Dover Bonehead

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BobbyFord said:
Here's a nice article on valvetrain stability. Disregard any contents that refer to flat tappet cams, NASCAR engines use roller cams.
Also, you'll see no mention of ANY lower end component with regard to valvetrain longevity, failure or stability.
http://www.aera.org/engine-professional/valve-train-stability/
Also, I was once in a NASCAR engine dyno room where tons of small block Chevy race parts were shelved. I noticed that the camshafts were larger diameter than those in production engines. The owner told me it was because with the smaller diameter cams they actually notice a loss in valve timing toward the rear of the block due to camshaft flex :eek:
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Bobby,Is it correct what I read on google somewhere that the Nascar engine block (Ford or Chev)has the cam shaft mounted higher up in the block and runs short pushrods to let them rev harder??
 
ozz said:
Bobby,Is it correct what I read on google somewhere that the Nascar engine block (Ford or Chev)has the cam shaft mounted higher up in the block and runs short pushrods to let them rev harder??
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Yes, the blocks are not the same as production blocks. The cam is positioned higher not to rev harder but to decrease pushrod deflection at high RPM's. From what I understand the longer pushrods flex at high RPM's, decreasing valve lift and ultimately horsepower.
 
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It's not thermal expansion they're trying to reduce with the shorter pushrods, it's pushrod deflection. The pushrods are still made of the same material with the same expansion rate as the longer pushrods ;)
Try again :D
 
BobbyFord said:
It's not thermal expansion they're trying to reduce with the shorter pushrods, it's pushrod deflection. The pushrods are still made of the same material with the same expansion rate as the longer pushrods ;)


That's exactly what I was going to say:rolleyes:
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C'mon man, you guys need to stick to a topic that you actually know something about :D[/quote]


If we all did that there wouldn't be a forum:D
 
Seriously though, thermal expansion doesn't even come into play. The block and heads are also subject to thermal expansion to a degree, but thermal expansion is not part of the shorter pushrod equation.
 
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BobbyFord said:
It's not thermal expansion they're trying to reduce with the shorter pushrods, it's pushrod deflection. The pushrods are still made of the same material with the same expansion rate as the longer pushrods ;)
Try again :D
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I am not an engine builder by any means, nor do I wish to pretend to be, but I understand that the length of a push rod will alter deflection, however the length also determines the amount of material within that push rod, which in turn will influence thermal expansion.
 
John c said:
I am not an engine builder by any means, nor do I wish to pretend to be, but I understand that the length of a push rod will alter deflection, however the length also determines the amount of material within that push rod, which in turn will influence thermal expansion.
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You should've stopped after the first nine words ;)
From Popular Mechanics:
..."1) Valvetrain

Virtually all modern engines operate their valves through one or two overhead camshafts that push the valves open from above. It used to be that a single camshaft mounted in the engine block opened the valves from below, using long pushrods to activate rocker arms that pressed the valves open. This is still how the GM small-block V8 and the Chrysler Hemi V8 operate, though the Hemis splay the valves apart to fit into a pentroof combustion-chamber design (sorry, Chrysler—it isn't really a semihemispherical "hemi" shape anymore, though it's close). But Nascar engines still use the older, less efficient wedge-combustion-chamber shape with the intake and exhaust valves aligned in the same plane.

Those long pushrods aren't ideal for 10,000-rpm operation—the high forces cause the rods to deflect, decreasing valve lift. So, the race engines have cams that are mounted high in the block to shorten the length of the pushrods.

Nascar team owner and renowned engine builder Jack Roush reckons that the metallurgy that permits steel valve springs to survive 10,000-rpm operation could well be the most important bit of technology in these engines. Hard surface coatings such as diamond-like carbon and titanium nitride are critical in helping highly stressed components survive. In production engines, roller tips on the valve lifters help them slide over the cam lobes with minimal friction. But roller lifters aren't permitted in Nascar; instead, the car builders use those surface coatings to help the cam lobes survive a race distance..."
http://www.popularmechanics.com/_mo...ays-nascar-stock-engines-arent-actually-stock
 
BobbyFord said:
You should've stopped after the first nine words ;)
From Popular Mechanics:
..."1) Valvetrain

Virtually all modern engines operate their valves through one or two overhead camshafts that push the valves open from above. It used to be that a single camshaft mounted in the engine block opened the valves from below, using long pushrods to activate rocker arms that pressed the valves open. This is still how the GM small-block V8 and the Chrysler Hemi V8 operate, though the Hemis splay the valves apart to fit into a pentroof combustion-chamber design (sorry, Chrysler—it isn't really a semihemispherical "hemi" shape anymore, though it's close). But Nascar engines still use the older, less efficient wedge-combustion-chamber shape with the intake and exhaust valves aligned in the same plane.

