rudefyet Posted March 4, 2004 Report Posted March 4, 2004 ok...this got me wondering...i thought i knew the anwser for sure now i'm doubting myself ok in my little head heres how i figured things...a pushrod engine uses pushrods...imagine that...it's a rod that connects to the rocker arm and pushes it up and down opening and closing the valve...i assume the other end goes to the crankshaft which act's similar to a cam for the pushrods...therefore a pushrod has no cams whatsoever...am i right...or just making this up? i know how an OHC engine works for sure so i won't go there... one other thing i've notice when looking at nissan engines earlier...that some are just DOHC and the other's are "roller rocker" DOHC engines...so what the difference? I assume we're talking about two different types of rocker arms here Quote
topless94style Posted March 5, 2004 Report Posted March 5, 2004 ok in my little head heres how i figured things...a pushrod engine uses pushrods...imagine that...it's a rod that connects to the rocker arm and pushes it up and down opening and closing the valve...i assume the other end goes to the crankshaft which act's similar to a cam for the pushrods...therefore a pushrod has no cams whatsoever...am i right...or just making this up? the other end of the pushrod goes to the cam. that would be one hell of a pushrod to go all the way down to the crankshaft. Quote
rudefyet Posted March 5, 2004 Author Report Posted March 5, 2004 haha...thanks...now i think i got that much figured out Quote
5speedz34 Posted March 5, 2004 Report Posted March 5, 2004 Yeah, on a pushrod the cam is in the middle of the block and has a chain attached to the crank, which turns the cam. Quote
Robby1870 Posted March 5, 2004 Report Posted March 5, 2004 ok in my little head heres how i figured things...a pushrod engine uses pushrods...imagine that...it's a rod that connects to the rocker arm and pushes it up and down opening and closing the valve...i assume the other end goes to the crankshaft which act's similar to a cam for the pushrods...therefore a pushrod has no cams whatsoever...am i right...or just making this up? the other end of the pushrod goes to the cam. that would be one hell of a pushrod to go all the way down to the crankshaft. Actually the pushrod goes into a lifter which is raised by the cam lobe. A hydraulic lifter will shoot oil though the lifter into the pushrod (they are hollow) and the oil goes through the pushrod and squirts from one end of teh rocker arm (theres a hole where the pushrod touches) to the other end which rests on the top of the valve stem Quote
hazmatic Posted March 5, 2004 Report Posted March 5, 2004 3.4 dohc is a pushrod how can there be no cams when dohc stand for dual over head cams hmmmmmmmm boggles the mind dont it Quote
rudefyet Posted March 5, 2004 Author Report Posted March 5, 2004 3.4 dohc is a pushrod how can there be no cams when dohc stand for dual over head cams hmmmmmmmm boggles the mind dont it thank you for the smartass comment...the 3.4 DOHC...is an OHC engine...i challenge you to find a pushrod inside one Quote
Z34door Posted March 5, 2004 Report Posted March 5, 2004 drr 3.4 TDC is a 4 cam motor............twin dual cam... 2 cams per head....hydraulic roller cams have a roller on the end and is held in alignment by a guideplate....... also if you didn't know....... on a hydaulic cam........ the lifters rotate..... and are offset slightly on the lobe of the cam so it rotates.... Quote
hazmatic Posted March 5, 2004 Report Posted March 5, 2004 3.4 dohc is a pushrod how can there be no cams when dohc stand for dual over head cams hmmmmmmmm boggles the mind dont it thank you for the smartass comment...the 3.4 DOHC...is an OHC engine...i challenge you to find a pushrod inside one sorry i had a completee brain fart i dunno wtf i was thinking Quote
rudefyet Posted March 5, 2004 Author Report Posted March 5, 2004 Thanks...like i said i know how a OHC engine works...such as the 3.4 DOHC...i just wasn't sure about the pushrod concept or roller rockers...i owned japanese cars before this so i had never heard of a pushrod engine It's ok haz...no hard feelings Quote
MaroonRegal Posted March 5, 2004 Report Posted March 5, 2004 Thanks...like i said i know how a OHC engine works...such as the 3.4 DOHC...i just wasn't sure about the pushrod concept or roller rockers...i owned japanese cars before this so i had never heard of a pushrod engine It's ok haz...no hard feelings Lol...you're kinda backwards, rudey. I've understood pushrod engines for as long as I've cared about cars...it's the OHC concept it took me longer to grasp. I was raised on a mucle car diet, though. Quote
rudefyet Posted March 5, 2004 Author Report Posted March 5, 2004 Thanks...like i said i know how a OHC engine works...such as the 3.4 DOHC...i just wasn't sure about the pushrod concept or roller rockers...i owned japanese cars before this so i had never heard of a pushrod engine It's ok haz...no hard feelings Lol...you're kinda backwards, rudey. I've understood pushrod engines for as long as I've cared about cars...it's the OHC concept it took me longer to grasp. I was raised on a mucle car diet, though. ah...yes but now that i own an american car i'd never go back...i like having torque too much i'm hoping to have multiple GM's in my garage someday...and well maybe a Nissan 300ZX TT Convert. since i do still have a small thing for Nissans plus it's fast Quote
Like2Play Posted March 5, 2004 Report Posted March 5, 2004 The roller rocker part is a two part issue. The first has to do with the rocker arm's pivot point. Some use just a rounded thingy (don't know what it actually is called), and roller rockers use needle bearings at that pivot point. The other issue is where the rocker tip comes in contact with the valve spring, instead of it being flat, rollers use another set of needle bearings and a rolling tip for less friction. Quote
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