2012 Pentastar - not the torque we had hoped for....
11-16-2010, 01:15 PM
#41
JK Jedi Master
as I readthrough these posts, there seems to be a little confusion about what different people are calling "push rod" engines. I think, the difference being compared is overhead cam vs a camshaft below the cylinders. The overhead cam is driven by a chain or belt and directly operates the valve lifters. A "V" designed engine will need at least 2 camshafts. The traditional cam position is driven off the crankshaft by a gear and operates the valve lifters either with a push rod or a hydrolic link. One camshaft can operate both banks of cylinders. Thus, what someone is calling a "push rod" engine might not have pushrods as it could have hydrolic lifters. The difference in engine design is considerable and is what everyone is talking about, not how the valves open and close.
My JK 3.8 has hydraulic lifters, push rods, and the cam is chain driven; and the lifters operate the push rods, not the other way around. The push rods operate the rocker arms, which open the valves.
Last edited by ronjenx; 11-16-2010 at 01:19 PM.
11-16-2010, 02:14 PM
#43
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11-16-2010, 03:06 PM
#45
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11-16-2010, 03:22 PM
#46
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Originally Posted by ronjenx
Sure they do..between the cam lobe and valve stem. Some are even hydraulic.
Last edited by jcs07jk; 11-16-2010 at 03:32 PM.
11-16-2010, 03:41 PM
#47
JK Jedi Master
Wouldn't that be a rocker arm, then on top of valve would be the hva. I would imagine they all have to be hydraulic or you'd be adjusting valve clearance in every car motor. I have not done a lot of auto engine repair, but lots of bikes. Most bike with ohc just have rocker arms then shims to take up valve clearance or the cams push right on buckets on top of the valves with the different thickness buckets being the shims A few do run hva's but not many. Want to see a bitch of a job, adjust valves on a ducati Desmo head when you have to adjust the closing rocker arm shims. No springs for valve closing. All mechanical opening and closing run off the cams
Most that I have worked on have the cam directly over the valve, with a lifter in between.
Looking at a cut-away of the Pentastar, (OHC), it looks like it uses rockers under the cam lobes, with hydraulic adjusters (lifters). But, they can't be called lifters in this case, because they support the stationary end of the rocker, rather than follow the cam lobe.
Last edited by ronjenx; 11-16-2010 at 03:56 PM.
11-16-2010, 04:31 PM
#48
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i've been trying to find a good cutaway shot of the valve train found one picture that really kinda sucked but can see the rollers on the arms. best description is Chain driven DOHC with 24 valves. Roller finger followers and hydraulic lash adjusters. I got out of the repair business a few years back and I miss it all the time.
11-16-2010, 04:36 PM
#49
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I'm not sure what you guys were expecting... the Pentastar is just Chryslers new base model engine that meets the new EPA guidelines. It's not supposed to be a game changer.