Those long pushrods aren't ideal for 10,000-rpm operation—the high forces cause the rods to deflect, decreasing valve lift. So, the race engines have cams that are mounted high in the block to shorten the length of the pushrods.

Nascar team owner and renowned engine builder Jack Roush reckons that the metallurgy that permits steel valve springs to survive 10,000-rpm operation could well be the most important bit of technology in these engines. Hard surface coatings such as diamond-like carbon and titanium nitride are critical in helping highly stressed components survive. In production engines, roller tips on the valve lifters help them slide over the cam lobes with minimal friction. But roller lifters aren't permitted in Nascar; instead, the car builders use those surface coatings to help the cam lobes survive a race distance..."
http://www.popularmechanics.com/_mo...ays-nascar-stock-engines-arent-actually-stock
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It's called "coefficient of thermal expansion"!
 
FenderBumper said:
That's what engine builders do. Thermal expansion of long pushrods ruining valve timing used to be a big problem with early motor cycle engines.
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It is also a big problem with the air cooled Volkswagon engines. They recommend an overnight cool down period before you adjust the valves. Also #3 cylinder is the cylinder that pops valves on the V.W. Design problem from the factory. It doesn't cool as well, so ""thermal Expansion" of the pushrod..not the valve dropping into the cylinder is the underlying symptom of the problem.
 
This might be another problem. They might want to spend the extra hours that Dodge did on their blocks and heads.

White said Toyota continues to work to improve reliability and cost. "The cylinder head right now is not lasting as long as we want," he said. "They're lasting through two or three rebuilds, and we want them to last five or six."
But because Toyota has engineered the best elements of its competitors directly into its own powerplant, prep work is minimal. "I know for a fact that it takes 80 hours to prepare a Dodge block," White said. "Our blocks come off the CNC machines, and we can literally blow them off and build them."
 
John c said:
I am not an engine builder by any means, nor do I wish to pretend to be, but I understand that the length of a push rod will alter deflection, however the length also determines the amount of material within that push rod, which in turn will influence thermal expansion.
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There's another man who gets it, and we didn't even build any engines. :D
 
The thermal expansion of the air cooled Volkswagen is similar to that of Harley Davidson motorcycles, because of the similarities of the separate head and barrel design. On early Harleys with solid lifters, we would adjust the valves with the engine hot. The barrels expand in height 100 thousandths of an inch when hot. If you adjusted the valves with the engine cold then you would get noticeable tappet noise once the barrels expanded, but on cold start-up you would sometimes get a backfire out of the exhaust or carb due to tight valves.
 
BobbyFord said:
Seriously though, thermal expansion doesn't even come into play. The block and heads are also subject to thermal expansion to a degree, but thermal expansion is not part of the shorter pushrod equation.
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Make sure you torque your push rods to the proper foot pounds to match the head bolts. :)
 
BobbyFord said:
The thermal expansion of the air cooled Volkswagen is similar to that of Harley Davidson motorcycles, because of the similarities of the separate head and barrel design. On early Harleys with solid lifters, we would adjust the valves with the engine hot. The barrels expand in height 100 thousandths of an inch when hot. If you adjusted the valves with the engine cold then you would get noticeable tappet noise once the barrels expanded, but on cold start-up you would sometimes get a backfire out of the exhaust or carb due to tight valves.
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doesn't nascar use aluminum heads? You would need to use a smaller valve lash gap to set valve lash on a cold engine vs hot engine, even when the block is compacted graphite iron as in nascar.
 
Head bolts, should be able to think of something here, but I'm blank. :confused:
 
Think outside the box guys. Every engine builder know the basics about engines, etc. You can google and argue all day about engines but how do you think these guys get an advantage on the other team? Googling for basic engine design or for which pushrods, rods, valve springs or cam to use? No. Toyota is obviously making power here. They were when KB kicked ass in his first year with Gibbs as well. I don't think the light rod was an accident either.
 
Yes, there are different specs for hot & cold valve lash.
Also, the heads and block expand/contract at different rates because of the two different materials. The NASCAR engine will not have the same dramatic expansion as the air cooled motorcycle design because the motorcycle has a block, barrel and cylinder head, whereas the V8 only has a block and head.
Passenger cars that have iron blocks and aluminum cylinder heads use a graphite composition head gasket because of the different expansion rates of the two metals.
 
