I have the same thing on mine after the
cam with the pushrods selected right (I had 3 different lengths on
hand) and good oil pressure. If you're really smacking the lifter on
the way up you can be leaving it slack on the way down and make
it "reload" before the next bump. Big stick and big spring, going to
squeeze some oil out.
I recommend a louder exhaust
Extreme lobe profiles let the valves land harder on the way down.
It's going to clatter more. I have the same thing on mine after the
cam with the pushrods selected right (I had 3 different lengths on
hand) and good oil pressure. If you're really smacking the lifter on
the way up you can be leaving it slack on the way down and make
it "reload" before the next bump. Big stick and big spring, going to
squeeze some oil out.
I recommend a louder exhaust
09-13-2007, 08:31 PM
#3
Smaller base circle of the high lift cam means you'll need longer pushrods to maintain factory plunger depth. An XE-R cam has a .113" smaller base circle (diameter) than a stock cam. That means the radius is .0565" smaller, thus the need for a .0565" longer pushrod than stock. Add .0565" to a stock 7.380" pushrod and you get something that falls in between a 7.425" and 7.450" pushrod. Most people err on the shallower size, hence the 7.425" recommendation.
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2018 Cadillac Escalade 6.2L A10 Pat G tuned.
LS1,LS2,LS3,LS7,LT1 Custom Camshaft Specialist For custom camshaft help press here.
Custom LSX tuning in person or via email press here.
09-13-2007, 08:53 PM
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so if im using the patriot 226 cam which i believe is ground on comp xe-r lobes and i'm using a 7.400" pushrod it is preloading and rebounding on the lifter and helping to increase the sounds i hear in the valvetrain. I have great oil pressure 45psi at hot idle and about 70-75psi WOT, and with what you said, and what i remember reading about smaller base circles maybe lengthen my pushrods will help quiet her down some? I posted a video the damn i got the car running after teh swap and you can get a great audio of how noisy the engine actually is.