V.W. clearance values were cold engine. Either way linear thermal expansion is at work. The hotter the pushrod gets, the longer it gets. Toyota moved up their cam in the engine like the Dodge engine to shorten the pushrods. That not only helps with the expansion, but the pushrods will be lighter.
you can tighten up on your tappet clearances and get the most out of your cam if you don't have to figure in a bunch of clearance. That also changes the angle of the pushrods, could be a problem with that, or heat could be in play, heads might not have good cooling around one cylinder, when they open the hood on some of them this year, they are always on the right side. Head gets too hot and the spring fails. If they figure out how to fix it, we might get to know what the problem was if they decide to talk about it. Kyle Bush said on T.V. that they told him they can't fix it. Other Toyota people say that they can. Either way to me..to me... I think it is more than a simple spring problem. They fixed their lower end problem in a heartbeat..said it was "bearings", I think it was a trick crankshaft myself. But the spring deal has been around for a long time.:idunno:
 
You're wrong about the VW pushrod. It isn't the pushrod that gets longer, it's the barrel and head that basically get farther away from the engine block, increasing valve lash. Your theory would decrease valve lash, which doesn't happen ;)
 
I while back, I started a poll for an automotive help section and it got shot down - that's no problem - but maybe I should try again;)
 
You guys don't have to believe me. You can continue with your opinions, theories etc that have no factual merit.
My uncle and my dad were stock car and drag racers. They were also mechanics that owned their own shops. My cousins are mechanics, my brother in law is a mechanic. I have been around cars and motorcycles my entire life. I am ASE certified in engines, brakes, suspension and driveline. When I worked for Ford I went to the factory training center for engines and manual & automatic transmissions. I went to GM training center for front wheel drive automatics. I went to Jeep/Chrysler for manual trans, ABS brake training and heavy line engine rebuilding. Hell, I even took a course for a BA10/5 Peugeot manual trans.
I never went to school for Harley Davidsons because my dad owned flatheads, knuckleheads, shovelheads, evos and eventually twin-cams. I got my first Harley when I was 22, paid cash for it.
I've been a grease monkey my whole life.
Y'all can continue on with your heads in the sand and throw opinions around about something you clearly don't understand. You guys evidently have no mechanical knowledge other that what you Google, copy & paste.
Carry on. ;)
 
BobbyFord said:
You guys don't have to believe me. You can continue with your opinions, theories etc that have no factual merit.
My uncle and my dad were stock car and drag racers. They were also mechanics that owned their own shops. My cousins are mechanics, my brother in law is a mechanic. I have been around cars and motorcycles my entire life. I am ASE certified in engines, brakes, suspension and driveline. When I worked for Ford I went to the factory training center for engines and manual & automatic transmissions. I went to GM training center for front wheel drive automatics. I went to Jeep/Chrysler for manual trans, ABS brake training and heavy line engine rebuilding.
I never went to school for Harley Davidsons because my dad owned flatheads, knuckleheads, shovelheads, evos and eventually twin-cams. I got my first Harley when I was 22, paid cash for it.
I've been a grease monkey my whole life.
Y'all can continue on with your heads in the sand and throw opinions around about something you clearly don't understand. You guys evidently have no mechanical knowledge other that what you Google, copy & paste.
Carry on. ;)
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I believe you! I can change my own oil and that's about it.
 
BobbyFord said:
Y'all can continue on with your heads in the sand and throw opinions around about something you clearly don't understand. You guys evidently have no mechanical knowledge other that what you Google, copy & paste.
Carry on. ;)
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Not me. I explained to you how a defective cam could affect just one valve. Remember how stumped you were about that? :p
 
yep, I don't know nothin either. Mechanical engineering degree don't count..just another office egg head that don't know jack spit. o_O
 
:lurk:
I ain't touchin this one with a 10 foot......................................fishin pole.
Just gonna sit back and enjoy the show.
 
StandOnIt said:
yep, I don't know nothin either. Mechanical engineering degree don't count..just another office egg head that don't know jack spit. o_O
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Mechanical engineering degree and automotive technician are two different things. How many automatic transmissions have you overhauled using your mechanical engineering degree? How many automotive engines have you rebuilt? How many motorcycle engines and transmissions have you overhauled? How many differentials and transfer cases have you rebuilt?
Just curious. o_O
 
FenderBumper said:
Not me. I explained to you how a defective cam could affect just one valve. Remember how stump d you were about that? :p
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Cant believe you haven't covered the unnecessary back windows, and the nascar artificially manufactured backpressure they create, and ultimately the unnecessary stress nascar places on the valve trains.
 
Greg said:
Cant believe you haven't covered the unnecessary back windows, and the nascar artificially manufactured backpressure they create, and ultimately the unnecessary stress nascar places on the valve trains.
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You're silly. :D
 
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